Antibiotics, painkillers and drug testing – GCSE Combined Science Biology

Start here

Drugs are chemicals that change how your body works. Doctors use them to treat illness. This lesson is about antibiotics, painkillers, and how a new drug is tested before anyone is allowed to take it.

It matters because antibiotics are some of the most useful medicines we have, and bacteria are learning to resist them. It also matters because you should be able to judge whether a drug trial is fair.

By the end you will be able to explain why antibiotics do not work on every illness. You will explain antibiotic resistance. You will also describe how drugs are tested and why placebos are used.

Antibiotics and painkillers

Antibiotics, such as penicillin, kill bacteria or stop them growing. Bacteria are tiny living cells that can cause infections. Different bacteria need different antibiotics, so a doctor picks the right one.

Antibiotics do not work on viruses. A virus lives inside your own cells, so it is hard to kill it without harming the cell. A cold is caused by a virus.

Painkillers are different. They relieve symptoms such as pain. They do not kill the pathogen, which is the microbe causing the disease.

How resistance starts

Bacteria can change by chance. A change in a gene is called a mutation. Sometimes a mutation makes a bacterium resistant, which means an antibiotic can no longer kill it.

Now think about a patient taking the antibiotic. It kills most of the bacteria, but the resistant ones survive. They reproduce, so there are more of them each time.

Soon most of the bacteria in the population are resistant. This is natural selection. MRSA is a bacterium resistant to many antibiotics. It is a serious risk in hospitals.

Slowing resistance down

We cannot stop mutations, but we can slow the spread of resistance. Doctors should not prescribe antibiotics for viral infections or very mild infections.

Patients should finish the whole course, even if they feel better. This kills all the bacteria, so fewer resistant ones are left to multiply.

Farmers should use fewer antibiotics on animals. New antibiotics are being developed, but this is slow. So we must use the ones we have with care. Otherwise, common infections could become dangerous again.

Where drugs come from

Many drugs were first found in plants and microorganisms. Microorganisms are living things too small to see without a microscope. Mould is one example.

Digitalis comes from the foxglove plant and is used to treat heart conditions. Aspirin was first made from a chemical in willow bark. It is a painkiller. Penicillin was found by Alexander Fleming, from the mould Penicillium.

Today most new drugs are made by chemists in laboratories. Scientists still study plants, because their chemicals might become new medicines.

Testing a new drug

New drugs are tested for safety, side effects and efficacy. Efficacy just means whether the drug works. This testing happens in stages, so people are not put at risk.

First the drug is tested on cells and tissues in a lab. Then it is tested on live animals. Next come clinical trials, which are tests on people.

A small trial on healthy volunteers uses a low dose to check safety. Then patients take part, to find the best dose and see if it works. Other scientists check the results before they are published. This is called peer review.

Placebos and double-blind trials

In a trial, some patients get the new drug. Others get a placebo, which is a tablet that looks the same but has no active drug in it.

The placebo group shows how much people improve just because they expect to. Without it, we could not tell if the drug really works. Think of a taste test where you do not know which crisps are which brand.

In a double-blind trial, neither the patients nor the doctors know who got which until the end. This stops bias. Larger trials give more reliable results.

Recap

Antibiotics kill bacteria but not viruses. Painkillers treat symptoms only.

Resistance starts with a chance mutation, and then natural selection makes it common. Finish your course of antibiotics.

Digitalis comes from foxglove, aspirin from willow bark and penicillin from a mould.

Drugs are tested on cells, animals, healthy volunteers, then patients. Placebos and double-blind trials keep the test fair.