Valproic acid is one of the major antiepileptic drugs. In animal models, valproate showed less anticonvulsant potency than the other three established antiepileptic drugs: phenobarbital, phenytoin and carbamazepine. In addition, two major side-effects, teratogenicity and hepatotoxicity, have been associated with valproate Iherapy. Due to the above and the shortage of new antiepileptic drugs there is a substantial need to develop improved derivatives of valproate. This paper analyses three kinds of valproate derivatives: valpromide, the primary amide of valproate, and its analogues; monoester prodrugs of valproate and an active metabolite of valproate, 2- n-propyl-2-pentenoate. The comparative evaluation was carried out by pharmacokinetic and pharmacodynamic analyses in animals. From the data accumulated so far, we can conclude that 2- n-propyl-2-pentenoatc and/or a valpromide isomer, which does not undergo amide acid biotransformation and preferably is not an epoxide hydrolase inhibitor, may prove to be improved derivatives of the parent compound valproic acid. [ABSTRACT FROM AUTHOR]