Dissolution kinetics of three component non-disintegrating compacts: Theophylline, benzoic acid and salicylamide

The dissolution characteristics of three component compacts containing theo phylline, benzoic acid and salicylamide were investigated over a wide range of compositions, the dissolution profiles of all three components being mo nitored. Benzoic acid and theophylline interacted to form a soluble complex with an apparent binding constant of 37.1 l/mol. Reasonable agreement betw een individual component steady state dissolution rates and those predicted by a three component diffusion controlled dissolution model, with two comp onents interacting to form soluble complexes, was obtained. Benzoic acid ra tes tended to be higher than predicted in the absence of salicylamide while theophylline dissolution tended to be lower than predicted. Plateaus in th e theoretical profiles for salicylamide rate versus composition reflected t he absence of complex formation by this component and its lower intrinsic d issolution rate, which resulted in it forming the surface layer over a wide r composition range. (C) 1999 Elsevier Science B.V. All rights reserved.