The cluster design for the postmarketing stability surveillance program

Postmarketing stability surveillance is necessary in order to (re)confirm the stability profile of a marketed pharmaceutical formulation throughout its lifecycle. In this paper the so-called ‘selected date’ or ‘cluster approach’ is described as an efficient alternative to the conventional ‘fixed-interval approach’ which is normally followed. The principle of the cluster approach is that samples of all batches of a formulation in a stability study are tested simultaneously at flexible time intervals. A statistical routine performed on the analytical results provides the opportunity to either confirm or reject the registered shelf life of the product tested. The cluster approach provides significant efficiency improvements, without losing the essential information about the stability of a product.