Antibiotics

A drug is a substance taken into the body that affects chemical reactions in the body. Antibiotics are drugs used to treat bacterial infections by killing bacteria.

Antibiotics do not affect viruses, so they cannot treat viral infections. An infection must be caused by bacteria for an antibiotic to be useful against it.

Some bacteria are resistant to an antibiotic: the antibiotic does not kill them effectively. If resistant bacteria cause an infection, that antibiotic may be less effective at treating it.

Choosing antibiotics for bacterial infections

An antibiotic must be chosen to match the bacterium causing an infection. Different antibiotics are effective against different bacteria, so a drug that treats one bacterial infection may not treat another.

A bacterium is susceptible to an antibiotic if the drug can act effectively against it. A bacterium that is resistant to an antibiotic is not effectively treated by that drug. The choice therefore depends on both the bacterium causing the infection and whether it is susceptible to the antibiotic.

Penicillin is an antibiotic used against susceptible bacteria. It will not effectively treat an infection caused by bacteria resistant to penicillin.

Antibiotic treatment has greatly reduced deaths from infectious bacterial diseases. However, choosing an antibiotic that is ineffective against the bacterium causing an infection will not cure that infection.

Symptom-relieving medicines

A disease can cause symptoms, such as pain, that make a person feel unwell. Symptom-relieving medicines reduce these effects, but they do not necessarily remove the cause of the disease.

For example, a painkiller can reduce the pain caused by an infection, but it does not kill the pathogen causing the infection. A person may therefore feel better even though the pathogen is still in their body.

The infection must be dealt with separately, either by the body’s defences or by an appropriate treatment. Relief from symptoms alone does not show that the infection has gone.

Challenges in antiviral drug development

Viruses reproduce inside body cells. They use the cells’ machinery to make the components needed to produce more viruses.

This makes viruses difficult to attack with drugs: a drug that disrupts the cell machinery used by a virus may also damage the host cell. If many cells are harmed, the body’s tissues can be damaged.

An antiviral drug must therefore target the virus or its reproduction while limiting harm to the host cells it uses. The challenge is to interfere with the virus without stopping the cells from functioning normally.

Emergence and spread of resistant bacterial strains

A mutation is a change in a bacterium’s genetic material. Mutations can produce new bacterial strains, including a strain that can survive treatment with a particular antibiotic. Such a strain is resistant to that antibiotic.

Bacteria reproduce rapidly, so many generations can arise in a short time. When a resistant bacterium reproduces, it can pass the resistance to its descendants. The descendants can then reproduce too, allowing a resistant strain to become established in the bacterial population.

A resistant strain can spread from one person to another. This is especially likely where people lack immunity to the strain, meaning their bodies are not already prepared to defend against it.

Resistance makes an infection harder to treat because the antibiotic to which the bacteria are resistant cannot readily eliminate them. If no effective antibiotic is available, the infection cannot readily be eliminated by antibiotic treatment, making its spread harder to limit.