Comparative cognitive effects of carbamazepine and gabapentin in healthy senior adults

Purpose: This study compared the cognitive effects of carbamazepine (CBZ) a nd gabapentin (GBP) in healthy senior adults by using a randomized, double- blind crossover design. Methods: Thirty-four senior adults were randomized to receive one of the tw o drugs followed by a 5-week treatment period. A 4-week washout phase prece ded initiation of the second drug. Antiepileptic drugs (AEDs) were titrated to target doses of either CBZ (800 mg/day) or GBP (2.400 mg/day). Primary outcome measures were standardized neuropsychological tests of attention/vi gilance, psychomotor speed, motor speed, verbal and visual memory, and the profile of Mood State (POMS), yielding a total of 17 variables. Each subjec t received cognitive testing at predrug baseline, end of first drug phase, end of second drug phase, and 4 weeks after completion of the second drug p hase. Results: Fifteen senior adults (mean ape, 66.5 years: range. 59-76 years) c ompleted the study. Seniors completing the study did not differ significant ly from noncompleting seniors in terms of demographic features or baseline cognitive performances. Fifteen of the 19 seniors not completing the study dropped our while receiving CBZ, Adverse events were frequently reported fo r both AEDs, although they were more common for CBZ. Mean serum levels for the completers were within midrange clinical doses (CBZ, 6.8 mug/ml; GBP, 7 .1 mug/ml). Significant differences between CBZ and GBP were found for only one of 11 cognitive variables, with better attention/vigilance for GBP, al though the effect was modest. Performances on the nondrug average were sign ificantly better on 45% of cognitive variables compared with CBZ and 36% co mpared with GBP. The overall pattern of means favored GBP over CBZ on 15 of 17 (p < 0.001), nondrug over CBZ on 17 of 17 (p < 0.0000), and nondrug ove r GBP on eight of 17 (NS). Conclusions: Mild cognitive effects were found for both AEDs compared with the nondrug average condition. The magnitude of difference between the two AEDs across the cognitive variables was modest. Self-reported mood was not significantly affected by either AED. However, overall tolerability and sid e-effect profile of CBZ were poorer than those of GBP in senior adults at d oses and titration rates reported in this study.