In a patient with COPD, which factor is known to decrease serum theophylline levels?

Cigarette smoking is known to decrease serum theophylline levels in patients with chronic obstructive pulmonary disease (COPD). This occurs because smoking induces certain liver enzymes, particularly cytochrome P450 enzymes, which increase the metabolism of theophylline. As a result, smokers may require higher doses of theophylline to achieve therapeutic effects compared to non-smokers.

Theophylline is primarily metabolized in the liver, and factors that induce liver enzyme activity can lead to reduced serum levels of this medication. Understanding this interaction is crucial for optimizing the treatment plan for patients with COPD who smoke, as it helps to avoid subtherapeutic dosing and potential treatment failure.