Erythromycin (Erymax / Erythrocin / Erythroped / Erythroped A) is an antibiotic drug that is often used in patients who are allergic to penicillin. It is active against a range of respiratory tract infections, as well as chlamydia, syphilis and gonorrhoea. It is produced from a fungus that grows in the soil, and works by preventing bacteria from making new protein molecules.

Erythromycin is available in tablets, capsules, suspensions, solutions for use in the eye, ointments and gels.

Erythromycin commonly causes the side-effects of diarrhoea, nausea, stomach pain and vomiting. It can also cause temporary hearing loss and allergic reactions in rare cases.

Drugs that delay the breakdown of erythromycin by interfering with the CYP3A4 enzyme may cause dangerous heart problems, which can be fatal. For this reason, it should be taken with care in patients taking the protease inhibitors fosamprenavir (Telzir), lopinavir, ritonavir (Norvir) or tipranavir (Aptivus). Other protease inhibitors and non-nucleoside reverse transcriptase inhibitors (NNRTIs) do not interact with erythromycin.