Drug-excipient compatibility studies by physico-chemical techniques - The case of indomethacin.

This work exemplifies a general method of studying the drug- excipient interactions, with the aim of predicting rapidly and inexpensively the long term stability of their mixtures. We study the physico-chemical properties of a drug (indomethacin) in the solid state and in different combinations with several excipients (PVP=polyvinylpyrrolidone, MGST=magnesium stearate, Avicel©). We compare the properties of pure compounds (untreated, or moisture/temperature conditioned) with those of binary mixtures drug:excipient which underwent the same treatment. The purpose is to find indications of interactions within the mixtures, which means a potential incompatibility of the excipient. Both morphological and thermal properties are sensitive to interactions which leave mostly unmodified the IR spectra and the X-rays patterns. In particular, we find that indomethacin does interact with PVP and MGST, but is certainly compatible with Avicel©.