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Some nephrologists welcomed the Aug. 23 approval of this new option for treating pruritus, a relatively common and often hard-to-resolve complication of dialysis in patients with chronic kidney disease (CKD) that can substantially impinge on quality of life for some patients, but also voiced uncertainty about the role of a new agent with a modest trial track record that may be expensive and face insurance-coverage hurdles.
“Uptake of difelikefalin will depend on awareness of itch among patients dependent on hemodialysis, and on payment policies,” predicted Daniel E. Weiner, MD, a nephrologist at Tufts Medical Center in Boston. “Pruritus is underdiagnosed among people with kidney failure, and in some patients ongoing pruritus can be highly impactful on sleep and quality of life. The clinical trial results were very encouraging that difelikefalin is effective and safe,” which makes recognition of pruritus as a significant issue for patients a key factor in uptake of the new drug, Dr. Weiner, an investigator in a difelikefalin clinical study, said in an interview.
Other nephrologists acknowledged the substantial problem that itch can pose for many patients with CKD on dialysis but questioned the weight of evidence behind difelikefalin’s approval.
Two pivotal trials with fewer than 900 total randomized patients
The data considered by the FDA primarily featured results from two pivotal trials, KALM-1 and KALM-2. KALM-1 randomized 378 patients with CKD and on hemodialysis and with moderate to severe pruritus to intravenous treatment with difelikefalin or placebo three times a week for 12 weeks with a primary endpoint of an improvement (decrease) of at least 3 points from baseline in their Worst Itching Intensity Numerical Rating Scale (WI-NRS) score, which averaged just over 7 points at baseline. After 12 weeks on treatment, 52% of patients who received difelikefalin had at least a 3-point drop, compared with 31% of patients who received placebo, a significant difference. The results appeared in a 2020 report in the New England Journal of Medicine.
Confirmatory results came in the second pivotal trial, KALM-2, a similarly designed, 12-week study that randomized 473 patients, with 54% of those in the active arm achieving at least a 3-point cut in their baseline WI-NRS score, compared with 42% of patients who received placebo, a significant difference. A report at the Kidney Week meeting sponsored by the National Kidney Foundation in October 2020 presented the KALM-2 results, but the findings have not yet appeared in a published article.
In sum, the data suggest that treatment with difelikefalin will, on average, produce a clinically meaningful effect on itch compared with placebo in about 20% of patients, with nearly half the patients who receive the active drug having a less robust response and many patients who receive no active treatment also show a meaningful cut in their pruritus severity in a trial setting, noted Paul Palevsky, MD, professor of medicine at the University of Pittsburgh and chief of the renal section at the Veterans Affairs Pittsburgh Healthcare System.
The upshot is that questions linger over which patients are the best candidates for this drug and how it might perform in real-world practice given difelikefalin’s limited track record, Dr. Palevsky said in an interview.
In addition, the labeling specifies the indication is for patients with moderate to severe pruritus, but itching severity is not routinely quantified in these patients in current practice, added Dr. Palevsky, who is also president of the National Kidney Foundation.
Dr. Weiner noted that another unknown is the appropriate duration of treatment in real-world use.