Background. Evaluation of mood-stabilizing treatment strategies usually focuses on their efficacy in preventing recurrences. The aim of this study is to supplement evaluation by two important aspects: inter-episodic morbidity and drop-out.

Methods. Using a global outcome measure, response to prophylactic lithium and carbamazepine was evaluated in N = 171 bipolar patients (DSM-IV) participating in a randomized controlled trial with an observation period of 2½ years (MAP study).

Results. The rates of re-hospitalization were similar for both treatments. However, the percentage of good clinical response (i.e. patients with a low score of inter-episodic morbidity and without both re-hospitalization and drop-out during the observation period) was significantly higher in patients randomized to lithium (40% v. 24%). This superiority of lithium resulted essentially from a lower drop-out rate in patients without re-hospitalization (17% v. 42%). Regarding severity of inter-episodic morbidity, no clear difference between the drugs was found. For both medications the predominant symptomatology was minor depressive (but not manic, mixed or schizoaffective) symptoms. In the lithium group, inter-episodic morbidity in patients without re-hospitalization significantly decreased during the first 10 months and remained on the lower level for the rest of the observation period. For carbamazepine, reduction of inter-episodic morbidity over time did not reach statistical significance. Inter-episodic morbidity was significantly related to drop-out and to re-hospitalization for both medications.

Conclusion. Taking inter-episodic morbidity, drop-out and re-hospitalization into consideration, the response rate in bipolar patients (DSM-IV) was higher for prophylactic lithium than for carbamazepine. The global outcome parameter used appears to be a valuable measure of clinical response to mood stabilizing drugs.