Nanobiotechnol (2009) 5:17–33 DOI 10.1007/s12030-009-9028-2

Nanotechnology-Based Drug Delivery Systems R. Ravichandran

Published online: 1 October 2009 # Humana Press Inc. 2009

Abstract In recent years, there has been a considerable interest in the development of novel drug delivery systems using nanotechnology. Nanoparticles represent a promising drug delivery system of controlled and targeted release. In this context, nanosuspensions will be effective in increasing the solubility and bioavailability of poorly soluble drugs. This review focuses on advantages, method of preparation, physical characteristics, and evaluation of drug nanosuspensions.

toxicity and side effect profiles, all of which must be dealt with simultaneously in order for the candidate to become a successful therapeutic [4]. Formulation scientists have always struggled to overcome these problems but with the advent of nanotechnology the conventional challenges can now be looked upon as new opportunities [5].

Keywords nanotechnology . nanoparticles . nanosuspensions . drug delivery

Nanotechnology, a multidisciplinary scientific undertaking, involves creation and utilization of materials, devices, or systems on the nanometer scale. The field of nanotechnology is currently undergoing explosive development on many fronts [6]. Nanotechnology deals with phenomena whose physics or chemistry differs from that of bulk materials of the same composition. Extending this interpretation, nanoparticles are particles in which the small size influences the intrinsic properties or behavior of the particle. Properties of interest may be surface properties, quantum mechanical properties, chemical or biological reactivity, etc. [7]. The term “nanoparticles” varies greatly based on the specific definition that is used. Nanotechnologists define nanoparticles as particles having dimensions of 1–100 nm. Interestingly, much of what we know about the bulk properties of materials breaks down at these scales. For example, nanomaterials such as carbon nanotubes and gold nanoparticles have physical properties that are different from their bulk counterparts [8]. Therefore, such technologies generate new opportunities and applications. Advances in nanotechnology and nanomedicine have heralded the advent of several innovative nanomaterials, which are set to revolutionize the field of drug delivery [9]. Excellent progress has been made in harnessing the potential of carbon nanotubes for several drug delivery and other applications [8]. In case of drug

Introduction Rapid advances in proteomics and genomics coupled with rational drug design and rapid screening techniques have led to revolution in the drug discovery process resulting in introduction of large number of novel therapeutics at proliferate rate [1]. However, the use of these novel therapeutics in medicine is frequently opposed by the lack of efficiency in delivery of these therapeutic agents to the target organs [2]. Consequently, in the last decade, there has been a great focus on the development of drug delivery systems for the treatment of diseases [3]. In very simple terms, drug delivery can be defined as the process of releasing a carried bioactive agent at a specific site, at a specific rate. The drug candidates often present a multiplicity of delivery challenges, including issues of solubility, in vivo stability, poor pharmacokinetics, and undesirable R. Ravichandran (*) Regional Institute of Education (NCERT), Bhopal 462 013, India e-mail: [email protected]

Nanotechnology

18

delivery, the properties that hold premier interest are surface properties (i.e., particle size, surface area, surface free energy, and surface-to-volume ratio) and biological reactivity (circumventing opsonization). These properties can be modulated at submicron size ranges, and there is no stringent requirement to hold on to the sizes of below 100 nm. Formulators, however, have their own way of defining nanoparticles, where the boundaries of size ranges dissolves away and anything submicron is considered to be a part of nanotechnology. To overcome the problems of gene and drug delivery, nanotechnology has gained interest in recent years. Nanosystems with different compositions and biological properties have been extensively investigated for drug and gene delivery applications [7]. Several anticancer drugs, including paclitaxel, doxorubicin, 5-fluorouracil, and dexamethasone, have been successfully formulated using nanomaterials [10]. Quantum dots, chitosan, polylactic/ glycolic acid (PLGA), and PLGA-based nanoparticles have also been used for in vitro RNAi delivery. Brain cancer is one of the most difficult malignancies to detect and treat mainly because of the difficulty in getting imaging and therapeutic agents past the blood–brain barrier and into the brain. Anticancer drugs such as loperamide and doxorubicin bound to nanomaterials have been shown to cross the intact blood–brain barrier and released at therapeutic concentrations in the brain. The use of nanomaterials, including peptide-based nanotubes to target the vascular endothelial growth factor receptor and cell adhesion molecules like integrins, cadherins, and selectins, is a new approach to control disease progression. Nanotechnology Properties in Drug Design In the following section, some of the fundamentals on which nanotechnology-based drug delivery systems are designed is given. Particle Size, Surface-to-Volume Ratio, Surface Area, and Surface Free Energy Around 40% of drugs developed today are poor candidates for drug delivery formulations owing to their limited water solubility. Nanosizing drug or formulating drug as a nanoparticulate system results in better dissolution and solubilization of drug. The “topdown” technique used for fabricating nanostructured materials results in increasing the effective surface area (surface area available for medium interaction) and imparting high free surface energy to the particles which in turn helps in entropically driven effective solubilization. Nanoparticles act as a carrier for drug delivery with number of drug molecules encapsulated in a single nanoparticle. Moreover, the enhanced surface-to-volume ratio further allows effective attachment of targeting moieties onto the surface of nanoparticles. Thus, the

Ravichandran

drug molecules are safely carried to the target site without undergoing any chemical modifications. The research on the surface parameters of nanosuspensions is very important, especially for the nanosuspensions to be administrated intravenously. Particle Size and Biological System Living organisms are built of cells that are typically 10 μm across. However, the cell parts are much smaller and are in the submicron size domain. Even smaller are the proteins with a typical size of just 5 nm, which is comparable with the dimensions of smallest manmade nanoparticles. This simple size comparison gives an idea of using nanoparticles as an effective tool in delivering drug to the target sites [11]. In fact, nanoparticles are the only colloids that can be given intravenous (i.v. route) because they do not settle or aggregate in the blood and thus cause no embolism. The smaller size also ensures easy and effective penetration not only through the biological membrane but also through the cellular pores achieving greater transfection and enabling manipulation at molecular level. Biological Reactivity The trek of a “therapeutic” from the point of administration to the intended target is full of perils, biological barriers might arise in form of tight junctions between epithelial cells, immunological hurdles are created by opsonization mediated by macrophages of reticulo endothelial system (RES), and biophysical obstacles include the charge-related agglomeration and biodistribution. Nanotechnology-based systems present themselves as well-equipped delivery agents by overcoming various barriers and other related hurdles by the virtue of their modified properties [12]. The small particle size and uniform particle distribution helps nanoparticles to overcome the biological barriers by effective and efficient transfer across biological membranes and tight junctions. Nanoparticles can be sized down below the cut-off range for easy penetration across the barriers, and because of the hydrophobicity of the particles, their journey across the membranes is not that difficult as the membranes themselves are made up of lipophilic moieties. Opsonization Opsonization, which is thought to be the greatest threat to any injectable xenobiotics, leads to engulfment of foreign particles injected into the blood stream by specific macrophages cells of RES, resulting in removal of therapeutics from the circulation and ultimately decreasing efficacy and potency of the therapy. The entire process of opsonization depends on the interaction of opsonin (endogenous proteins) with the foreign object; this interaction in turn depends on the surface physiochemical properties, i.e., size, shape, charge, density, and surface hydrophobicity. All of these can be modulated based on the techniques used for fabrication and postfabrication modifi-

Nanotechnology-Based Drug Delivery Systems

cation of nanostructured particles for, e.g., PEGylation, which includes hydrophilic coating of poly ethylene glycol on nanoparticle surface. Other non-covalent approaches include layer by layer deposition of ionic polymers, such as quantum dots. Layer by layer methods alter the surface charge of nanoparticles resulting in prevention of particle agglomeration and regulated nanoparticle biodistribution. The Pharma Industries The most promising aspect of pharmaceuticals and medicine as it relates to nanotechnology is currently drug delivery [13]. In the words of LaVan and Langer: “It is likely that the pharmaceutical industry will transition from a paradigm of drug discovery by screening compounds to the purposeful engineering of targeted molecules.” At present, there are 30 main drug delivery products on the market. The total annual income for all of these is approximately US$33 billion with an annual growth of 15% (based on global product revenue). Two major drivers are primarily responsible for this increase in the market [13]. First, present advances in diagnostic technology appear to be outpacing advances in new therapeutic agents. Highly detailed information from a patient is becoming available, thus promoting much more specific use of pharmaceuticals. Second, the acceptance of new drug formulations is expensive and slow, taking up to 15 years to obtain accreditation of new drug formulas with no guarantee of success. In response, some companies are trying to hurry the long clinical phase required in Western medicine. However, powerful incentives remain to investigate new techniques that can more effectively deliver or target existing drugs [14]. In addition, many of these new tools will have foundation in current techniques: A targeted molecule may simply add spatial or temporal resolution to an existing assay. Thus, although many potential applications are envisaged, the actual near future products are not much more than better research tools or aids to diagnosis [15, 16]. These are summarized in the following three tables (Tables 1, 2, and 3) [5].

