J Therm Anal Calorim DOI 10.1007/s10973-015-4447-x

Thermal behavior and decomposition of oxytetracycline hydrochloride Priscila Cervini • Beatriz Ambrozini • Luis Carlos M. Machado • Ana Paula Garcia Ferreira E´der Tadeu Gomes Cavalheiro

•

Received: 17 October 2014 / Accepted: 14 January 2015 Ó Akade´miai Kiado´, Budapest, Hungary 2015

Abstract The thermal behavior of oxytetracycline hydrochloride (OTC) antibiotic was evaluated using TG–DTA, TG–FTIR and DSC. Information was obtained regarding thermal stability and decomposition steps. From TG–FTIR, it was possible to identify some of the products of its thermal decomposition as chloridric acid, water, isocyanic acid, dimethylamine, methane, carbonic gas and ammonia, and carbon dioxide from the decomposition of the isocyanic acid. According to DSC data, melting occurred concomitantly with decomposition. The TG/DTG, DTA and DSC curves, together with the FTIR spectra of the volatile decomposition products, were used to propose a mechanism for oxytetracycline decomposition. Keywords Oxytetracycline
Thermal behavior
Evolved gas analysis

Introduction A number of investigations have been carried out regarding application of thermal analytical techniques including differential thermal analysis (DTA), thermogravimetry (TG) and differential scanning calorimetry (DSC) in the study of thermal decomposition, thermal stability [1–4], polymorphism [5], solid-state reactions, drug formulations [6–9], purity [10] and other properties of solid compounds used in

P. Cervini
B. Ambrozini
L. C. M. Machado
A. P. G. Ferreira
E´. T. G. Cavalheiro (&) Departamento de Quı´mica e Fı´sica Molecular, Instituto de Quı´mica de Sa˜o Carlos, USP, Av. Trabalhador Sa˜o-Carlense, 400, Caixa Postal 780, Sa˜o Carlos, Sa˜o Paulo CEP 13560-970, Brazil e-mail: [email protected]

pharmaceutical industry [11, 12]. Because of the numerous issues involved in drug formulation, usage, storage and final disposal, it is important understanding thermal properties of pharmaceutical materials. The evolved gas analysis data obtained from coupled thermogravimetry–infrared spectroscopy (TG–FTIR) allow to characterize evolution of solvent molecules eventually incorporated into the crystal lattice of the drug [13, 14] as well as to detect volatile compounds produced during its thermal decomposition [15–17]. Oxytetracycline (Fig. 1) is part of an antibiotics family that has been used for more than 50 years in the treatment of bacterial infections in both human and veterinary medicines [18]. Their basic chemical structure includes a hydronaphthacene backbone consisting of four fused rings [19]. The natural tetracycline’s oxytetracycline (terramycin), chlortetracycline (aureomycin) and tetracycline itself were discovered and isolated in the 1940s and 1950s from the metabolic products of actinomycetes as Actinomyces rimosus and A. aureofaciens [20]. They are active against a wide range of gram-(?) and gram-(-) aerobic and anaerobic bacteria, including Spirochete, Actinomyces, Ricketsia and Mycoplasma [21]. Even though tetracyclines may be considered carcinogenic and have been implicated in the growing prevalence of antibiotic resistance in humans, they are still largely used against respiratory tract infections, urethritis and severe acne. It also has a role in the treatment of multidrug resistant malaria. Adverse effects include gastrointestinal disturbances, renal dysfunction, hepatotoxicity, raised intracranial pressure and skin infections, like rosacea and perioral dermatitis [21]. A recent literature survey showed that there are few studies regarding thermal analysis of TC’s. These include the use of DSC as a tool to detect antibiotic residues in whole milk [22]

