Increased serum conc of theophylline, digoxin. Increased plasma conc of carbamazepine, terfenadine. Increased steady-state plasma conc of omeprazole. Decreased steady-state zidovudine conc. Potentiated effects of oral anticoagulants. Elevated conc of CYP3A-metabolized drugs. Increased serum levels of warfarin, ergot alkaloids, midazolam, lovastatin, phenytoin, ciclosporin. Torsade de pointes w/ quinidine/disopyramide. QT prolongation & cardiac arrhythmias w/ domperidone. QT prolongation & Torsade de pointes w/ astemizole. Concomitant use w/ alprazolam, cisapride, methylprednisolone, pimozide, rifabutin, simvastatin, tacrolimus, triazolam.