Which drug is known to increase the concentration of lidocaine in the blood?

Propranolol is known to increase the concentration of lidocaine in the blood due to its effects on liver metabolism and blood flow. Lidocaine is primarily metabolized in the liver by cytochrome P450 enzymes. Propranolol, a beta-blocker, has been shown to inhibit these enzymes, leading to decreased clearance of lidocaine from the bloodstream. This results in higher plasma levels of lidocaine, which could enhance both its therapeutic effects and its potential for toxicity.

In contrast, the other options do not have this effect on lidocaine levels. For example, Prozac primarily affects serotonin levels and does not influence the metabolism of lidocaine. Aspirin, while having blood-thinning properties, does not interact with lidocaine metabolism. Fentanyl, an opioid analgesic, is also not known to affect lidocaine levels significantly. Thus, understanding the metabolic pathways and interactions between these drugs helps to clarify why propranolol specifically leads to increased lidocaine concentrations.