This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Chemotherapy: General Principles, Subject name: Pharmacology
Ciprofloxacin should not be given to an asthmatic using theophylline because: 
Select and explain. 
A. Ciprofloxacin inhibits theophylline metabolism, B. Theophylline inhibits ciprofloxacin metabolism, C. Ciprofloxacin decreases effect of theophylline, D. Theophylline induces metabolism of ciprofloxacin
A: Ciprofloxacin inhibits theophylline metabolism
Answer: A: Ciprofloxacin inhibits theophylline metabolism 
Explanation: Ans. (A) Ciprofloxacin inhibits theophylline metabolism(Ref: KDT 8/e p761)Theophylline has a narrow margin of safety (low therapeutic index) Ciprofloxacin inhibits theophylline metabolism and increases its plasma level leading to toxicity. Thus, ciprofloxacin should not be given to an asthmatic using theophylline.