In vitro release test (IVRT): Principles and applications.

In vitro drug release test has become one of the most important tools for drug development and approval process of semisolid dosage forms. In vitro release test (IVRT) has the ability to reflect the combined effects of several physicochemical characteristics, particle or droplet size, viscosity, microstructure arrangement of the matter and state of aggregation of dosage form. Genesis of IVRT, its principles and rank order relationship with pharmacodynamic response such as vasoconstriction or dermatopharmacokinetic (skin stripping) results and the evolution of test requirements for regulatory approval is discussed. IVRT reflects various parameters and is an essential part of the stepwise approach to compare topical formulation and its ability to release active in similar quantity at similar rate. Therefore, it is an essential tool, in addition to similar qualitative and quantitative composition (Q1 Q2), to assess the similarity of microstructural arrangement (Q3) as proposed in the Topical drug Classification System (TCS) approach of classes 1 and 3. The TCS system along with evolving concept for topical dermatological drug products from Q1, Q2, Q3 sameness to Q1, Q2, Q3 similar allowing greater permissiveness in formulation changes is discussed.