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H

HO

CH3

OH

without further purification and stored at room conditions before analysis. Simultaneous TG/DTG and DTA analyses were carried out in a-alumina sample holders (90 lL) in simultaneous SDT Q600 modulus controlled by the Thermal Advantage Q-Series (v. 5.4.0 software, both from TA Instruments). Experimental parameters for TG curves were: sample mass of c.a. 10.0 mg (± 0.1 lg), heating rate of 10 °C min-1 under dynamic air atmosphere flowing at 100 mL min-1 from room to 1,000 °C temperature. The apparatus was calibrated for temperature with a zinc standard as recommended by the manufacturer instructions. DSC curves were obtained using sample mass of c.a. 6.0 mg (± 0.1 mg), heating rate of 10 °C min-1 under N2 dynamic atmosphere flowing at 50 mL min-1, in a temperature interval of -50 to 170 °C, using covered aluminum pans with a central pinhole (/ = 0.7 mm) in the lid. Curves were obtained in the heat–cool–heat successive cycles mode. Posterior measurement was made up to 230 °C, in order to better observe the melting phenomena. A TA DSC-Q10 unit controlled by the Thermal Advantage for Q-Series (v. 5.4.0 software, both from TA instruments) was used. Calibrations of the equipment for temperature and enthalpy measurements were performed using the indium metal (99.99 % purity) as a standard, according to the manufacturer’s manual. The analyses of the evolved gaseous products were carried out by connecting the exhaust of the TG–DTA equipment to a Nicolet iS10 spectrophotometer (Thermo Scientific), with gas cell operating at 250 °C and a DTGS KBr detector. The coupling was performed using a stainless steel line transfer (length 1,200 mm; diameter 3 mm) heated until 225 °C and purged with nitrogen. FTIR spectra were recorded in the spectral domain with 32 scans per spectrum at a resolution of 4 cm-1. The interferometer and

.HCl

N CH3 OH

OH

OH OH O

O

C

O

NH2

Fig. 1 Chemical formulae of oxytetracycline hydrochloride

and study of thermal stability in tablet formulations using DTA [23], but no reports concerning the analysis of the volatile products formed during the decomposition of this drug were found. Only two references have been published on the application of TG–DTA [24] and DSC [25] in the comparative study and thermal behavior of tetracycline. Oxytetracycline polymorphism was also investigated by Toro and co-workers that characterized different crystallization products by several techniques, including TG and DSC [26]. At another perspective, thermogravimetry was used to evaluate the stability of composites used as photocatalysts on the photocatalytic degradation of oxytetracycline [27]. In a recent publication, thermogravimetry was employed to characterize chitosan–montmorillonite nanocomposites used to improve oxytetracycline bioavailability via oral route [28]. Thus, this paper aims to investigate the gases evolved during heating of oxytetracycline by TG–FTIR and together with DSC curves, and propose a mechanism for oxytetracycline decomposition.

Materials and methods Oxytetracycline hydrochloride (OTC) pharmaceutical grade min. About 99.0 % (Sigma-Aldrich) was used

(a)

0.1

(b) 5

TG DTA DTG

100

0.6

4 0.0

–1

DTG/% °C

Mass/%

60

40

–0.1 0.3

–0.2

20

3 2

2 mW 1 0

–1

0.0 –0.3

0

DTA/°C mg

–1

80

Heat flow/W g –1

CH3

–2

Endo

182.9 °C

Endo –3

0

200

400

600

Temperature/°C

800

1000

40

60

80

100

120

140

160

180

200

220

Temperature/°C

Fig. 2 a TG/DTG–DTA curves of the oxytetracycline (m = 10.75 mg) in air atmosphere. b DSC up to the decomposition start presenting an endothermic peak related to melting

123

Thermal behavior and decomposition of OTC

Table 1 Description of the process for each step in TG–DTA curves of oxytetracycline hydrochloride: temperature ranges, mass losses and peak temperatures Process

OTCb(s) ? ’ H2O(g) ? HCl(g) ? resc1 ? HNCOd(g) ? (CH3)2NH(g) resc2 burning a

resc1 ? H2O(g) ? CO2(g) ? resc2

TG data

Mass loss/%

Trange/°C

TG

25–128.3

9.66

128.3–338.8 338.8–643.9

30.9 59.2

DTA peaks/°Ca Calculated 9.79

52 (endo)

30.2 60.0

215 (exo) 531, 659 (exo)

Exo—exothermic process; endo—endothermic process

b

Solid-state oxytetracycline hydrochloride in

c

Solid residue

d

Partially decomposes in the transfer line as CO2 and NH3

the gas cell compartments were purged with high purified N2. The TG curve was obtained at a heating rate of 10 °C min-1 and samples weighing about 12 mg in a-alumina crucibles, using the same purified N2 for the furnace atmosphere control flowing at 50 mL min-1.

