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A Phase One Study:
Phase I studies are primarily concerned with assessing a drug's safety. This initial phase of testing in humans is done in a small number of volunteers (20 to 100), who are usually paid for participating in the study. The study is designed to determine what happens to the drug in the human body--how it is absorbed, metabolized, and excreted. A Phase I study will investigate side effects that occur as dosage levels are increased. This initial phase of testing typically takes several months. About 70 percent of experimental drugs pass this initial phase of testing. Please note phase one studies may also be conducted in disease specific populations (e.g. cancer).
A Phase Two Study:
Once a drug has been shown to be relatively safe, it must be tested for efficacy. This second phase of testing may last from several months to two years, and involve up to several hundred patients. Most Phase II studies are randomized trials. One group of patients will receive the experimental drug, while a second "control" group will receive a standard treatment or placebo. Often these studies are "blinded"--neither the patients nor the researchers know who is getting the experimental drug. In this manner, the study can provide the pharmaceutical company and the FDA comparative information about the relative safety of the new drug, and its effectiveness. Only about one-third of experimental drugs successfully complete both Phase I and Phase II studies.
A Phase Three Study:
In a Phase III study, a drug is tested in several hundred to several thousand patients. This large-scale testing provides the pharmaceutical company and the FDA with a more thorough understanding of the drug's effectiveness, benefits, and the range of possible adverse reactions. Most Phase III studies are randomized and blinded trials.
Phase III studies typically last several years. Seventy to 90 percent of drugs that enter Phase III studies successfully complete this phase of testing. Once a Phase III study is successfully completed, a pharmaceutical company can request FDA approval for marketing the drug.
posted: 02/10/2006
