[Stability of medicine: its relationship with their expiration date and with degradation products]

The expiration date of medicines is an application and direct interpretation of the knowledge obtained from stability studies, which are conducted under rigorous conditions, employing appropriate statistical and conceptual procedures. Instability of an active compound may result on one hand in efficacy decrease and on other in the possible presence of toxic degradation products. In this review, we analyze the reasons underlying the definition of the expiration date of medicines and their relationship with the stability, we mention the essays that must be performed to support this definition and finally give examples of degradation products and of their possible adverse effects.