The Different Phases of Clinical Trials
Clinical trials are classified into Phase 1, Phase 2, Phase 3 or Phase 4 studies depending on where in the life of the new treatment the trial commences. Click on the links for further details relating to the phases of trials and trial design .
Phase 1 (Phase I) Trials
These are the earliest trials in the life of a new drug or treatment. They are usually small trials, recruiting anything up to 30 patients (often a lot less).They involve ‘healthy volunteers’ not patients with a disease.
Phase 1 trials are done to find out:
- the safe dose/dose range for the drug
- the side effects of the medication
- how the body clears (excretes) the drug and the pharmacokinetics of the drug
Healthy volunteers will be exposed to increasing doses of the novel treatment. As with all trials the will be closely monitored and any side effects noted.
The aim of Phase 1 trials is to look at doses and side effects. Phase 1 trials are important because they are the first step in finding new treatments for the future. Only once the results of the Phase 1 study are known will the Phase 2 study commence.
Phase 2 (Phase II) Trials
About 70 out of every 100 new treatments tested at Phase 1 make it to a Phase
2 trial. Phase 2 studies are larger than Phase 1 studies and this is when
further safety information is gathered, the dose and dosage range and the
maximum dose decided. If the results of Phase 2 trials indicate that a new
treatment may be as good as the existing treatment, or even better, then
the medication will be trialled in a larger Phase 3 study.
Phase 2 trials are designed to find out:
- if the new drug is effective in the indicated disease
- further details of side effects/adverse effects and how to manage them
- the most effective dose to use from the range of doses highighted in the Phase I studies
Phase 3 (Phase III) Trials
Phase 3 trials compare new treatments with the best currently available treatment
(the standard treatment).
They may compare :
- different doses or ways of giving a standard treatment
- a new treatment schedule with the standard medication
Phase 3 trials are usually much larger than Phase 1 or 2 trials. Phase 3 trials generally involve thousands of patients in many different hospitals and even different countries.
Phase 4 (Phase IV) Trials
Phase 4 trials are done after a drug has been shown to be effective and
has been granted a product license by the MHRA. The trials compare
drugs that are already available for doctors to prescribe, rather than new
drugs that are still being developed.
The main reasons pharmaceutical companies run Phase 4 trials are to find out :
- more about the side effects and safety of the drug
- the long term risks and long term benefits
- how effective the drug is when it is used more widely than in small clinical trials
Some useful references are:
Di Giovanna I., Hayes G. (Eds) Principles of Clinical Research.
(The Institure of Clinical Research): 2001. Wrightson Biomedical Publishing Ltd.
Flather M., Aston H., Stables R. (Eds) Handbook of Clinical Trials:2001 Remedica Publishing Ltd.