Active pharmaceutical ingredient (API), small molecule

A chemically synthesized active ingredient of relatively low molecular weight, usually isolated as a crystalline solid. Impurities can carry through a multistep synthesis, so control relies on starting material selection, in-process controls and studies of how impurities are purged, not only on final testing. GMP for APIs follows ICH Q7, and the choice of regulatory starting material follows ICH Q11. For Japan, API makers often register a Master File so the drug product MAH can reference confidential process details without seeing them.