The Phases of a Clinical Trial

Published on Nov 22, 2017
Authored by Pfizer Medical Team

Understanding the Phases of Clinical Trials

Prescription drugs don’t just show up on pharmacy shelves one day. Each one is first subjected to thorough scientific testing during what are known as clinical trials.

Clinical trials are conducted in phases, each of which is designed to assess a treatment or drug’s safety as well as answer different questions researchers may have about a drug or treatment. Clinical trial phases range from phase 0 to phase 4.

Phase 1

Phase 1

Focus: Safety and Side Effects

In a Phase 1 clinical trial, an experimental drug is given to humans, often for the first time. The purpose of this phase is to determine the most frequent and serious side effects of the drug. During this phase of the study, investigators may also begin to determine dosing of the drug.

 

 

 

Clinical trials


Who Participates:

20-80 people

 

Participants are usually healthy, though for some drugs, the first trials in human participants are patients with the disease that the experimental drug is intended to treat.


Phase 2

Phase 2

Focus: Effectiveness and dosage

In this phase, researchers work to collect preliminary evidence that a treatment is effective for the disease it is intended to treat. They also determine the most effective dosages for the experimental drug and the most appropriate method of delivering it (e.g., tablets, extended release capsules, infusions, injections, etc.). Information about the experimental drug’s safety, side effects, and potential risks is collected, too.

 

 

 

Clinical Trials


Who Participates:

100-300 people

Participants studied in Phase 2 clinical trials are usually patients who have the medical condition that the experimental drug is intended to treat.

 


Phase 3

Phase 3

Focus: Effectiveness

Phase 3 trials test the results of earlier trials in larger populations. Researchers gather additional information about the effectiveness and safety of an experimental drug. These trials are often randomised and "single-blinded" or "double-blinded," meaning either the investigator or the participant (single) or both (double) do not know who in the trial is getting the experimental drug versus a placebo (commonly referred to as a sugar pill).

 

 

 

Clinical trials


Who Participates:

100-1000 people

Phase 3 trials will usually involve several hundred to several thousand participants with many physician-investigators. Participants will typically have the disease the experimental drug is intended to treat.

 


Phase 4

Phase 4

Focus: Long-term effectiveness and safety

Also called post-marketing studies, phase 4 trials are conducted after the drug has been approved for marketing by the Australian Therapeutic Goods Administration (TGA) or Medsafe in New Zealand and made available to the public. Researchers collect additional information about long-term risks, benefits, optimal use, and use in different populations.

 

 

 

Clinical Trials


Who Participates:

100-1000 people


These trials often involve a large number of participants from diverse populations. Safety information from phase 4 trials and beyond is reported to the TGA and/or Medsafe to allow continued monitoring of the drug’s safety even after approval.

 


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