The authors describe two female patients with bipolar I depression who did not respond to tricyclic antidepressants in their previous depressive episodes and were prophylactic lithium nonresponders. Both patients showed a high pretreatment platelet MAO activity and responded well and rapidly to monoamine oxidase inhibition (MAOI) treatment. These findings suggest that although bipolar depressed patients show a low platelet MAO activity, there may be a subgroup with high enzyme activity. These patients revealed a low tendency to respond to tricyclic antidepressants and showed rapid improvement on MAOI therapy.
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