Antibiotics that stop bacteria making proteins by binding the bacterial ribosome, used for chest, ear, skin and sexually transmitted infections and as the main alternative in penicillin allergy. Azithromycin, clarithromycin and erythromycin differ mainly in how long they last and how much they interact with other medicines.
Macrolides bind the 23S ribosomal RNA in the exit tunnel of the bacterial 50S ribosomal subunit and block the growing peptide chain, halting protein synthesis; the effect is bacteriostatic against most organisms. They concentrate inside cells, including the white cells that travel to infected tissue, so they work against intracellular pathogens such as Mycoplasma, Chlamydia and Legionella that penicillins cannot reach. Erythromycin and clarithromycin are strong inhibitors of the liver enzyme CYP3A4 and of P-glycoprotein and so raise the levels of statins, calcium channel blockers, warfarin, some anticoagulants and many other drugs; azithromycin barely inhibits CYP3A4 and interacts less. All macrolides can prolong the QT interval. Long-term low-dose azithromycin has anti-inflammatory effects used in COPD and bronchiectasis.
Nausea, diarrhoea, abdominal pain (most with erythromycin, which stimulates gut motility)
QT prolongation and arrhythmia, particularly with other QT-prolonging drugs or low potassium
Liver enzyme rise and cholestatic jaundice
Taste disturbance (clarithromycin), hearing loss with high or prolonged doses
Cautions
Heart rhythm disorders, long QT, electrolyte disturbance
Liver disease
Myasthenia gravis
Clarithromycin and erythromycin: many interactions through CYP3A4 (statins, some anticoagulants, calcium channel blockers, colchicine, warfarin)
Class warnings
All macrolides can prolong the QT interval and have been associated with torsades de pointes and sudden cardiac death; risk is greatest with other QT-prolonging drugs, hypokalaemia, hypomagnesaemia, bradycardia and existing heart disease. UK
Clarithromycin and erythromycin are potent CYP3A4 inhibitors: simvastatin and some other statins, colchicine, ticagrelor and several other drugs are contraindicated or need dose reduction while they are taken. Azithromycin lacks most of these interactions. UK
Class interactions
With
Effect
Source
Statins (simvastatin, atorvastatin) with clarithromycin or erythromycin
Greatly increased statin levels and rhabdomyolysis risk; simvastatin is contraindicated with clarithromycin and paused during erythromycin.
Educational content. A drug class page describes what a family of medicines has in common. Individual medicines differ in dose, licensing and interactions; treatment choices belong to a prescriber.
