Clinical Research Trial Phases

Clinical trials are traditionally classified into four phases, with precise distinctions between the phases. Each phase of the development process leads to a greater understanding of the indications of the investigational product. The four phases may take years for a pharmaceutical company to accomplish. The following are the four phases.
Phase I: Human Pharmacology Phase.
The experimental drug is administered to small numbers of normal human volunteers or to a carefully defined subject population under controlled conditions to obtain preliminary data on drug tolerability, pharmacokinetics and pharmacodynamics. These trials have a smaller number of study participants.
Phase II: Therapeutic Exploratory Phase.
The investigational product is administered to limited numbers of subjects with the medical indication, in order to define a therapeutic dose range and to establish efficacy, side effects, and clinical toxicity of the drug. Often this phase is separated into Phase 11a and Phase 11b types of studies.
Phase III: Therapeutic Confirmation Phase.
The investigational product is administered in large scale trials to establish efficacy and safety of the drug. These studies are required for submission to the regulatory authorities in support of a product license application for the new drug. These studies may also be divided into Phase IIIa and Phase IIIb.
Phase IV: The Therapeutic Use Phase.
These trials are undertaken after local regulatory approval has been obtained. The trials are limited to the drug’s approved indications, dosage ranges, dosage forms, routes of administration and subject population.