Amoxicillin: Uses, Side Effects, Allergy and Safety Tips

6 min read · Medicines · By the Asthra Health Care team

What amoxicillin is used for

Amoxicillin is one of the most commonly prescribed antibiotics in the world. It belongs to the penicillin family and treats infections caused by bacteria. Doctors use it for middle ear infections, bacterial sinus and throat infections, some chest infections and pneumonia, dental infections, urinary tract infections and certain skin infections. It is also part of the combination used to clear the ulcer germ Helicobacter pylori.

It is often combined with clavulanic acid, known as co-amoxiclav, to work against bacteria that can otherwise destroy amoxicillin. Amoxicillin does not work against viruses, so it will not help common colds, most sore throats, flu, dengue or most coughs.

• Ear, sinus and bacterial throat infections
• Some chest infections and pneumonia
• Dental abscesses and gum infections
• Urinary tract and some skin infections
• Helicobacter pylori treatment, with other medicines

How amoxicillin works

Bacteria are protected by a strong outer wall. Amoxicillin stops bacteria from building this wall properly, so they burst and die. Human cells do not have this kind of wall, which is why amoxicillin can target bacteria while leaving the body's own cells alone.

Some bacteria make an enzyme that breaks down amoxicillin. Clavulanic acid blocks that enzyme, which is why doctors sometimes prescribe the combination. Overuse of antibiotics helps bacteria become resistant, which means these medicines stop working when they are really needed.

Amoxicillin side effects: common and serious

Common side effects include loose stools, nausea, stomach upset and a mild skin rash. Women may get vaginal thrush, with itching and white discharge, because antibiotics disturb the normal balance of germs. These effects are usually mild. They often settle after the course ends. Keep drinking fluids if stools are loose, and tell your doctor if side effects are troublesome rather than stopping on your own.

Serious side effects include allergic reactions, which can range from hives to anaphylaxis with swelling of the face and throat, breathing difficulty and collapse. Severe watery or bloody diarrhoea can signal a serious gut infection called Clostridioides difficile. Rarely, liver problems occur, more often with co-amoxiclav. Severe skin reactions with blisters are very rare but need emergency care.

Who should avoid amoxicillin or take extra care

Anyone with a known allergy to penicillin must not take amoxicillin, and people allergic to cephalosporin antibiotics should tell their doctor. Always tell your doctor and pharmacist about any past reaction to an antibiotic. People with glandular fever, a viral infection, often get a widespread rash with amoxicillin, so doctors avoid it in that situation.

People with kidney disease may need an adjusted amount, and those with liver disease need care with co-amoxiclav. Amoxicillin is widely used in pregnancy and breastfeeding when a doctor decides it is needed. For children, the amount is based on weight, and it is given only as the doctor prescribes.

Amoxicillin interactions to know

Amoxicillin can increase the effect of the blood thinner warfarin, so extra blood tests may be needed. Taken with allopurinol, a gout medicine, it is more likely to cause a skin rash. It can raise methotrexate levels. Probenecid, sometimes used with antibiotics, keeps amoxicillin in the body longer. Tell your doctor about any regular medicines before starting.

Antibiotics that cause diarrhoea or vomiting may make the oral contraceptive pill less reliable during that illness; ask your doctor or pharmacist about extra precautions. Doctors sometimes combine amoxicillin with other medicines, such as for Helicobacter pylori, but that is always their decision.

Practical tips for using amoxicillin

Amoxicillin is only on a doctor's prescription. Do not take it on your own for fever, cold or cough, and do not use leftover tablets or someone else's antibiotics. Take it exactly as your doctor prescribes and complete the course unless your doctor tells you to stop, even if you feel better.

Liquid forms for children should be mixed and stored as the pharmacist explains, often in the fridge, and measured with the device provided. Drink enough fluids, rest, and eat light food. If a rash appears, stop and contact your doctor promptly so it can be checked for allergy.

When to talk to your doctor about amoxicillin

See your doctor if symptoms are not improving after a few days of treatment, if fever returns, or if you develop a rash or ongoing diarrhoea. Seek emergency care for swelling of the face or throat, difficulty breathing, blistering skin or bloody diarrhoea. Ask your doctor or pharmacist if you have any questions about your antibiotic.

This article is general health information, not medical advice. Do not start, stop or combine medicines on your own — always follow your doctor's prescription and ask your pharmacist if unsure.