The objective of this study was to provide a better understanding of SUPAC-IR and its application in handling postapproval changes to immediate release solid oral dosage forms. Originally, SUPAC-IR was aimed at reducing the regulator burdern of the industry when they were making postapproval changes, but still at maintaining the formulation quality and performance of a drug product. The postapproval changes that were covered under SUPAC-IR included variations in the components ad composition of formulation, the site of manufacturing, batch size, manufacturing equipment, and manufacturing process. The guidance defined levels of changes, based on the likelihood of risk ocurrence and potential impact of postapproval changes upon the safety and efficacy of a drug product I suggested what a type of fing report should be submitted to the FDA for each level of change. Chemist, manufacturing, and control tests to be executed were also recommended for each change level The important tests specified in the guidance included batch release, stability, in vitro dissolution, and in vivo bioequivalence tests. However, there have been strong demands on revising the current SUPAC-IR in order to resolve some issues and to improve its usefulness in evaluating postapproval changes to immediate release solid oral dosage forms. In particular, the rigorous requirement of case C dissolution test and the definition of batch size were challenged by both academia and the industry. A revision work was in progress to reflect these inputs and to expand the utility of SUPAC-IR. As a result of these concerted efforts, an updated 2nd version of SPAC-IR would be likely to be issued ver soon to the public.