Changes in human whole blood 5-hydroxytryptamine (5-HT) and platelet 5-HT uptake during treatment with paroxetine, a selective 5-HT uptake inhibitor.

The effects of the specific 5-hydroxytryptamine (5-HT) reuptake inhibitor parox etine on whole blood 5-HT and the uptake of (3)H-5-HT by platelets was determined in 17 patients with resistant depression. The biochemical parameters were measured before paroxetine treatment, during treatment and after withdrawal of treatment. Two of the 17 subjects failed to complete the trial; of the remaining subjects 12 showed a marked decrease in whole blood 5-HT and (3)H-5-HT uptake into platelets. The remaining three patients showed a variable response both in terms of whole blood 5-HT and platelet uptake during paroxetine treatment. At the end of treatment blood 5-HT tended to return towards normal although this was delayed. There was no significant correlation between the change in blood 5-HT and Hamilton score during paroxetine treatment. The results confirm that inhibition of 5-HT uptake mech anisms are associated with decreased whole blood 5-HT but that changes in whole blood 5- HT do not necessarily reflect the clinical efficacy of 5-HT uptake blocking drugs in the treatment of depression.