Erythromycin: uses, side effects and interactions

Erythromycin is a long-established antibiotic. The NHS describes its main uses as bacterial chest infections, dental abscesses and sexually transmitted infections, and notes it is sometimes used for skin conditions such as acne and rosacea, where it is taken over a longer spell.

Acne and rosacea use is the unusual one: those are not infections in the usual sense, so a course for them is set by the prescriber and may differ from an infection course. The NHS page does not explain how the drug works, and a pharmacist can answer that if you want to know.

The NHS says most people need to take erythromycin 2 to 4 times a day for a few days or weeks, with doses spaced evenly. Swallow tablets or capsules whole with water, use the measure supplied for the liquid, and check the pack about whether food matters for your particular product.

Keep going until the course is finished even if you feel better.

For acne or rosacea the course is not the few days typical of an infection, so the instructions on your own label are the ones to follow, and a review with the prescriber is how you judge whether it is helping.

• Missed dose: take it when you remember unless the next dose is close; skip it then. Never double up.

• Overdose: speak to a pharmacist or NHS 111 promptly, and 999 if you feel seriously unwell.

• Alcohol: the NHS advises limiting it.

The NHS lists liver or kidney problems, myasthenia gravis, porphyria (a blood condition) and any previous allergic reaction to erythromycin as reasons the medicine may not be suitable.

In pregnancy it should be used only when the benefits outweigh the risks, and it passes into breast milk, so discuss both situations with the prescriber.

Because several of the conditions on this list, such as porphyria and myasthenia gravis, are long-term and may not come up in a short appointment, it helps to mention them whenever you are prescribed an antibiotic. A pharmacist checking your prescription against your medicines can also catch an interaction before the first dose.

Common effects are digestive: nausea, vomiting, diarrhoea, loss of appetite, bloating and indigestion. Talk to a pharmacist if they persist or worry you.

• Call 999 for allergic reactions with a swollen throat or tongue, a rash or difficulty breathing.

• Call NHS 111 for severe stomach pain, which can signal a pancreas problem.

• Call NHS 111 for yellow skin or eyes, or pale stools with dark urine, which can signal a liver or gallbladder problem.

• Call NHS 111 for severe diarrhoea containing blood or mucus.

The NHS names domperidone, the anticoagulants warfarin and rivaroxaban, the antipsychotics pimozide and amisulpride, and certain statins (simvastatin and lovastatin are given as examples). It also warns against St John's wort.

Because the list is not complete, always give the prescriber a full account of everything you take.

Other macrolides such as clarithromycin and azithromycin are used for similar infections and are covered in separate guides. A prescriber may prefer one of these, or a different antibiotic family, depending on the infection and your other medicines.

Suspected side effects can be reported to the MHRA Yellow Card scheme.