Theophylline with ciprofloxacin increases risk of toxicity due to decreased clearance. What is the recommended action?

• A. Ciprofloxacin increases theophylline clearance
• B. Theophylline is unaffected by ciprofloxacin
• C. No interaction
• D. Theophylline toxicity risk increased

Answer: (D)

The main concept here is that some drug pairs can cause serious toxicity when one drug affects the clearance of another. Theophylline is cleared mainly by CYP1A2, and ciprofloxacin inhibits this enzyme. When ciprofloxacin is added, theophylline isn’t cleared as quickly, so its levels rise and toxicity risk increases. That heightened risk is the reason for changing therapy: avoid the combination or use a non-interacting antibiotic, or closely monitor and adjust theophylline dosing if no alternatives exist. So saying that theophylline toxicity risk is increased correctly identifies the consequence of the interaction and justifies taking preventive action.