The thermal behavior of probenecid tablets. An example of the thermoanalytical complexity encountered in the pharmaceutical Industry

The complexities met in utilizing thermal analysis to describe the physico-chemical behavior of pharmaceutical compounds are demonstrated by discussing that of probenecid tablets. The DSC-TG characteristics (supported when necessary by X-ray diffraction measurements) of the active drug and major excipient components of the formulation are presented and discussed as an example of the information necessary to interpret the thermal behavior of the tabletted drug. Certain expected events are not observed with the tablets, and greater than expected weight losses are encountered. This complicates the interpretation of the thermal response, which is shown to be due to a variety of simultaneous and contiguous events. Loss of absorbed moisture and chemical dehydration, change in physical state, cold crystallization of amorphous material, sublimation, fusion and evaporation all contribute to the overall behavior.