This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Other topics and Adverse effects, Subject name: Pharmacology
Which of the follwoing statements about theophylline is TRUE? 
Select and explain. 
A. Its use in astham has declined because of narrow safety margin, B. Its dose needs to be reduced in the smokers, C. It acts by increasing the formation of cAMP, D. Its plasma half life is longer in children as compared to that in adults
A: Its use in astham has declined because of narrow safety margin
Answer: A: Its use in astham has declined because of narrow safety margin 
Explanation: (Ref: KDT 6/e p221) Theophylline has a narrow therapeutic index. Its use has been declined due to narrow safety margin. It inhibits the enzyme phosphodiesterase and thus decreases the metaboism of cAMP. It does not increase the formation of cAMP. Smoking is a powerful enzyme inducer. Dose of theophylline should be increased in smokers. Children metabolize theophylline faster than adults whereas elderly metabolize it slowly. Therefore, half life of theophylline is shoer in children as compared to adults.