This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Pharmacology
Which of the following statements about theophylline is TRUE 
Select and explain. 
A. Its use in asthma 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 asthma has declined because of narrow safety margin
Answer: A: Its use in asthma has declined because of narrow safety margin 
Explanation: 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 metabolism 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, the half-life of theophylline is shorter in children as compared to adults.