Measurement of 5-hydroxyindole compounds during L-5-HTP treatment in depressed patients

L-5-hydroxytryptophan (L-5-HTP), an immediate serotonin precursor, was given to the hospitalized depressed patients in an open clinical trial of the Phase 2 study for antidepressive effects of the agent. A relatively small dose, 150mg orally for seven days, was employed, and seven of 14 patients responded to the treatment with mild or moderate emelioration of their depressive symptoms. Urinary excretion levels and plasma concentrations of three 5-hydroxyindole compounds, 5-HTP, 5-HT and 5-HIAA, were measured during the drug treatment. Approximately 70% of the orally administered dose of L-5-HTP was recovered from the urine of depressed patients. Major part of urinary indoleamine metabolites was free and conjugate 5-HIAA. Excretion levels of these compounds in urine were not consistenly altered in the depressed patients as compared to those in normal subjects. Clinical response to L-5-HTP treatment appeared to have some correlation with the biochemical measures in the depressed patients, that is, non-responders exhibited significantly lower excretion levels of 5-HT and 5-HIAA in urine, and lower plasma levels of 5-HT than responders. Administered L-5-HTP may not be fully utilized in the depressed patients who did not react to the agent.