Digoxin toxicity secondary to clarithromycin therapy

OBJECTIVE: To report a case of digoxin toxicity thought to be secondary to clarithromycin therapy. CASE SUMMARY: A 78-year-old white woman with congestive heart failure taking digoxin 0.25 mg po qd presented to our hospital with nausea, vomiting, and diarrhea. She had taken clarithromycin 500 mg po bid for 3 days, and a serum digoxin concentration obtained the day of admission was 4.4 mug/L. An electrocardiogram (ECG) done on admission revealed ST segment changes consistent with digoxin effect and later asymptomatic, nonsustained ventricular tachycardia (NSVT). Clarithromycin was discontinued and digoxin was withheld at admission, resulting in the resolution of symptoms, ECG abnormalities, and NSVT on day 3 of hospitalization. On day 5 her serum digoxin concentration was 1.5 micrograms/L and digoxin therapy was reinstituted at a dose of 0.125 mg/d po. DISCUSSION: This is the fourth published case implicating clarithromycin as the cause of digoxin toxicity. This interaction is most likely due to clarithromycin eradication of digoxin-metabolizing gut flora, thereby increasing digoxin bioavailability. CONCLUSIONS: Approximately 10% of patients are thought to be extensive presystemic metabolizers of digoxin and may therefore be most susceptible to a drug interaction with clarithromycin. Serum digoxin concentrations in such patients should be monitored closely during clarithromycin therapy.