Which of the following drugs is a known substrate of the CYP450 enzyme system?

Theophylline is recognized as a substrate of the CYP450 enzyme system, specifically being metabolized primarily through the CYP1A2 isoenzyme. This means that its clearance and plasma concentration can be significantly altered by the presence of other drugs that induce or inhibit CYP1A2 activity.

Theophylline's metabolism is influenced by various factors, including diet and disease states, making it an important consideration in pharmacotherapy and the management of conditions such as asthma and chronic obstructive pulmonary disease (COPD). When other medications that interact with CYP450 enzymes are introduced into a patient's regimen, it can lead to variations in theophylline levels, prompting adjustments in dosing.

While other options mentioned also have interactions with the CYP450 system, theophylline is specifically well-characterized as a true substrate of this enzyme system, making it the correct choice in this context.