This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Asthma, Subject name: Pharmacology
Theophylline levels are increased in all, except 
Select and explain. 
A. Erythromycin, B. Smoking, C. Cimetidine, D. CHF
B: Smoking
Answer: B: Smoking 
Explanation: Ans. is 'b' i.e., Smoking Smoking induces theophylline metabolism and decreases its plasma level.In certain conditions theophylline concentration is increased, so its dose has to be reduced.These conditions are - Age > 60 years CHFPneumonia Liver failureDrugs causing increased concentration of theophyllineErythromycinCiprofloxacinCimetidineOral contraceptivesAllopurinol