Ongoing monitoring of product quality is essential. A product does not stand still; it changes over time. Not just in its stability, but in the materials and processes that contribute to manufacture. Perhaps the manufacturing equipment is replaced with something more modern? Or one of the ingredients is no longer available from the same supplier. Or the old pack size is no longer economically viable and marketing wants a pack that holds twice the quantity. Or storage conditions in the field are more extreme than was envisaged. Or the manufacturer wishes to extend the shelf life that was approved at first registration. The sponsor must ensure that there is no change to quality, safety or efficacy, including bioavailability. The key word here is validation. It must be demonstrated that changes/variations do not lead to a reduction in quality, either at batch release or on storage. Guidelines exist as to how to validate such changes^{35, 36, 37}.

In addition, random postmarket testing by regulatory authorities is intended to (as we say in Australia) keep the bastards honest. Targetted sampling is more efficient when a history is available for the type of product or for the manufacturer.