In general, clinical studies are broken down into 4 phases of drug approval, with each phase being treated as a separate clinical trial. If a drug satisfies all requirements to pass phase I, II and III, it will generally be given the authorisation of the appropriate regulatory body to be released into market. Phase IV are the post-approval/post-marketing studies of that particular drug.
Phase I is concerned with conducting tests to confirm the safety of a drug. These tests, which are carried out on about 20-100 individuals, will determine how the drug reacts in the human body, as well as any side effects that may be experienced.
Phase II is focused on the efficacy of the drug and this is tested by conducting tests on a larger population, of approximately 100-300 individuals. These tests are carried out on individual who have the disease or condition. This phase can be categorised in to both IIa and IIb trials, with the latter being the more progressed experimental stage.
Phase III determines the effect of a drug for a specific therapeutic use. The scale of the tests is again increased and up to 3000 candidates may be used in phase III trials. This is the last round of pre-approval tests and here the drug is tested against a standard treatment, for the disease in question, with the aim of further confirming safety and efficacy. Around 80% of drugs that make it this far will pass phase III tests and manufacturers can seek approval to produce and sell the treatment.
Phase IV trials are also known as ‘post-marketing’ trials. Tests at this stage are on-going, and concerned with surveillance on adverse effects of the drug on patients, as well as benefits of the treatment. Any harmful demonstrations at this stage could result in the drug being taken off the market.