digoxin and clarithromycin

Clarithromycin inhibits the P-glycoprotein (P-gp) transporter, which is responsible for the efflux of digoxin from intestinal epithelial cells and renal tubular cells. This inhibition increases digoxin absorption and decreases its renal and biliary excretion, leading to elevated serum digoxin concentrations. Additionally, clarithromycin may alter gut flora, reducing the bacterial metabolism of digoxin, further contributing to increased digoxin levels.

Serum digoxin concentrations can rise significantly, potentially causing digoxin toxicity. Symptoms include nausea, vomiting, anorexia, visual disturbances, confusion, bradycardia, and life-threatening cardiac arrhythmias such as ventricular tachycardia or heart block. The onset is usually within a few days of starting clarithromycin, but toxicity can occur at any time during co-administration.

Avoid co-prescription when possible. If use is necessary, consider reducing the digoxin dose and closely monitoring serum digoxin concentrations and renal function before and during therapy. Monitor the patient for signs of digoxin toxicity, including heart rate and rhythm. Consider alternative antibiotics that do not inhibit P-glycoprotein (e.g., azithromycin has a less pronounced effect) where appropriate.

This interaction is well established through numerous case reports, clinical studies, and prescribing information. The mechanism involving P-glycoprotein inhibition is supported by pharmacokinetic studies. Guidance from regulatory agencies and clinical guidelines recommends caution and monitoring.