The Problems in Drug Delivery During the last two decades, many modern technologies have been established in the pharmaceutical research and development area. The automation of the drug discovery process by technologies such as high-throughput screening, combinatorial chemistry, and computer-aided drug design is leading to a vast number of drug candidates possessing a very good efficacy [17]. Unfortunately, many of these drug candidates are exhibiting poor aqueous and non-aqueous solubility (thus insufficient bioavailability) and or erratic absorption and hence require innovative formulations and

19

drug delivery systems to reach a sufficiently high bioavailability after oral administration or at least to make available intravenously injectable forms [18]. The problem is more complex for drugs such as itraconazole and carbamazepine (belonging to BCS class II; http://en.wikipedia.org/wiki/ Biopharmaceutics_Classification_System) as they are poorly soluble in both aqueous and organic media and for those drugs having a log P value of 2. (Partition coefficient P is the ratio of concentrations of a drug at equilibrium in the two immiscible phases in the body. Log P is the logarithm of the ratio of the concentrations of the un-ionized drug in the body). The performance of these drugs is dissolution ratelimited (for class II and IV drugs) and is affected by the fed/fasted state of the patient. Dissolution rates of sparingly soluble drugs are related to the shape as well as the particle size. Therefore decrease in particle size results in an increase in dissolution rate. The Biopharmaceutics Classification System BCS is a guide for predicting the intestinal drug absorption provided by the US Food and Drug Administration: class I—high permeability, high solubility; class II— high permeability, low solubility; class III—low permeability, high solubility; and class IV—low permeability, low solubility. There are number of formulation approaches like micronization, solubilization using cosolvents, use of permeation enhancers, oily solutions, surfactant dispersions, salt formation, precipitation techniques, etc. to resolve the problems of low solubility and low bioavailability [2]. These techniques have their own limitations and hence have limited utility. Micronization by colloid mills or jet mills increases the dissolution rate of drug due to increase in surface area but does not increase the saturation solubility. Other techniques like liposomes, emulsions, microemulsions, solid dispersions, and inclusion complexes using cyclodextrins show reasonable success but they lack in universal applicability to all drugs [19]. These are not applicable for drugs which are insoluble in both aqueous and organic media [3]. Also they cause toxicity problem due to the high dosage required and are crucial in injection and ophthalmic preparations. This is also evident as has been clearly demonstrated by the relatively low number of products on the market based on such technologies. In addition, poorly water-soluble drugs are specially challenging, as they cannot achieve dissolution, and therefore, they have a very difficult pass through the dissolving fluid to contact the absorbing mucosa and to be absorbed [1]. If the dissolution process of the drug molecule is slow, due to the physicochemical properties of the drug molecules or formulation factors, then dissolution may be the rate-limiting step in absorption and will influence drug bioavailability. This is the case of class II drugs, e.g., ibuprofen, rutin, hesperidin, and coenzyme Q10. For this specific kind of drugs, micronization [20–23], nanonization [24–26], complexation (e.g., cyclodextrins)

20

Ravichandran

Table 1 Application areas for nanoscale pharmaceuticals and medicine in diagnostics [5]. Material/technique Diagnostics Nanosized markers, i.e., the attachment of nanoparticles to molecules of interest “Lab-on-a-chip” technologies

Quantum dots

Property

Applications

Timescale (to market launch)

Minute quantities of a substance can be detected down to individual molecules Miniaturization and speeding up of the analytical process

For example, detection of cancer cells to allow early treatment

?

The creation of miniature, portable diagnostic laboratories for uses in the food, pharmaceutical, and chemical industries; in disease prevention and control; and in environmental monitoring Diagnosis

Although chips currently cost over £125 (US$2085) each to make, within 3 years, the costs should fall dramatically, making these tools widely available

Quantum dots can be tracked very precisely when molecules are “bar-coded” by their unique light spectrum

[19, 27–32], preparation of liposomes [33–35] and amorphous solid dispersions [36–40] have been proposed to increase the rate of dissolution and especially the drug bioavailability after oral administration for systemic drug absorption. In many cases these did not lead to a sufficiently high bioavailability. Hence there is need of some different and simple approach to tackle the formulation

In early stage of development, but there is enough interest here for some commercialization

problems to improve their efficacy and to optimize the therapy with respect to pharmacoeconomics. The Alternative Approach: Nano Nanotechnology can be used to resolve the problems associated with these conventional approaches for solubility

Table 2 Application areas for nanoscale pharmaceuticals and medicine in drug delivery [5]. Material/ technique Drug delivery Nanoparticles in the range of 50–100 nm Nanosizing in the range of 100–200 nm Polymers Ligands on a nanoparticle surface Nanocapsules

Property

Applications

Timescale (to market launch)

Larger particles cannot enter tumor pores, while nanoparticles can easily move into a tumor Low solubility

Cancer treatment

?

More effective treatment with existing drugs

?

Nanobiological drug-carrying devices

?

These molecules can be engineered to a high degree of accuracy These molecules can be engineered to a high degree of accuracy

The ligand target receptors can recognize ? damaged tissue, attach to it, and release a therapeutic drug Evading the body’s immune system while A Bucky ball-based AIDS treatment is Early clinical directing a therapeutic agent to the desired site just about to enter clinical trials Increased particle Degree of localized drug retention increased Slow drug release ? adhesion Nanoporous Evading the body’s immune system while When coupled to sensors, drug-delivering Pre-clinical: an materials directing a therapeutic agent to the desired site implants could be developed insulin-delivery system is being tested in mice “Pharmacy-onMonitor conditions and act as an artificial For example, diabetes treatment More distant than a-chip” means of regulating and maintaining the “lab-on-a-chip” body’s own hormonal balance technologies Sorting Nanopores and membranes are capable of Gene analysis and sequencing Current–? biomolecules sorting, for example, left- and right-handed versions of molecules

Nanotechnology-Based Drug Delivery Systems

21

Table 3 Application areas for nanoscale pharmaceuticals and medicine in tissue regeneration, growth, and repair [5]. Material/technique

Property

Tissue regeneration, growth, and repair Nanoengineered Increased miniaturization, prosthetics increased prosthetic strength and weight reduction, and improved biocompatibility Cellular Manipulation and coercion manipulation of cellular systems

Applications

Timescale (to market launch)

Retinal, auditory, spinal, and cranial implants

Most immediate will be external tissue grafts, dental and bone replacements, and internal tissue implants

Persuasion of lost nerve tissue to grow; growth of body parts

More distant, 5–7 years

and bioavailability enhancement. Nanotechnology is defined as the science and engineering carried out in the nanoscale that is 10−9 m. The drug microparticles/micronized drug powder is transformed to drug nanoparticles by techniques like bottom-up technology (the drug is dissolved in a solvent, which is then added to non-solvent to precipitate the crystals) and top-down technology (the drug is disintegrated to nanosize). Nano is a Greek word, which means “dwarf.” Nano means it is the factor of 10−9 or one billionth. Some comparisons of nanoscale are given below, 0.1 nm=diameter of one hydrogen atom 2.5 nm=width of a DNA molecule17 1 μm=1,000 nm 1 nm=10−9 m=10−7 cm=10−6 mm Micron=10−6 m=10−4 cm=10−3 mm Nanoparticles This alternative and promising approach is a transformation of the micronized drug to drug nanoparticles and nanosuspensions. Nanoparticulate drug delivery system [41] may offer plenty of advantages over conventional dosage forms, which include improved efficacy, reduced toxicity, enhanced biodistribution, and improved patient compliance. Nanoparticles are colloidal particles, which are less than 1 μm in diameter. They have the unique property to accumulate at the site of inflammation and, therefore, are very suitable for targeted drug delivery. Different kinds of drugs like pilocarpine, hydrocortisone, ibuprofen, flubiprofen, Rose Bengal, and ganciclovir have been delivered by entrapping in nanoparticles [42, 43]. Nanosuspensions Nanosuspension technology [44] offers novel solution for poorly soluble drugs. Nanosuspensions are submicron colloidal dispersion of pure particles of drug stabilized by surfactants. The average particle size ranges between 200 and 600 nm. The drugs, which have high crystal energy,

i.e., high melting point, reduces the solubility of drug substances. Nanosuspension technology is used for these drugs without the necessary to solubilize them. Nanosuspension provides chemically and physically stable product. Nanosuspensions are formed by building particles as in precipitation or breaking as in milling. In both cases, new surface area is formed. Therefore, it has more free energy, and the system tends to agglomerate which is prevented by addition of surfactants. Surfactants causes high-energy barrier and prevents particles coming together. Nanosuspensions differ from nanoparticles, which are polymeric colloidal carriers of drugs (nanospheres and nanocapsules), and from solid-lipid nanoparticles, which are lipidic carriers of drug. A nanosuspension not only solves the problems of poor solubility and bioavailability but also alters the pharmacokinetics of drug and thus improves drug safety and efficacy. Potential benefits of nanosuspension technology over other conventional formulations technologies for poorly soluble drugs are given below (Tables 4 and 5) [45]. In nanosuspension technology, the drug is maintained in the required crystalline state with reduced particle size, leading to an increased dissolution rate and therefore improved bioavailability. An increase in the dissolution rate of micronized particles (particle size <10 μm) is related to an increase in the surface area. Nanosized particles can increase solution rate and saturation solubility because of the vapor pressure effect [46]. In addition, the diffusion distance on the surface of drug nanoparticles is decreased, thus leading to an increased concentration gradient. The increases in surface area and concentration gradient lead to a much more pronounced increase in the dissolution rate as compared to a micronized product. Furthermore, the saturation solubility is increased as well. Another possible explanation for the increased saturation solubility is the creation of high-energy surfaces when disrupting the more or less ideal drug microcrystal to nanoparticles. Dissolution experiments can be performed to quantify the increase in the saturation solubility of a drug when formulated into a nanosuspension. The stability of the particles obtained in the nanosuspension is attributed to their uniform particle size, which

