Bipolar I and II disorder residual symptoms: Oxcarbazepine and carbamazepine as add-on treatment to lithium in a double-blind, randomized trial

Bipolar affective disorders often require adjunctive therapy to treat persistent symptoms. In order to evaluate bipolar symptoms inadequately responsive to lithium, we have compared the effects of two structurally related compounds carbamazepine (CBZ) and oxcarbazepine (OXC). We evaluated the efficacy and safety of CBZ and OXC administration in residual symptoms as an adjunctive therapy in Bipolar I (BP I) and Bipolar II (BP II) patients while on lithium maintenance treatment. We selected from 153 bipolar patients in treatment those fulfilling Research Diagnostic Criteria for mania or hypomania, according to the SADS-L and conducted in 52 bipolar patients (27 BP I, 25 BP II) a double-blind, randomized, parallel-group, single centre, clinical trial. Bipolar I and II outpatients, were randomly assigned on a 1:1 ratio to OXC (n = 26) or CBZ (n = 26) for an 8-week period as add-on treatment to the existing lithium regimen. Outcome measures included the Young Mania Rating Scale (YMRS), Hamilton Depression Rating Scale 21 items (HDRS-21) and Montgomery–Asberg Depression Rating Scale (MADRS), Clinical Global Impression severity (CGI-S) and improvement illness (CGI-I). These scales were administered at baseline and at the end of weeks 2, 4 and 8. All the fifty-two patients completed the trial. Overall, females were 35 (65%) and mean (S.D.) age was 39.4 (11.9) years; final doses at the end of week 8 in OXC group was 637.7 (210) mg/day and in the CBZ group 673.5 (179) mg/day; lithium plasma levels were 0.73 (0.25) meq/l and 0.71 (0.28) meq/l, respectively. Both OXC and CBZ were effective in reducing bipolar scores from baseline to endpoint (p < 0.01). OXC was more effective than CBZ at weeks 4 and 8 on all 5 outcome measures. OXC resulted in greater significant mean reductions in YMRS, HDRS-21, MADRS, CGI-S and CGI-I scores from baseline to week 4 (p < 0.05) and from baseline to week 8 (p < 0.001), except YMRS (p < 0.01). OXC appeared to be significantly more effective and with better tolerability than CBZ as add-on strategy treatment in BP I and BP II patients. This pilot, randomized clinical trial, suggests the potential usefulness of OXC as adjunctive therapy to lithium both in acute and long-term treatment of bipolar disorder. However, further adequately placebo-controlled trials are needed to expand these findings.