<unk>  has high bioavailability after an oral dose, meaning that most of the drug that is ingested will enter the systemic blood stream. Peak serum concentrations can be seen 1 to 6 hours after ingestion of an oral dose. While the plasma half-life is about 20 hours, it is quite variable, and can range from 12 to 27 hours. During oral loading with<unk> , a steady state equilibrium is typically achieved in 3 to 5 days. The majority of<unk>  is eliminated by the kidneys, with the remainder metabolized by the cytochrome P450 2D6 isoenzyme in the liver. Therefore, alterations in renal function or urine pH will greatly affect the elimination of<unk> , as more is eliminated by the kidney than by the hepatic route. Because of the dual elimination routes of<unk>  and its tendency to decrease myocardial contractility,<unk>  interacts with numerous pharmaceuticals and can potentiate the effects of other myocardial depressants and AV node blocking agents. In addition,<unk>  can decrease the metabolism or elimination of many (but not all) agents that use the cytochrome P450 enzyme system. A full list of drug interactions with<unk>  can be obtained from the manufacturer. Some important drug interactions with<unk>  include: * Alcohol – may further depress normal heart function * Amiodarone – inhibits cytochrome P450 2D6 and may increase<unk>  levels * Cimetidine – increases<unk>  levels by 30% and half-life by 10% * Digoxin – may increase digoxin levels * Paroxetine – increased effect of both drugs * Propafenone – increased effect of both drugs and increased risk of toxicity * Quinidine – inhibits cytochrome P450 2D6 and may increase<unk>  levels
Flecainide
Tocainide
Procainamide
Acecainide
Amiodarone
Ibutilide
Verapamil
Dofetilide