A candidate drug must pass a number of development stages before it can obtain market approval. These stages can be separated into discovery, preclinical and clinical phases. In parallel with this development, a commercially viable manufacturing process must be secured.
The drug candidate is identified and selected. The identification phase may rely on an understanding of the mechanism of a pathological process or on pharmacological knowledge about a particular substance. The identification phase may take several years.
In the preclinical phase, the candidate drug is tested in experimental systems and disease models to establish safety and efficacy. These studies are essential for obtaining approval from the regulatory authorities to begin human trials.
After successfully completing the preclinical phase, the drug is tested on a limited number of human volunteers in order to confirm the safety of the drug, and to provide indications of any possible adverse effects.
Phase II trials are carried out in patients with the actual disease that is to be treated, prevented or alleviated. The aim is to establish the optimal dosage of the drug, prove that it is efficacious, find out how it is distributed in the body, and further establish its safety profile.
The candidate drug is now tested in a larger group of patients in order to prove statistically that it is safe and efficacious. The effects on the disease are studied, and any possible side effects recorded. If the results in Phase III achieve the stated objectives, the sponsor can apply to the regulatory authorities for marketing approval.
Phase IV studies are carried out, after the drug has been introduced onto the market. The aim is to study the drug in everyday clinical use over an extended period of time, and to record any rare adverse effects that may later emerge. New patient groups may also be evaluated during Phase IV.