title: Linear relationship of valproate serum concentration to response and optimal serum levels for acute mania.
abstract: OBJECTIVE
  Several studies have shown that achieving adequate serum valproate levels is critical to rapid stabilization of acute mania, but estimates of the target therapeutic level have been imprecise. A post hoc analysis of pooled intent-to-treat data from three randomized, placebo-controlled studies of divalproex treatment for acute mania was performed to test a hypothesized linear relationship between serum concentration and response and to determine optimal blood levels for treatment of acute mania.
  
  
  METHODS
  Subjects (N=374) were stratified into seven groups (six valproate serum level ranges and placebo), and effect size was determined for each. Linearity of dose response was tested with both parametric and nonparametric techniques. ANOVA was used to compare the response at each serum level range with that of placebo as well as the lowest valproate level (< =55.0 microg/ml). The mean serum valproate level was then determined for all subjects with an effect size greater than or equal to the maximal effect derived from linear modeling.
  
  
  RESULTS
  The fit of blood level and response to a linear model was good. Efficacy was significantly greater than placebo beginning at the 71.4-85.0 microg/ml range and for all higher valproate levels; the 94.1-107.0 and >107.0 microg/ml groups were superior to the lowest valproate serum level group. The effect size associated with highest serum levels (>94 microg/ml) was 1.06 (0.59 after placebo correction). Subjects obtaining this effect or greater (N=84) had a mean serum level of 87.5 microg/ml. Blood levels in the lowest effective range were 60% more effective than placebo and in the higher ranges were 120% more effective. Tolerability appeared similar for all groups.
  
  
  CONCLUSIONS
  The results of this study suggest that there is a linear relationship between valproate serum concentration and response and that the target blood level of valproate for best response in acute mania is above 94 microg/ml.
authors.affiliation: University of Colorado School of Medicine, 4200 East 9th Ave., Box A011-95, Denver, CO 80220, USA. michael.allen@uchsc.edu
authors.forename: Michael H
authors.initials: MH
authors.lastname: Allen
authors.forename: Robert M
authors.initials: RM
authors.lastname: Hirschfeld
authors.forename: Patricia J
authors.initials: PJ
authors.lastname: Wozniak
authors.forename: Jeffrey D
authors.initials: JD
authors.lastname: Baker
authors.forename: Charles L
authors.initials: CL
authors.lastname: Bowden
mesh_terms: D000208:Acute Disease; D000328:Adult; D000704:Analysis of Variance; D018692:Antimanic Agents / Q000008:administration & dosage / Q000097:blood* / Q000627:therapeutic use; D001714:Bipolar Disorder / Q000097:blood* / Q000188:drug therapy* / Q000523:psychology; D004305:Dose-Response Relationship, Drug; D004334:Drug Administration Schedule; D005260:Female; D006801:Humans; D016014:Linear Models; D008297:Male; D010919:Placebos; D016032:Randomized Controlled Trials as Topic; D016896:Treatment Outcome; D014635:Valproic Acid / Q000008:administration & dosage* / Q000097:blood* / Q000627:therapeutic use
chemical_list: D018692:Antimanic Agents; D010919:Placebos; D014635:Valproic Acid