Pharmacotherapy of Major Depressive Disorder: Focus on Duloxetine

The serotonin-noradrenaline reuptake inhibitor duloxetine is a second-generation antidepressant for the treatment of major depressive disorder (MDD). Its inhibitory potency for serotonin (5-HT) and noradrenaline (NA) reuptake has been demonstrated in animal and in vitro studies. Human studies of peripheral markers of neurotransmission show inhibition of 5-HT reuptake by duloxetine and also support its potency in NA reuptake inhibition. Moreover, a positron emission tomography study in human brains shows that therapeutic doses of duloxetine result in .80% occupancy of 5-HT transporters. Duloxetine is metabolized by hepatic enzymes and cytochromes P450 CYP2D6 and CYP1A2, and plasma duloxetine concentrations increase linearly according to oral dose. In double-blind, randomized, placebo-control studies of MDD, duloxetine-treated patients show significantly increased response and remission rates and significantly longer time to relapse compared to placebo-treated patients. Moreover, duloxetine is efficacious for the treatment of generalized anxiety disorder (GAD) and pain-related diseases such as diabetic peripheral neuropathic pain (DPNP). A daily dose of 60 mg daily seems most effective for treating MDD, GAD and DPNP. Duloxetine is similar in efficacy to fluoxetine, paroxetine and escitalopram for MDD, although escitalopram is better for improving sleep. The most common treatment-emergent side effects of duloxetine are nausea, dry mouth, fatigue and decreased appetite. Studies suggest an association with the incidence of increased sweating or somnolence at higher doses and an association with irritability or anxiety at high plasma levels of duloxetine. Discontinuation rates due to adverse events are higher in patients who receive duloxetine versus placebo in short-term but not long-term studies. Interestingly, there is not a strong correlation between clinical efficacy and plasma levels of duloxetine. Therefore, although duloxetine is safe and tolerated at therapeutic doses of 60–120 mg/day, the dose should be adjusted while the patient is carefully monitored for efficacy and adverse events.