To study the changes in plasma concentration of homovanillic acid (pHVA) and its relation with clinical outcome during treatment of Bipolar I patients with olanzapine plus lithium.

Fifty six (33 women and 23 men) Bipoar I patients, age 35.1±9.4 (SD) years, diagnosed according to DSM-IV, were treated initially with 10mg/day of olanzapine for 4 days and subsequently with 20 mg/day. On the 8th day lithium was added until a concentration of 0.6 to 1.2 mEq/L was reached in plasma. Patients were, at least, a week without neuroleptic or mood stabilizer medication.

Their clinical state was evaluated before and during 28 days of treatment with the Young scale and with the Clinical Global Impression.

Morning fasting levels of pHVA were analyzed the same days that scales were passed.

Plasma HVA after 28 days of treatment does not decline as habitually happens with neuroleptic treatment alone. Moreover, there was a trend toward significance of a Positive Correlation between pHVA and clinical improvement.

The addition of Lithium to Olanzapine altered the pattern of pHVA response from the first days of treatment up to day 28, suppressing the habitual decline in pHVA concentration. These results are similar to those observed by Bowers et al. (1992) when lithium was combined with perphenazine. The correlation between changes in pHVA concentration during 28 days of treatment and clinical outcome was the opposite to that found in schizophrenic patients treated with neuroleptics alone.