Differential effect of number of previous episodes of affective disorder on response to lithium or divalproex in acute mania

Objective: The authors investigated the relationship between number of life time episodes of affective disorder and the antimanic response to lithium, divalproex, or placebo. Method: The subjects were 154 of the 179 inpatients with acute mania who entered a 3-week parallel group, double-blind study. The primary efficacy measure was the manic syndrome score from the Schedule for Affective Disorders and Schizophrenia. The relationship between improv ement and number of previous episodes was investigated by using nonlinear r egression analysis. Results: An apparent transition in the relationship bet ween number of previous episodes and response to antimanic medication occur red at about 10 previous episodes. For patients who had experienced more ep isodes, response to lithium resembled the response to placebo but was worse than response to divalproex. For patients who had experienced fewer episod es, however, the responses to lithium and divalproex did not differ and wer e better than the response to placebo. This differential response pattern w as not related to rapid cycling or mixed states. Conclusions: A history of many previous episodes was associated with poor response to lithium or plac ebo but not to divalproex.