Why there are phases
A medicine cannot be given to a large group of people straight away: first it must be clear whether it is safe and at what dose it works. So studies go in order, and the results of each phase decide whether the next one can begin. Only after clinical studies can a medicine be registered and used for treatment.
Phase I: safety and dose
The first use of a medicine in humans. A small group usually takes part — as a rule, 20 to 100 people: healthy volunteers or patients (depending on the medicine). The studies examine safety, tolerability, side effects and a suitable dose, as well as how the substance is absorbed and eliminated.
Phase II: dosing regimen and efficacy
The medicine is given to patients with a particular disease — usually 100 to 500 people. The aim is to select the dosing regimen and dose and to assess efficacy. The medicine is compared with a placebo or with the standard treatment for the disease.
Phase III: confirmation in a large group
The medicine is studied in a wide group of patients — up to several thousand. The study confirms the preliminary results on efficacy, tolerability and safety. It is often multicentre: it takes place in several clinics, sometimes in different countries.
Phase IV: after registration
Carried out when the medicine is already registered. Additional data are collected on safety and on interactions with other medicines, and therapy is observed in everyday practice. Many such studies are observational: the doctor treats the patient as usual, and the data are collected under a single protocol.
How bioequivalence is different
A bioequivalence study is not one of these phases: it applies to generic medicines. Its aim is to show that a generic reaches the bloodstream in the same way as the original. More in “What is bioequivalence”.
Participation and rights
Participation is voluntary in any phase. Before enrolment, the doctor explains the aim of the study, the procedures, the risks and the benefits, and the participant signs informed consent. More for patients on the “Patients” page, and for volunteers on the “Volunteers” page.
Questions and answers
How many people take part in each phase?
Approximately 20 to 100 in Phase I, 100 to 500 in Phase II, and up to several thousand in Phase III. In Phase IV the number depends on the aims of the observation. The exact number is always stated in the protocol of the specific study.
Which phase is a bioequivalence study?
It is a separate type of study for generic (reproduced) medicines. Phases I–IV apply to the development of new medicines.
See also
Phase I clinical trials in Moscow
Phase I is the first use of a new medicine in humans. It studies safety, tolerability and how the medicine behaves in the body, and helps to find a suitable dose. A small group of healthy volunteers or patients usually takes part.
Learn more
Phase II, III and IV clinical trials
Phases II–IV are conducted in patients. Phase II finds the dosing regimen and assesses efficacy, Phase III confirms efficacy and safety in a broad group, and Phase IV follows the medicine after registration. The clinic takes part in multicentre and international studies.
Learn more
What is bioequivalence? Cmax, AUC and Tmax in plain language
Bioequivalence is the similarity in how two medicines with the same active substance enter the bloodstream. It is tested in volunteers by comparing concentration–time curves using Cmax and AUC.
Learn more