What is a possible side effect of long-term INH therapy?

Long-term therapy with isoniazid (INH) can lead to peripheral neuropathy due to its effect on vitamin B6 (pyridoxine) metabolism. INH is known to inhibit the action of pyridoxine, which is essential for the synthesis of neurotransmitters and the maintenance of nerve health. When B6 levels are depleted, it can result in nerve damage, manifesting as symptoms including numbness, tingling, and weakness in the extremities. This side effect is particularly significant in individuals who are malnourished or have additional risk factors such as diabetes, as these populations may already have compromised nerve function.

While increased appetite, joint pain, and severe headaches can occur with various medications or conditions, they are not commonly associated with INH therapy in the way that peripheral neuropathy is, making peripheral neuropathy the primary concern to monitor in patients undergoing long-term treatment with this medication. This particular side effect underscores the importance of monitoring and possibly supplementing with vitamin B6 for patients on INH.