Erythromycin

Key facts

• Erythromycin (found in products like Erythrocin and Eryc) is a macrolide antibiotic. It stops susceptible bacteria from making the proteins they need to grow and multiply.
• It treats chest, throat, skin and some sexually transmitted infections, and is a standard choice for people allergic to penicillin. Adults typically take it two to four times a day, often timed around meals.
• Erythromycin can prolong the QT interval, the heart's electrical recovery time, and trigger a dangerous heart rhythm. The risk rises sharply when it is combined with other QT-prolonging drugs or medicines that raise erythromycin levels.
• Seek urgent care for a fast or irregular heartbeat, fainting, or severe watery or bloody diarrhoea.

What erythromycin treats

Erythromycin treats bacterial infections of the chest (bronchitis, pneumonia), throat and sinuses, and skin, plus some sexually transmitted infections such as chlamydia. It is the usual alternative for people with a penicillin allergy who need treatment for infections like streptococcal throat infection. Doctors also prescribe it, off-label and at low doses, to speed up stomach emptying in people with delayed gastric motility. It does not treat colds, flu, or other viral illnesses.

How erythromycin works

Bacteria need to keep building proteins to survive and multiply. Erythromycin attaches to the bacterial ribosome, the structure that assembles proteins, and blocks it from finishing the job. This stops the bacteria growing so the immune system can clear the infection.

Before you take it

• Avoid erythromycin if you have had an allergic reaction to it or another macrolide antibiotic, or if you have long QT syndrome.
• Tell your prescriber about other heart medicines, statins (especially simvastatin or lovastatin), ergotamine, theophylline, warfarin, or colchicine. Erythromycin raises the blood levels of many of these drugs and can cause serious harm.
• People with significant liver disease need caution or a lower dose, since erythromycin is cleared by the liver.
• Infants exposed to erythromycin in the first weeks of life have a small increased risk of a stomach-outlet narrowing called pyloric stenosis. Tell your child's doctor about forceful vomiting or feeding problems.

Side effects

Common effects include nausea, stomach cramps and diarrhoea, since erythromycin also stimulates gut muscle contractions.

Stop and seek urgent medical care for any of these:

• A fast, irregular or pounding heartbeat, or fainting.
• Severe or bloody diarrhoea, which can signal a serious gut infection.
• Yellowing of the skin or eyes, dark urine, or persistent fatigue.
• Facial swelling, hives, or difficulty breathing.
• Severe skin blistering or peeling.

Safety essentials

• Do not combine erythromycin with other drugs that prolong the QT interval, including certain antipsychotics, antiarrhythmics and antihistamines, without medical advice. The combination can trigger a fatal heart rhythm called torsades de pointes.
• Erythromycin strongly inhibits the liver enzyme CYP3A4. Taking it with simvastatin or lovastatin can cause life-threatening muscle breakdown, and with ergotamine can severely restrict blood flow to the limbs; both combinations should be avoided.
• Finish the full course even once you feel better, so the infection does not return with resistant bacteria.

This page is educational and does not replace advice from a doctor or pharmacist who knows your health history.