Rapid response to paroxetine is associated with plasma paroxetine levels at 4 but not 8 weeks of treatment, and is independent of serotonin transporter promoter polymorphism in Japanese depressed patients.

In the present study, we investigated the relationship between the serotonin transporter gene linked polymorphic regions (5-HTTLPR) or plasma paroxetine levels and clinical response to paroxetine in depressed patients. Sixty patients who met the DSM-IV criteria for major depressive disorder were enrolled in the study. Twenty-two were male and 38 were female, with ages ranging from 25 to 71 (mean +/- SD = 42 +/- 16) years. The clinical improvement of patients was assessed using the Hamilton rating scale for depression (Ham-D) before and every week after paroxetine administration. According to the data reported previously, patients with an at least 50% decrease in their Ham-D score were classified as responders. The results showed that the plasma paroxetine levels at 4 weeks were significantly higher in responders (rapid responders) than in nonresponders. On the other hand, no significant associations were found between the L genotype (L/L, L/S) or S genotype (S/S) and the response rates either at 4 weeks or 8 weeks. These results suggest that patients with higher plasma levels at 4 weeks might respond rapidly to paroxetine treatment, but the final response rate at 8 weeks will be independent of the plasma paroxetine levels and the 5-HTTLPR L/S genotype. 2009 John Wiley & Sons, Ltd.