Clinical trials

Phase I trials usually last for between a few months and 1–3 years. They often involve having quite a lot of blood tests or other investigations done.

Phase I trials are the first-stage of testing in human subjects. Normally a small group of healthy volunteers will be selected (20 – 40 people). This phase includes trials designed to answer questions such as: is the drug safe for humans? What are the side effects? How much of the drug do you need to give? Does it have any effect on cancer?

These trials are almost always conducted in hospital, where full-time medical staff can observe the subject. The  subject is usually observed until the medical staff can be certain that the entire trial drug has been excreted from the body. Phase I trials also normally include dose-ranging studies so that doses for clinical use can be refined. Many drugs don’t get past phase I. Phase I trials are often only for people who have disease that is not responding to standard therapies. This is because it is not ethical to give someone an unknown treatment unless there are no other suitable treatments available.

Once the initial safety of the therapy has been confirmed in Phase I trials, Phase II trials are performed on larger groups of people (20 – 300) and are designed to assess clinical efficacy of the therapy; as well as to continue Phase I assessments in a larger group of volunteers and patients. If a new drug fails during its development process it most commonly fails during Phase II trials.  Failure is normally due to the discovery of poor efficacy or intolerable side-effects.

Phase II trials are not always about testing a new drug. Sometimes phase II trials will test an existing drug administered in a different way or at a different dose – or they might want to test it in people with a different type or stage of cancer.

Phase III studies are randomised controlled trials on large patient groups (300–3,000 or more depending upon the condition) and are aimed at being the definitive assessment of the effectiveness of the therapy, in comparison with current ‘Gold Standard’ treatment.

Phase III trials are the most expensive, time-consuming and difficult trials to design and run; especially in therapies for chronic conditions. Once a drug has proven satisfactory in Phase III trials, the trial results are usually combined into a large document containing a comprehensive description of the methods and results of human and animal studies, manufacturing procedures, formulation details, and shelf life.

Good phase II or III trial results are required before a drug gets a licence. A licence means that a drug can be marketed as a treatment for a particular condition. Drugs usually have to go through a few phase III trials before they become accepted as standard therapy.

Phase IV clinical trials are done after a treatment has been shown to be effective and after it has been licensed. They are usually carried out by drug companies to find out more about a treatment and side effects.

Phase IV trials involve the safety surveillance (pharmacovigilance) and ongoing technical support of a drug after it receives permission to be sold. The safety surveillance is designed to detect any rare or long-term adverse effects over a much larger patient population and longer time period than was possible during the Phase I-III clinical trials. Harmful effects discovered by Phase IV trials may result in a drug being no longer sold, or restricted to certain uses.