Clinical trials of new drugs and vaccines begin with a phase I trial on a small number, typically fewer than 50, of healthy volunteers to study pharmacological properties, mode of action, and safety. A phase I trial also can test routes of administration and doses. A phase II trial is the initial trial of efficacy, a small randomized trial (perhaps 200 to 300 participants) to compare the safety and efficacy of the new drug with existing alternatives. A phase III trial is a larger study, with perhaps thousands of volunteer participants with random allocation and sometimes multiple study centers. All phases require ethical review and an assurance that informed consent requirements have been met.
Subjects: Public Health and Epidemiology.