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About Clinical Trials

Phase I clinical trials

Phase I trials

Phase I trials are carried out on healthy volunteers and are primarily focused on further exploring a drug’s potential toxicity and tolerability in humans. Alongside this are extensive PK and PD studies. These trials normally consist of a small number of healthy volunteers (20-100) and usually include studies on ways of administering the substance, dose ranging, or dose escalation, where the different amounts of the drug are administered to help ascertain the optimum balance of effectiveness versus adverse events (side effects).

If the drug is proved safe and well tolerated in phase I, the drug will progress to phase II trials where the focus is on the substance’s ‘activity’. This phase traditionally consists of 100-1000 patients and has a maximum trial length of two years. Patient numbers will vary, however, according to the rarity of the indication being studied in the trial.

Phase II trials

Phase II trials involve assessing the activity of a drug on patients suffering from a specific disease or disorder (indication) where the clinical trial may lead to scientific evidence that a drug is effective in preventing, treating or curing a condition, without posing an unacceptable risk to the patient population. During this phase adverse events are monitored and optimal dosages are assessed.

Phase II is often the point at which many drugs fail to meet clinical trial endpoints, as they prove to be ineffective for the chosen indication or the treatment is discovered to be impractical or inefficient. If a drug shows that it is effective in treating an indication, it will progress to phase III.

Phase III trials

Phase III trials aim to provide a definitive study of a drug and, if there is an existing treatment for the indication, to prove that the new treatment is its equal or better. The primary focus is on a drug’s efficacy and the gathering of statistical proof of this, while continuing to monitor safety. These trials can involve between 1000 and 5000 patients and run for up to several years.

Phase IV trials

Phase IV trials are carried out after authorisation has been granted by a regulator and a drug is on the market; often Phase IV trials are a requirement of a drug’s approval. Their role is to monitor a drug’s safety and efficacy over a longer time period and with a broader group of patients than can be included in clinical trials prior to approval of the drug.