After a patient stops smoking while taking theophylline, what is the most likely change in theophylline plasma concentration?

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Study for the Foundation Year Pharmacy – Clinical Practice Test. Prepare with detailed questions, step-by-step explanations, and test format insights. Enhance your readiness and confidence!

Multiple Choice

After a patient stops smoking while taking theophylline, what is the most likely change in theophylline plasma concentration?

Explanation:
Smoking induces the liver enzyme CYP1A2 that metabolizes theophylline, so smokers clear theophylline faster and have lower plasma levels. When the patient stops smoking, this enzyme induction fades, hepatic clearance of theophylline decreases back toward baseline, and the drug begins to accumulate, raising the plasma concentration. Because theophylline has a narrow therapeutic window, even a modest increase can raise toxicity risk. The rise in concentration happens gradually as the body readjusts, so monitoring levels and adjusting the dose may be needed over days to weeks.

Smoking induces the liver enzyme CYP1A2 that metabolizes theophylline, so smokers clear theophylline faster and have lower plasma levels. When the patient stops smoking, this enzyme induction fades, hepatic clearance of theophylline decreases back toward baseline, and the drug begins to accumulate, raising the plasma concentration. Because theophylline has a narrow therapeutic window, even a modest increase can raise toxicity risk. The rise in concentration happens gradually as the body readjusts, so monitoring levels and adjusting the dose may be needed over days to weeks.

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