Clinical Trials

How do clinical trials work?

Clinical trials take place near the end of the research process, after scientists have conducted preclinical studies. Preclinical studies, or laboratory studies, are tests that determine if a proposed treatment is likely to be effective and if it’s safe to test on people. Preclinical studies may involve cell studies (testing the new treatment on human cells) or animal studies (testing the treatment on an animal that has the disease/condition). If preclinical studies are successful, then the proposed treatment enters into clinical trials.

Every clinical trial follows a protocol – a detailed plan for the studying the treatment. The clinical trial protocol states:

• who is sponsoring the study
• who is conducting the study
• why the study is being done
• who is eligible to participate in the study
• what treatment will be given, and how
• what medical tests the participants will take
• what information will be gathered about the participants and the results of the treatment

Clinical trials are usually organized into four separate phases. Each phase is designed to answer specific questions about the proposed treatment.

Phase I clinical trials ask, “Is the treatment safe?”
In phase I trials, new treatments are tested on humans for the first time. These trials help researchers determine how a drug should be given, how often it should be given, and how much is safe.

Only a few people (15 to 40) participate in phase I trials because the treatment may have little benefit and significant risk. Participants are usually people who don’t have any good treatment options left. Phase I trials are usually conducted at major teaching hospitals.

Phase II clinical trials ask, “Does the treatment work?”
If phase I trials show that the treatment is safe, then the treatment enters into phase II trials. In phase II trials, researchers begin to evaluate how well the treatment works.

More people participate in phase II trials (25 to 100), they usually have the same type of disease/condition and they all receive the same dose of the drug. Participants are usually people who have not responded to standard treatments or who are likely to benefit more from the experimental treatment. Phase II trials are usually conducted at major teaching hospitals, but they may also be done at smaller community hospitals and clinics.

Phase III clinical trials ask, “Is the new treatment better than existing treatments?”
If enough participants respond to the treatment in phase II trials, then the treatment enters into phase III trials. In phase III trials, researchers compare the new treatment’s safety and effectiveness against the current standard treatment. They determine if the new treatment:

Prolongs life or improves the quality of life for people who have the disease/condition
Reduces the risk of recurrence
Has fewer or milder side effects than existing treatment

Phase III trials usually involve at least several hundred people, and they’re often conducted in many cities across Canada or North America at the same time. Phase III trials are usually randomized – participants are chosen at random to receive either the new treatment or the standard treatment. These trials may also be blinded (the participants don’t know which treatment they’re getting) or double-blinded (neither the participants nor their doctors know which treatment the patient is getting). Randomization, blinding, and double-blinding support scientific objectivity and reduce bias (human beliefs or actions that can affect the results of a study).

If phase III trials show that a treatment is safe and effective, then the drug manufacturer can apply to Health Canada for approval to sell the drug by prescription in Canada.

Phase IV clinical trials ask, “Is there a better way to use this treatment?”
Phase IV trials study drugs that have already been approved by Health Canada and are being used as standard treatments. Researchers use phase IV trials to better understand treatments that have already been proven to work. A phase IV trial may show, for example, that a drug is more effective if it’s given for a longer period, or that a lower dose of a drug works as well as a higher dose, but with fewer side effects.


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