Amiodarone-digoxin interaction: Clinical significance, time course of development, potential pharmacokinetic mechanisms and therapeutic implications

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Administration of amiodarone (600 to 1,600 mg/day) to 28 patients during long-term digoxin therapy (0.25 ± 0.05 mg/day) increased serum digoxin level from 0.97 ± 0.45 to 1.98 ± 0.84 ng/ml (p < 0.001). Gastrointestinal side effects occurred in nine patients, central nervous system reactions occurred in five and cardiovascular reactions occurred in four. Pharmacokinetic studies in six patients with a 1 mg intravenous digoxin dose before and during amiodarone therapy increased serum digoxin level at 30 minutes from 8.59 ± 1.68 to 10.07 ± 1.70 ng/ml (p < 0.05). Amiodarone caused a 31% prolongation of digoxin elimination half-life from 49.5 8.8 to 65.0 ± 28.8 hours, but the increase in half-life was not statistically significant. Total body clearance was reduced significantly (29%, p < 0.05) from 2.05 ± 0,76 to 1.46 ± 0.64 ml/min per kg. Nonrenal clearance also showed a significant decrease (33%, p < 0.05) from 1.20 ± 0.46 to 0.80 ± 0.30 ml/min per kg. The renal clearance decreased by 22% and the volume of distribution decreased by 11% after amiodarone therapy, but these changes were not significant. The data show that the mechanism of digoxin-amiodarone interaction is multifactorial and emphasize the need for close monitoring of serum digoxin levels and clinical features during concurrent digoxin-amiodarone therapy.

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From the Department of Cardiology, Wadsworth Veterans Administration Medical Center, and Department of Medicine, University of California, Los Angeles, School of Medicine, Los Angeles, California.