Comparison of the anticonvulsant efficacies and neurotoxic effects of valproic acid, phenytoin, and the ketogenic diet.

PURPOSE: The purpose of this study was to measure quantitatively the effectiveness of the ketogenic diet (KD) in comparison to two clinically important anticonvulsant drugs (AEDs), valproic acid (VPA) and phenytoin (PHT), and to evaluate possible associated neurotoxicity.
METHODS: Rats were maintained on either a calorie-restricted, KD or calorie-restricted, rodent-chow diet for 3-5 weeks, after which neurobehavioral and seizure testing was completed. AEDs (either VPA or PHT) were injected acutely at the time to peak effect before neurotoxic and seizure assessment. Seizures were induced by timed infusion of pentylenetetrazole (PTZ) and maximal electroshock (MES).
RESULTS: VPA protected from both MES- and PTZ-induced seizures, whereas the KD only elevated PTZ seizure threshold; PHT only attenuated MES-induced seizures. The KD was as effective as a high dose of VPA (i.e., 300 mg/kg) and combined treatment (i.e., KD + VPA) showed an additive increase in PTZ seizure threshold. No observed neurobehavioral deficits were associated with either diet treatment; however, drug-related side effects were noted with high doses of either VPA or PHT.
CONCLUSIONS: These data suggest that the KD ranks among VPA and PHT as an effective treatment for seizures, without observed drug-associated neurobehavioral contraindications. In combination with AEDs, our results indicate that the KD plus VPA work synergistically to increase seizure threshold, whereas the KD plus PHT may be complementary, elevating seizure threshold (KD) and reducing seizure severity (PHT). These findings may provide insights into future directions for rational polytherapy; however, it is important to be aware that the KD has been shown to elevate VPA-induced hepatotoxicity.