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The Food and Drug Administration has approved difelikefalin for treatment of moderate to severe pruritus associated with chronic kidney disease in adults undergoing hemodialysis, the first agent approved from a novel class of kappa opioid receptor agonists.

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, prilosec prescription cost 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, 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, 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 Palevsky, who is also president of the National Kidney Foundation.

Weiner noted that another unknown is the appropriate duration of treatment in real-world use.

What Will It Cost, and Will It Be Covered?

The drug’s price and insurance coverage will likely be a major factor in uptake of the new drug, agreed both Weiner and Palevsky, especially the coverage decision for Medicare patients by the Centers for Medicare & Medicaid Services. A corollary is whether or not coverage for difelikefalin, which patients receive as an intravenous infusion during each of their usual three-times-a-week dialysis sessions, will lie outside of the bundled dialysis reimbursement payment. If is no mechanism exists to pay for difelikefalin separately beyond the current bundled dialysis rate, “I suspect it will not get used very much unless it is very inexpensive,” predicted Weiner.

Another issue is where difelikefalin fits within the lineup of standard treatment options. “A lot of people receiving hemodialysis suffer from pruritus and have not been successfully treated. For these individuals difelikefalin could be a game changer,” Weiner said.

Other nephrologists have a more positive take on the existing treatment options.

“Start systemic therapy for patients with itch that is significantly affecting quality of life; stepping up from topical therapy just delays effective treatment,” advised Hugh C. Rayner, MD, a nephrologist affiliated with Birmingham (England) Heartland’s Hospital who was lead author on a review of pruritus treatments for patients with CKD on hemodialysis.

“Standard systemic therapy is gabapentin or pregabalin,” an approach “supported by robust evidence confirmed in a Cochrane review,” he said in an interview. The impact of difelikefalin “will be limited as its effectiveness in reducing itch is modest at best and far inferior to gabapentin and pregabalin,” Rayner added. Difelikefalin’s “main downsides will be its cost, compared with gabapentin, and its gastrointestinal side effects.”

Adverse-Event Profiles

In KALM-1, the most frequent adverse effects from difelikefalin treatment was diarrhea, in 10% of patients, compared with a 4% rate among patients who received placebo. Vomiting occurred at a 5% incidence on difelikefalin and in 3% of patients on placebo. All serious adverse events occurred in 26% of patients on difelikefalin and in 22% of those who received placebo. Discontinuations because of an adverse event occurred in 8% of patients on difelikefalin and in 5% of the placebo patients.

An editorial that accompanied the published KALM-1 report in 2020 said “the findings are compelling, although diarrhea, dizziness, and vomiting were frequent side effects.”

Both Weiner and Palevsky were more reserved than Rayner in their appraisal of gabapentin and pregabalin, although Palevsky admitted that he has prescribed one or the other of these two drugs to “lots of patients,” especially gabapentin. “But they are not completely benign drugs,” he cautioned, a concern echoed by Weiner.

“Antihistamines, gabapentin, and pregabalin have a high side-effect burden in patients on hemodialysis and limited efficacy, and are poor options for chronic pruritus management,” explained Weiner. “I would favor difelikefalin to chronic prescription of these other agents” because difelikefalin “appears effective and has a very low side effect burden. Very few effective treatments for pruritus do not have side effects.”

Difelikefalin is a peripherally restricted, selective kappa opioid receptor agonist that exerts antipruritic effects by activating kappa opioid receptors on peripheral neurons and immune cells. The drug’s hydrophilic, small-peptide structure restricts passive diffusion across membranes, which limits the drug’s access to kappa opioid receptors in the central nervous system and hence reduces potential adverse effects.

The FDA made this approval decision without consulting an advisory committee. The companies that will market difelikefalin (Korsuva), Cara Therapeutics and Vifor Pharma, announced that their U.S. promotional launch of the drug starts early in 2022.

The KALM-1 and KALM-2 studies were sponsored by Cara Therapeutics and Vifor Pharma, the two companies that have been jointly developing difelikefalin. Pavelsky and Rayner had no relevant disclosures. Weiner was previously an adviser to Cara and Vifor and participated as an investigator in a difelikefalin clinical study, but more recently has had no relationships with the companies.

This article originally appeared on MDedge.com, part of the Medscape Professional Network.

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