The valproate serum level in maintenance therapy for bipolar disorder in Japan

The appropriate therapeutic serum valproate level in maintenance therapy for bipolar disorder is not well known. We studied the serum valproate levels in seventeen bipolar I and twenty-four bipolar II disorder outpatients who had been treated with stable doses of valproate successfully for at least 12 months as prophylactic therapy. The trough serum valproate levels were 52.2 +/- 20.4 microg/ml in bipolar I, and 41.0 +/- 18.3 microg/ml in bipolar II disorder patients, respectively. A greater trend towards a higher trough level (p = 0.07) was indicated in the bipolar I disorder group. We speculate that these valproate levels may be an approximation to the appropriate valproate levels in maintenance therapy and that there may be a correlation between the level of valproate required for stabilization and the subtype of the bipolar disorder. However, when interpreting these findings, certain limitations to this study? Need to be taken into account as follows. The sample size was small. We could not look at a group on valproate that had relapsed and a group that had dropped out of maintenance therapy. Further studies are needed.