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 Dr. Weiner and Dr. 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 Dr. 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,” Dr. 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,” Dr. 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 Dr. Weiner and Dr. Palevsky were more reserved than Dr. Rayner in their appraisal of gabapentin and pregabalin, although Dr. 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 Dr. 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 Dr. 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. Dr. Pavelsky and Dr. Rayner had no relevant disclosures. Dr. 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.