A client taking isoniazid (INH) should be monitored for side effects which include which of the following?

• A. Peripheral neuropathy
• B. Hypertension
• C. Weight gain
• D. Elevated blood glucose levels

Answer: (A)

Isoniazid can cause peripheral neuropathy because it induces a deficiency of vitamin B6 (pyridoxine). INH interferes with the body's ability to use and recycle vitamin B6, leading to a shortage of pyridoxal phosphate, a crucial cofactor for nerve function and neurotransmitter synthesis. When B6 levels drop, nerves—especially the long nerves of the hands and feet—become dysfunctional, producing numbness, tingling, or burning sensations in a glove-and-stocking distribution. Because this neuropathy is predictable with INH therapy, clinicians often prevent it by giving a small daily amount of vitamin B6 alongside the drug.

The other options don’t fit as common adverse effects of isoniazid. Hypertension, weight gain, and elevated blood glucose aren’t typical drug-related effects of INH, so they’re less likely explanations for symptoms seen during INH treatment.