The results of the present study are consistent with
those of previous studies in which valproate was
favored over lithium for relapse prevention in bipolar
patients. Lambert and Venaud conducted a comparative
study of valproate versus lithium for the prophylaxis
of bipolar disorders.20 This 18-month open,
randomized study reported 0.51 episodes per subject
in the valproate group and 0.61 episodes per subject in
the lithium group; although this difference was not
statistically significant, these figures reflect a 20%
lower rate of new episodes among valproate-treated
than among lithium-treated patients. Bowden et al.17
conducted the first double-blind, randomized, controlled
maintenance study in bipolar I disorder, which
involved following patients from an index manic
episode through a subsequent 52-week maintenance
phase. The mean durations of survival in maintenance
treatment were 198 days for the divalproex group and
152 days for the lithium group, reflecting a significant
difference between the divalproex- and lithiumtreated
groups in favor of divalproex.
A few previous studies have compared the effectiveness
of lithium and valproate monotherapy for
preventing relapses of bipolar disorder. Findling
et al.14 reported that lithium and divalproex treatment
groups did not differ in the time to symptoms
of relapse or to discontinuation for any reason.
Another 20-month, double-blind study comparing
lithium and divalproex monotherapy15 reported no
significant differences in the time to relapse due to
any kind of episode, the time to relapse due to a
depressive episode, or the time to relapse due to a
hypomanic/manic/mixed episode. However, these
studies included pediatric bipolar patients14 or
rapid-cycling bipolar patients,15 and methodological
differences make it hard to compare the effectiveness
of pharmacological treatments. Moreover,
lithium monotherapy was more likely to prevent
relapse than was valproate monotherapy according
to a recent randomized, open-label trial.16 However,
as the trial was primarily designed to compare
lithium and valproate combination therapy with
lithium or valproate monotherapy, conclusions
about the comparative efficacy of the two agents
should be made cautiously