Phases Of Clinical Drug Development

The case described represents just one of many decisions that must be made before beginning clinical trials. Clinical drug trials are described as Phases I-V. The first trials in humans that test the drug for safety are considered Phase I. These studies usually employ normal volunteers, and may expose about 50 individuals to the drug. For known toxic compounds such as anticancer agents, only patients with the targeted illness would be used.

The first studies to define efficacy are considered Phase II. These studies are typically conducted to determine the best dosage regimen for the Phase III efficacy studies. In general, 100-300 patients would be entered into various con trolled clinical trials during this phase. Phase III, considered an extension of Phases I and II, exposes a larger number of patients (e.g., 1000-3000) to the test drug under controlled trials to further delineate the safety and efficacy profile of the drug. For example, special studies in the pediatric or elderly population may be performed during Phase III (although the studies themselves may be Phase I-type studies). After a successful Phase III program, an NDA may be filed with the appropriate regulatory agency.

Phase IV studies may be done for two different reasons. Marketing-oriented trials may extend the recommended duration of treatment, or they may be primarily instructive in nature to help familiarize more practitioners with the drug's efficacy and side effects. Phase IV trials may be required by the FDA as a condition of approval to extend the knowledge of the pharmacological effects of a drug while allowing simultaneous availability to patients. Phase V studies may extend the indications of a drug to an entirely different disease state. For example, propranolol (Inderal) was first marketed for the management of angina pectoris caused by coronary atherosclerosis. Indications were later extended to management of hypertension, reduction of mortality after myocardial infarction, ad-junctive therapy for pheochromocytoma, management of hypertrophic subaortic stenosis, and prophylaxis of migraine headaches.

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