A clinical trial is conducted in four phases, each one representing an important stage that needs to be successfully completed in order to proceed to the next one.
This is the initial stage of any clinical trial, where a drug gets tested on human beings for the first time. The number of participants is restricted (usually between 20 and 80) and the people involved are healthy volunteers, except from special cases like cancer and HIV where Phase I trials are performed on patients suffering from the respective diseases. During Phase I, safety, acceptability, absorption, distribution, metabolism and excretion of a drug are tested. The trials are generally conducted in the clinics with the inpatient facility so that the subject or the volunteer who has been given the drug can be under round-the-clock observation.
As soon as the initial safety of the drug is ensured by Phase I trials, Phase II trials recruit a larger group of participants to whom the drug has to be administered (20 to 500 volunteers). Phase II mainly assesses the drug on the basis of its performance in the previous phase and it involves a development process crucially important for the success of the drug being studied in order to make it to market. At this stage a drug’s safety, efficacy and dosing on humans is tested.
Following the successful conclusion of Phase II, Phase III trials are initiated on a very large group of people or patient groups (300-5,000 participants, a number that may increase as per the study’s requirement). As opposed to Phase I trials, Phase III trials are performed in several centres or clinics with geographical dispersion allowing to compare results on a wider range of population groups. Obtaining varied results is highly beneficial for the study as a whole.
This Phase starts after the drug has received permission to be sold in the market or is made available for the general public. Phase IV trials are carried out in order to test drug-drug interactions, safety surveillance and also to discover new markets for the specific drug.