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Objective: The aim of this study was to assess the safety and efficacy of risperidone augmentation of lithium in preschool-onset bipolar disorder (BD) among youth who insufficiently respond to lithium monotherapy.

Method: Thirty-eight subjects between the ages of 4 and 17 years (mean age = 11.37 ± 3.8 years) with onset of BD in preschool years (manic or mixed episode) entered this 12-month trial. All subjects received lithium monotherapy. Patients who failed to adequately respond to lithium monotherapy after 8 weeks and those who relapsed after an initial response were given risperidone augmentation for up to 11 months. The Young Mania Rating Scale (YMRS) was the primary outcome measure. Response was defined as a ≥50% decrease from baseline. Additional data were collected on diagnostic comorbidity, family history, number of hospitalizations, perinatal risk factors, history of physical or sexual abuse, Child Depression Rating Scale—Revised (CDRS-R), Clinical Global Impression (CGI) scale for BD (CGI-BP), Children's Global Assessment Scale (C-GAS), and adverse medication effects.

Results: Of the 38 subjects treated with lithium monotherapy, 17 responded, whereas 21 required augmentation with risperidone. Response rate in the youths treated with lithium + risperidone was 85.7% (n = 18/21). Significant predictors of inadequate response to lithium monotherapy requiring augmentation were: (1) attention-deficit/hyperactivity disorder (ADHD), (2) severity at baseline, (3) history of sexual or physical abuse, and (4) preschool age. Combination treatment of lithium and risperidone was found to be safe and well tolerated.

Conclusions: A substantial proportion of youth with a history of preschool-onset BD treated with lithium were either nonresponders or partial responders. Subsequent augmentation of lithium with risperidone in these cases was well tolerated and efficacious. Potential predictors of lithium nonresponse identified in this study may guide the choice of medications earlier in the treatment process.