Minimum plasma lithium levels required for effective prophylaxis in DSM III bipolar disorder: a prospective study

Four groups of DSM III bipolar patients, whose plasma lithium levels were maintained at 0.30-0.45 (group A), 0.46-0.60 (group B), 0.61-0.75 (group C), and 0.76-0.90 (group D) mEq/l respectively, were followed-up for two years. The mean number of affective episodes and the mean total morbidity during the lithium treatment period were significantly decreased in all groups except group A when compared with the pre-lithium period. Moreover, in group A, the mean total scores on CPRS depressive and manic items during the interepisodic periods were significantly higher than in each of the other groups. As a result of the low scores of patients in group A and the high scores of patients in group D on the side effect checklist, the frequency and intensity of side effects differed significantly among the four groups. These data suggest that, in the prophylactic treatment of bipolar patients, plasma lithium levels should, as a rule, be adjusted to the range 0.46-0.75 mEq/l.