A clinical trial of pharmaceutical product is a long-term process. A study can take several years. Depending on stage of development, it is divided into phases. There are four main phases of clinical trials:
Phase I is the first test of a drug in humans, generally in healthy volunteers (no less then 10 subjects). These trials are often called clinical pharmacological trials as they are designed to establish the safety, tolerability, therapeutiс action, pharmacokinetic and pharmacodynamic characteristics, and sometimes the initial efficacy rate in humans.
In Phase II, a drug is evaluated for its efficacy and safety in patients with specific diseases. As a rule, these are placebo - controlled trials. Sometimes, Phase II of a clinical trial is divided into phases IIa and IIb. The purposes of Phase II trial are to evaluate short-term safety of a drug (IIa) and to confirm clinical efficacy of a drug and determine the therapeutic dose range (IIb).
In Phase III clinical trials, the study drug is given to large groups of patients (thousands of subjects) of different age groups, with different concomitant diseases. These trials are conducted at multiple scientific research sites in different countries. Phase III trials are often randomized controlled studies. These trials investigate all aspects of treatment including assessment of risk / benefit ratio. According to the results of Phase III clinical trials, the decision on registration of the drug product or refusal in its registration is made. Phase III of a clinical trial may be divided into phases IIIa and IIIb as well.
A Phase IV clinical trial is performed after a drug product has been approved. These trials are often called post-marketing (post-registration) studies. The purposes of these trials are to identify differences between a new pharmaceutical product and other drugs in this pharmacological group, to compare its efficacy with already marketed analogs, and to demonstrate a new drug benefit in relation to health economics and to identify and determine previously unknown or ill-considered side effects as well. As a result, the safety and efficacy of a drug may be reviewed periodically according to new clinical data on its use.