Drug dissolution rate measurements--evaluation of the rotating disc method.

Dissolution rate measurements are important to understand the behaviour of drugs or drug formulations. Many methods for measuring dissolution rates are available and a good choice should be based on method limitations as well as drug characteristics. In the present study the rotating disc method was critically evaluated for dissolution rate measurements, using aspirin and benzoic acid as model substances. Existing theory for the rotating disc was compared with experiments and a computational fluid dynamics (CFD) model simulating the USP vessel. Simulations showed that it is possible to predict mass transfer controlled drug release rates within the laminar flow regime. Mass transfer coefficients obtained from the CFD model were in better agreement with experimental data than those obtained from existing theory. It was concluded that the hydrodynamic boundary layer controlling release rates was in reality thicker than existing theory would suggest.