Comparison of Three Methods to Determine the “Safety Margin” Used to Determine Final Release Time of Short-Lived Products per USP

The introduction of USP offers a new regulatory pathway for shortening the release of short-lived pharmaceutical products, including cell and gene therapies, by allowing manufacturers to optimize growth conditions such as media formulation and temperature. The chapter dictates the final time to release is determined by the time to detection (TTD) of the slowest growing organism plus a provided "safety margin" formula. This formula relies on calculation of doubling time of the slowest growing microorganism which can be derived by various methods.We evaluated three methods to determine this doubling time: traditional plate enumeration, optical density, and a novel approach using the kinetics of the BACT/ALERT® system. The latter allows estimation of generation time directly from TTD curves based on CO2 production as measured by the BACT/ALERT® system. The benefits of this method include minimal handling time, offering a scalable, practical alternative to traditional methods.We compare all three methods across multiple organisms, including slow-growing anaerobes such as C. acnes, to assess applicability, repeatability, and robustness.The results demonstrate that BACT/ALERT®-based TTD analysis enables precise and efficient safety margin determination, supporting confident, faster release decisions in line with USP .