A phase of a clinical trial refers to the stage of development that a potential new drug therapy is in. The various phases are characterized, among other things, by different objectives and participant numbers. A clinical trial can be a Phase I, Phase II, Phase III or Phase IV trial (post- marketing surveillance trial), with the greatest differences lying between Phase I and Phase II:
Overview of clinical trial phases
Phase I Clinical Trial
Phase I clinical trials are typically conducted in a low number of healthy volunteers, but there are exceptions where they are conducted patients instead, e.g. in case of cytotoxic cancer drugs or when testing in healthy volunteers wouldn’t be meaningful. They include the first administration in humans, called “first in man” or “first in human” trials. Phase I clinical trials are often done in specialized units due to the fact that participants are monitored intensively in the course of evaluation of the IMP’s safety. These trials’ objective usually is the evaluation of tolerability & safety.
Phase II Clinical Trial
Typically a proof-of-concept study in clinical development but a phase II clinical trial can also be a pivotal clinical trial. Efficacy, safety, short term side effects, optimal dose, best population and treatment duration are evaluated by including a midsize number of participants. The duration is normally 1 year or more. Phase II clinical trials set the requisites for phase III clinical trials.
Phase III Clinical Trial
The final phase of clinical trials before a potential submission of a marketing authorization application. Typically, Phase III clinical trials are conducted with a large number of participants, often as part of a global approach, to include a highly diverse patient population and to collect data on efficacy, superiority (as it may compare an experimental treatment directly against the current standard of care), and safety, including side effects. In some cases, e.g. for rare diseases, Phase III may be skipped if sufficient data are available from pivotal Phase II clinical trials for marketing authorization application.
Phase VI Clinical Trial
After Marketing Authorization, post-marketing surveillance trials are conducted for ongoing safety surveillance and to study how well the new treatment works over a longer time. They are often observational studies, meaning that researchers/investigators don’t actively control the patient’s treatment.