Antibiotics, such as penicillin, are medicines that help to cure bacterial disease by killing infective bacteria inside the body. It is important that specific bacteria should be treated by specific antibiotics. The use of antibiotics has greatly reduced deaths from infectious bacterial diseases. However, the emergence of strains resistant to antibiotics is of great concern. Antibiotics cannot kill viral pathogens.


Painkillers and other medicines are used to treat the symptoms of disease but do not kill pathogens. It is difficult to develop drugs that kill viruses without also damaging the body’s tissues.

Discovery of Drugs

Traditionally drugs were extracted from plants and microorganisms. The heart drug digitalis originates from foxgloves. The painkiller aspirin originates from willow. Penicillin was discovered by Alexander Fleming from the Penicillium mould.

Development of Drugs

Scientists study bodies and diseases to see how they work. They try to find ‘targets’ for medicines to aim at. Targets are things that cause diseases such as tiny protein molecules. Most new drugs are synthesised by chemists in the pharmaceutical industry. However, the starting point may still be a chemical extracted from a plant. New medical drugs have to be tested and trialled before being used to check that they are safe and effective. New drugs are extensively tested for toxicity, efficacy and dose.

The first stage of the preclinical trial is to use computers and cell samples are used to find chemicals that seem to work on the target. Tens of thousands of known chemicals are tested like this. Very low doses of the drug are given at the start of the clinical trial. If the drug is found to be safe, further clinical trials are carried out to find the optimum dose for the drug. The second stage of the preclinical trial may be tested on animals, cells and tissues to see how they would all respond to the medication. The most promising treatments are tested to see how much is safe and how much is poisonous. Scientists need to know how quickly and where the body absorbs the chemical and how quickly it flushes it out.

The first clinical trial can now begin, where new medicines are tested on healthy volunteers and patients to make sure there are no unexpected side effects. The second clinical trial involves a much bigger group of patients, to see if the drug works on the disease it is designed for.

Double blind randomised trials involve large numbers of patients. Some are given the new medicine and some a placebo that does nothing at all. Neither the patients nor the people giving them the medicine know which group is which.

If a medicine passes all the clinical trials it can get a licence from the government which means doctors can use it. Doctors prescribe licensed medicines, but they continue to monitor the effects on patients. This is sometimes called the ‘phase 4’ clinical trial.

If a medicine has passed all clinical trials, what will happen next?
Your answer should include: Company / Licence / Government / Doctors / Prescribe
Explanation: The company will have to get a license from the government so that doctors can use and prescribe it.
What happens during the second stage of the preclinical trial?
Your answer should include: Drugs / Tested / Animals / Cells / Tissues
Explanation: The drugs are tested on animals, cells and tissues to see how they would all respond to the medication.
What is the effect of taking painkillers?
Your answer should include: Treat / Symptoms / Disease / Pathogens
Explanation: Painkillers treat the symptoms of disease but do not kill pathogens.