"Visually clean" as a sole acceptance criterion for cleaning validation protocols

The role of visual examination as the sole acceptance criterion in cleaning validation protocols is explored, including the proper definition of "visual limit" for a given residue. Such a visual limit is specific to the surface the residue is on, and is further defined by viewing conditions, such as lighting, distance, and angle of viewing. A visually clean standard may only be properly utilized if the visual limit is below any scientifically calculated residue limit, such as that determined by a traditional dose-based limit determination. While such an approach, properly applied, has scientific justification and appears to be accepted by the proposed Annex 15 to the European GMPs, the approach is still untested with regulatory authorities.