In adults, valproate (VPA) has been reported to be associated with thrombocytopenia. However, few studies have investigated this association in children, and the factors affecting platelet counts remain controversial. This study was undertaken to investigate changes in platelet counts following VPA therapy and related factors in children with epilepsy.

Our subjects comprised 75 epileptic children who had received VPA monotherapy for at least 1 year between January 2000 and December 2005. We regularly examined platelet counts at intervals of 6 to 12 months after baseline platele t counts before VPA treatme nt. We analyze d changes in platelet counts according to seve ral factors such as sex, seizure type, underlying causes of epilepsy, age at the start of medication as well as at the last follow up, duration of VPA administration, VPA dose, serum VPA level, and body weight at the last follow up.

Overall, the platelet counts decreased significantly after VPA therapy. The average baseline platelet count was 312.5±109.1×10⁶/mL. At the last follow up, the average platelet count was 261.7±72.2×10⁶/mL. We observed the relationship between platelet counts and serum levels of VPA; while children with serum VPA <75 µg/mL showed no change in platelet counts ( P =0.102), children with serum VPA >75 µg/mL showed a significant decrease in platelet counts.

VPA may cause a significantly decreased platelet count in children with epilepsy. High serum VPA levels were associated with development of thrombocytopenia.