22

Ravichandran

Table 4 Potential benefits of nanosuspension technology [45]. Route of administration

Potential benefits

Oral

Rapid onset Reduced fed/fasted ratio Improved bioavailability Rapid dissolution Tissue targeting Higher bioavailability More consistent dosing Higher bioavailability

Intravenous Ocular Inhalation

More consistent dosing Higher bioavailability Rapid onset Reduced tissue irritation

Subcutaneous/intramuscular

is created by various manufacturing processes. The absence of particles with large differences in their size in nanosuspensions prevents the existence of different saturation solubility’s and concentration gradients, consequently preventing the Oswald ripening effect [4]. Oswald ripening is responsible for crystal growth and subsequently formation of microparticles. It is caused by a difference in dissolution pressure/saturation solubility between small and large particles. Molecules diffuse from the higher concentration area around small particles, which have higher saturation solubility to an area around larger particles possessing a lower drug concentration. This leads to the formation of a supersaturated solution around the large particles and consequently to drug crystallization and growth of the large particles. The major advantages of nanosuspension technology are its general applicability to most drugs and its simplicity and are now the universal formulation approach for most drugs [18]. Nanosuspension technology is used for these drugs without the necessary to solubilize them. By this technology, the drug is maintained in required crystalline state with Table 5 Status of some nanosuspension formulations [45].

reduced particle size, and this cause increased dissolution rate and therefore improved bioavailability. Nanosuspension provides chemically and physically stable product for hydrophobic drugs. Nanosuspensions are formed by building particles as in precipitation or breaking as in milling. In both cases, new surface area is formed. Therefore, it has more free energy, and the system tends to agglomerate, which is prevented by addition of surfactants. Surfactants causes high-energy barrier and prevents particles coming together. When to Have Nanosuspensions Preparing nanosuspensions is preferred for the compounds that are insoluble in water (but are soluble in oil) with high log P value. Conventionally the drugs that are insoluble in water but soluble in oil phase system are formulated in liposome emulsion systems but these lipidic formulation approaches are not applicable to all drugs. In these cases nanosuspensions are preferred. In case of drugs that are insoluble in both water and in organic media instead of using lipidic systems nanosuspensions are used as a formulation approach. Nanosuspension formulation approach is most suitable for the compounds with high log P value, high melting point, and high dose [47]. The selection criteria for formulation approach to enhance solubility of poorly soluble drugs are given below (Fig. 1).

Nanosuspension Techniques/Preparation Nanosuspension engineering processes currently used are preparation by precipitation, high-pressure homogenization, emulsion, and milling techniques [18]. Mainly, there are two methods for preparation of nanosuspensions [5]. The conventional methods of precipitation (hydrosols) are called “bottom up technology.” In bottom up technology, the drug is dissolved in a solvent, which is then added to non-solvent to precipitate the crystals. The basic advantage

Drug

Indications

Route

Status

Paclitaxel Rapamuane Emend Budesonide Busulfan Fenofibrate Thymectacin Insulin Calcium Phosphate Silver Cytokine inhibitor

Anticancer Immunosuppressant Antiemetic Antiasthmatic Anticancer Hypolidemic Anticancer Antidiabetic Mucosal vaccine adjuvant for herpes Eczema, atopic dermatitis Crohn’s disease

i.v. Oral Oral Pulmonary Intrathecal Oral i.v. Oral Oral Topical Oral

Phase IV Marketed Marketed Phase I Phase I Phase I Phase I/II Phase I – Phase I Phase II

Nanotechnology-Based Drug Delivery Systems

23

Fig. 1 Selection criteria for formulation approach.

of precipitation technique is the use of simple and low cost equipments. The basic challenge of this technique is that during the precipitation procedure the growing of the drug crystals needs to be controlled by addition of surfactant to avoid formation of microparticles. The limitation of this precipitation technique is that the drug needs to be soluble in at least one solvent, and this solvent needs to be miscible with non-solvent. Moreover precipitation technique is not applicable to drugs, which are simultaneously poorly soluble in aqueous and non-aqueous media. The top-down technologies are the disintegration methods and are preferred over the precipitation methods. The top-down technologies include media milling (nanocrystals), high-pressure homogenization in water (Dissocubes), highpressure homogenization in non-aqueous media (nanopure), and combination of precipitation and high-pressure homogenization (nanoedge). Few other techniques used for preparing nanosuspensions are emulsion as templates, microemulsion as templates, etc. The methods of preparation of nanosuspensions by various methods are given below (Fig. 2).

process (is a registered trademark of Baxter International Inc. and its subsidiaries) relies on the precipitation of friable materials for subsequent fragmentation under conditions of high shear and/or thermal energy [48]. This is accomplished by a combination of rapid precipitation and high-pressure homogenization. Rapid addition of a drug solution to an antisolvent leads to sudden super saturation of the mixed solution and generation of fine crystalline or amorphous solids. Precipitation of an amorphous material may be favored at high super saturation when the solubility of the amorphous state is exceeded. Advantage: Simple process, low-cost equipment, and ease of scale-up. Disadvantage: Drug has to be soluble in at least in one solvent and that this solvent needs to be miscible with a non-solvent. Growing of drug crystals needs to be limited by surfactant addition. Drugs produced are carbamazepine [49], cyclosporine [50], griseofulvin [51], and retinoic acid [52].

Precipitation Media Milling (Nanocrystals or Nanosystems) Using a precipitation technique, the drug is dissolved in an organic solvent, and this solution is mixed with a miscible antisolvent. In the water–solvent mixture, the solubility is low and the drug precipitates. Mixing processes vary considerably. Precipitation has also been coupled with high-shear processing. The NANOEDGE

This method is first developed and reported by Liversidge et al. in 1992 [53]. The nanosuspensions are prepared by using high-shear media mills. The milling chamber charged with milling media, water, drug, and stabilizer is rotated at a very high shear rate under controlled temperatures for

24

Ravichandran

Fig. 2 Methods of preparation of nanosuspensions.

several days (2–7 days). The milling medium is composed of glass, zirconium oxide, or highly cross-linked polystyrene resin. The high-energy shear forces are generated as a result of the impaction of the milling media with the drug resulting into breaking of microparticulate drug to nanosized particles. Wet milling is the process by which active drug in the presence of surfactant is defragmented by milling. Advantages: & & & & &

Media milling is applicable to the drugs that are poorly soluble in both aqueous and organic media. Ease of scale-up with little batch to batch variation. High flexibility in handling large quantities of drugs. Very diluted as well as highly concentrated nanosuspensions can be prepared by handling 1 to 400 mg/ml drug quantity. Nanosize distribution of final nanosize products. Disadvantages:

& & & & &

Nanosuspensions contaminated with materials eroded from balls (generation of residue of milling) media may be problematic when it is used for long therapy. The media milling technique is time consuming (hours to days). Some fractions of particles are in the micrometer range. Scale-up is not easy due to mill size and weight. Prolonged milling may induce the formation of amorphous lead to instability.

preparation of nanosuspension, one has to start with the micronized drug particle size less than 25 µm to prevent blocking of homogenization gap; hence, it is essential to prepare a pre-suspension of the micronized drug in a surfactant solution using high speed stirrer. The suspension is forced under pressure through a valve that has nanoaperture. This causes bubbles of water to form, which collapses as they come out of valves. This mechanism cracks the particles. Principle In piston gap homogenizer, particle size reduction is based on the cavitation principle. Particles are also reduced due to high shear forces and the collision of the particles against each other. The dispersion is contained in a 3-cmdiameter cylinder and suddenly passes through a very narrow gap of 25 µm. According to Bernoulli’s law, the flow volume of liquid in a closed system per cross section is constant. The reduction in diameter from 3 cm to 25 µm leads to an increase in dynamic pressure and decrease of static pressure below the boiling point of water at room temperature. Due to this, water starts boiling at room temperature and forms gas bubbles, which implode when the suspension leaves the gap (called cavitation) and normal air pressure is reached. The size of the drug nanocrystals that can be achieved, which mainly depends on factors like temperature, number of homogenization cycles, and power density of homogenizer and homogenization pressure. Advantages:

Drugs produced are cilostazol [54], danazol [55], and naproxen [56].

&

Homogenization in Water (Dissocubes)

&

Muller developed Dissocubes technology in 1999 [46]. The instrument can be operated at pressure varying from 100 to 1,500 bars (2,800–21,300 psi) and up to 2,000 bars with volume capacity of 40 ml (for laboratory scale). For

&

Simple technique. It does not cause the erosion of processed materials. Very diluted as well as highly concentrated nanosuspensions can be prepared by handling 1 to 400 mg/ml drug quantity. General applicability to most drugs. It is applicable to the drugs that are poorly soluble in both aqueous and organic media.

