What is a clinical trial?

'Clinical trial' is the name given to any study involving the testing of a drug, device or other intervention in humans.

In the first case, the drug may be new, and never before tested in humans, or it may be an existing drug being tested in a novel therapeutic application.

In drug development, clinical trials follow 'preclinical' trials that are conducted in the laboratory or in appropriate animal models of human disease. Results from preclinical trials are collected to establish that a new compound is likely to be safe for testing in humans.

Clinical trials are conducted under strict regulations and protocols determined by a governing body such as the US Food and Drug Administration (FDA) or the Therapeutic Goods Administration (TGA) in Australia.

Are all clinical trials designed in the same way?

No. Before new drugs, devices or procedures reach the market, clinical trials are carried out in three phases of increasing complexity. Each phase of trial is designed to answer different questions.

What are the different stages in a clinical trial?

Phase I clinical trials

Phase I trials primarily determine the safety of a treatment in humans and whether it is well tolerated by a relatively small number of healthy participants. Phase I trials may also determine the best route of administration of a drug and the tolerated dose. Participants are closely monitored during the Phase I trial for any side effects and tested for how the drug is handled once it enters the body. Phase I trials may take from weeks to months.

Phase II clinical trials

Phase II trials are designed to provide the first evidence that the treatment is effective in a small, well-defined sample of patients with the target disease, and provide evidence that the treatment is safe in patients as well as healthy people. Phase II trials are likely to take several months.

Phase III clinical trials

Phase III trials involve a larger number of participants from a more general population of people with the disease. They extend the evidence gained from Phase I and II trials related to safety, dosing, effectiveness, side effects and cost-effectiveness. Phase III trials are often conducted at multiple sites nationally or internationally. Depending on the disease, it can take years before the final results of Phase III trials are available.

The best design for a Phase III trial is a double-blinded, randomised controlled trial. This is one in which patients are randomised to receive the test treatment or standard care (if it exists), or a placebo that contains no active ingredient. 'Double-blinded' refers to the ideal situation in which neither the patients nor the healthcare professionals involved in the trial know who is receiving what until the trial is completed.

Phase IV clinical trials

Phase IV trials take place after a drug has received regulatory approval based on the evidence gathered from Phases I to III trials. Ongoing testing in Phase IV examines questions about cost-effectiveness of the new compound compared to existing drugs.