Cognitive profile of topiramate as compared with lamotrigine in epilepsy patients on antiepileptic drug polytherapy: relationships to blood serum levels and comedication.

RATIONALE: This retrospective study was conducted to identify cognitive domains affected by topiramate (TPM), and to evaluate the role of blood serum levels of TPM and comedication in the etiology of TPM-induced cognitive impairment.
METHODS: Forty-two patients on AED polytherapy containing topiramate and a random sample of 42 patients with lamotrigine as the corresponding agent underwent extensive neuropsychological testing. Current blood serum levels of TPM were correlated with test scores.
RESULTS: Patients on TPM scored significantly worse in phonematic verbal fluency, memory spans, and working memory; language and memory function were not affected per se. In few cognitive domains, serum levels of TPM and performance were correlated before correction for multiple testing. Drug load of additional medication did not account for differences between or within groups. DISCUSSION: Consistent with previous reports, patients on AED polytherapy including TPM display a cognitive pattern with specific impairment in executive functions. The severity of the cognitive side effects of TPM may be related to dosing to a certain extent, but this relationship may be disclosed only with larger sample sizes. Accordingly, TPM dosage does not appear to be a good indicator of TPM-related cognitive side effects in the individual patient.