Nanotechnology-Based Drug Delivery Systems

& &

It allows aseptic production of nanosuspensions for parenteral administration. Low risk of product contamination. Disadvantages:

& & & &

Prerequisite for drug to be in micronized state and suspension formation before homogenization. High-cost instruments are required that increases the cost of dosage formation. High number of homogenization cycles. Possible contamination of product could occur from metal ions coming off from the wall of the homogenizer.

Drugs produced are albendazole [57, 58], amphotericin B [59], aphidicolin [60], atovaquone [61], azithromycin [62], budesonide [63], bupravaquone [64], clofazamine [61], disodium cromoglycate [21], fenofibrate [65], glucocorticoid drugs [66], ibuprofen [67], itraconazole [68], mitotane [69], nifedipine [70], oleanolic acid [71], omeprazole [72], paclitaxel [55], and spironolactone [73]. Homogenization in Non-aqueous Media (Nanopure) The drugs that are chemically labile can be processed in such non-aqueous media or water-miscible liquids like polyethyleneglycol-400 (PEG), PEG1000, etc. The homogenization can be done at room temperature, 0°C, and below freezing point (−20°C). Combined Precipitation and Homogenization (Nanoedge) The precipitated drug nanoparticles have tendency to continue crystal growth to the size of microcrystals. They need to be processed with high-energy forces (homogenization). They are completely amorphous, partially amorphous, or completely crystalline, which create problems in long-term stability as well as in bioavailability, so the precipitated particle suspension is subsequently homogenized, which preserve the particle size obtained after the precipitation step (Table 6). Lipid Emulsion/Microemulsion Template Lipid emulsions as templates are applicable for drugs that are soluble in either volatile organic solvents or partially water-miscible solvents. This technique follows an organic solvent or mixture solvent loaded with the drug dispersed in an aqueous phase containing suitable surfactants to form an emulsion. The organic phase is then evaporated under reduced pressure to make drug particles precipitate instantaneously to form the nanosuspension, which is stabilized by surfactants. Another way to produce nanosuspensions is to use an emulsion, which is formed by the conventional

25

method using a partially water-miscible solvent as the dispersed phase. Nanosuspensions are obtained by just diluting the emulsion. Moreover, microemulsions as templates can produce nanosuspensions. Microemulsions are thermodynamically stable and isotropically clear dispersions of two immiscible liquids such as oil and water stabilized by an interfacial film of surfactant and cosurfactant. The drug can be either loaded into the internal phase or the pre-formed microemulsion can be saturated with the drug by intimate mixing. Suitable dilution of the microemulsion yields the drug nanosuspension. An example of this technique is the griseofulvin nanosuspension, which is prepared by the microemulsion technique using water, butyl lactate, lecithin, and the sodium salt of taurodeoxycholate [75]. The advantages of lipid emulsions as templates for nanosuspension formation are that they are easy to produce by controlling the emulsion droplet and easy for scale-up. However, the use of organic solvents affects the environment, and large amounts of surfactant or stabilizer are required. Advantage: High drug solubilization, long shelf life, and ease of manufacture. Disadvantage: Use of hazardous solvent and use of high amount of surfactant and stabilizers. Drugs produced are breviscapine [76], griseofulvin [75], ibuprofen [67], and mitotane [69]. Dry Cogrinding Nanosuspensions prepared by high-pressure homogenization and media milling using pearl-ball mill are wetgrinding processes. Recently, nanosuspensions can be obtained by dry-milling techniques. Successful work in preparing stable nanosuspensions using dry-grinding of poorly soluble drugs with soluble polymers and copolymers after dispersing in a liquid media has been reported [77]. Itoh et al. reported the colloidal particle formation of many

Table 6 Overview of the technologies and patents on homogenization processes [74]. Nanocrystal

Company

Patent

Hydrosol

Novatis (prev. Sandoz)

Nanomorph™ Nanocrystal™

Soligs/Abbott Élan Nanosystems

GB 22 69 536 GB 22 00 048 D 1963 7517 US 5,145,684

Dissocubes® Nanopure NANOEDGE™

SkyePharma PharmaSol Baxter

US 5,858,410 PCT/EP00/0635 US 6,884,436

26

poorly water-soluble drugs: griseofulvin, glibenclamide, and nifedipine obtained by grinding with polyvinylpyrrolidone (PVP) and sodium dodecylsulfate [77]. Many soluble polymers and copolymers such as PVP, PEG, hydroxypropyl methylcellulose (HPMC), and cyclodextrin derivatives have been used. Physicochemical properties and dissolution of poorly water-soluble drugs were improved by cogrinding because of an improvement in the surface polarity and transformation from a crystalline to an amorphous drug. Dry cogrinding can be carried out easily and economically and can be conducted without organic solvents. The cogrinding technique can reduce particles to the submicron level and a stable amorphous solid can be obtained. Advantage: Easy process, no organic solvent, requires short grinding time. Disadvantage: Generation of residue of milling media. Drugs produced are clarithromycin [78], glibenclamide [77], glisentide [79], griseofulvin [77], indomethacin [80], naproxen [81], nifedipine [77], phenytoin [82], and pranlukast [83]. Other technique involves the spraying of a drug solution in a volatile organic solvent into a heated aqueous solution. Rapid solvent evaporation produces drug precipitation in the presence of surfactants. High-pressure homogenization has advantages like general applicability to most drugs, useful in the formation of very diluted as well as highly concentrated nanosuspension, a simple technique, aseptic production is possible, and low risk of product contamination and disadvantages like high number of homogenization cycles, prerequisite for drug to be in micronized state and suspension formation before homogenization, and possible contamination of product could occur from metal ions coming off from the wall of the homogenizer.

Properties of Nanosuspensions Physical Long-Term Stability Dispersed systems show physical instability due to Oswald ripening, which is responsible for crystal growth to form microparticles. Oswald ripening is defined as the tendency for a particle dispersion to grow in diameter over time by a process in which the smaller particles dissolve because of their higher solubility, with subsequent crystallization onto larger particles to form microparticles. Oswald ripening is due to the difference in dissolution rate/saturation solubility of small and large particles. In nanosuspensions, all particles are of uniform size; hence, there is little difference between saturation solubility of drug particles. The difference in the concentration of the saturated solutions around a small

Ravichandran

and large particle leads to the diffusion of dissolved drug from the outer area of the large particles. As a result, the solution around large particles is supersaturated leading to the drug crystallization and growth of the large crystals or microparticles. Oswald ripening is totally absent in nanosuspensions due to uniform particle size, which is also responsible for long-term physical stability of nanosuspensions [84]. Increase in Saturation Solubility and Dissolution Rate of Drug Dissolution of drug is increased due to increase in the surface area of the drug particles from micro- to the nanometer size. According to the Noyes–Whitney equation (given below), dissolution rate increases due to increase in the surface area from micron size to particles of nanometer size. dx=dt ¼ ½ðD
A=h½Cs  X =V , where D is the diffusion coefficient, A is the surface area of particle, dx/dt is the dissolution rate, V is the volume of dissolution medium, and X is the concentration in surrounding liquid. According to the Prandtl equation, for small particles, the diffusion distance h decreases with decreasing particle size. The decrease in h increases Cs (saturation solubility) and leads to an increase in gradient ðCs  CxÞ=h and thus to an increase in the dissolution rate. According to Oswald– Freundlich equation, decrease in the particle size below 1 μm increases the intrinsic solubility or saturation solubility [85]. Internal Structure of Nanosuspensions The high-energy input during disintegration process causes structural changes inside the drug particles. When the drug particles are exposed to high-pressure homogenization, particles are transformed from crystalline state to amorphous state. The change in state depends upon the hardness of drug, number of homogenization cycles chemical nature of drug, and power density applied by homogenizer [84]. Evaluation/Characterization Technique for Nanosuspensions [85] In vitro evaluations [86] & & & &

Particle size and size distribution Particle charge (zeta potential) Crystalline state and morphology Saturation solubility and dissolution rate

In vivo evaluation Evaluation for surface-modified nanosuspensions [87] & & &

Surface hydrophilicity Adhesion properties Interaction with body proteins

Nanotechnology-Based Drug Delivery Systems

Mean Particle Size and Size Distribution The mean particle size and the width of particle size distribution (called polydispersity index) are determined by photon correlation spectroscopy (PCS). Particle size and polydispersity index (PI) governs the saturation solubility, dissolution rate, and biological performance. It is proved that change in particle size changes saturation solubility and dissolution rate. PCS measures the particle size in the range of 3 nm–3 µm only. PI governs the physical stability of nanosuspension and should be as low as possible for longterm stability (should be close to zero). PCS is a versatile technique but has low measuring range. In addition to PCS analysis, nanosuspensions are analyzed by laser diffractometry (LD). LD measures volume size distribution and measures particles ranging from 0.05–80 up to 2,000 µm. Atomic force microscopy is used for visualization of particle shape [88]. To study particle growth, field emission low-voltage scanning electron is used to image individual particles, and atomic force spectroscopy is used for visualization of particle shape. With near-infrared sedimentation rate, studies and online monitoring of particle size can be done. Particle Charge (Zeta Potential) Particle charge determines the stability of nanosuspension. For electrostatically stabilized nanosuspension, minimum zeta potential should be ±30 mV, and for combined steric and electrostatic stabilization, it should be a minimum of ±20 mV. Crystalline State and Particle Morphology Differential scanning calorimetry (DSC) determines the crystalline structure (polymorph stability) [89]. When nanosuspensions are prepared, drug particles get converted to amorphous form; hence, it is essential to measure the extent of amorphous drug generated during the production of nanosuspensions. The X-ray diffraction (XRD) is also used for determining change in physical state and extent of amorphous drug [90]. Saturation Solubility and Dissolution Rate The nanosuspension increases the saturation solubility as well as dissolution rate. Saturation solubility is a compound-specific constant depending upon temperature and the properties of dissolution medium. Kelvin equation and the Oswald–Freundlich equations can explain increase in saturation solubility [91]. Particle size distribution in response to accelerated aging and shipping can be studied by free thaw cycling, mechanical agitation, and centrifugation. Syringibility of injection nanosuspension should be studied. Biological tests like