in Fig. 3. In the first heating, a broad endothermic event with peak at 98 °C was observed and attributed to the release of water adsorbed on the sample, followed by a 0.2 1st and 2nd cooling

0.0

Results and discussion Heat flow/W g

–0.2

–0.4

Endo

1st heating

–0.6

–0.8 –50

0

50

100

150

200

Temperature/°C

Fig. 3 Heat–cool–heat (m = 5.90 mg)

DSC

curves

of

the

oxytetracycline

Temperature/°C 230

430

0.04

630

830

TG EGA

100

0.03

80

0.01

60

Mass/%

30

Intensity/a.u.

Oxytetracycline TG/DTG–DTA curves are presented in Fig. 2. TG curve shows mass losses in three consecutive overlapping steps between 25 and 643.9 °C, without a flat plateau between them and without evidence concerning the formation of stable decomposition intermediaries. Quantitative data, temperature intervals and DTA peak description are presented in Table 1. After dehydration, the thermal decomposition of oxytetracycline occurs in two steps: the second step (128.3–338.8 °C) and the third step (338.8–643.9 °C) involve losses of 30.9 and 59.2 %, respectively. The first mass loss was attributed to overlapping consecutive dehydration and HCl release steps as depicted from the DTG curve, as will be confirmed latter by EGA. In DTA curve, in Fig. 2, the first endothermic peak, at 52 °C, is ascribed to the dehydration and corresponds to the first mass loss observed in the TG/DTG curves. The sharp exothermic peak at 215 °C is attributed to the thermal decomposition, and the two exothermic peaks at 531 and 659 °C are ascribed to oxidative decomposition of the remaining carbonaceous matter. Although the literature describes a melting of OTC at 180 °C [29], it appeared in DTA curve as a slight endothermic signal, masked by the consecutive exothermic decomposition event probably due to decomposition. A detail of the DSC curve that confirms this proposition is presented in Fig. 2b. Heat–cool–heat DSC curves of oxytetracycline in temperatures that preceded the decomposition are shown

–1

2nd heating

40

0.00

0

20

40

60

80

100

Time/min

Fig. 4 TG and Gram–Schmidt curves of the oxytetracycline

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shoulder at 135 °C, probably related to the HCl displacement. Both events are not seen in the following consecutive cycles.

(a)

0.03 Spectrum at 0 min

0,01 Spectrum at 15 min

Absorbance/a.u.

Fig. 5 IR spectra of gaseous products evolved during the decomposition of oxytetracycline: a 0–18 min, b 23–62 min and c full-time range three-dimensional IR spectra

The investigation of gases evolved during the oxytetracycline thermal decomposition revealed gas evolution all along the experiment (Fig. 4). The identification of the

experimental spectra

0.02 Spectrum at 18 min

0.3 CO2 0.2

H2O

0.3

HCl

4000

databases library spectra

3500

3000

2500

2000

1500

1000

500

Wavenumbers/cm –1

(b)

Spectrum at 23 min Spectrum at 33 min

experimental spectra

Absorbance/a.u.

Spectrum at 48 min 0.01 Spectrum at 62 min

(CH3)2NH NH3

databases library spectra

HNCO 0.2

CH4

4000

3000

3500

2500

2000

1500

1000

500

–1

Wavenumbers/cm

(c)

HNCO CO2

0.15

Absorban

ce/Abs

NH3

CH4

R1N(R2)2

H2O

H2O 0.10

HCl

0.05 100 90 80 70 60 50 40 30

m

in

–0.00

123

Ti

ven

m

e/

3000

Wa

2000

um

ber

s/cm

–1

1000

20 10

Thermal behavior and decomposition of OTC

CH3 HO

CH3

.HCl

N CH3

OH

OH

OH

C

OH OH O

O

O

solid

NH2 CH3

HO

OH

CH3

.HCl

N CH3 OH

OH

C

OH OH O

O

OH

CH3

CH3 OH

N CH3

C

OH OH O

O

liquid

NH2

- H2 O - HCl

HO

O

-HNCO (

O

NH2

-(CH 3) 2NH -CO2

OH

CH3 OH

O

Conclusions

NH 3 + CO2)

