Tolvaptan administration does not affect steady state amiodarone concentrations in patients with cardiac arrhythmias.

Background: Tolvaptan, a nonpeptide selective vasopressin receptor (V2) antagonist, is in development for the treatment of congestive heart failure and hyponatremia. Tolvaptan is primarily metabolized via CYP3A4. This study was conducted to determine the extent of the pharmacokinetic interaction between tolvaptan and steady state amiodarone, an antiarrhythmic drug commonly prescribed for patients with congestive heart failure and a known inhibitor of other drugs metabolized by CYP3A4.