Reduced bioavailability & weakened efficacy w/ rifampicin. Increased exposure w/ macrolides, anti-HIV PIs, azole antimycotics, fluoxetine, nefazodone, quinupristin/dalfopristin, cisapride, valproic acid, cimetidine, diltiazem. Decreased exposure w/ rifampicin, phenytoin, carbamazeine, phenobarb. Increased BP-lowering effect of antihypertensives. Deterioration of heart failure w/ β-receptor blockers. Reduced digoxin clearance. Lowered plasma quinidine levels. Concomitant use w/ tacrolimus. Elevated plasma conc & prolonged action w/ grapefruit juice. Falsely increased spectrophotometric values of urinary vanillymandelic acid.