Penetration of valproate and its active metabolites into cerebrospinal fluid of children with epilepsy.

Levels of the antiepileptic drug valproate (VPA) and five of its active metabolites (2-en-VPA, 3-keto-VPA, and 3-,4-, and 5-hydroxy-VPA) were determined by gas chromatography-mass spectrometry in cerebrospinal fluid (CSF) of 15 epileptic children undergoing chronic treatment with VPA. In eight of these children, total and free drug and metabolite concentrations in plasma were also measured. All VPA metabolites present in plasma could also be detected in CSF, although concentrations were substantially lower than those of the parent compound. CSF concentrations of VPA and most of its metabolites were positively correlated with total and free concentrations in plasma. However, concentrations in CSF were always significantly lower than free plasma concentrations, which may be explained by asymmetric transport at the blood-CSF barrier. The data on low CSF levels of VPA metabolites do not exclude the possibility that accumulation of active metabolite(s) may occur in certain brain areas during chronic treatment of epileptic patients with VPA.