Effects of acute and chronic treatment with fluvoxamine on extracellular and platelet serotonin in the blood of major depressive patients. Relationship to clinical improvement.

The effects of the treatment with fluvoxamine (FVX) on platelet and plasma serotonin (5-HT) have been examined in eleven drug-free major depressive patients. Acute FVX was without effect, whereas the repeated oral treatment (100-150 mg daily, 12 weeks) reduced platelet 5-HT (-89%, P less than 0.001) and plasma 5-HT (-60%, P less than 0.02). Patients who responded to the treatment at 6 weeks (Hamilton score less than or equal to 10) had significantly lower (-39%, P less than 0.02) pretreatment values of platelet 5-HT than the rest. This suggests that 'low 5-HT' patients may have a more rapid improvement after fluvoxamine. Platelet 5-HT and HDRS correlated significantly along the treatment (r = 0.679, P less than 0.01). These data demonstrate a marked action of fluvoxamine as 5-HT uptake inhibitor at therapeutic doses and confirm that this mechanism is relevant for its efficacy as antidepressant drug.