Comparative study of five antiepileptic drugs on a translational cognitive measure in the rat: relationship to antiepileptic property.
BACKGROUND
Antiepileptic drugs (AEDs) have been available for many years; yet, new members of this class continue to be identified and developed due to the limitations of existing drugs, which include a propensity for cognitive impairment. However, there is little preclinical information about the cognitive effects they produce, which clinically include deficits in attention and slowing of reaction time.


OBJECTIVE
The purpose of this study was to profile two first-generation AEDs, phenytoin and valproate, and three second-generation AEDs, levetiracetam, pregabalin and lacosamide. Initially, each drug was examined across a range of well characterised preclinical seizure tests, and then each drug was evaluated in the five-choice serial reaction time test (5-CSRTT) based on efficacious doses from the seizure tests.


METHODS
Each AED was tested for anti-seizure efficacy in either (1) the maximal electroshock seizure test, (2) s.c. PTZ seizure test, (3) amygdala-kindled seizures and (4) the genetic absence epilepsy rat of Strasbourg model of absence seizures. On completion of these studies, each drug was tested in rats trained to asymptotic performance in the 5-CSRTT (0.5 s SD, 5 s ITI, 100 trials). Male rats were used in all studies.


RESULTS
Each AED was active in at least one of the seizure tests, although only valproate was active in each test. In the 5-CSRT test, all drugs with the exception of levetiracetam, significantly slowed reaction time and increased omissions. Variable effects were seen on accuracy. The effect on omissions was reversed by increasing stimulus duration from 0.5 to 5 s, supporting a drug-induced attention deficit. Levetiracetam had no negative effect on performance; indeed, reaction time was slightly increased (i.e. faster).


CONCLUSIONS
These results highlight somewhat similar effects of phenytoin, valproate, pregabalin and lacosamide on attention and reaction time, and comparison to efficacious doses from the seizure tests support the view that there may be a better separation with the newer AEDs. Levetiracetam had no detrimental effect in the 5-CSRTT, which may be consistent with clinical experience where the drug is considered to be well tolerated amongst the AED class.
NPS Pharmaceuticals, 101 College Street, Toronto, Canada. guyh@cancog.com
Guy A
GA
Higgins
Nathalie
N
Breysse
Elijus
E
Undzys
D Richard
DR
Derksen
Melanie
M
Jeffrey
Brian W
BW
Scott
Tao
T
Xin
Corinne
C
Roucard
Karine
K
Bressand
Antoine
A
Depaulis
W M
WM
Burnham
D000818:Animals; D000927:Anticonvulsants / Q000009:adverse effects / Q000494:pharmacology*; D001288:Attention / Q000187:drug effects; D003071:Cognition / Q000187:drug effects*; D004195:Disease Models, Animal; D008297:Male; D051381:Rats; D017207:Rats, Sprague-Dawley; D011930:Reaction Time / Q000187:drug effects; D012640:Seizures / Q000188:drug therapy*
D000927:Anticonvulsants