Lithium ratio and maintenance treatment response.

Erythrocyte/plasma lithium ratios were determined in 41 polar manic depressive outpatients maintained on lithium for a mean of 64 months. Sixteen patients experienced affective episodes requiring additional pharmacologic intervention during periods when their plasma lithium averaged 0.7 meq/l or above for at least 3 preceding months and they were on no concurrent medication known to induce depression or mania. These patients considered to be a homogeneous group of non-responders to lithium, had a mean lithium ratio of 0.50 (range 0.15-1.16). Seven patients experienced affective symptoms at plasma levels below 0.7 meq/1 and/or while taking concurrent medication known to induce affective symptoms, and therefore could not be categorized clinically as lithium non-responders or responders. Eighteen remaining patients, who had no affective episodes during lithium maintenance, were found to have a mean erythrocyte/plasma ratio of 0.52 (range 0.19-1.05). This latter group of apparent responders should be considered heterogeneous in that it may include spontaneous remitters. The difference in mean ratios between the non-responder group and the apparent responder group was not statistically significant. These findings support the contention that the erythrocyte/plasma lithium ratio does not correlate with response of bipolar outpatients to maintenance lithium.