Duloxetine (Cymbalta): SSNRI approved for the management of fibromyalgia

Duloxetine is a selective serotonin and norepinephrine reuptake inhibitor (SSNRI). This agent's exact mechanism of action is unknown but is believed to be related to its ability to potentiate serotonergic and noradrenergic activity in the central nervous system. Duloxetine was previously approved for the treatment of major depressive disorder (MDD), generalized anxiety disorder, and diabetic peripheral neuropathic pain; the agent was approved on June 13, 2008, for the management of fibromyalgia.

Efficacy. The efficacy of duloxetine for the management of fibromyalgia was assessed in 2 randomized, double-blind, placebo-controlled, fixed-dose studies in adult patients who met the American College of Rheumatology criteria for fibromyalgia. Study 1 (3 months' duration) enrolled female patients only (N=354); Study 2 (6 months' duration) enrolled both male and female patients (N=520). In Study 1, patients were treated with either duloxetine 60 mg once daily or 120 mg administered as divided doses or with placebo. In Study 2, patients were treated with either duloxetine 60 mg once daily or 120 mg once daily or with placebo; this study also compared treatment with duloxetine 20 mg once daily versus placebo during the initial 3 months of the trial. Across both studies, treatment with duloxetine 60 or 120 mg was associated with a statistically significant improvement in mean pain scores from baseline compared with placebo. Duloxetine treatment also increased the proportion of patients who experienced ≥50% reduction in pain score from baseline compared with placebo. The studies did not demonstrate an increased benefit with duloxetine 120 mg/d versus 60 mg/d.

Safety. Patients with MDD may experience worsening of depression or suicidal ideation and behavior regardless of whether they are taking antidepressants. All patients treated with antidepressants should be monitored for signs of clinical worsening, suicidality, and unusual behavior changes. Cases of hepatic failure have been reported in patients treated with duloxetine; some of these cases have been fatal. Patients treated with duloxetine have experienced orthostatic hypotension and syncope. A potentially life-threatening serotonin syndrome can occur during duloxetine treatment, particularly when duloxetine is used concomitantly with serotonergic drugs and drugs that impair the metabolism of serotonin. This agent may increase the risk of bleeding events. Duloxetine treatment has been associated with increases in systolic and diastolic blood pressure. The most common adverse events associated with duloxetine for the management of fibromyalgia include nausea, headache, dry mouth, insomnia, constipation, and fatigue.