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Clinical Trial Phases

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There are four phases of Clinical Trials, plus "IND Exempt Clinical Trials."  Each phase has different purposes and entails different levels of risks for participants.

The phases, which are discussed in other sections of this document, are:

Phase I Clinical Trial

  • In General: A Phase I cinical trial is the most experimental phase of clinical trials. Previously, the drug has not been testsed in humans.
  • Purpose: The primary purpose of a Phase I trial is to evaluate the safety of a new drug or treatment. A Phase I trial seeks to determine:
    • An initial dosage range.
    • The best method of administration (oral, injection).
    • Possible side effects.
  • There are generally no conclusions about how well a drug works in Phase I trials.
  • Number Of Participants: In Phase I trials, researchers generally administer the new treatment to a small group of people, usually 10-80 participants.
  • What Happens For drug studies, the researchers generally begin by providing a very lose dose. The dosage level is slowly increased as new patients enter the trial.
  • Monitoring For Side Effects 
    • Patients are carefully monitored for harmful side effects. Although the treatments have been well tested in the lab prior to the trial, there may still be significant risk.
    • Because the treatment being studied is new, researchers don't always know the expected side effects. Side effects or adverse reactions may include headache, nausea, hair loss, and skin irritation, among others. In some rare cases the side effects may be serious or even life threatening.
    • Many side effects are only temporary and go away when the treatment is completed or stopped. Other side effects can be permanent. For this reason, some phase I trials may be limited to patients whose condition cannot be helped by other known or proven treatments.
  • Duration Phase I trials generally last for several months.
  • Conclusion:  If the drug or treatment appears to be safe, it moves to Phase II. Approximately 70% of drugs or treatments tested in Phase I trials proceed to the next phase.

Phase II Clinical Trial

  • Purpose The primary purpose of a Phase II trial is to determine the effectiveness of a treatment and to further evaluate its safety.
  • Number of Participants The treatment is administered to a larger group, usually 100-300 patients, who are closely monitored for treatment response and side effects.
  • Duration Phase II trials may last from several months to 2 years.
  • Conclusion If a significant number of patients (usually at least one-fifth) respond favorably to a treatment, it proceeds to Phase III. Approximately 33% of drugs and treatments proceed to the next phase.

Phase III Clinical Trial

  • Purpose The primary purposes of a Phase III trial are to: 
    • Confirm the effectiveness of a drug or treatment
    • Test the safety of the drug or treatment
    • Determine the most effective dosage levels.
  • Phase III studies look for a treatment that will provide a longer life expectancy, better quality of life, fewer side effects, and/or a lowered chance of the condition returning.
  • Number of Participants This larger trial group may include 300-5,000 people or more.
  • What Happens  
    • Phase III compares standard (proven) drugs or treatments or placebos (no treatment) with the drugs or treatments that appeared to be effective in the Phase II studies. The people who participate are divided into those receiving the standard treatment or placebo, and those receiving the experimental treatment. The responses of the groups are then compared.
    • If during the trial it is determined that one treatment is superior to another, the trial may be stopped. If that is the case, all participants are given the more effective treatment.
  • Duration Phase III trials may range in length from 1-4 years. Approximately 25-30% of drugs and treatments will clear this phase. According to the FDA, about 20% of drugs and treatments that are tested in people will ultimately be approved for marketing.

Phase IV Clinical Trial

Phase IV studies are done after a drug or treatment has been approved by the FDA and marketed. These studies continue testing a drug or other treatment to collect information about their effect in various populations, changes in how a treatment is administered, and any side effects associated with long-term use. There may also be studies comparing a drug with other drugs. 

IND Exempt Clinical Trials

“IND Exempt Clinical Trials” are a slight variation on approved drugs. For example, the trial tests a change in scheduling or dosage. These trials are not really Phase IV, but are similar.

IND Exempt Clinical Trials are usually initiated by an investigator, not a pharmaceutical company.

The FDA doesn’t review these trials. It sets the criteria for IND Exempt Clinical Trials in regulations. If a trial wants to go outside the regulations, it requires FDA review.

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