Efficacy and Safety of Difelikefalin in Japanese Patients With Moderate to Severe Pruritus Receiving Hemodialysis: A Randomized Clinical Trial

IMPORTANCE: Patients with pruritus receiving hemodialysis frequently experience oppressive physical and psychiatric symptoms that directly affect their quality of life and increase mortality. However, treatment options are limited. OBJECTIVE: To determine the clinically recommended dose of difelikefalin, a κ-opioid receptor agonist, based on the efficacy, dose response, safety, and pharmacokinetics. DESIGN, SETTING, AND PARTICIPANTS: This randomized, double-blind, placebo-controlled, 4-arm phase 2 trial was conducted from February 1, 2019, to October 22, 2019, at 94 sites in Japan. Patients with moderate to severe pruritus receiving hemodialysis were enrolled. INTERVENTIONS: Difelikefalin (0.25, 0.5, and 1.0 μg/kg) and placebo were intravenously administered 3 times a week at the end of each hemodialysis session for 8 weeks. MAIN OUTCOME AND MEASURES: The primary end point was the change from baseline in the weekly mean Worst Itching Intensity Numerical Rating Scale (NRS) score at week 8. Secondary outcomes measured changes in itch-related quality-of-life score using the Skindex-16 and 5-D itch scale. Safety was assessed according to adverse events, laboratory tests, vital signs, body weight, and 12-lead electrocardiogram. RESULTS: A total of 247 Japanese patients (186 male [75%]; mean [SD] age, 64.5 [11.7] years) were randomized to placebo (n = 63), 0.25 μg/kg of difelikefalin (n = 61), 0.5 μg/kg of difelikefalin (n = 61), or 1.0 μg/kg of difelikefalin (n = 62). The changes from baseline in the adjusted mean (SE) of the 24-hour Worst Itching Intensity NRS score at week 8 were −2.86 (0.29) in the placebo group, −2.97 (0.29) in the 0.25 μg/kg of difelikefalin group, −3.65 (0.30) in the 0.5 μg/kg of difelikefalin group, and −3.64 (0.30) in the 1.0 μg/kg of difelikefalin group. Significant differences were found in the 0.5 μg/kg of difelikefalin group (adjusted mean difference, −0.80; 95% CI, −1.55 to −0.04; P = .04) and the 1.0 μg/kg of difelikefalin group (adjusted mean difference, −0.78; 95% CI, −1.54 to −0.03; P = .04) compared with placebo. The Skindex-16 overall score and 5-D itch scale total score indicated an improvement with treatment with 0.5 and 1.0 μg/kg of difelikefalin (adjusted weekly mean [SE] Skindex-16 overall score at week 8, −27.79 [2.05]; 95% CI, −31.83 to −23.74 for 0.5 μg/kg of difelikefalin and −22.69 [2.04]; 95% CI, −26.71 to −18.68 for 1.0 μg/kg of difelikefalin; adjusted weekly mean [SE] 5-D itch scale total score at week 8, −6.5 [0.4]; 95% CI, −7.2 to −5.8 for 0.5 μg/kg of difelikefalin and −6.8 [0.3]; 95% CI, −7.5 to −6.2 for 1.0 μg/kg of difelikefalin). The incidence of adverse events was 67% (42 of 63 patients) in the placebo group, 72% (44 of 61 patients) in the 0.25 μg/kg of difelikefalin group, 77% (47 of 61 patients) in the 0.5 μg/kg of difelikefalin group, and 85% (53 of 62 patients) in the 1.0 μg/kg of difelikefalin group. No dependency was reported. CONCLUSIONS AND RELEVANCE: The findings of this phase 2 randomized clinical trial of difelikefalin suggest that 0.5 μg/kg of difelikefalin should be the clinically recommended dose as a new option for treating moderate to severe pruritus in patients undergoing hemodialysis because of its efficacy, acceptable tolerability, and manageable safety profile. TRIAL REGISTRATION: ClinicalTrials.gov Identifier: NCT03802617