Which factor explains why stopping smoking can raise theophylline levels?

Which factor explains why stopping smoking can raise theophylline levels?

• A. Increased hepatic metabolism
• B. Decreased hepatic metabolism
• C. No change
• D. Fluctuation

Answer: (B)

Stopping smoking reduces the induction of liver enzymes that break down theophylline. Theophylline is mainly metabolized by hepatic cytochrome P450 enzymes, especially CYP1A2. Smoking induces these enzymes, speeding up metabolism and lowering theophylline levels. When smoking stops, the induction fades, hepatic metabolism slows, clearance decreases, and theophylline accumulates, raising its plasma levels. This explains why quitting can lead to higher theophylline levels. If the metabolism stayed increased, levels would stay low; if there were no change or only fluctuations, there wouldn't be a sustained rise.

Stopping smoking reduces the induction of liver enzymes that break down theophylline. Theophylline is mainly metabolized by hepatic cytochrome P450 enzymes, especially CYP1A2. Smoking induces these enzymes, speeding up metabolism and lowering theophylline levels. When smoking stops, the induction fades, hepatic metabolism slows, clearance decreases, and theophylline accumulates, raising its plasma levels. This explains why quitting can lead to higher theophylline levels. If the metabolism stayed increased, levels would stay low; if there were no change or only fluctuations, there wouldn't be a sustained rise.