Which drug increases the concentration of lidocaine in the blood?

• A. Prozac
• B. Aspirin
• C. Propanolol
• D. Ibuprofen

Answer: (C)

The correct answer is the drug that increases the concentration of lidocaine in the blood is a beta-blocker, specifically propranolol. Propranolol can inhibit the hepatic metabolism of lidocaine by affecting the cytochrome P450 enzyme system, which is responsible for the breakdown of many drugs, including lidocaine. When this metabolism is inhibited, the clearance of lidocaine from the blood is reduced, resulting in higher concentrations in the bloodstream.

This effect is clinically relevant because when lidocaine is utilized, especially in higher doses or in patients with compromised liver function, its concentration monitoring is important to avoid toxicity. Propranolol's role in this context reinforces the necessity of understanding drug interactions, particularly with medications that can affect liver enzyme activity.

Other options such as Prozac, aspirin, and ibuprofen do not have a significant effect on the metabolism of lidocaine in the same manner, hence they do not lead to increased concentrations of lidocaine in the blood. Understanding such interactions is crucial for safe and effective pharmacotherapy.