Amoxicillin: uses, side effects and cautions

Amoxicillin belongs to the penicillin family of antibiotics. The NHS lists chest infections, pneumonia and dental abscesses among the main uses, and ear and chest infections in children are also mentioned.

A second, less obvious use is stomach ulcers. In that setting amoxicillin is not given alone: it is combined with other antibiotics and with a medicine that lowers stomach acid, as part of a regimen aimed at the bacteria involved in some ulcers.

Because it only acts on bacteria, it is not a treatment for colds, most sore throats or influenza. A prescriber decides whether an antibiotic is warranted at all, and which one, based on the site of the infection and your history.

The NHS describes amoxicillin simply: it works by killing the bacteria that cause the infection. In practice that means it treats the infection itself rather than easing symptoms.

That is also why finishing the course matters. If you stop the moment you feel better, some bacteria may still be present and the infection can return. The NHS advises contacting your doctor if you have not improved after 3 to 5 days, or at any point if you feel worse.

For capsules, the NHS page gives a usual range of 250 mg to 500 mg taken three times a day, with lower amounts for children. Your own dose will be on the pharmacy label and may differ, so follow that rather than any general figure.

Liquid amoxicillin is made up by the pharmacist, and the NHS notes strengths of 125 mg in 5 ml or 250 mg in 5 ml. Use the syringe or spoon supplied; a kitchen teaspoon is not accurate enough.

• Food does not matter: the NHS says you can take amoxicillin before or after eating, and you can eat and drink normally.

• Space the doses through the day as directed and keep going until the course is finished, even if you feel well.

• A missed dose can be taken when you remember unless the next one is nearly due; never double up.

• One extra dose is unlikely to do harm, but ask a pharmacist or call NHS 111 if you are worried, and especially if you have taken more than prescribed and develop stomach pain, vomiting, blood in the urine or trouble passing urine.

Most adults and children can take amoxicillin. The main exclusion is a previous allergic reaction to amoxicillin, to another penicillin or to other medicines, which you should always tell the prescriber about.

The NHS also asks you to mention liver or kidney problems, any vaccines you have recently had or are due, and any blood or urine tests coming up, because the antibiotic can affect some results. Glandular fever deserves a special mention: taking amoxicillin while you have it can bring out a rash, so tell the prescriber if you have been diagnosed or have the symptoms.

People who tend to get thrush after antibiotics should say so beforehand, since an antibiotic course can allow the yeast to overgrow.

The NHS says the common side effects, affecting up to 1 in 10 people, are a skin rash, feeling sick and diarrhoea. For a mild rash a pharmacist may suggest an antihistamine; for nausea, simple meals and taking the dose after food can help; for diarrhoea, drink plenty of fluids.

Delayed allergic reactions can appear around 7 to 12 days after starting capsules, with a mild rash, fever, joint pain and swollen glands. Tell a doctor if this happens.

• See a doctor or call NHS 111 for bloody or mucus-filled diarrhoea, pale stools with dark urine and yellowing of the skin or eyes, unusual bruising, joint or muscle pain after about two days, or circular red rash patches with a high temperature.

• The NHS notes some serious effects can appear up to two months after the course ends.

• Call 999 for swelling of the lips, mouth, throat or tongue, wheezing or severe breathing difficulty, throat tightness, blue, grey or pale skin, confusion or loss of consciousness, or a raised, itchy, blistering rash.

The NHS states that it is safe to take amoxicillin during pregnancy, while still asking you to tell the prescriber you are pregnant. Only small amounts reach breast milk. Rare effects in a nursing baby include diarrhoea, drowsiness or a rash, so watch for poor feeding, vomiting, oral thrush or unusual sleepiness and speak to a health professional or NHS 111 if you notice any. There is no evidence that it affects fertility in men or women.

The NHS names methotrexate, warfarin and the gout medicines probenecid and allopurinol as ones to check before combining, and also mentions other antibiotics. Herbal and complementary products are not tested in the same way as licensed medicines, so mention them too.

Amoxicillin is available only on prescription in the UK. The NHS page for it does not list brand names, so you will normally see it dispensed under its generic name.

Similar penicillins include flucloxacillin and phenoxymethylpenicillin, and the NHS says the choice between antibiotics depends on the type of infection. If you are allergic to penicillin the prescriber will pick a different class. Teeth staining can occur with the liquid form, but it is temporary and brushing removes it.

Suspected side effects can be reported through the MHRA Yellow Card scheme by patients as well as professionals.