Duloxetine Plasma Concentrations and Its Effectiveness in the Treatment of Nonorganic Chronic Pain in the Orofacial Region

The purpose of this study was to examine the relationship between the pain-relieving effects of duloxetine and its plasma concentrations in patients with burning mouth syndrome and atypical odontalgia characterized by chronic nonorganic pain in the orofacial region. We administered duloxetine to 77 patients diagnosed as having burning mouth syndrome or atypical odontalgia for 12 weeks. The initial dose of duloxetine was established as 20 mg/d and was increased to 40 mg/d after week 2. We evaluated pain using the visual analog scale and depressive symptoms using the Structured Interview Guide for the Hamilton Depression Rating Scale at weeks 0, 2, 4, 6, 8, 10, and 12 and measured plasma concentrations of duloxetine 12 weeks after the start of its administration. Visual analog scale scores were significantly lower 12 weeks after than at the start of the administration of duloxetine (paired t test, t = 6.65, P < 0.0001). We examined the relationship between the rate of decreases in visual analog scale scores and plasma concentrations of duloxetine. There was no significant linear regression or quadratic regression. Duloxetine significantly relieved pain in patients with chronic nonorganic pain in the orofacial region. However, no relationship was observed between its pain-relieving effects and plasma concentrations.