Interactions

Amiodarone is metabolised by hepatic cytochrome P450 3A4(CYP 3A4) isoenzyme:

• concomitant administration of CYP 3A4 inhibitors should either be avoided or used only with caution
• CYP 3A4 inducers (e.g. carbamazepine, rifampicin) may lead to a reduction in amiodarone's plasma concentration and therefore reduce efficacy
• amiodarone itself inhibits CYP 3A4 and therefore will increase plasma concentrations of drugs such as ciclosporin, phenytoin and verapamil

Other important interactions with amiodarone include:

• potentiation of the effects of warfarin (inhibits metabolism via CYP 3A4)
  
  
• reduces excretion of digoxin (leads to increased plasma concentration)
  
  
• contra-indicated with other drugs that prolong the QT interval (e.g. disopyramide, quinidine, procainamide); only specialists should co-prescribe and monitor such drug therapy

Reference:

1. Drug and Therapeutics Bulletin (2003), 41 (2), 9-12.