American Board of Internal Medicine (ABIM) Certification Practice Exam

What should be administered with isoniazid to prevent peripheral neuropathy?

1. Folic acid

2. Vitamin C

3. Pyridoxine (vitamin B6)

4. Calcium

The correct answer is: Pyridoxine (vitamin B6)

Isoniazid is a medication commonly used to treat tuberculosis, but it can cause peripheral neuropathy as a side effect due to the depletion of pyridoxine, or vitamin B6, in the body. This happens because isoniazid can inhibit the enzyme that converts pyridoxine to its active form, pyridoxal phosphate, which is crucial for various metabolic processes, including the synthesis of neurotransmitters. To mitigate the risk of peripheral neuropathy associated with isoniazid use, it is recommended to co-administer pyridoxine. The typical dosage is often 25-50 mg of pyridoxine daily, especially in patients who may be at higher risk for neuropathy, such as those with diabetes, alcoholism, or other conditions that affect nerve health. While folic acid, vitamin C, and calcium are essential nutrients, they do not specifically prevent the peripheral neuropathy that can occur with isoniazid treatment. Therefore, pyridoxine is the correct answer as it directly addresses the mechanism of isoniazid-induced neuropathy and helps maintain adequate levels of vitamin B6 in the body.