18.01.4.4 Macrolides

Erythromycin is an example of a macrolide. The macrolides inhibit the translocation step in bacterial protein synthesis (i.e. the separation of the protein, after another amino acid has been added). Erythromycin is bateriostatic and broad spectrum. It is effective against Gram-positive and against a few Gram-negative bacteria. Erythromycin is used as an alternative to penicillin and cephalosporins in people who are allergic to these antibiotics. Erythromycin is also used in respiratory tract infections.

Erythromycin is suitable for oral or intravenous use. Erythromycin is metabolised by the liver enzyme CYP 3A4. Consequently, drugs that inhibit CYP 3A4 (grapefruit juice, ketoconazole) increase the levels of erythromycin, and this can lead to toxic effects of erythromycin. The toxic effects of erythromycin include a prolongation of QT interval, which indicates a slowing of ventricular repolarisation and can lead to cardiac arrhythmia.