Which drug may reduce the effectiveness of carbamazepine in a patient undergoing treatment for tuberculosis?

Rifampin is known to induce liver enzymes, particularly cytochrome P450 isoenzymes, which play a crucial role in the metabolism of many drugs, including carbamazepine. When rifampin is administered alongside carbamazepine, it increases the metabolic breakdown of carbamazepine in the liver, thereby reducing its plasma levels and overall effectiveness. This interaction can lead to decreased therapeutic effects of carbamazepine, which is often used to control seizures or manage bipolar disorder.

The other options, while they are part of tuberculosis treatment, do not significantly affect the metabolic pathway of carbamazepine in the same manner as rifampin. For instance, isoniazid can increase carbamazepine levels due to its inhibitory effect on the same enzymes, while pyrazinamide and ethambutol do not have a notable impact on carbamazepine metabolism. Therefore, rifampin's enzyme-inducing properties clearly position it as the drug that may reduce the effectiveness of carbamazepine in this scenario.