27

sterility and pyrogenicity should be studied. Unstable formulation can be lyophilized, and this nanosuspension can be reconstituted without any significant change in particle size. No substantial change occurs even after steam sterilization and thermal cycling. Stability of formulation can be increased up to 2 years at room temperature. Time is crucial in product development, and often a new drug is only available in extremely limited quantity. Experiment can be designed with help of computational tools and formulation process time can be reduced. Process strategy and surfactant choice depends on rate of crystallization and solubility of nascent crystal relative to rate of particle breakdown in homogenizer. Analytical Data Management Software (ACD labs; www.acdlabs.com/solutions/ preform.html (March 2009)) helps in accelerated drug preformulation by Helping Reduce Risk and Solve Workflow Bottlenecks by Automated data management (aggregates and collates analytical data from different sources in real time), “Live” data that are searchable and directly analyzable (provides a unified and centralized work system), and multiuser and multi-site sharing and visualization of knowledge (presents data in a single interface with customizable data layouts). Oral nanosuspensions have been specifically used to increase the rate and extend absorption of drugs [1]. Evidence for enhanced onset of action, reduction of fed/fasted ratio, and enhanced dose proportionality and reduced gastric irritancy have been found. To target lungs, aerosols have smaller drug particles, but they show statistical homogeneity in partitioning of drug particles among carrier droplets. Nanosuspension provides solution to this by increasing the number of particles per droplets and as a result leads to increased onset of action and bioavailability [44]. Nanosuspension helps in the administration of huge drug concentration of poorly water-soluble drugs to brain with decreased systemic effects. Pharmaceutical applications of nanosuspensions in drug delivery involve parenteral administration, oral administration, ophthalmic drug delivery, pulmonary drug delivery, target drug delivery, and topical formulations. A fusion of the novel nanosuspension technology with the traditional dosage forms, e.g., incorporating drug nanoparticles into pellets or tablets for oral delivery is also a noteworthy advantage. Supercritical fluid technology has also been tried in drug formulations by Vasu Kumar Kakumanu and Arvind K Bansal in 2004 (Business briefing: Labtech, pp 71–73). Formulation development: & &

Formulate poorly soluble drug nanosuspensions suitable for oral application using various stabilizer Investigate the chemical (drug content) and physical (particles size distribution) stability of the formulated drug nanosuspensions

28

&

Ravichandran

Investigate the improvement in dissolution rate and saturation solubility of the prepared poorly soluble nanocrystals Solid dosage form of poorly soluble drugs:

&

&

Prepare tablets, capsules, pellets, and effervescent granules containing drug nanocrystals using simple methods for lab scale Characterize the products to identify the improvement in dissolution obtained using suitable techniques In vitro evaluation:

&

&

Perform the in vitro characterization of the drug nanosuspensions with respect to particle size analyses, morphology, physical stability, and investigate the influence of physicochemical characteristics of different drug nanosuspensions such as degree of crystallinity of the nanocrystals, kinetic solubility, and dissolution behavior Evaluate the drug release from the solid dosage forms (tablet, capsules, pellet, and effervescent granule) and compare with commercial ones

Formulations of Drug Nanosuspensions Aqueous or non-aqueous drug nanosuspensions exhibiting a physical long-term stability should be sufficient to place them on the market as liquid products. In general, a dry oral dosage form as tablet or capsule is preferred. In the case of drug nanosuspensions in pure water or in water containing mixtures, they can be used as granulation fluid in the granulation process for the production of tablets or alternatively as wetting agents for the extrusion mass to produce pellets. Spray drying of the nanosuspension is also possible. The produced powders can then be used again for tablet or pellet production or alternatively be filled in hard gelatin or HPMC capsules. The drug nanocrystals produced in non-aqueous media such as oils or liquid/solid PEG can be used directly for filling in capsules. Production of drug nanosuspensions in melted PEG, which is solid at room temperature, opens further perspectives. Direct filling of capsules with the hot nanosuspension is possible. Alternatively after solidification of the PEG, the drug nanocrystalcontaining mass can be ground and filled as a powder into the capsules [74]. To summarize, there are different ways to transfer the drug nanocrystals to a final dry oral dosage form for the patient. With regard to parenteral products, the drug nanosuspensions can be used as they are; a shelf life of up to 3 years was shown for selected nanosuspensions. Alternatively, lyophilized products can be offered to be reconstituted prior to administration (Table 7).

Pharmaceutical Applications of Nanosuspensions in Drug Delivery Parenteral Administration Nanosuspensions can be administered via different parenteral administration routes ranging from intraarticular via intraperitonal to intravenous injection. For administration by the parenteral route, the drug either has to be solubilized or has particle/globule size below 5 µm to avoid capillary blockage. The current approaches for parenteral delivery include salt formation and solubilization using cosolvents, micellar solutions, complexation with cyclodextrin, and recently liposomes. However, there are limitations on the use of these approaches because of the limitations on their solubilization capacity and parenteral acceptability. In this regard, liposomes are much more tolerable and versatile in terms of parenteral delivery. However, they often suffer from problems such as physical instability, high manufacturing cost, and difficulties in scale-up. Nanosuspensions would be able to solve the problems mentioned above. In addition, nanosuspensions have been found to increase the efficacy of parenterally administered drugs. Paclitaxel nanosuspensions revealed their superiority over taxol in reducing the median tumor burden [55]. Similarly, aphidicolin, a poorly water-soluble new antiparasitic lead molecule, when administered as a nanosuspension, resulted in an improvement in EC50 in comparison to DMSO-dissolved drug [60]. Clofazimine nanosuspension, a poorly water-soluble antileprotic drug, revealed an improvement in stability and efficacy over the liposomal clofazimine in Mycobacterium avium-infected female mice [93]. Rainbow and coworkers reported that an intravenous itraconazole nanosuspension enhanced efficacy of antifungal activity relative to a solution formulation in rats. Peroral Administration Nanosizing of drugs can lead to a dramatic increase in their oral absorption and subsequent bioavailability. Improved bioavailability can be explained by the adhesiveness of drug nanoparticles to the mucosa, the increased saturation solubility leading to an increased concentration gradient between gastrointestinal tract lumen and blood, and the increased dissolution rate of the drug. Aqueous nanosuspensions can be used directly in a liquid dosage form and a dry dosage form such as tablet or hard gelatin capsule with pellets. Ketoprofen nanosuspensions have been successfully incorporated into pellets to release the drug over a period of 24 h [94]. The aqueous nanosuspension can be used directly in the granulation process or as a wetting agent for preparing the extrusion mass pellets. A similar process has been reported for incorporating solid-lipid

Nanotechnology-Based Drug Delivery Systems

29

Table 7 Current marketed pharmaceutical products utilizing nanocrystalline formation [92]. Product

Drug compound

Indication

RAPAMUNE ® Sirolimus Immunosuppressant EMEND ® Aprepitant Antiemetic TriCor® Fenofibrate Treatment of hypercholesterolemia MEGACE® ES Megestrol acetate Appetite stimulant Triglide™ Fenofibrate Treatment of hypercholesterolemia

Company

Nanoparticle technology

Wyeth Merck Abbott PAR Pharmaceutical First Horizon Pharmaceutical

Elan Drug Delivery Nanocrystals® Elan Drug Delivery Nanocrystals® Elan Drug Delivery Nanocrystals® Elan Drug Delivery Nanocrystals® SkyePharma IDD® technology

nanoparticles into pellets. Granulates can also be produced by spray drying of nanosuspensions. Atovaquone, an antibiotic used for treating opportunistic Pneumocystis carinii infections for HIV patients, non-complicated Plasmodium falciparum malaria, and leishmanial infections, was also prepared in the form of a nanosuspension [95]. Administration of atovaquone as a nanosuspension resulted in an increase in oral bioavailability when compared to the commercial product Wellvone®, which contains the micronized drug [61, 96]. This is because of the high adhesiveness of the drug particles sticking on biological surfaces of the epithelial gut wall. Amphotericin B, an antibiotic used for treatment of gastrointestinal mycosis and leishmaniasis, lacks good oral bioavailability. However, oral administration of amphotericin B as a nanosuspension produced a substantial improvement in its oral absorption in comparison to the orally administered commercial formulations such as Fungizone, AmBisome and micronized amphotericin B [59, 61]. Bupravaquone nanosuspensions have been used for the Cryptosporidium parvum infection, the main pathogen causing severe diarrhea in immunosuppressant HIV patients. In comparison to the micronized drug powder, the infectivity score was reduced from 2.0 to 1.47 for micronized bupravaquone and even to 1.02 for equivalent nanosuspensions [61]. In addition, oral fenofibrate nanosuspensions showed bioavailability enhancement in comparison to conventional suspensions of micronized drugs.

nanosuspension intended for ophthalmic controlled delivery was developed as a polymeric nanosuspension of ibuprofen [97]. This nanosuspension is successfully prepared using Eudragit RS100 by a quasi-emulsion and solvent diffusion method. Nanosuspensions of glucocorticoid drugs (hydrocortisone, prednisolone, and dexamethasone) enhance rate and drug absorption and increase the duration of drug action [66].

