Available online at www.sciencedirect.com Journal of Pharmaceutical and Biomedical Analysis 47 (2008) 248–254 Evaluation of thermal stability of indinavir sulphate using diffuse reflectance infrared spectroscopy Parul Singh a , L. Premkumar a , Ranjana Mehrotra a,∗ , H.C. Kandpal a , A.K. Bakhshi b a Optical Radiation Standards, National Physical Laboratory, K.S. Krishnan Road, New Delhi 110012, India b Department of Chemistry, University of Delhi, Delhi 110007, India Received 22 October 2007; received in revised form 31 December 2007; accepted 2 January 2008 Available online 6 January 2008 Abstract Indinavir sulphate is a potent and specific protease inhibitor of human immunodeficiency virus (HIV). It is used for the treatment of acquired immune deficiency syndrome (AIDS). At elevated temperature the drug which otherwise remains crystalline undergoes a phase transition to an amorphous phase to form degradation products. In the present study, thermal stability of indinavir sulphate is evaluated using diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy. Infrared spectra of the drug before and after the exposure to thermal radiation at different temperatures were acquired in the diffuse reflectance mode using a Fourier transform infrared (FTIR) spectrophotometer. The differential scanning calorimetry (DSC) and the X-ray diffraction (XRD) studies were used as complimentary techniques to adequately implement and assist the interpretation of the infrared spectroscopy results. The DRIFT spectra reveal that the drug remains stable up to 100 ◦ C, degrades slightly at 125 ◦ C and undergoes complete degradation at about 150 ◦ C to produce degradation products. The degradation products can easily be characterized using the infrared spectra. © 2008 Elsevier B.V. All rights reserved. Keywords: Indinavir sulphate; HIV protease inhibitors; Diffuse reflectance; Infrared spectroscopy; Thermal stability; ICH 1. Introduction Indinavir sulphate [N-[2(R)-hydroxy-1(S)-indanyl]-5-{[2(S) -tertiary-butylaminocarbonyl]-4-(3-pyridylmethyl)piperazino} -4(S)-hydroxyl-2(R)-phenyl-methyl-pentanamide] (Fig. 1) is among the selective, potent and specific reversible inhibitors of the human immunodeficiency syndrome (HIV) protease. HIV protease is an enzyme that plays an essential role in HIV replication and the formation of an infectious virus. Indinavir is a structural analogue of the HIV phe-Pro protease cleavage site. The drug’s structure inhibits the function of HIV protease, blocking virus replication and causing the formation of immature, noninfectious virions [1,2]. Indinavir is active in both acutely and chronically infected cells. At elevated temperatures the drug which otherwise is crystalline undergoes ∗ Corresponding author. E-mail address: ranjana@mail.nplindia.ernet.in (R. Mehrotra). a phase transition to an amorphous substance leading to the formation of degradation products [3]. The primary degradation pathway for indinavir sulphate is amide bond hydrolysis to form lactone and aminoindanol [4,5] (Fig. 1). Several high-performance liquid chromatography (HPLC) methods [6–9], liquid chromatography/mass spectroscopy (LC/MS) methods [10,11], capillary electrophoresis [12–14] and thin-layer chromatography (TLC) methods [15,16] were developed for the determination of indinavir sulphate in blood and plasma. A capillary electrophoresis (CE) method was developed for the separation of indinavir from its degradation impurities in capsules [17]. A few liquid chromatography (LC) methods [18,19] were also developed for the assay and purity control of indinavir formulations. According to the International Conference on Harmonization (ICH) parent drug stability test guidelines “Q1A (R2)” [20], the stress testing is mandatory to determine inherent stability char- acteristics of the drug substances. Heat treatment is one of the important stress conditions defined by ICH guidelines. To the 0731-7085/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.jpba.2008.01.001