This page collects terms found in materials on clinical trials and bioequivalence. The definitions are in plain language; where a term has a legal meaning, the source is given. The regulations themselves are on the page “Regulatory framework”.
A
- Adverse event · AE
- Any unfavourable medical occurrence in a trial participant, not necessarily caused by the medicine.
- AUC · area under the curve
- The area under the concentration–time curve: the total amount of the active substance that has entered the bloodstream over the observation period. Together with Cmax it is the main measure in bioequivalence studies. See Cmax, AUC and Tmax.
- Audit
- An independent check of a trial against the protocol, SOPs, good clinical practice and the law, carried out by a specialist who does not take part in the trial.
B
- BCS · Biopharmaceutics Classification System
- A classification of active substances by solubility and permeability across the intestinal wall. It underlies biowaivers for solid dosage forms.
- Bioanalysis
- Measurement of the concentration of the active substance in biological samples (most often blood plasma) with a validated method. Its results are the raw data for calculating Cmax and AUC.
- Bioavailability
- The rate and extent to which the active substance from a dosage form enters the bloodstream and then reaches the site of action.
- Bioequivalence
- No significant difference in the rate and extent to which the active substance of two products becomes available at the site of action at the same molar dose (the definition in clause 11 of the EAEU Rules). In practice it is shown by comparing blood concentrations. See What is bioequivalence.
- Biowaiver
- An exemption from a bioequivalence study in people: equivalence is confirmed by a laboratory comparison of dissolution (in vitro) if the product meets the set conditions. See Biowaiver.
C
- Case report form · CRF
- The document, on paper or electronic, in which the data for each participant are entered according to the protocol.
- Clinical trial
- A study of the diagnostic, therapeutic, preventive and pharmacological properties of a medicine as it is used in humans, by scientific methods, to obtain evidence of safety, quality and efficacy (Law 61-FZ, Art. 4).
- Cmax · maximum concentration
- The highest concentration of the active substance in the blood after the medicine is taken. It reflects the rate of absorption.
- Confidence interval, 90 %
- A range of values for the ratio of the two products’ measures that is compatible with the study data: if the study were repeated many times, 90 % of such intervals would contain the true ratio. Bioequivalence is accepted if, for Cmax and AUC, the interval fits within the equivalence limits (usually 80.00–125.00 %, clauses 81 and 87 of the EAEU Rules). You can check an interval in the calculator.
- Contract research organisation · CRO
- An organisation to which a sponsor transfers, by contract, part of its trial functions: organisation, monitoring, data management.
- Crossover study
- A design in which each participant receives both products in different periods and in a different order, so that each is compared with themselves. The standard design for bioequivalence studies is two-period with two sequences (clause 15 of the EAEU Rules).
E
- Eligibility criteria · inclusion and non-inclusion criteria
- The conditions that decide whether a person may take part: age, examination results, concomitant diseases and medicines. The protocol must set them out clearly (clause 28 of the EAEU Bioequivalence Rules).
- Ethics committee · IEC/IRB; “ESO (NEK)” in the EAEU Rules
- The independent body that protects the rights, safety and well-being of participants: before the trial starts it approves the protocol, the informed consent form and the terms of payments.
- Ethics Council
- The body under the Russian Ministry of Health that reviews the trial documents on ethical grounds and issues an opinion on ethical acceptability (Law 61-FZ, Art. 39.1; Ministry of Health Order No. 586n). See Regulatory framework.
F
- Feasibility
- An assessment before a project starts: can the protocol be run at a particular site — are there suitable participants, staff and equipment, and are the timelines realistic. See Feasibility assessment.
G
- GCP · Good Clinical Practice
- The international standard of ethics and quality for clinical trials: the rights, safety and well-being of participants outweigh the interests of science, and the data are reliable. The EAEU applies its GCP Rules (Decision No. 79 as restated by Decision No. 63, since 10 March 2026). See Regulatory framework.
- Generic medicine · reproduced medicine
- A medicine whose active substances are equivalent in qualitative and quantitative composition to those of the reference product (most often the original) in an equivalent dosage form, and whose bioequivalence or therapeutic equivalence to the reference product has been shown by studies (Law 61-FZ, Art. 4, item 12).
H
- Healthy volunteer
- A person in whom the examination finds no diseases or conditions that rule out participation under the protocol. The EAEU Rules require bioequivalence studies to be conducted in healthy volunteers, except where the product poses an obvious threat to their health and such a study would be unethical (clause 27). Article 4 of the Law on the circulation of medicines has no separate definition of the term.
I
- Informed consent
- The process by which a person voluntarily confirms their willingness to take part in a specific trial after receiving information on all aspects relevant to the decision. It is documented by signing and dating the form (EAEU GCP Rules, clause 1.16). See Informed consent.
