This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Respiratory system, Subject name: Pharmacology
Relatively higher dose of theophylline is required to attain therapeutic plasma concentration in 
Select and explain. 
A. Smokers, B. Congestive hea failure patients, C. Those receiving erythromycin, D. Those receiving cimetidine
A: Smokers
Answer: A: Smokers 
Explanation: 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