Doxofylline tablets should not be administered together with other xanthine derivatives. Toxic synergism with ephedrine has been documented for xanthine. Like other xanthines, concomitant therapy with erythromycin, troleandomycin, lincomycin, clindamycin, allopurinol, cimetidine, ranitidine, propranolol and anti-flu vaccine may decrease the hepatic clearance of xanthines causes an increase in blood levels. No evidence of a relationship between Doxofylline serum concentration and toxic events have been reported.