- Insurance of participants
- Compulsory life and health insurance of the participant against harm connected with the trial. Participation is impossible without an insurance contract (Law 61-FZ, Art. 44, Part 14).
- Investigator
- The physician who is responsible for conducting the trial at the clinic and for the health of the participants. By law the investigator has a medical specialty matching the trial and at least three years of experience in clinical trial programmes (Law 61-FZ, Art. 40).
- Investigator’s brochure
- A compilation of the available data on the investigational product, both non-clinical and clinical. It is part of the package of documents for ethics review.
M
- Monitoring
- Systematic oversight of a trial by a representative of the sponsor: checking that the rights and safety of participants are observed and that the data are recorded accurately and completely.
- Multicentre trial
- A trial under one protocol at several clinics, sometimes in different countries.
P
- Participant · trial subject
- A person who takes part in a trial. The Law on the circulation of medicines calls them a “patient”; the GCP Rules call them a “subject”.
- Patient information sheet · PIS
- The document with information on the trial on which the participant confirms voluntary consent by signature. It may be on paper or electronic (Law 61-FZ, Art. 4, item 49).
- Phase I
- The first use of a medicine in humans: safety, tolerability, dose selection, how the substance is absorbed and eliminated. Healthy volunteers or patients take part, usually 20 to 100 people. See Clinical trial phases.
- Phase II
- Use of a medicine in patients with a particular disease, usually 100 to 500 people: selecting the regimen and assessing efficacy.
- Phase III
- Confirmation of efficacy, tolerability and safety in a wide group of patients, up to several thousand; often a multicentre trial.
- Phase IV
- A study of a medicine that is already registered: additional safety data and use in routine practice.
- Placebo
- A product without an active substance that looks the same as the investigational product. It is used to separate the effect of the substance from the effect of expectation.
- Power of a study
- The probability that a study shows equivalence if the true ratio of the products and the variability are as assumed in the calculation (for example, a ratio of 95 % and a CV of 20 %). Power determines the number of volunteers: you can work it out in the calculator.
- Pre-analytical stage
- Everything that happens to a sample before it is measured: collection, labelling, centrifugation, freezing, storage, transfer to the laboratory. Mistakes at this stage distort the result, so it is described in the protocol and SOPs.
- Protocol
- The main document of a trial: aim, design, eligibility criteria, procedures, sampling schedule, statistical model. A trial is run strictly according to the protocol.
R
- Randomisation
- Random assignment of participants to groups or dosing sequences so that the groups are comparable.
- Reference product
- The product against which the investigational product is compared; as a rule, the original medicine. The EAEU Rules set how the reference product is chosen (clause 18).
S
- Screening
- The examination of a candidate before enrolment: a conversation, an examination, tests. On the results the investigator physician decides whether the person is suitable. See How volunteer selection works.
- Serious adverse event · SAE
- An adverse event that resulted in death, was life-threatening, required hospitalisation or prolonged it, resulted in persistent disability or in a congenital anomaly. Such events are reported to the sponsor within the set time limits.
- Single and double blinding
- A way of conducting a trial in which participants (single blind), or participants and investigators (double blind), do not know which product is used, so that expectations do not influence the assessment.
- SOP · standard operating procedure
- A detailed written instruction on how to perform a particular operation so that it is done the same way every time. A clinic’s quality system is built on SOPs.
- Sponsor
- The organisation or person responsible for initiating, organising and (or) financing a trial. Often the manufacturer of the medicine.
T
- T/R ratio
- The ratio of the geometric mean of a measure for the test product (T) to that for the reference product (R), usually as a percentage. 100 % means the same entry into the blood.
- T½ · half-life
- The time in which the concentration of a substance in the blood falls by half. It sets the length of the break between dosing periods: five half-lives is usually enough (clause 15 of the EAEU Rules).
- Tmax · time of maximum concentration
- The time it takes for the concentration of a substance in the blood to reach its maximum (Cmax).
W
- Washout period
- The break between dosing periods of a crossover study, long enough that by the start of the next period the concentration of the substance in the blood is below the limit of quantification. Five half-lives is usually enough (clause 15 of the EAEU Rules).
See also
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
Regulatory framework: the rules for clinical trials and bioequivalence studies in Russia and the EAEU
Clinical trials in Russia are governed by Federal Law No. 61-FZ “On the Circulation of Medicines”, the Good Clinical Practice Rules and the Bioequivalence Rules of the Eurasian Economic Union (EAEU), and orders of the Ministry of Health. This page shows what each document contains and which open registers let you check a clinic.
Learn more
Calculator: how many volunteers a bioequivalence study needs
The calculator estimates how many volunteers a standard crossover bioequivalence study (2×2) needs in its analysis, from intra-subject variability, the expected T/R ratio, power and the 80–125 % limits. The output is the number in the analysis, the number to enrol with a dropout allowance, and a power curve.
Learn more