Characterization of emtricitabine related substances by liquid chromatography coupled to an ion trap mass spectrometer.

Emtricitabine (FTC) is an antiretroviral compound that inhibits the HIV-1 reverse transcriptase. For the quantification of FTC related substances, a liquid chromatography (LC) method coupled with ultraviolet (UV) detection was developed earlier in our laboratory. Several unknown compounds were detected during the analysis of a commercial sample. However, most of these impurities were not characterized. In this study, impurity profiling in a selected FTC sample was done using LC-mass spectrometry (MS). Due to the presence of a non-volatile buffer, a desalting procedure was carried out before sending the impurity into the MS. Totally, nine peaks were studied and most of them could be characterized.

Validated specific HPLC method for determination of zidovudine during stability studies.

The objective of the current study was to develop a validated stability-indicating assay method (SIAM) for zidovudine (3'-azido-3'-deoxythymidine) after subjecting it to forced decomposition under hydrolysis, oxidation, photolysis and thermal stress conditions. The drug decomposed under hydrolytic stress upon refluxing, and also on exposure to light. It was stable to oxidation and thermal stress. The same major decomposition product could be seen in all the decomposed solutions, which was identified as thymine through comparison with the standard. Separation of drug from major and minor degradation products was successfully achieved on a C-18 column utilising water-methanol in the ratio of 77:23. The detection wavelength was 265 nm. The method was validated and response was found to be linear in the drug concentration range of 25-500 microg ml(-1). The mean values (+/-R.S.D.) of slope and correlation coefficient were 21,859 (+/-0.213) and 0.9995 (+/-0.00578), respectively. The R.S.D. values for intra- and inter-day precision were <0.9 and <1.6%, respectively. The method was established to have sufficient intermediate precision as similar separation was achieved on another instrument handled by a different operator. The recovery of the drug from a mixture of degraded samples ranged between 100.6 and 100.9%. PDA peak purity test confirmed the specificity of the method. The method was also successful in analysis of drug in marketed tablets subjected to stability testing under accelerated conditions of temperature, humidity, and to thermal and photolytic stress.

Establishment of inherent stability of stavudine and development of a validated stability-indicating HPLC assay method.

The present study describes degradation of stavudine under different stress conditions (hydrolysis, oxidation, photolysis and thermal stress), and establishment of a stability-indicating reversed-phase HPLC assay method. The drug was found to hydrolyse in acidic, neutral and alkaline conditions and also under oxidative stress. The major degradation product formed under various conditions was thymine, as evidenced through comparison with the standard and spectral studies (NMR, IR and MS) on the isolated product. Separation of drug, thymine and another minor degradation product was successfully achieved on a C-18 column utilising water-methanol in the ratio of 90:10. The detection wavelength was 265 nm. The method was validated with respect to linearity, precision (including intermediate precision), accuracy and specificity. The response was linear in the drug concentration range of 25-500 microg ml(-1). The mean values (+/-R.S.D.) of slope and correlation coefficient were 24256 (+/-0.679) and 0.9994 (+/-0.0265), respectively. The R.S.D. values for intra- and inter-day precision studies were <0.210 and <1%, respectively. The recovery of the drug ranged between 99.7 and 101.5% from a mixture of degraded samples. The method even proved to be affective on application to a stressed marketed capsule formulation.