GMP criteria for retest and failure analysis. Handling out-of-specification results in the pharmaceutical quality control laboratory.

The Food and Drug Administration's current Good Manufacturing Practices guidelines for the inspection of pharmaceutical quality control laboratories stress the need for explicit standard operating procedure's requirements for retesting criteria and the investigation of specification failures. Out-of-specification results are best handled through a priori procedures for the evaluation of their validity. These procedures should also specify the degree of retesting or resampling permitted. Initial investigations should focus on uncovering apparent laboratory-related or sampling errors. Should this initial investigation prove inconclusive, an expanded investigation should be conducted to uncover any less conspicuous cause, which could include process or operator-dependent as well as analytical errors. A schematic approach to controlling retesting through a rigorous policy of investigating failures, limiting retest analyses, and documenting and reporting all results is described.