Toxic synergism w/ ephedrine. Decreased hepatic clearance w/ erythromycin, troleandomycin, lincomycin, clindamycin, allopurinol, propranolol, digoxin, anti-flu vaccine. Increased clearance w/ shorter mean t
½ w/ phenytoin, other anticonvulsants; smoking. Not to be administered w/ other xanthine derivatives.