The nurse is providing teaching to a patient taking tetracycline. Which statement by the nurse is correct?

Choice A reason: Fluconazole inhibits hepatic CYP2C9, which metabolizes warfarin, increasing warfarin’s plasma levels. This enhances its anticoagulant effect, inhibiting vitamin K-dependent clotting factors, leading to a higher risk of bleeding. Monitoring INR and bleeding signs is critical to prevent hemorrhage in patients on this combination.

Choice B reason: Warfarin does not decrease fluconazole’s antifungal efficacy. Fluconazole inhibits fungal ergosterol synthesis, and its action is unaffected by warfarin’s anticoagulant mechanism. The primary interaction is fluconazole’s effect on warfarin metabolism, not a reduction in fluconazole’s ability to treat fungal infections.

Choice C reason: Fluconazole increases, not reduces, warfarin’s anticoagulant effect by inhibiting CYP2C9, slowing warfarin metabolism. This leads to elevated warfarin levels, prolonging INR and increasing bleeding risk. Reduced anticoagulant action would occur with enzyme inducers, not inhibitors like fluconazole.

Choice D reason: Hypokalemia is not a known interaction between fluconazole and warfarin. Fluconazole’s side effects include hepatotoxicity, and warfarin affects clotting, but neither significantly alters potassium levels. Electrolyte imbalances are more associated with diuretics or amphotericin B, not this drug combination.

Choice A reason: Hair loss is not a common side effect of isoniazid, nor is it prevented by pyridoxine. Isoniazid primarily causes hepatotoxicity or neurotoxicity due to its metabolism and pyridoxine depletion. Hair loss may occur with other drugs, but pyridoxine supplementation is unrelated to this effect.

Choice B reason: Pyridoxine (vitamin B6) is given with isoniazid to prevent peripheral neuropathy. Isoniazid depletes pyridoxine by forming inactive complexes, impairing nerve function and causing numbness or tingling. Supplementation restores pyridoxine levels, protecting peripheral nerves while allowing isoniazid to effectively treat tuberculosis by inhibiting mycolic acid synthesis.

Choice C reason: Heart failure is not associated with isoniazid or prevented by pyridoxine. Isoniazid’s primary toxicities are hepatic and neurological. Pyridoxine supports nerve health, not cardiac function, and heart failure is more linked to drugs like anthracyclines, not antitubercular therapy.

Choice D reason: Renal failure is not a common side effect of isoniazid, nor is it prevented by pyridoxine. Isoniazid is metabolized by the liver, and its toxicities include hepatotoxicity and neuropathy. Pyridoxine addresses neurological side effects, not renal function, making this an incorrect choice.