Ophthalmic Drug Delivery

Nanosuspensions can also be used for targeted delivery as their surface properties and in vivo behavior can easily be altered by changing either the stabilizer or the milieu. Their versatility, ease of scale-up, and commercialization product enable the development of commercial viable nanosuspensions for targeted delivery. The engineering of stealth nanosuspensions by using various surface coatings for active or passive targeting of the desired site is the future of targeted drug delivery systems. Targeting of C. parvum, the organism responsible for cryptosporidiosis, was achieved by using surface-modified mucoadhesive nanosuspensions of bupravaquone [17, 98]. Similarly, conditions such as pulmonary aspergillosis can easily be targeted by using suitable drug candidates, such as amphotericin B, in

Nanosuspensions could prove to be vital for drugs that exhibit poor solubility in lachrymal fluids. Suspensions offer advantages such as prolonged residence time in a cul-de-sac, which is desirable for most ocular diseases for effective treatment and avoidance of high tonicity created by water-soluble drugs. Their actual performance depends on the intrinsic solubility of the drug in lachrymal fluids. Thus the intrinsic dissolution rate of the drug in lachrymal fluids governs its release and ocular bioavailability. However, the intrinsic dissolution rate of the drug will vary because of the constant inflow and outflow of lachrymal fluids. One example of a

Pulmonary Drug Delivery Aqueous nanosuspensions can be nebulized using mechanical or ultrasonic nebulizers for lung delivery. Basically the nanosuspensions can be used in all nebulizers. The dispersions can be relatively highly concentrated. Due to the presence of many small particles instead of a few large microparticles, all aerosol droplets are likely to contain drug nanoparticles. Budesonide, a poorly water-soluble corticosteroid, has been successfully prepared as a nanosuspension for pulmonary delivery [63]. A good relationship was obtained between increasing the drug concentration in the formulation and the number of micrograms of drug delivered per actuation. In addition, bupravaquone nanosuspensions were formulated for treatment of lung infections by using nebulization [64]. Targeted Drug Delivery

30

Ravichandran

the form of pulmonary nanosuspensions instead of using stealth liposomes [99]. Surface Modification and Targeted Delivery The earliest concept for targeting therapeutic to specific site included attachment of targeting moieties to the drug molecule (immunoconjugates). This concept was hardly considered convincing as it required attachment of one targeting moiety per drug molecule; also the attachment of immunoglobulin (targeting moiety) to naked drug molecule posed a big risk of affecting the biological activity of drug. Nanosuspensions can be used for targeted delivery as their surface properties and in vivo behavior can be easily be altered by changing the used stabilizer. That is what Muller [100] raised as the concept of “differential protein absorption.” After intravenous injection, the particles absorb proteins from the blood; these absorbed proteins determine the in vivo fate of the particles. The qualitative and quantitative composition of the protein adsorption pattern depends on the physicochemical surface properties of the particle, which can be adjusted by choosing a different stabilizer [101]. In the PathFinder technology proposed by Muller [100], atvaquone nanocrystals were produced by high-pressure homogenization, the surface was modified with the surfactant Tween 80 leading to in vivo preferential absorption of apolipoprotein E, the particles accumulated to a sufficient amount in the blood– brain barrier, where the receptors of apolipoprotein E abound, and then a therapeutic level was achieved. Natural targeting of MPS by nanosuspensions is well known. However, the natural targeting progress could pose an obstacle when macrophages are not the desired targets. Then, to bypass the phagocytic uptake of the drug, its surface properties need to be altered, as in the case of stealth liposomes [102]. To sum up, for the targeted delivery of nanosuspensions, the development of stealth nanocrystals and active targeting nanocrystals modified with functionalized surface coatings will be the next focal point. Topical Formulations Drug nanoparticles can be incorporated into creams and water-free ointments. The nanocrystalline form leads to an increased saturation solubility of the drug in the topical dosage form, thus enhancing the diffusion of the drug into the skin [103].

Characterization of Nanosuspensions [104] & &

Preparation of drug nanosuspensions with integrated approach. Characterization of drug nanosuspensions: particle size and its distribution, crystal nature and zeta potential

& & & &

& & & & & &

(particle charge) by LD, PCS, polarized light microscopy, scanning electron microscopy, kinetic solubility measurement, and HPLC method to determine the content of the drugs. Preparation of dried nanocrystals by spray- and freezedrying processes. Re-dispersability can be studied by tilting and phase separation by visual. Characterization of the drugs crystals by DSC, powder XRD, in vitro dissolution behavior, and HPLC method to determine the dissolved drugs. Solid dosage form can be prepared by direct compression of the tablet, extruding and spheronizing of the pellet, fusion method of the effervescent granule, and capsule development (mixing and filling capsule). Dissolution performance of the solid dosage forms. Stability of drug nanosuspension and powdered formulation. In vitro/in vivo studies of drug nanosuspension and marketed formulation. Adhesion properties (in case of mucoadhesive particles). Surface hydrophilicity/hydrophobicity. Interaction with body proteins.

Conclusion The emergence of nanotechnology is likely to have a significant impact on drug delivery sector, affecting just about every route of administration from oral to injectable. And the payoff for doctors and patients should be lower drug toxicity, reduced cost of treatments, improved bioavailability, and an extension of the economic life of proprietary drugs. The aim is “maximizing solubility and boosting bioavailability” of drugs. The Biopharmaceutics Classification System class II (high permeability, low solubility), class III (low permeability, high solubility), and class IV (low permeability, low solubility) drugs will be benefited by nanosuspension technology. The poorly soluble and low bioavailable drug, the so-called brick dust candidate, once abandoned from formulation development, can be rescued by formulating into nanosuspension. Nanosuspension technology not only offers solution to solubility of drug but also alters the pharmacokinetics of drug and thus improves drug safety and efficacy. Nanoparticles represent a promising drug delivery system of controlled and targeted release. It is clear that an era will emerge when soluble drug will be intentionally made to insoluble complex to take advantage of nanosuspension technology. However, significant challenges remain in pushing this field into clinically viable therapies. As Feynman had predicted, there has been plenty of room at the bottom to modify and

Nanotechnology-Based Drug Delivery Systems

enhance existing technologies by controlling material properties at the nanoscale. Therefore, with sufficient time and research, the promise of nanotechnology-based medicine may become a reality. Drug delivery can further be benefited if we exploit true nanotechnology principles to designing of novel delivery systems.

References 1. Nielloud F, Marti-Mestres G. Drugs and the pharmaceutical sciences. 2nd ed. New York: Informa Health Care; 2008. ISBN10: 0824703049. 2. Liu R. Water-insoluble drug formulation: pharmaceutical emulsions and suspensions. 2nd ed. Boca Raton: CRC; 2008. ISBN-10: 1574911058. 3. Gao L, Zhang D, Chen M. Drug nanocrystals for the formulation of poorly soluble drugs and its application as a potential drug delivery system. J Nanopart Res. 2008;10(5):845–62. 4. Shradhanjali B. Production and in vitro characterization of solid dosage form incorporating drug nanoparticles. Drug Dev Ind Pharm. 2008;34(11):1209–18. 5. Torchilin VP. Nanotechnology in drugs. 2nd ed. London: Imperial College Press; 2008. ISBN-10: 1860946305. 6. Sahoo SK, Labhasetwar V. Nanotech approaches to drug delivery and imaging. Drug Discov Today. 2008;8(24):1112– 20. 7. Suri SS, Fenniri H, Singh B. Nanotechnology-based drug delivery systems. J Occup Med Toxicol. 2007;1:2–16. 8. Prakash S, Kulamarva AG. Recent advances in drug delivery: potential and limitations of carbon nanotubes. Recent Pat Drug Deliv Formul. 2007;1(3):214–21. 9. Salata OV. Applications of nanoparticles in biology and medicine. Journal of Nanobiotechnology. 2004;2(3):1–6. 10. Ferrari M. Cancer nanotechnology: opportunities and challenges. Nat Rev. 2005;5:161–71. 11. la Van DA, Mcguire T, Langer R. Small scale systems for in-vivo delivery. Nat Biotechnol. 2003;21(10):1184–91. 12. Fettah Kosar T, Tourovskaia A, Stucky NL. Nanoparticles administered to the human body: impacts and implications. News from the Bottom. 2004:1–8. 13. Kirupakar BR. Nanosuspension drug delivery: technology and application. Express Pharma Pulse. 2009:1–6. 14. Gao L. Preparation and characterization of an oridonin nanosuspension for solubility and dissolution velocity enhancement. Drug Dev Ind Pharm. 2007;33(12):1332–9. 15. Filippos K, Santipharp P, Yunhui W. Application of nanoparticles in oral delivery of immediate release formulations. Current Nanoscience. 2007;3(2):183–90. 16. Das S, Banerjee R, Bellare J. Aspirin loaded albumin nanoparticles by coacervation: implications in drug delivery. Trends Biomater Artif Organs. 2005;18(2):203–12. 17. Arnall AH. Future technologies, today’s choices nanotechnology, artificial intelligence and robotics; a technical, political and institutional map of emerging technologies. Research report. London: Greenpeace Environmental Trust; 2008. 18. Chingunpituk J. Nanosuspension technology for drug delivery. Walailak J Sci & Tech. 2007;4(2):139–53. 19. Stella VJ, He Q. Cyclodextrins. Toxicol Pathol. 2008;36(1):30–42. 20. Rasenack N, Steckel H, Muller BW. Micronization of antiinflammatory drugs for pulmonary delivery by a controlled crystallization process. J Pharm Sci. 2003;92(1):35–44.

