Most clinical trials are designated as phase I, II, III, or IV, based on the type of questions that study is seeking to answer:
In Phase I clinical trials, researchers test a new drug or treatment in a small group of people (20-80) for the first time to evaluate its safety, determine a safe dosage range, and identify side effects.
In Phase II clinical trials, the study drug or treatment is given to a larger group of people (100-300) to see if it is effective and to further evaluate its safety.
In Phase III clinical trials, the study drug or treatment is given to large groups of people (1,000-3,000) to confirm its effectiveness, monitor side effects, compare it to commonly used treatments, and collect information that will allow the drug or treatment to be used safely.
In Phase IV clinical trials, post marketing studies delineate additional information including the drug's risks, benefits, and optimal use.
These phases are defined by FDA in the Code of Federal Regulations.
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