Relative influences of adjunctive topiramate and adjunctive lamotrigine on scanning and the effective field of view

A subsample of 67 adult patients with partial seizures participating in a randomized, double-blind study comparing the cognitive effects of adjunctive lamotrigine (LTG) and adjunctive topiramate (TPM) was administered Performance On-Line (POL) in addition to a battery of neuropsychological tests at baseline, week 8 and week 16 of treatment. The POL is a self-administered computer task that measures scanning, divided-attention, and the effective field of view. Although the POL does not measure driving performance, POL scores are correlated with driving performance. The results show that adjunctive TPM, but not adjunctive LTG, negatively impacted cognition. Both simple target identification and divided-attention performance on POL were compromised in the TPM group but not in the LTG group. The relative POL impairment associated with chronic TPM treatment was similar to that observed with the acute effects of alcohol with a breath level of .045% or a low dose of alprazolam (0.5 mg). Thus, driving-related visual and cognitive skills were compromised by adjunctive TPM treatment. Therapeutic doses of adjunctive TPM pose a potential risk of impaired scanning and divided-attention skills.