Phase I studies include the first introduction of an investigational new drug into humans.
Clinical trials are primarily concerned with evaluating the safety profile of the drug and are designed to determine:
- The metabolism and pharmacologic actions of the drugs in humans
- The side effects associated with increasing doses
The safety aspects of the drug are usually assessed by obtaining multiple blood and serum samples.
Phase II studies are done to:
- Study further safety of the drug in a larger group of patients
- To determine the common short-term side effects and risks associated with the drug
- To evaluate the effectiveness of the drug for a particular indication or indications
- Determine the most effective and best tolerated dose to be used in the larger, Phase III studies
Phase III studies are performed after preliminary information suggesting effectiveness of the drug has been obtained.
They are intended to gather the additional information on the drug’s safety and effectiveness that is needed to:
- Evaluate the overall benefit-risk relationship of the drug
- Determine whether or not the drug is marketable
- The information which is necessary for the labeling of the product
Phase IV clinical trials refer to studies conducted after the product has been approved.
Phase IV studies are done to:
- Gain additional information about the drug’s risks, benefits and optimal use
- Evaluate different doses or schedules of administration than were evaluated in the previous phases
- Evaluate the use of the drug over longer periods of time
NOTE: If a new indication or new disease is identified for which the drug may be used, the sponsor must conduct clinical studies and resubmit an NDA for the specific indication, prior to marketing the drug for that indication.
Historically, Phase IV studies also focused on pharmacoeconomic (cost effectiveness) and quality of life data, although there is a trend towards including these aspects into Phase II and III trials.