Amiodarone increases the blood levels of digoxin (Lanoxin) when the two drugs are given together. It is recommended that the dose of digoxin be cut by 50% when amiodarone therapy is started. Flecainide (Tambocor) blood concentrations increase by more than 50% with amiodarone. Procainamide (Procan-SR, Pronestyl) and quinidine (Quinidex, Quinaglute) concentrations increase by 30%-50% during the first week of amiodarone therapy. Additive electrical effects occurs with these combinations, and worsening arrhythmias may occur as a result. Some experts recommend that the doses of these other drugs be reduced when amiodarone is started. Amiodarone can result in phenytoin (Dilantin) toxicity because it causes a two- or three-fold increase in blood concentrations of phenytoin. Symptoms of phenytoin toxicity including unsteady eye movement (temporary and reversible), tiredness and unsteady gait.
Ritonavir (Norvir), tipranavir (Aptivus), indinavir (Crixivan), and saquinavir (Invirase) can inhibit the enzyme that is responsible for the metabolism (break-down) of amiodarone. They should not be combined with amiodarone.
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