OBJECTIVE: This study compared the effect of two different serum lithium
levels on the psychosocial functioning of patients with bipolar I disorder.
METHOD: Ninety patients with bipolar I disorder were enrolled in a
prospective, double-blind, maintenance trial of lithium. The patients were
randomly assigned to treatment with doses of lithium adjusted to achieve a
serum lithium concentration of either 0.8 to 1.0 mmol/liter (standard) or
0.4 to 0.6 mmol/liter (low). The Longitudinal Interval Follow-Up Evaluation
was used to assess psychosocial functioning in the areas of work,
interpersonal relationships, and global functioning. All observed values
were analyzed with a mixed- effects analysis of covariance. Independent
variables included treatment group (low or standard lithium serum level),
relapse status, socioeconomic status, time from random treatment assignment
to assessment, termination of protocol before or after relapse, length of
remission before random treatment assignment, polarity of the last mood
episode before random treatment assignment, and number of mood episodes in
the 3 years before random treatment assignment. RESULTS: Relapse was
associated with large negative effects on psychosocial functioning.
Patients in higher socioeconomic brackets had better psychosocial
functioning than did those in lower brackets. Patients receiving lithium
doses that achieved standard serum levels had better psychosocial
functioning than those receiving doses that achieved low serum levels; this
effect was partially but not wholly mediated through relapse prevention.
CONCLUSIONS: For patients with bipolar I disorder, standard serum lithium
levels may enhance psychosocial functioning, above and beyond the effects
of relapse prevention.