Preventing, treating and curing diseases - AQA SynergyTesting new drugs

New drugs are being developed all the time. Historically drugs have come from nature, as parts of plants and microorganisms have been extracted. One of the most famous discoveries was made by Sir Alexander Fleming, who discovered penicillin from the Penicilliummould.

This antibiotic is still very important in the fight against disease.

Plant extracts

Another example is the heart drug, digitalis which is extracted from the foxglove plant.

Plants are still important in providing new drugs today, but most plant drugs are now created in a laboratory by scientists at pharmaceutical companies. Many of these companies now produce synthetic versions of the plant extracts, and also use these as the starting point to develop new drugs.

New medical drugs have to be tested to ensure that they work, and are safe, before they can be prescribed.

What drugs are tested for

New drugs need to be tested and trialled before doctors prescribe them and patients take them. This allows drugs to be checked for:

1. safety (toxicity) - this is important as the potential drugs may be toxic and have other side effects that might harm people
2. effectiveness (efficacy) - to check how effective the new drug will be against the disease
3. dosage - the optimum quantity required to treat the disease is investigated - it is likely that a certain dose of the new drug will be required for it to be effective, but too high a dose might be toxic, or would be wasteful

Three stages of testing drugs

There are three main stages of testing:

Preclinical drug trials

• The drugs are tested using computer models and skin cells grown using human stem cells in the laboratory. This allows the efficacy and possible side effects to be tested. Many substances fail this first test of a preclinical drug trial because they damage cells or do not seem to work.

Animal testing

• Drugs that pass the first stage are tested on animals. In the UK, new medicines have to undergo these tests. But it is illegal to test cosmetics and tobacco products on animals. A typical test involves giving a known amount of the substance to the animals, then monitoring them carefully for any side effects.

Human clinical trials

• Drugs that have passed animal tests are used in human clinical trials. They are tested on healthy volunteers to check that they are safe. The substances are then tested on people with the illness to ensure that they are safe and that they work. Low doses of the drug are used initially, and if this is safe the dosage increases until the optimum dosage is identified.

The placebo effect occurs when someone feels they are better when they have been given a dummy form of the drug, not the drug itself.

To reduce the placebo effect in drug testing:

• in blind trials only, the doctor knows which patients have been given the drug and which have been given the placebo
• in double blind trials, neither the doctor nor the patient knows who has been given the drug or placebo

There is a small amount of risk involved in many choices we take in our lives. There is some risk involved in volunteering to be in a drug trial. Some people choose to do this though. Sometimes sick people volunteer to try a newly developed type of treatment. Other volunteers are healthy. They are paid a small sum of money to participate. Drug testing on humans is an important part of the process described above.

Learn more about drug discovery with Dr Alex Lathbridge.

Listen to the full series on BBC Sounds.