Clinical Trials are done in phases, the phase it is in tells you where the drug or treatment is in the trial process.
Phase I Studies: These studies involve testing the investigational drug in a small number of healthy volunteers. The main objective of these studies is safety, designed to determine how the drug is metabolized by the body and what pharmacologic actions the drug has. One objective of these studies is to determine preferred route to administer the drugs.
Phase II Studies: This phase determines how safe and effective a drug is, common short-term side effects of the drug, pharmacokinetic effects of the drug, (pharmacokinetic is how muc of the drug reaches the bloodstream, how quickly it gets into the bloodstream, and how long it stays there) and pharmacodynamic effects of the drug (pharmacodyamic is the effects of the drug on the body). This phase of the study involves a larger group of patients usually 100 to 200 patients and are generally conducted in patients who have the medical condition for which the drug is being studied. Results from this phase are used to determine the dose range of the drug that will be tested in subsequent larger studies.
Phase III Studies: This phase is to explore further the safety and efficacy when the drug is used in the way it is intended to be marketed. This phase of study is only initiated after earlier studies have demonstrated that there is an acceptable risk, meaning that the potential benefit to the patient outweighs the risk of taking the drug. Phase III studies are larger usually conducted at many different study centers often between 10-30 study centers and between 500 and 5,000 patients may be included. This phase will confirm the indication and best dosage for the drug.
Phase IV Studies: Once the drug is available for sale post-marketing studies are conducted and are used to evaluate how safe and effective the drug is when exposed to the “real” population. Used to evaluate parameters such as different formulations, dosages, treatment durations, and drug interactions. The Food and Drug Administration (FDA) may require a company to conduct certain Phase IV studies as a provision for product approval. These studies may include new age groups, races and other types of patients. These studies are useful for detecting and defining previously unknown or inadequately quantified adverse events and related risk factors. The size of these studies is broad and can range from 5,000 to 20,000 patients.