| Recently, the combination of risperidone (RIS) and valproate (VPA) is effective regimen and frequently used in treatment manic episodes associated with bipolar disorder. Individual case reports of a potential drug interaction between risperidone and valproate are controversial with increased or decreased or unchanged valproate concentrations. Objective=The aim of this study was to examine the effect of risperidone on valproate pharmacokinetics (such as steady state concentration, clearance, volume of distribution) in bipolar patients. Methods and patients= The study was a retrospective analytical study.Data were reviewed and collected during year 2011 to 2013 from of Prasrimahabhodi mental hospital database. One-hundred and twenty nine patients with bipolar disorder, aged between 18-60 years, who met inclusion criteria were recruited into the study. All enrolled subjects had been received stable dose of VPA for at least 5 days and monitored to steady-state VPA concentrations.Ninety-one subjects receiving VPA monotherapy and 38 subjects receiving the combination of VPA-RIS were in control and treatment groups, respectively. Demographic data and valproate pharmacokinetic parameters were analyzed and compared between two groups (control and treatment groups) using descriptive, Chi-square test and independent t-test statisticswhere it was appropriate. Results=There were no statistically significant differences in baseline characteristics (for example= age, weight, VPA dosage, gender ratio) between two groups. There were statistically significant differences in steady state VPA concentration and clearance of valproate between two groups (p = 0.012andp=0.037, respectively). However, when clearances of VPA were normalized by weight, there were no statistically significant difference found between groups. Volume of distributionswere similar in both groups (P<0.05). Conclusions= These results indicated that valproate clearanceswere not significantly affected byrisperidone using as anadjunctive treatment. |