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Friday 25th May 2018

How trials work

18th March 2006

14032006_SyringePink1.jpgBefore any drug can be used to treat diseases in humans, it must first be proven to be safe and effective. The process can be lengthy, often taking several years, and is divided into a number of stages:

Preclinical Testing
Drugs are first tested for effectiveness on human and animal cells in a laboratory setting. Computer simulations can also be run. Live animals (usually rodents) are then used to ensure that the drug maintains its properties in a whole-body setting and isn't toxic.

Phase 1
The principal aim of phase 1 trials is to determine the safety of a drug and test for any side effects. Some toxicity may be acceptable, depending on the disease targeted. A small number of healthy volunteers are usually paid to participate in studies which try to determine what happens to the drug in the body. Phase I trials use between 20 and 100 volunteers and typically take several months. About 70 percent of experimental drugs pass this initial phase of testing.

Phase 2
Phase 2 trials are performed on people with the relevant disease. They are larger in scope than phase 1 trials and help determine the dosages that will be used in phase 3 trials. These trials are usually double-blinded with placebo controls (neither the investigator nor patient know if the patient is receiving active drug or not). This phase can last up to two years and usually involves several hundred patients. A well designed phase 2 trial can identify a drug unlikely to pass the more expensive phase 3 trial.

Phase 3
These studies can involve thousands of patients over several years. They are usually double-blinded and placebo controlled to establish effectiveness and side-effect profiles for the drug under test. Because phase 1 and 2 trials have already established the safety of the drug, the risks of phase 3 trials are minimal. Between 70 and 90 percent of drugs that enter phase 3 studies successfully complete this phase of testing.

Phase 4
Following a successful phase 3 trial, the drug can then be licensed. Once on the market, pharmaceutical companies can undertake phase 4 studies which aim to compare the new drug with other drugs already in the market or to monitor a drug's long-term effectiveness and impact on a patient's quality of life. Many phase 4 studies are designed to determine the cost-effectiveness of a drug therapy relative to other traditional and new therapies.

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