Increased absorption w/ food. Decreased AUC∞
w/ strong CYP3A4 inducers eg, phenytoin, carbamazepine, rifampicin, rifabutin, rifapentine, phenobarb, St. John's wort (Hypericum perforatum
). Increase AUC of dextromethorphan. Drugs metabolised by CYP2D6 particularly w/ drugs that have narrow therapeutic index eg, metoprolol, propranolol, desipramine, venlafaxine, haloperidol, risperidone, propafenone, flecainide, codeine, oxycodone & tramadol. Drugs known to prolong the QT interval or induce Torsades de Pointes eg, class IA (eg, quinidine, disopyramide) or class III (eg, amiodarone, sotalol, dofetilide, ibutilide) antiarrhythmics, methadone, moxifloxacin, antipsychotics. Increased prostate specific antigen w/ spironolactone.