-H 2O

HO

structural water and CO2, as confirmed by the TG analysis. Around 23 min (260 °C), it can be seen the evolution of volatiles in higher intensity, corresponding to the loss of dimethylamine, as observed in FTIR spectrum, presented in Fig. 5. CO2 and ammonia from the decomposition of the isocyanic acid could also be observed. It is interesting to highlight that the dimethylamine appears concomitantly with the isocyanic acid. At 33 min (373 °C), the intensity of bands related to dimethylamine decreases, however, ammonia bands regarding N–H wagging remains. At 48 min (510 °C), it can be noticed the evolution of methane, according to the bands at 3,015 and 1,304 cm-1, assigned to stretching and bending of C–H. [31] It is also observed remaining water, probably retained in the transfer line. Around 62 min (650 °C), only CO2 and water signals were observed. The TG/DTG, DTA and DSC curves, together with the FTIR spectra of the volatile decomposition products, were used to propose a mechanism for oxytetracycline thermal behavior and decomposition, as shown in Fig. 6.

OH -CH4

Complete Decomposition

Fig. 6 Proposed mechanism for oxytetracycline decomposition under N2

species was made according to Nicolet TGA Vapor Phase and EPA Vapor Phase database library contained in the Omnic 8.0 software (Thermo Scientific) [30]. As observed in the gaseous spectra of the evolved gases in Fig. 5a, at 15 min (180 °C), it can be noticed the evolution of water and HCl in agreement with the quantitative data in Table 1. In the second thermal event, one should expect the release of isocyanic acid, dimethylamine, water and CO2. However, the gaseous spectra taken at 18 min (210 °C) revealed that the release of HCl still occurs, together with

TG, DTG, DTA and DSC curves provide information on the thermal behavior and thermal decompositions of the oxytetracycline hydrochloride and permit identification of some of the gaseous products evolved during its thermal decomposition. Melting occurred concomitantly with decomposition. These gases included HCl, CO2, dimethylamine (C2H7N), water, isocyanic acid (HNCO), methane, NH3 and CO2 from the decomposition of the isocyanic acid. Acknowledgements The authors are grateful to agencies FAPESP (Process: 2012/09911-3), CNPq, as well as Procontes/USP and CiTecBio/NAP’s–PRP/USP programs, for support.

References 1. Bannach G, Cervini P, Cavalheiro ETG, Ionashiro M. Using thermal and spectroscopic data to investigate the thermal behavior of epinephrine. Thermochim Acta. 2010;499:123–7. 2. Bannach G, Arcaro R, Ferroni DC, Siqueira AB, Treu-Filho O, Ionashiro M, Schnitzler E. Thermoanalytical study of some antiinflammatory analgesic agents. J Therm Anal Calorim. 2010;102:163–70. 3. Giron D. Thermal-analysis and calorimetric methods in the characterization of polymorphs and solvates. Thermochim Acta. 1995;248:1–59. 4. Silva ACM, Ga´lico DA, Guerra RB, Legendre AO, Rinaldo D, Galhiane MS, Bannach G. Study of some volatile compounds evolved from the thermal decomposition of atenolol. J Therm Anal Calorim. 2014;115:2517–20.

