Investigation of the thermal degradation of indinavir sulfate

The thermal behavior of the antiviral drug indinavir sulfate was investigated by TG/DTG, TG/DTA, DSC, hot stage microscopy and TG-FTIR. TG curve indicated the loss of water followed by four decomposition steps after melting at 150 °C. DSC curves on heat–cool–heat mode showed no evidence of recrystallization of the drug on cooling. From thermoanalytical techniques, mass spectrometry and characterization of the evolved gases, it was suggested that the decomposition starts with the release of water, carbon dioxide, isocyanic acid, ammonia, 2-indanol and 2-pentanol. At higher temperatures, the release of water, isocyanic acid, carbon dioxide, ammonia and 2-pentanol was observed. In addition, carbonyl sulfide was also present as a gaseous product of thermal decomposition and detected by the first time. Mass spectra of the sample heated up to 150 °C confirmed the release of 2-indanol and ammonia just after melting. Finally, a complete description of the thermal behavior of the drug is presented based on all these results.