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Theophylline toxicity — SCE Respiratory MCQ

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HardRare and miscellaneousTheophylline toxicitySCE Respiratory

A 67-year-old man with severe COPD is prescribed oral theophylline by a private clinic. He presents with nausea, tremor and palpitations after starting clarithromycin for a chest infection. ECG shows atrial tachycardia and serum theophylline concentration is above the therapeutic range. Renal function is normal. What is the most likely underlying cause?

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Correct answer: B — Reduced theophylline clearance due to macrolide interaction

Theophylline has a narrow therapeutic index and interacting drugs such as macrolides can increase levels and cause arrhythmias, tremor and gastrointestinal symptoms. Beta-agonists can cause tremor but do not explain a raised theophylline concentration. The clinical pearl is to check interactions before prescribing antibiotics in patients taking theophylline.

Reference: BNF; NICE NG115 COPD