- - clinical t. a controlled experiment involving a defined set of human subjects, having a clinical event as an outcome measure, and intended to yield scientifically valid information about the efficacy or safety of a drug, vaccine, diagnostic test, surgical procedure, or other form of medical intervention.Four phases of clinical t. are distinguished. Phase I trials usually involve fewer than 100 healthy volunteers who are exposed to a new drug or vaccine. Such studies seek to establish optimal dosage and route of administration and to detect adverse reactions. Phase II trials generally involve 200–500 volunteers randomly assigned to control and study groups. These are pilot efficacy studies, with emphasis on immunogenicity in the case of vaccines, and on relative efficacy and safety in the case of drugs. Phase III trials, often multicenter, involve thousands of volunteers, randomly assigned to control and study groups. The aim is to generate statistically relevant data. Phase IV trials are conducted after a national drug registration authority (in the U.S., the Food and Drug Administration) has approved an agent for distribution or sale. They may explore specific pharmacologic effect, adverse reactions, or long-term effects.- randomized controlled t. (RCT) an epidemiologic experiment in which subjects in a population are allocated randomly into groups, called “experimental” or “study” and “control” groups to receive or not receive an experimental therapeutic or preventive regimen, procedure, maneuver, or intervention.
* * *tri·al 'trī(-ə)l n2) one of a number of repetitions of an experiment
* * *tri·al (triґəl) (trīl) a test, study, or experiment.
Medical dictionary. 2011.