AQA GCSE Biology: Medicines and Drug Development

Once someone is ill, medicines are used to cure the disease or treat its symptoms. This guide explains the difference between antibiotics and painkillers, the growing problem of antibiotic resistance, where drugs come from, and the careful testing every new drug goes through before it can be used. The testing process, in particular, comes up often in exams.

Antibiotics and painkillers

These two kinds of medicine do very different things.

• Antibiotics help cure bacterial diseases by killing the bacteria inside the body without harming body cells. A specific antibiotic is used for a specific bacterium; penicillin is one example. Antibiotics cannot kill viruses.
• Painkillers and similar medicines only treat the symptoms of a disease, such as pain. They do not kill pathogens.

Antibiotics have hugely reduced deaths from bacterial diseases, but the rise of antibiotic-resistant strains, bacteria that are no longer killed by antibiotics, is a serious concern.

It is difficult to develop drugs that kill viruses, because viruses reproduce inside the body's own cells, so a drug that destroys the virus can easily damage the body's cells too.

Where drugs come from

Traditionally, drugs were extracted from plants and microorganisms.

• Digitalis, a heart drug, comes from foxgloves.
• Aspirin, a painkiller, comes from willow trees.
• Penicillin, an antibiotic, comes from Penicillium mould. It was discovered by Alexander Fleming, who noticed that bacteria in a Petri dish had been killed by mould, and worked out that the mould released a chemical that killed the bacteria.

Most new drugs today are synthesised by chemists in the pharmaceutical industry, though the starting point may still be a chemical from a plant.

Testing new drugs

New drugs are extensively tested for three things: toxicity (how safe they are), efficacy (whether they work), and dose (the best amount to use). Testing happens in stages.

• Preclinical testing is done in the laboratory on cells, tissues and live animals, to check for toxicity and whether the drug works.
• Clinical trials use human volunteers. Phase 1 uses healthy volunteers and very low doses, to check the drug is safe. Phases 2 and 3 use patients who have the disease, first a small number and then a larger number, to test efficacy, side effects and the best dose.

Clinical trials are usually double-blind: patients are randomly split into two groups, one given the drug and one a placebo (a treatment with no active drug), and neither the patients nor the doctors know who received which, so the results are not biased. Before results are accepted, they are peer reviewed by other scientists to check for errors and bias.

Every stage of that process exists for a reason, and AQA asks for the reasons far more often than the list.

Preclinical testing comes first because it would be unethical to give a completely untested substance to a person. Cells and tissues are used before live animals, and live animals before humans, so that each stage rules out the worst risks before the next one begins.

Phase 1 uses healthy volunteers and very low doses because the only question at that point is whether the drug is safe. Testing it on ill patients would make side effects impossible to separate from the symptoms of the disease itself.

The placebo is there because people often improve simply from believing they are being treated, which is called the placebo effect. Without a placebo group there is no way to tell whether the drug did anything or the belief did.

The trial is double-blind, not just blind, because doctors who know who received the real drug may unconsciously treat those patients differently or read their symptoms more favourably. Blinding the patients removes one bias; blinding the doctors removes the other.

Peer review matters because the company that stands to profit from a drug is also the one running the trial. Having independent scientists check the methods and the data before publication is what makes the result trustworthy.

A further point sometimes asked for is that this whole process takes many years and a great deal of money, which is part of why new drugs are expensive, and why developing replacements for antibiotics that bacteria have become resistant to is so slow.

How this fits together

This guide covers medicines in general. A more advanced, targeted kind of treatment uses specially made antibodies, which is the subject of the monoclonal antibodies guide.