Post-marketing drug surveillance--concepts, insights and applications.

At the present drug approval process consists of preclinical animal testing, followed by three phases of clinical testing. Phase I is usually conducted on non-patient volunteers; phase II involves administration of the drug to a small number of selected patients; and phase III is the final premarketing test of the drug's safety and efficacy. These trials have major limitations, such as restricted patient populations, limited duration of patient exposure, and limited patient numbers. Considerable information remains unknown after the end of phase III testing, including: less common adverse effects; delayed adverse effects; efficacy and toxicity in types of patient usually excluded from premarketing testing, e.g. children, pregnant women and old people; efficacy and toxicity in patients with other illnesses and/or ingesting other drugs; efficacy and toxicity relative to other drugs used for the same purpose; efficacy and toxicity when used for indications other than those initially tested; the toxic effects of a massive overdose; physicians' prescribing habits, etc. The attempt to obtain this information after marketing is postmarketing drug surveillance.