Which statement about theophylline interactions with cimetidine or ciprofloxacin is true?

Which statement about theophylline interactions with cimetidine or ciprofloxacin is true?

• A. Both interactions increase theophylline toxicity
• B. Both interactions decrease theophylline toxicity
• C. Theophylline is unaffected
• D. Only ciprofloxacin increases toxicity, not cimetidine

Answer: (A)

Both cimetidine and ciprofloxacin slow the breakdown of theophylline in the liver by inhibiting enzymes that metabolize it, especially CYP1A2. Because theophylline has a narrow therapeutic index, even small decreases in clearance can raise its levels enough to cause toxicity. Cimetidine and ciprofloxacin each raise theophylline concentrations on their own, so using them together with theophylline increases the risk of toxicity. Signs to watch for include nausea, vomiting, tremor, restlessness, tachycardia, and in severe cases seizures. So the statement that both interactions increase theophylline toxicity is true. When these drugs are used together, clinicians often consider reducing theophylline dose or choosing alternatives and closely monitoring levels.

Both cimetidine and ciprofloxacin slow the breakdown of theophylline in the liver by inhibiting enzymes that metabolize it, especially CYP1A2. Because theophylline has a narrow therapeutic index, even small decreases in clearance can raise its levels enough to cause toxicity. Cimetidine and ciprofloxacin each raise theophylline concentrations on their own, so using them together with theophylline increases the risk of toxicity. Signs to watch for include nausea, vomiting, tremor, restlessness, tachycardia, and in severe cases seizures. So the statement that both interactions increase theophylline toxicity is true. When these drugs are used together, clinicians often consider reducing theophylline dose or choosing alternatives and closely monitoring levels.