Shelf-life and its estimation in drug stability studies
One important property of any drug product is its stability over time. Drug stability studies are routinely carried out in the pharmaceutical industry in order to measure the degradation of an active pharmaceutical ingredient of a drug product. One important study objective is to estimate the shelf-life of the drug; the estimated shelf-life is required by the US Food and Drug Administration to be printed on the package label of the drug. This involves a suitable definition of the true shelf-life and the construction of an appropriate estimate of the true shelf-life. In this paper, the true shelf-life <italic>T</italic><sub>β</sub> is defined as the time point at which 100β% of all the individual dosage units (e.g. tablets) of the drug have the active ingredient content no less than the lowest acceptable limit <italic>L</italic>, where β and <italic>L</italic> are prespecified constants. The value of <italic>T</italic><sub>β</sub> depends on the parameters of the assumed degradation model of the active ingredient content and so is unknown. A lower confidence bound <italic>Tˆ</italic><sub>β</sub> for <italic>T</italic><sub>β</sub> is then provided and used as the estimated shelf-life of the drug.
