Treatment with the selective kappa opioid receptor agonist difelikefalin showed modest reduction in itch intensity scores among patients with notalgia paresthetica—a nerve disorder characterized by a persistent itch in the upper back—vs placebo, according to findings from a phase II study published by Kim et al in The New England Journal of Medicine. The study enrolled 126 patients who were randomly assigned to receive difelikefalin or placebo; the primary endpoint of the trial was the change from baseline to week 8 in the weekly mean score on the daily Worst Itch Numeric Rating Scale (WI-NRS; scores range from 0 [no itch] to 10 [worst itch imaginable]). At week 8, the changes in score were –4.0 points in the difelikefalin group and –2.4 points in the placebo group; at baseline, the WI-NRS score was 7.6 in both groups. Adverse events were more likely to occur in the difelikefalin group than the placebo group—56% vs 51%—and headache, constipation, dizziness, and increased urine output were more common among patients receiving difelikefalin. Adverse events led to treatment discontinuation in 19% of patients in the experimental group vs 6% in the placebo group; reported adverse events in the difelikefalin group that led to discontinuation included dizziness and nausea. The study authors concluded, “Among patients with notalgia paresthetica, the reduction in itch intensity over an 8-week period was modestly greater with difelikefalin treatment than with placebo. Larger and longer trials are required to determine the effect and risks of difelikefalin treatment in this disorder.”
April 30, 2023