In-use stability modeling

Experimental design and modeling of in-use stability testing are presented in this paper. In-use open container degradation is considered in terms of time open container or/and the number of instances that the same container is used. Degradation is estimated based on two models, the fixed and the general model. The fixed model estimates in-use degradation for those fixed time points of closed container where the in-used experimental data is collected. The general model estimates in-use degradation for any time point of closed container using the estimated relationship between closed container time and the degradation rate of open container. Data for in-use open container stability does not have to be collected at a closed container time of interest to estimate in-use degradation at this time point as long as this point is within the range of the experiment. Stability of the product in terms of drift from the initial time to the time of interest is calculated as the sum of closed and in-use open containers drifts.