Multi-product lot scheduling with backordering and shelf-life constraints

In this paper, we revisit the economic lot scheduling problem (ELSP), where a family of products is produced on a single machine, or facility, on a continual basis. Our focus is on the determination of a feasible production schedule, including the manufacturing batch size of each item. We assume that total backordering is permissible and that each of the products has a limited post-production shelf life. Several studies examining this problem have suggested a rotational common cycle approach, where each item is produced exactly once every cycle. To ensure schedule feasibility, we resort to the technique of reducing individual production rates and allow the flexibility of producing any item more than once in every cycle, in conjunction with appropriate timing adjustments. In order to solve this more generalized model, which is NP hard, we suggest a two-stage heuristic algorithm. A numerical example demonstrates our solution approach.     

Estimating Drug Shelf-life with Unknown Lot-to-lot Variability

This article addresses the problem of estimating the shelf-life of a drug through a standard stability study that is routinely performed in the pharmaceutical industry. Based upon a dataset of the degradation of the drug efficacy over time, the objective is to estimate at what time point the drug efficacy falls below a minimally acceptable level. In this article, attention is directed toward the different roles played by lot-to-lot variability and measurement error in the performances of various estimation methodologies. The standard estimation method, as proposed by the United States Food and Drug Administration, for example, in accordance with current international guidelines, is compared with some new approaches. Simulation results are presented, which illustrate the advantages and disadvantages of the different estimation methodologies, and some recommendations and suggestions are made for shelf-life estimations.