A client on isoniazid (INH) reports numbness in their fingers. What is the most likely reason for this symptom?

The symptom of numbness in the fingers reported by a client on isoniazid (INH) is most likely due to the client metabolizing the drug slowly, which can lead to toxicity. Isoniazid is associated with peripheral neuropathy, a condition that can manifest as numbness or tingling in the extremities.

This peripheral neuropathy is often due to a deficiency in vitamin B6 (pyridoxine), which is a cofactor in many enzymatic reactions, including those involved in nerve function. When isoniazid is metabolized slowly, it can build up in the body, increasing the risk of adverse effects such as peripheral neuropathy. This is especially pertinent in individuals who may have genetic variations affecting their metabolism of the drug or those with a pre-existing deficiency in vitamin B6.

In contrast, allergic reactions to the drug would typically present with a different set of symptoms, such as rashes or allergic responses. The rapid metabolism of drugs could lead to reduced efficacy rather than toxicity, while interactions with other medications might produce varied side effects but would not specifically cause the numbness directly associated with the metabolism of isoniazid.