Relatively higher dose of theophylline is required to attain therapeutic plasma concentration in

Drug interactions:- 1) Agents which enhance theophylline metabo lism primarily by inducing CYP1A2 lower its plasma level so, dose has to be increased in case of Smoking, phenytoin, rifampicin, phenobarbitone, Charcoal broiled meat meal. 2 ) Drugs which inhibit theophylline metabolism and increase its plasma level are--erythromycin, ciprofloxacin, cimetidine, oral contraceptives, allopurinol; dose should be reduced. 3. Theophylline enhances the effects of--furosemide, sympathomimetics, digitalis, oral anticoagulants, hypoglycaemics. 4. Theophylline decreases the effects of--phenytoin, lithium. Ref:- kd tripathi; pg num :-226,227