Science-Based Risk Assessment for the Categorization of Visual Inspection Defects of Sterile Dosage Forms

Background/Objectives: Visual inspection of parenteral drug products is a mandatory and critical unit operation, typically followed by an Acceptable Quality Level (AQL) check, as required by current Good Manufacturing Practices (cGMP) and regulatory authorities worldwide. Visual inspection and AQL checks need to ensure—probabilistically and statistically—that sterile product units with critical, major, or minor defects are excluded from the acceptable portion of a batch, thereby preventing such defective units from reaching distribution and eventually patients. Despite clearly defined batch defect categories, classifying individual defects and assigning them to the correct category remains challenging and has historically lacked standardization and scientific rationale. This paper presents a science-based risk assessment methodology for categorizing defects in sterile dosage forms, incorporating considerations of severity (with emphasis on patient safety), probability of occurrence, and probability of detection. Methods: The methodology is based on a modified Failure Mode and Effects Analysis (FMEA), tailored specifically for visual inspection defect classification. Results: Three examples demonstrate the practical application of this risk-based approach across different container formats: vials, pre-filled syringes, and cartridges. Conclusions: This standardized methodology offers a clear, consistent, and scientifically justified framework for defect classification. Its use enables pharmaceutical manufacturers to establish robust, risk-based defect categorization for the visual inspection of clinical and commercial sterile products.