FTIR, dissolution and anti-viral activity of nevirapine co-crystals
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The study uses Fourier Transform Infrared (FTIR) spectroscopy to identify five Nevirapine (NV) co-crystals, determines the dissolution profile of the co-crystals and the antiviral activity comparative to pure NV. Hot stage microscopy measured the purity and integrity of each co-crystal. FTIR analysis was used to identify the co-crystals to make recommendations regarding the future use of the technique to identify the NV co-crystals. Dissolution studies of the NV co-crystals prepared with maleic acid, salicylic acid and glutaric acid (NVMLE, NVSLI and NVGLT, respectively) were completed using the rotating basket method. Assays were conducted using High Performance Liquid Chromatography and compared to pure NV and the five NV: co-former mixtures. The antiviral activity was tested to determine whether the co-crystals had an improved activity against HIV-1 compared to pure NV. All co-crystals, except NVTTA (a NV co-crystal prepared with rac-tartaric acid), were pure and maintained their integrity for approximately one year. NVGLT, NVMLE and NVTTA, 1:1 molar ratio co-crystals were identified by FTIR. The C=O stretching frequency of the carboxylic acid groups of NV and GLT were observed at 1638.15 cm-1 and 1719.23 cm-1 in the NVGLT co-crystal which corresponded with spectra of NVMLE and NVTTA. In NVMLE the C=O stretching frequency of the C=O of NV and MLE were observed at 1640.58 cm-1 and 1694.10 cm-1 and in NVTTA it was at 1637.25 cm-1 and 1708.50 cm-1, suggesting the presence of both parent molecules in the new phase for NVGLT, NVMLE and NVTTA. Dissolution studies suggested that NVGLT was the only co-crystal that yielded better results than both NV and its physical mixture. The antiviral activity of the NVSC (an NV co-crystal prepared with saccharin) and NVSLI cocrystals in DMSO was significantly different to pure NV, demonstrating an improvement in anti-viral activity.