Phases in Clinical Trial

Clinical trial is needed to support effectivity and safety claims of a medicine, and also to support data for approval need by regulatory system. Before a clinical trial is conducted in human, a compound (experimental medicine) is tested to animals first, to show whether the compound gives benefit or not. Animal study is using several dose level, from small to large doses. This is needed to determine how high is lethal dose, how low is an effective dose, how high is safe dose, and how wide/narrow is the safety margin, etc. When the animal trial data would be extrapolated into propose human trial with same agent, dose should be calculated by scientist so that human dose is much smaller than animal dose.

There are four phases of clinical trials: phase I, II, III, and IV. Phase I-III are called experimental trials, and phase IV is postmarket study.