Duloxetine in the long-term management of diabetic peripheral neuropathic pain: An open-label, 52-week extension of a randomized controlled clinical trial.

BACKGROUND: Duloxetine hydrochloride, a selective serotonin (5-HT) and norepinephrine (NE) reuptake inhibitor, is relatively balanced in its affinity for both 5-HT and NE reuptake inhibition and is the first US Food and Drug Administration-approved prescription drug for the management of diabetic peripheral neuropathic pain (DPNP).

OBJECTIVES: The aim of this study was to determine whether management of DPNP with duloxetine interferes with the treatment of diabetes. It also examined the tolerability of long-term exposure to duloxetine with regard to the progression of diabetic complications, and assessed the impact of DPNP management with duloxetine versus routine care.

METHODS: This was a 52-week, multicenter, re-randomized, open-label extension of a parallel, double-blind, randomized, placebo-controlled, acute (12-week) study. Patients who completed the duloxetine or placebo acute treatment period were randomly reassigned in a 2:1 ratio to treatment with duloxetine 60 mg BID or routine care for an additional 52 weeks. The study included male and female outpatients aged ≥18 years with a diagnosis of DPNP caused by type 1 or type 2 diabetes. Over the course of the 52-week study, visits were scheduled on the following weeks (of the extension phase of the study): 1 (via phone only), 2, 4, 8, 12, 20, 28, 40, and 52. Tolerability was assessed by review and analyses of discontinuation rates, adverse events (AEs), laboratory data, vital signs, electrocardiographic results, concomitant medications, and diabetic complications. Treatment-emergent AEs (TEAEs) were defined as AEs that appeared during therapy (were not present at baseline) or were exacerbated during treatment. Data on AEs and concomitant medications were collected at every visit. Data on blood pressure, heart rate, and significant hypoglycemic events were collected at every visit starting from week 2. Fasting clinical chemistry and electrolyte group laboratory assessments were done at every visit, starting from week 4. Electrocardiographic data was collected at weeks 4 and 52, and glycosylated hemoglobin and lipid profile data were collected at weeks 20 and 52. Hematology and urinalysis laboratory assessments and diabetic complication assessments were done at week 52. All safety data was assessed in cases of early discontinuation. Treatment differences on quality of life (QOL) were compared using the Short Form-36 Health Status Survey (SF-36) and the EQ-5D instrument of the European Health-Related Quality of Life Measures. This was assessed at the last visit or at early discontinuation.

RESULTS: The open-label extension-phase study included 337 patients (duloxetine, n = 222; routine care, n = 115). For the duloxetine group, mean age was 60.2 years, 61.3% were male, and 78.4% were white. For the routine-care group, mean age was 58.9 years, 60.0% were male, and 74.8% were white. Mean weight was 95.3 kg for both groups. None of the TEAEs occurred significantly more often in the duloxetine-treated group than in the routine-care-treated group. No TEAEs were reported by >10% of patients in the duloxetine group. The TEAEs reported by >10% of patients in the routine-care group included dizziness (11.3%), somnolence (13.0%), headache (10.4%), and vomiting (10.4%). No significant differences were found between treatment groups in the occurrence of serious AEs or in the number of patients discontinuing because of AEs. Duloxetine was significantly better than routine care on the bodily pain subscale of the SF-36 (mean change: 1.5 vs -4.1; P= 0.021) and on the EQ-5D (mean change: -0.00 vs -0.09; P = 0.001).

CONCLUSIONS: Over 52 weeks of follow-up, treatment of these diabetic patients with duloxetine for peripheral neuropathic pain was associated with outcomes similar to, or significantly better than, that of routine care on most measures of tolerability, diabetic complications, and QOL.