Doxofylline should not be administered concomitantly with other methylxanthines, including beverages and foods containing caffeine.
Xanthine half-life may be increased and clearance decreased by interaction with cimetidine, allopurinol, propranolol, erythromycin, troleandomycin, lincomycin, ciprofloxacin, and anti-flu vaccine. In these cases, the dose of doxofylline may be reduced.
Xanthine half-life may be decreased and clearance increased by phenytoin, anticonvulsants, and smoking. In these cases, a higher dose of doxofylline may be required.
Synergistic toxicity with ephedrine and other sympathomimetics have been reported for xanthines.
Xanthines may potentiate hypokalemia caused by hypoxia or associated with the use of beta2-adrenoceptor stimulants (beta2-agonists), corticosteroids, and diuretics.