DIGOXIN TOXICITY SECONDARY TO CLARITHROMYCIN THERAPY

OBJECTIVE: To report a case of digoxin toxicity thought to be secondly to clarithromycin therapy. CASE SUMMARY: A 78-year-old white woman wi th congestive heart failure taking digoxin 0.25 mg po qd presented to our hospital with nausea, vomiting, and diarrhea. She had taken clarit hromycin 500 mg po bid for 3 days, and a serum digoxin concentration o btained the day of admission was 4.4 mu g/L. An electrocardiogram (ECG ) done on admission revealed ST segment changes consistent with digoxi n effect and later asymptomatic, nonsustained ventricular tachycardia (NSVT). Clarithromycin was discontinued and digoxin was withheld at ad mission, resulting in the resolution of symptoms, ECG abnormalities, a nd NSVT on day 3 of hospitalization. On day 5 her serum digoxin concen tration was 1.5 mu g/L and digoxin therapy was reinstituted at a dose of 0.125 mg/d po. DISCUSSION: This is the fourth published case implic ating clarithromycin as the cause of digoxin toxicity. This interactio n is most likely due to clarithromycin eradication of digoxin-metaboli zing gut flora, thereby increasing digoxin bioavailability. CONCLUSION S: Approximately 10% of patients are thought to be extensive presystem ic 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 therap y.