Clinical trials phase I to IV

Clinical trials phase I to IV

Very often we hear of phase II trial, phase III trial etc. These have been defined by the United States Food and Drug Administration (US FDA) in the Code of Federal Regulations. All these phases apply to clinical trials and the four phases are as follows:
Phase I: A new drug or treatment is initially tested in a small group of people (20-80) for the first time to evaluate its safety, determine a safe dosage range, and identify side effects. It is done in healthy human volunteers and also checks how it is metabolized and excreted.
Phase II: The study drug or treatment is given to a larger group of people (100-300) who have a certain disease or condition to see if it is effective and to further evaluate its safety. Short term safety is evaluated. Drug may be compared against placebo or another drug.
Phase III: The study drug or treatment is given to large groups of people (1,000-3,000) to confirm its effectiveness, monitor side effects, compare it to commonly used treatments, and collect information that will allow the drug or treatment to be used safely. Different populations, dosages and combination with other drugs are evaluated in this phase.
Phase IV: Post marketing studies delineate additional information including the drug’s risks, benefits, and optimal use. This occurs after US FDA has approved a drug for marketing. These are postmarketing requirement and are studies required or agreed by the sponsor.

First three phases are before a drug is launched in the market while phase IV is post marketing surveillance.

Reference:

1. Adapted from http://clinicaltrials.gov/ct2/help/phase_desc