An in vitro study of drug displacement interactions: warfarin-salicylate and warfarin-phenylbutazone.

The binding interactions between warfarin-salicylate and warfarin-phenylbutazone in the presence of 4 g percent bovine serum albumin at 37 degrees C were studied using equilibrium dialysis. Methods of representing and analysing drug binding interactions are discussed. Scatchard plots, double reciprocal plots and the like are shown to be of no use in representing drug displacement interactions since they display only one drug and they can be potentially misleading. It is argued that a preferable method of analysing drug displacement interaction data is in terms of a stepwise multiple equilibria model. The numerical problems associated with fitting this kind of model to the data are discussed. A three-dimensional representation of the binding surface is proposed as a superior means of visualizing drug displacement interactions.