Types of Intervention Studies


Individual versus Group (Community) Trials

The Kingston-Newburgh Fluoride Trial

 

 

Prevention trials (or prophylactic trials) versus Therapeutic Trials

Clinical trials might also be distinguished based on whether they are aimed at assessing preventive interventions or evaluating new treatments for existing disease. The Physicians Health Study established that low-dose aspirin reduced the risk of myocardial infarctions (heart attacks) in males. Other trials have assessed whether exercise or low-fat diet can reduce the risk of heart disease or cancer. A study currently underway at BUSPH is testing whether peer counseling is effective in helping smokers who live in public housing quit smoking. All of these are prevention trials. In contrast, there have been many trials that have contributed to our knowledge about optimum treatment  of many diseases through medication, surgery, or other medical interventions.

Phases of Trials Evaluating New Drugs

Clinical trials for new drugs are conducted in phases with different purposes that depend on the stage of development.

  1. Phase I trials: ClinicalTrials.gov describes phase I trials as "Initial studies to determine the metabolism and pharmacologic actions of drugs in humans, the side effects associated with increasing doses, and to gain early evidence of effectiveness; may include healthy participants and/or patients." Frequently, an experimental drug or treatment initially is tested in a small group of people (8-80) to evaluate its safety and to explore possible side effects and the doses at which they occur.
  2. Phase II trials: ClinicalTrials.gov describes these as "Controlled clinical studies conducted to evaluate the effectiveness of the drug for a particular indication or indications in patients with the disease or condition under study and to determine the common short-term side effects and risks." The new treatment might be tested in a somewhat larger group (80-200) to get more information about effectiveness and potential side effects at different dosages.
  3. Phase III trials: ClinicalTrials.gov defines these as "Expanded controlled and uncontrolled trials after preliminary evidence suggesting effectiveness of the drug has been obtained, and are intended to gather additional information to evaluate the overall benefit-risk relationship of the drug and provide and adequate basis for physician labeling." These are typically conducted in larger groups (200-40,000) to formally test effectiveness and establish the frequency and severity of side effects compared to no treatment, or, compared to currently used treatments ("usual care")
  4. Phase IV refers to post-marketing "surveillance" to collect information regarding risks, benefits, and optimal use. This phase can be particularly important for identifying rare, but potentially devastating side effects. Example: Safety of Influenza A (H1N1) Vaccine in Post-marketing Surveillance in China