Dissolution Equipment and Hydrodynamic Considerations for Evaluating Modified‐Release Behavior

After oral administration of modified-release (MR) formulations, a broad range of release patterns can be obtained and thus, at least theoretically, oral MR formulations can be tailored to the needs of specific patient populations. This chapter discusses the dissolution equipment that is currently used for the in vitro evaluation of dosage forms. It points out the important parameters to consider when designing in vitro methods aimed to simulate the hydrodynamic conditions in the different sections of the human GI tract that are relevant to in vivo drug release in both fasted and fed state dosing conditions. By providing the possibility to apply different flow rates and to create pH (media) profiles, the USP apparatus 4 theoretically offers the opportunity to simulate GI hydrodynamics in an in vitro experiment. Consequently, the dynamic gastric model appears to be a more attractive in vitro model than various compendial and noncompendial apparatus.