Phase 3 clinical trials follow phase 1 and 2 clinical trials. In a phase 1 clinical trial, the tolerability and safety of the new drug is studied, usually in a small number of healthy volunteers. Phase 2 is aimed at determining the drug's efficacy and optimal dosing regimen. After phase 2, the drug is entered into the next phase of testing in a phase 3 trial.
The main focus of phase 3 trials is to demonstrate and confirm the prelimary evidence gathered in the previous trials that the drug is, a safe, beneficial and effective treatment for the intended indication.
Phase 3 is the last phase of testing to be completed before the drug's details and clinical trial results are submitted to the regulatory authorities for approval of the drug's release on the open market. Phase 3 is therefore a vital phase of drug development and billions may be spent progressing the drug to a phase 3 trial, only for the drug to prove ineffective in a larger patient population or have serious safety concerns that prevent its approval.
Phase 3 trials are often multicentre trials involving up to 3,000 participants. Aside from testing safety and efficacy variables again, other aspects of the drug that may be studied in phase 3 are further exploration of the dose-response relationship, the drug's effects in wider populations and its efficacy at different stages of disease or when used in combination with other agents.
The drug may also be tested in subgroups with co-morbidities such as kidney or liver disease or heart disorders. Much of the information that is given on the label of a drug is derived from the phase 3 trial results.
Other factors that may be considered inphase 3 include improvement in patients' quality of life and secondary benefits of the drug.
Reviewed by Sally Robertson, BSc