lower confidence bound lower specification limit shelf life
In practice, an additional amount of active ingredients is sometimes added to account for the possible stability loss over a desired expiration period provided that the resulting initial value is within the USP/NF upper specification limit. The additional amount of active ingredient is called an overage of the drug product. For example, suppose that the desired shelf life of a drug product is 36 months, the expected stability loss over 36 months is 15% of label claim, and USP/NF specifications limits are (90%, 110%) of label claim. Then the pharmaceutical company may consider adding an overage of 5% of the label claim to the drug product to ensure that the drug product will remain within (90%, 110%) specification limits by the end of shelf life. The overage of 5% may result in an average potency of 105%, which is still within USP/NF specification limits. However, it should be noted that adding an overage of 5% may
p e r c e n t o f l ab e l cl ai m
increase the manufacturing cost and/or the chance of causing a potential safety problem.