Antidepressant-induced mood conversions in bipolar disorder: a retrospective study of tricyclic versus non-tricyclic antidepressant drugs.

OBJECTIVES The aim of this retrospective study was an analysis of antidepressant-induced mood conversions to mania/hypomania occurring in bipolar inpatients treated with antidepressants in the Affective Disorder Unit of the Institute of Psychiatry and Neurology, Warsaw, in the years 1972-1996. METHODS The data for analysis were obtained retrospectively from clinical records. In a subgroup of patients prone to mood conversions, a comparison was done of depressive episodes treated with antidepressants with and without a switch to mania/hypomania as well as the frequency of mood conversions induced by particular antidepressant drugs, especially tricyclic (TCA) versus non-TCA drugs. RESULTS Among 333 bipolar patients hospitalized in this period, mood conversions were observed in 118 subjects, significantly more frequently in female (44%) than in male patients (25%), and in patients with depressive episode at the onset of illness (80 vs. 40%). Among mood converters, it was found that the depressive episodes with a switch to mania were less severe, shorter, and with shorter duration of antidepressant treatment. The risk of switching was higher during treatment with TCA than with non-TCA drugs (36 vs. 17%), the highest with amitriptyline (42% of treated episodes), imipramine (40%) and clomipramine (35%). CONCLUSIONS Our results suggest that bipolar patients prone to mood conversion constitute one third of the inpatient population with this illness. The switch from depression to mania occurred significantly more frequently during treatment with TCA than with non-TCA drugs. It is hypothesized that anticholinergic activity may contribute to the higher frequency of TCA-induced mood conversions.