Clinical trials: The phases
Clinical trials are conducted by physicians or hospital teams and proceed along 3 successive phases:
During Phase 1, the compound is tested on a limited number of healthy subjects*, who may receive compensation and are under strict medical supervision. The compound is tested over a short period of time. The purpose is to evaluate the product’s safety, how it evolves within the body, the tolerance threshold, and adverse events.
During Phase 2, the compound is tested in larger groups of patients. The purpose is to test the product’s efficacy and determine optimal dosage regimen. These studies are usually comparative: one group of patients is administered the product, and the other is given a placebo.
A larger number of patients participates in Phase 3. The purpose is to compare the therapeutic efficacy of the compound with a reference treatment (if there is one) or to a placebo (when there is no alternative therapy). Such studies frequently involve many study centers. Generally, neither the patient nor the medical professionals involved are aware of what treatment is given to which patient (double blind trial). This is to avoid any bias or prejudiced opinion on either side regarding efficacy or adverse events.
* Patients are recruited to phase I studies especially in cases such as cancer therapies.
Once the three phases have been completed successfully, the resulting data, together with the results of preclinical testing, are collected to compose a registration file that will be submitted to public health authorities for license to market.
Trials do not cease once the treatment is on the market: studies continue throughout the marketing life of any treatment. Phase 4 trials are carried out after approval in conditions close to those of usual medical care. One important goal is to detect any possible rare, undesirable side effects that may have escaped attention in the previous phases (i.e. pharmacovigilance). Another is to define conditions of use for certain groups of at-risk patients.
During this phase drug interactions can be listed, and researchers can develop optimized formulations and therapeutic indication extensions.