A Case of Valproate Toxicity Related to Isoniazid

This document described a case of valproate toxicity in an 80-year-old man after starting isoniazid for latent tuberculosis. The patient, who had been on valproic acid for schizophrenia and seizure disorder, experienced severe lethargy and functional decline, with serum valproic acid levels rising to 110.0 μg/mL. After reducing the valproic acid dosage, his condition improved. This case highlighted a potential pharmacokinetic interaction between valproic acid and isoniazid, which could lead to increased serum levels of valproic acid due to competition for cytochrome P450 isoenzymes. The authors emphasized the importance of monitoring for this interaction in elderly patients, particularly in nursing homes, where concurrent use of these medications is common.