cyclosporine and erythromycin

Erythromycin inhibits the cytochrome P450 enzyme CYP3A4, which is primarily responsible for the metabolism of cyclosporine. This inhibition decreases the clearance of cyclosporine, leading to increased plasma concentrations. Additionally, erythromycin may inhibit P-glycoprotein, an efflux transporter involved in cyclosporine disposition, further raising cyclosporine levels.

Coadministration can cause significant elevation of cyclosporine blood concentrations, increasing the risk of cyclosporine-associated toxicities, including nephrotoxicity, neurotoxicity (tremor, confusion), hypertension, and gingival hyperplasia. The interaction is clinically important and can occur within days of starting erythromycin.

Avoid concomitant use if possible. If co-prescription is necessary, consider a non-interacting macrolide (e.g., azithromycin). When erythromycin is required, closely monitor cyclosporine trough levels, renal function, and blood pressure. Expect to reduce the cyclosporine dose, often by 25-50%, and adjust based on levels. Monitor levels frequently during therapy and for several days after stopping erythromycin.

The interaction is well established. Numerous case reports, observational studies, and pharmacokinetic studies have documented increases in cyclosporine concentrations and toxicity with erythromycin co-administration. It is a classic example of CYP3A4-mediated drug interaction.