Design for Drug-Excipient Interaction Studies

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Abstract
For routine drug-excipient interaction studies, 2 methods are available, Differential Scanning Calorimetry (DSC) and quantitative assay after an isothermal stress test. Although DSC is generally regarded as one of the methods of first choice in assessing drug-excipient incompatibilities, the evaluation of the curves is often difficult and ‘hard’ conclusions are rarely obtained. Better results can be achieved if the curves are compared with those of samples stored at 55°C for 3 weeks. Quantitative assays after isothermal stress, however, are still needed. A stress temperature of 55°C and a storage time of 511 hours was found acceptable. To evaluate the degradation, a procedure is used in which the reaction rate and the degradation limits are derived from a requirement of maximum degradation at room temperature. When using this procedure, it is essential to realize the assumptions (both kinetic and analytical) which are implicitly made. However, together with the DSC technique this method forms a rational basis of drug-excipient interaction studies.