Flow-Through Cell Apparatus (USP Apparatus 4): Operation and Features

INTRODUCTION Dissolution testing plays an important role in several areas during drug development. It can be used as a quality control tool to monitor batch-to-batch consistency of drug release from a dosage form and as an in vitro surrogate for in vivo performance that can guide formulation development and ascertain the need for bioequivalence tests. Several apparatus (compendial and noncompendial) are used for the study of dissolution of compounds and dosage forms. The flow-through cell method for the study of dissolution first appeared in 1957 as a flowing medium dissolution apparatus developed by FDA (1). The method was adapted by USP, the European Pharmacopoeia (Ph. Eur.), and the Japanese Pharmacopoiea (JP), and the flowthrough cell became an official apparatus (Apparatus 4 for the USP and Ph. Eur., Apparatus 3 for JP). Specifications and methodology are described in the relevant chapters of the pharmacopeias—USP Chapter Dissolution (2), Ph. Eur. 2.9.3 (3), and JP XV, 6.10 Dissolution Test (4)—and there is good harmonization among them.