Increased serum theophylline levels. Elevated digoxin serum levels. Increased anticoagulant effects w/ oral anticoagulants. Acute ergot toxicity w/ ergotamine or dihydroergotamine. Decreased clearance of triazolam & midazolam. Rhabdomyolysis w/ lovastatin. Elevated serum w/ CYP450-metabolized drugs eg, carbamazepine, alfentanil, disopyramide, lovastatin, bromocriptine, cyclosporine, hexobarbital & phenytoin. Antagonized effects of chloramphenicol & lincomycins. Interfered bactericidal effect of penicillins. Concomitant use w/ hepatotoxic or ototoxic drugs.