31 21. Steckel H, Rasenack N, Muller BW. In-situ-micronization of disodium cromoglycate for pulmonary delivery. Eur J Pharm Biopharm. 2003;55(2):173–80. 22. Steckel H. In vitro characterization of jet-milled and in-situ micronized fluticasone-17-propionate. Int J Pharm. 2003;258 (1–2):65–75. 23. Rasenack N, Muller BW. Micron-size drug particles: common and novel micronization techniques. Pharm Dev Technol. 2004;9 (1):1–13. 24. Liversidge GG. Surface modified drugs nanoparticles. US Patent 5,145,684. Sterling Drug New York; 1992. 25. Muller RH. Pharmaceutical nanosuspensions for medicament administration as systems with increased saturation solubility and rate of solution, US Patent 5,858,410. 1999. 26. Ostrander KD, Bosch HW, Bondanza DM. An in-vitro assessment of a NanoCrystal beclomethasone dipropionate colloidal dispersion via ultrasonic nebulization. Eur J Pharm Biopharm. 1999;48 (3):207–15. 27. Sri KV. Preparation and characterization of quercetin and rutin cyclodextrin inclusion complexes. Drug Dev Ind Pharm. 2007;33 (3):245–53. 28. Calabro ML. The rutin/beta-cyclodextrin interactions in fully aqueous solution: spectroscopic studies and biological assays. J Pharm Biomed Anal. 2005;36(5):1019–27. 29. Brewster ME, Loftsson T. Cyclodextrins as pharmaceutical solubilizers. Adv Drug Deliv Rev. 2007;59(7):645–66. 30. Loftsson T. Cyclodextrins in drug delivery. Expert Opin Drug Deliv. 2005;2(2):335–51. 31. Loftsson T, Brewster ME. Pharmaceutical applications of cyclodextrins. 1. Drug solubilization and stabilization. J Pharm Sci. 1996;85(10):1017–25. 32. Loftsson T, Brewster ME, Másson M. Role of cyclodextrins in improving oral drug delivery. Am J Drug Deliv. 2004;2(4):1–15. 33. Mu X, Zhong Z. Preparation and properties of poly(vinyl alcohol)stabilized liposomes. Int J Pharm. 2006;318(1–2):55–61. 34. Johnston MJ. Characterization of the drug retention and pharmacokinetic properties of liposomal nanoparticles containing dihydrosphingomyelin. Biochim Biophys Acta. 2007;1768 (5):1121–7. 35. Kreuter A. Liposomal pegylated doxorubicin versus low-dose recombinant interferon Alfa-2a in the treatment of advanced classic Kaposi's sarcoma; retrospective analysis of three German centers. Cancer Invest. 2005;23(8):653–9. 36. Dannenfelser RM. Development of clinical dosage forms for a poorly water soluble drug I: application of polyethylene glycolpolysorbate 80 solid dispersion carrier system. J Pharm Sci. 2004;93(5):1165–75. 37. Joshi HN. Bioavailability enhancement of a poorly water-soluble drug by solid dispersion in polyethylene glycol-polysorbate 80 mixture. Int J Pharm. 2004;269(1):251–8. 38. Karavas E. Investigation of the release mechanism of a sparingly water-soluble drug from solid dispersions in hydrophilic carriers based on physical state of drug, particle size distribution and drugpolymer interactions. Eur J Pharm Biopharm. 2007;66(3):334–47. 39. Overhoff KA. Solid dispersions of itraconazole and enteric polymers made by ultra-rapid freezing. Int J Pharm. 2007;336(1):122–32. 40. Serajuddin AT. Solid dispersion of poorly water-soluble drugs: early promises, subsequent problems, and recent breakthroughs. J Pharm Sci. 1999;88(10):1058–66. 41. Keck CM, Muller RH. Drug nanocrystals of poorly soluble drugs produced by high pressure homogenization. Eur J Pharm Biopharm. 2006;62:3–16. 42. Thassu D, Deleers M, Pathak Y. Nanoparticulate drug delivery systems. Boca Raton: CRC; 2008. 43. Shinde AJ. Solubilization of poorly soluble drugs: a review. Pharmaceutical Reviews Latest Reviews. 2007;5(6):1–13.

32 44. Rama Rao N, Prasanthi NL, Ramakrishna R, Babu Nageswararao K. Nanosuspensions: an emerging carrier for delivery of bioactive agents, The Pharma Review. New Delhi: KONGPOSH; 2008. p. 23–31. 45. Chaubal MV. Application of formulation technologies in lead candidate selection and optimization. Drug Discov Today. 2004;9(14):603–9. 46. Müller RH, Jacobs C, Kayer O. Nanosuspensions for the formulation of poorly soluble drugs. In: Nielloud F, MartiMestres G, editors. Pharmaceutical emulsion and suspension. New York: Marcel Dekker; 2000. p. 383–407. 47. Barrett RE. Nanosuspensions. Nature Reviews/Drug Discovery. 2004;3:785–96. 48. Kipp JE, Wong JCT, Doty MJ, Rebbeck CL. Micro precipitation method for preparing submicron suspensions. US Patent 6,607,784 2003. 49. Sarkari M, Brown J, Chen X, Swinnea S, Williams RO III, Johnston KP. Enhanced drug dissolution using evaporative precipitation into aqueous solution. Int J Pharm. 2002;243:17– 31. 50. Chen X, Yong TJ, Sarkari M, Williams RO III, Johnston KP. Preparation of cyclosporine a nanoparticles by evaporative precipitation into aqueous solution. Int J Pharm. 2002;242:3–14. 51. Zili Z, Sfar S, Fessi H. Preparation and characterization of polyε-carprolactone nanoparticles containing griseofulvin. Int J Pharm. 2005;294:261–7. 52. Zhang X, Xia Q, Gu N. Preparation of all-trans retinoic acid nanosuspensions using a modified precipitation method. Drug Dev Ind Pharm. 2006;32:857–63. 53. Liversidge GG, Cundy KC, Bishop JF, Czekai DA. Surface modified drug nanoparticles. US Patent 5, 145, 684, 199. 54. Jinno J-I, Kamada N, Miyake M, Yamada K, Mukai T, Odomi M, et al. Effect of particle size reduction on dissolution and oral absorption of a poorly water-soluble drug, cilostazol, in beagle dogs. J Control Release. 2006;111:56–64. 55. Merisko-Liversidge E, Liversidge GG, Cooper ER. Nanosizing: a formulation approach for poorly-water-soluble compounds. Eur J Pharm Sci. 2003;18:113–20. 56. Liversidge GG, Conzentino P. Drug particle size reduction for decreasing gastric irritancy and enhancing absorption of naproxen in rats. Int J Pharm. 1995;125:309–13. 57. Rao YM, Kumar MP, Apte S. Formulation of nanosuspensions of albendazole for oral administration. Current Nanoscience. 2008;4(1):53–8. 58. Kumar MP, Rao YM, Apte S. Improved bioavailability of albendazole following oral administration of nanosuspension in rats. Curr Nanosci. 2007;3:191–4. 59. Kayser O, Olbrich C, Yardley V, Kiderlen AF, Croft SL. Formulation of amphotericin B as nanosuspension for oral administration. Int J Pharm. 2003;254:73–5. 60. Kayser O. Nanosuspensions for the formulation of aphidicolin to improve drug targeting effects against Leishmania infected macrophages. Int J Pharm. 2000;196:253–6. 61. Müller RH, Jacobs C, Kayser O. Nanosuspensions as particulate drug formulations in therapy rationale for development and what we can expect for the future. Adv Drug Deliv Rev. 2001;47:3–19. 62. Zhang D, Tan T, Gao L, Zhao W, Wang P. Preparation of azithromycin nanosuspensions by high pressure homogenization and its physicochemical characteristics studies. Drug Dev Ind Pharm. 2007;33:569–75. 63. Müller RH, Jacobs C. Production and characterization of a budesonide nanosuspension for pulmonary administration. Pharm Res. 2002;19:189–94. 64. Hernández-Trejo N, Kayser O, Steckel H, Müller RH. Characterization of nebulized bupravaquone nanosuspensions—effect of nebulization technology. J Drug Target. 2005;13:499–507.