123

P. Cervini et al. 5. Giordano F, Novak C, Moyano JR. Thermal analysis of cyclodextrins and their inclusion compounds. Thermochim Acta. 2001;380:123–51. 6. Wesolowski M. The influence of various tablet components on thermal-decomposition of some pharmaceuticals. Mikrochim Acta. 1980;1:199–213. 7. Neto HS, Novak C, Matos JR. Thermal analysis and compatibility studies of prednicarbate with excipients used in semi solid pharmaceutical form. J Therm Anal Calorim. 2009;97:367–74. 8. Kumar N, Goindi S, Saini B, Bansal G. Thermal characterization and compatibility studies of itraconazole and excipients for development of solid lipid nanoparticles. J Therm Anal Calorim. 2014;115:2375–83. 9. Lira AM, Arau´jo AAS, Bası´lio IDJ, Santos BLL, Santana DP, Macedo RO. Compatibility studies of lapachol with pharmaceutical excipients for the development of topical formulations. Thermochim Acta. 2007;457:1–6. 10. Lvova MSH, Kozlov EI, Wishnevezkaya IA. Thermal-analysis in the quality-control and standardization of some drugs. J Therm Anal Calorim. 1993;40:405–11. 11. Giron D. Applications of thermal analysis and coupled techniques in pharmaceutical industry. J Therm Anal Calorim. 2002;68:335–57. 12. Giron D, Goldbronn C. Use of DSC and TG for identification and quantification of the dosage form. J Therm Anal Calorim. 1997;48:473–83. 13. Materazzi S, Curini R, Gentili A, A’Ascenzo G. TG-FTIR, DSC and ESCA characterization of histamine complexes with transition metal ions. Thermochim Acta. 1997;307:45–50. 14. Rodriguez C, Bugay DE. Characterization of pharmaceutical solvates by combined thermogravimetric and infrared analysis. J Pharm Sci. 1997;86:263–6. 15. Fulias A, Vlase G, Vlase T, Tit AB, Tit AD, Doca N. Thermal study of cefoperazone monohydrate. Rev Roum Chim. 2010;55:481–6. 16. Fulias A, Vlase T, Vlase G, Doca N. Thermal behaviour of cephalexin in different mixtures. J Therm Anal Calorim. 2010;99:987–92. 17. Jingyan S, Yuwen L, Zhiyong W, Cunxin W. Investigation of thermal decomposition of ascorbic acid by TG-FTIR and thermal kinetics analysis. J Pharm Biomed Anal. 2013;77:116–9.

123

18. Marr TR. Thermal analysis of tetracycline hydrates: 1. Preparation and identification. Thermochim Acta. 1973;5:285–91. 19. Mitchell JM, Griffiths MW, McEwen SA, McNab WB, Yee AJ. Antimicrobial drug residues in milk and meat: causes, concerns, prevalence, regulations, tests, and test performance. J Food Prot. 1998;61:742–56. 20. Maia ECP, Silva PP, Almeida WB, dos Santos HF, Marcial BL, Ruggiero R, Guerra W. Tetraciclinas e glicilciclinas: uma visa˜o geral. Quim Nova. 2010;33:700–6. 21. Calixto CMF, Cervini P, Cavalheiro ETG. Determination of tetracycline in environmental water samples at a graphite-polyurethane composite electrode. J Braz Chem Soc. 2012;23:938–43. ¨ , Unluturk S. Differential scanning calorimetry as a tool 22. Yildiz O to detect antibiotic residues in ultra high temperature whole milk. Int J Food Sci Technol. 2009;44:2577–82. 23. Lee KC, Hersey JA. Oxytetracycline tablet formulations: preformulation stability screening using differential thermal-analysis. J Pharm Pharmacol. 1977;29:515–6. 24. Changa PH, Jeana JS, Jianga WT, Li Z. Mechanism of tetracycline sorption on rectorite. Colloids Surf A. 2009;339:94–9. 25. Fernandes NS, Carvalho Filho MAS, Mendes RA, Ionashiro M. Thermal decomposition of some chemotherapic substances. J Braz Chem Soc. 1999;10:459–62. 26. Toro R, de Delgado DG, Bahsas A, Delgado JM. The presence of polymorphism in oxytetracycline hydrochloride shown by X-ray powder diffraction techniques. Z. Krist Cryst Mater. 2007;26:563–8. 27. Li F, Li H, Guan L, Yao M. Nanocrystalline Co2?/F- codoped TiO2–SiO2 composite films for environmental applications. Chem Eng J. 2014;252:1–10. 28. Salcedoa I, Aguzzi GS, Bonferoni C, Cerezo P, Sa´nchez-Espejo R, Viseras C. Intestinal permeability of oxytetracycline from chitosan-montmorillonite nanocomposites. Colloids Surf B. 2014;117:441–8. 29. http://www.lookchem.com/cas-205/2058-46-0.html. 30. Nicolet EPA Vapor Phase database. Omnic 8.0 software. Thermo Scientific. 31. Silverstein RM, Bassler GC, Morril TC. Spectrometric identification of organic compounds. 3rd ed. New York: Wiley; 1991.