Relationships between low red blood cell count and clinical response to fluoxetine in depressed elderly patients

Biological variables specifically linked with serotonin deficiency were ass essed in geriatric depression. Sixteen depressed patients, all greater than or equal to 60 years of age and with scores on the Montgomery-Asberg Depre ssion Rating Scale (MADRS) greater than or equal to 20, were treated with f luoxetine (20 mg/day) for 42 days. Biological variables measured on days 1 and 42 included whole blood and plasma serotonin, plasma total and free try ptophan, and platelet paroxetine and ketanserin binding. Seven of the 16 pa tients showed a positive clinical response (i.e. MADRS score less than or e qual to 12 at day 42). The pre-treatment red blood cell count was the varia ble most related to clinical response; low levels were found in almost all responders. To a lesser extent, plasma free tryptophan before treatment was also correlated to therapeutic response, with lower values being found in responders. During treatment, plasma free tryptophan was increased in respo nders and decreased in non-responders. The finding that elderly depressed p atients with low pre-treatment red blood cell counts subsequently responded to fluoxetine treatment is consistent with the view that tryptophan, the p recursor of serotonin in brain, is taken up by red blood cells. (C) 1998 El sevier Science Ireland Ltd. All rights reserved.