Plasma free 3-methoxy-4-hydroxyphenylglycol predicts response to fluoxetine.

This study was designed to investigate the relationship between platelet serotonin (5-HT) and plasma free 3-methoxy-4-hydroxyphenylglycol (MHPG) measures in depressed outpatients obtained from the same patient with unipolar depression during the pretreatment period and subsequent response to 6 weeks of treatment with either fluoxetine or maprotiline. Compared to the nonresponder group, the fluoxetine responders showed significantly higher pretreatment levels of MHPG, but no difference in pretreatment 5-HT levels. There were no significant differences in either 5-HT or MHPG levels between maprotiline responders and nonresponders. As to posttreatment levels, there were no between-group differences in 5-HT or MHPG between responders and nonresponders to either fluoxetine or maprotiline. When the relationships between changes in 5-HT or MHPG levels and treatment response were examined, 5-HT values showed a marked decrease in both fluoxetine responders and nonresponders, but no significant changes were found in the maprotiline treatment groups. On the other hand, MHPG levels in the fluoxetine nonresponders tended to increase (borderline significance), whereas the MHPG levels for fluoxetine responders and maprotiline responders and nonresponders were unaffected from pre- to posttreatment. Pretreatment levels of plasma free MHPG appear to predict response to fluoxetine.