Abstracts

Two of the newer antiepileptic drugs (AEDs), topiramate (TPM) and zonisamide (ZNS), have a similar chemical structure and produce similar cognitive side effects (Weatherly et al., 2004). Yet providers continue to prescribe each of these drugs independent of patient response to the other medication. The current study aims to clarify whether patients who experienced cognitive side effects on one of the drugs is likely to experience similar side effects on the other drug., Adult neuropsychological files were retrospectively reviewed. Epilepsy patients were included if they had undergone neuropsychological testing during therapy with TPM and again while on ZNS. All patients had a baseline IQ of 70 or greater and did not have a progressive neurological disorder. The cognitive test battery included measures of working memory, verbal fluency, visual-motor speed, and manual dexterity. Due to the limited number of subjects, neuropsychological data were reviewed without formal statistical comparisons., Eight patients were identified who underwent neuropsychological testing while treated with TPM who had also been tested separately while on ZNS. The mean TPM dose was 200 mg and the mean ZNS dose was 312.5 mg daily. Impaired performance on both drugs independently was observed on measures of visual-motor speed (62% of patients), digit repetition and mental sequencing (50% of patients), and phonemic verbal fluency (88% of patients), but not manual dexterity. 5/8 (62%) patients had been clinically judged to be experiencing cognitive side effects of TPM, while 6/8 (75%) were thought to be experiencing side effects while on ZNS. Those who did not experience side effects on ZNS were on lower doses (100 and 200 mg) than patients who did. Overall, 5/8 (62%) patients had the same response to both drugs. Of the 3 that were discordant, 2 had side effects on ZNS but not TPM, and 1 had side effects with TPM but not ZNS., In this small sample, at least half of patients studied showed similar impairment on neuropsychological measures while independently taking TPM and ZNS. The observed impairments were consistent with previous studies suggesting these drugs are associated with deficits in cognitive processing rather than motor speed. A majority, but not all, patients showed the same response to both drugs. Data suggested lower doses of ZNS may be better tolerated than higher doses. Additional study with larger sample sizes is clearly needed to clarify factors contributing to cognitive side effects of these drugs.,