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