Metrologic approaches to setting acceptance criteria: unacceptable and unusual characteristics

Decisions regarding acceptance criteria in regulatory or compendial contexts are among the most difficult to make. Acceptance criteria aid in the identification, on the one hand, of materials with unacceptable characteristics that should not pass the tests and procedures or, on the other hand, of unusual characteristics that indicate materials that are unlikely to pass the tests and procedures. For relatively complex procedures metrological approaches can differentiate between intra- and inter-laboratory variation and clarify unacceptable and unusual data. Such testing requires collaborative studies in which each participating laboratory essentially compares itself to the other laboratories in the collaborative study. Laboratories that use the reference standard established by the collaborative study are conducting a performance verification test in which they compare their capabilities to those of laboratories in the collaborative study. This paper considers aspects of a series of complex issues involving unacceptable/unusual characteristics primarily in the context of USP's work but with implications for manufacturing science via considerations of process capability and Quality by Design and to measurement science. Ultimately, acceptance criteria support the availability of good quality, safe, and effective medicines for patients and consumers.