Abstract
A 73-year-old woman had been taking amiodarone (200mg/day) for the treatment of ventricular tachycardia and old myocardial infarction. Digoxin (0.125mg/day) was added because of reduced left ventricular contractility. Two weeks later, she consulted our hospital because of dizziness and anorexia. Electrocardiogram at that time revealed junctional escape rhythm and sinus arrest, and she was hospitalized with diagnosis of digitalis intoxication. Serum digoxin concentration on admission was 2.56ng/ml and digoxin was ceased. Serum digoxin concentration on the 18th hospital day was 0.60ng/ml and digoxin half-time was 167 hours that was longer than expected from her body status and renal function with therapeutic drug monitoring (95 hours), suggesting that amiodarone influenced digoxin clearance in this case as reported previously. Optimal dose of digoxin predicted from measured digoxin concentration curve was 0.07mg/day. Careful observations for signs of digitalis intoxication are necessary when amiodarone and digoxin are given as combination therapy. The therapeutic drug monitoring system is helpful to decide optimal digoxin dose.