Ravichandran 65. Hanafy A, Spahn-Langguth H, Vergnault G, Grenier P, Grozdanis MT, Lenhardt T. Pharmacokinetic evaluation of oral fenofibrate nanosuspension and SLN in comparison to conventional suspensions of micronized drug. Adv Drug Del Rev. 2007;59:419–26. 66. Kassem MA, Abdel Rahman AA, Ghorab MM, Ahmed MB, Khalil RM. Nanosuspension as an opthamic delivery system for certain glucocorticoid drugs. Int J Pharm. 2007;340:126–33. 67. Kocbek P, Baumgartner S, Kristl J. Preparation and evaluation of nanosuspensions for enhancing the dissolution of poorly soluble drug. Int J Pharm. 2006;312:179–86. 68. Rainbow B, Kipp J, Papadopoulos P, Wong J, Glosson J, Gass J, et al. Itraconazole IV nanosuspension enhances efficacy through altered pharmacokinetic in the rat. Int J Pharm. 2007;339:251–60. 69. Trotta M, Gallarete M, Pattarino F, Morel S. Emulsions containing partially water-miscible solvents for the preparation of dry nanosuspensions. J Control Release. 2001;76:119–28. 70. Hecq J, Deleers M, Fanara D, Vranckx H, Amighi K. Preparation and characterization of nanocrystals for solubility and dissolution rate enhancement of nifedipine. Int J Pharm. 2005;299:167–77. 71. Chen JY, Yang LX, Zhao LX, Xu BH. Preparation of oleanolic acid nanosuspension. Chin Pharm J. 2006;41:924–7. 72. Möschwitzer J, Achleitner G, Pomper H, Müller RH. Development of an intravenously injectable chemically stable aqueous omeprazole formulation using nanosuspension technology. Eur J Pharm Biopharm. 2004;58:615–9. 73. Langguth P, Hanafy A, Frenzel D, Grenier P, Nhamias A, Ohlig T, et al. Nanosuspension formulations for low-soluble drugs: pharmacokinetic evaluation using spironolactone as model compound. Drug Dev Ind Pharm. 2005;31:319–29. 74. Keck CM, Müller RH. Drug nanocrystals of poorly soluble drugs produced by high pressure homoginisation. Eur J Pharm Biopharm. 2006;62:3–16. 75. Trotta M, Gallarate M, Carlotti ME, Morel S. Preparation of griseofulvin nanoparticles from water-dilutable microemulsions. Int J Pharm. 2003;254:235–42. 76. She Z-Y, Ke X, Ping Q-N, Xu B-H, Chen L-L. Preparation of breviscapine nanosuspension and its pharmacokinetic behavior in rats. Chin J Nat Med. 2007;5:50–5. 77. Itoh K, Pongpeerapat A, Tozuka Y, Oguchi T, Yamamoto K. Nanoparticle formation of poorly water soluble drugs from ternary ground mixtures with PVP and SDS. Chem Pharm Bull. 2003;51:171–4. 78. Yonemochi E, Kitahara S, Maeda S, Yamamura S, Oguchi T, Yamamoto K. Physicochemical properties of amorphous clarithromycin obtained by grinding and spray drying. Eur J Pharm Sci. 1999;7:331–8. 79. Mura P, Cirri M, Faucci MT, Ginès-Dorado JM, Bettinetti GP. Investigation of the effects of grinding and co-grinding on physicochemical properties of glisentide. J Pharm Biomed Anal. 2002;30:227–37. 80. Watanabe T, Ohno I, Wakiyama N, Kusai A, Senna M. Stabilization of amorphous indomethacin by co-grinding in a ternary mixture. Int J Pharm. 2002;241:103–11. 81. Mura P, Faucci MT, Bettinetti GP. The influence of polyvinyl pyrrolidone onnaproxen complexation with hydroxypropyl- βcyclodextrin. Eur J Pharm Sci. 2001;13:187–94. 82. Otsuka M, Matsuda Y. Effect of co-grinding with various kinds of surfactants on the dissolution behavior of phenytoin. J Pharm Sci. 1995;84:1434–7. 83. Wongmekiat A, Tozuka Y, Oguchi T, Yamamoto K. Formation of fine drug particles by co-grinding with cyclodextrin. I. the use of βcyclodextrin anhydrate and hydrate. Pharm Res. 2002;19:1867–72. 84. Patravale VB, Date AA, Kulkarni RM. Nanosuspensions: a promising drug delivery strategy. J Pharm Pharcol. 2004;56:827– 40.

Nanotechnology-Based Drug Delivery Systems 85. Muller RH, Bohm BHL, Grau J. Nanosuspensions: a formulation approach for poorly soluble and poorly bioavailable drugs. In: Wise D, editor. Handbook of pharmaceutical controlled release technology. New York: Marcel Dekker; 2000. p. 345–57. 86. Muthu MS, Singh S. Poly (D, L-Lactide) nanosuspensions of risperidone for parenteral delivery: formulation and in-vitro evaluation. Current Drug Delivery. 2009;6(1):62–8. 87. Muller RH, Jacobs C, Kayser O. Nanosuspensions as particulate drug formulations in therapy rationale for development and what we can expect for the future. Adv Drug Deliv Rev. 2001;47:3– 19. 88. Montasser HF, Coleman AW. Atomic force microscopy imaging of novel type of polymeric colloidal nanostructures. Eur J Pharm Biopharm. 2002;54:281–4. 89. Bond L, Allen S, Davies MC, Roberts CJ, Shivji AP, Tendler SJB, et al. Differential scanning calorimetry and scanning thermal microscopy analysis of pharmaceutical materials. Int J Pharm. 2002;243:71–82. 90. Scholer N, Krause K, Kayser O, Muller RH, Borner K, Hahn H, et al. Atovaquone nanosuspensions show excellent therapeutic effect in a new murine model of reactivated toxoplasmosis. Antimicrob Agents Chemother. 2001;45:1771–9. 91. Waterbeemd H, Lennernäs H, Artursson P. Drug bioavailability: estimation of solubility, permeability, absorption and bioavailability. Weinheim: Wiley; 2003. ISBN 3-527-30438-X. 92. Kesisoglou F, Panmai S, Wu Y. Nanosizing-oral formulation development and biopharmaceutical evaluation. Adv Drug Deliv Rev. 2007;59:631–44. 93. Peters K, Leitzke S, Diederichs JE, Borner K, Hahn H, Müller RH, et al. Preparation of a clofazamine nanosuspension for intravenous use and evaluation of its therapeutic efficacy in murine Mycobacterium avium infection. J Antimicrob Chemother. 2000;45:77–83.

33 94. Remon JP, Vergote GJ, Vervaet C, Driessche I, Hoste S, Smedt S, et al. An oral controlled release matrix pellet formulation containing nanocrystalline ketoprofen. Int J Pharm. 2001;219:81–7. 95. Looareesuwan S, Chulay JD, Canfield CJ, Hutchinson DB. Atovaquone and proguanil hydrochloride followed by primaquine for treatment of Plasmodium vivax malaria in Thailand. Trans R Soc Trop Med Hyg. 1999;93:637–40. 96. Schöler N, Krause K, Kayser O, Müller RH, Borner K, Hahn H, et al. Atovaquone nanosuspensions show excellent therapeutic effect in a new murine model of reactivated toxoplasmosis. Antimicrob Agents Chemother. 2001;45:1771–9. 97. Pignatello R, Bucolo C, Ferrara P, Maltese A, Pvleo A, Puglisi G. Eudragit RS100®nanosuspensions for the ophthalmic controlled delivery of ibuprofen. Eur J Pharm Sci. 2002;16:53–61. 98. Kayser O. A new approach for targeting to Cryptosporidium parvum using mucoadhesive nanosuspensions: research and applications. Int J Pharm. 2001;214:83–5. 99. Kohno S, Otsubo T, Tanaka E, Maruyama K, Hara K. Amphotericin B encapsulated in polyethylene glycol immunoliposomes for infectious diseases. Adv Drug Del Rev. 1997;24:325–9. 100. Muller RH, Keck CM. Challenges and solutions for the delivery of biotech drugs—a review of drug nanocrystal technology and lipid nanoparticles. J Biotechnol. 2004;113:151–70. 101. Goppert TM, Muller RH. Adsorption kinetics of plasma proteins on solid lipid nanoparticles for drug targeting. Int J Pharm. 2005;302:172–86. 102. Allen TM. Liposomes: opportunities in drug delivery. Drugs. 1997;54:8–14. 103. Chen X, Lo CY-L, Sarkari M, Williams RO III, Johnston KP. Ketoprofen nanoparticle gels formed by evaporative precipitation into aqueous solution. AIChE J. 2006;52:2428–35. 104. Jignyasha A. Raval nanosuspensions as particulate drug delivery systems. Pharm Rev. 2006;4(6):1–18.