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Difelikefalin

Also known as: Korsuva, CR845, MR13A9

Difelikefalin is a synthetic D-amino acid tetrapeptide that acts as a selective, peripherally restricted kappa-opioid receptor (KOR) agonist. FDA-approved in 2021 as Korsuva, it is the first-in-class KOR agonist approved for the treatment of moderate-to-severe pruritus (itching) associated with chronic kidney disease (CKD-aP) in adults undergoing hemodialysis. Unlike traditional opioids, difelikefalin does not cross the blood-brain barrier, avoiding the euphoria, respiratory depression, and addiction associated with mu-opioid receptor activation. It represents a paradigm shift in treating uremic pruritus.

3 cited references·5 researched benefits

Quick Answer

Difelikefalin (Korsuva) is a synthetic tetrapeptide and the first FDA-approved peripherally selective kappa-opioid receptor (KOR) agonist. Approved in 2021 for moderate-to-severe itching in hemodialysis patients with chronic kidney disease-associated pruritus (CKD-aP), it reduces itch intensity by 40–50% without crossing the blood-brain barrier. This avoids the euphoria, addiction, and respiratory depression of traditional opioids, representing a breakthrough in treating one of the most burdensome symptoms in kidney disease.

Key Facts

Mechanism
Difelikefalin is a tetrapeptide composed entirely of D-amino acids (D-Phe-D-Phe-D-Leu-D-Lys) conjugated to a polyethylene glycol (PEG) moiety, designed to prevent blood-brain barrier penetration. It selectively agonizes kappa-opioid receptors (KOR) on peripheral sensory neurons, immune cells (particularly keratinocytes and mast cells in the skin), and dorsal root ganglia. KOR activation on peripheral C-fibers and keratinocytes inhibits itch signaling by reducing pruritogenic cytokine release (IL-31, IL-4, IL-13), suppressing neuronal excitability, and counteracting the pro-pruritic effects of endogenous dynorphin/mu-opioid signaling imbalance seen in CKD. In uremic pruritus, accumulation of uremic toxins sensitizes itch pathways; difelikefalin directly counteracts this sensitization at the peripheral nerve level. Anti-inflammatory effects through KOR on immune cells further reduce skin inflammation.
Research Status
approved
Half-Life
~2 hours
Molecular Formula
C₃₆H₅₃N₅O₆
Primary Use
Other
Table of Contents

Benefits

  • CKD-associated pruritus relief — reduces Worst Itching Intensity NRS score by ≥3 points in 40–50% of hemodialysis patients (KALM-1 and KALM-2 phase 3 trials)strong
  • No CNS opioid effects — peripheral restriction eliminates euphoria, respiratory depression, abuse potential, and sedation associated with central opioid agonistsstrong
  • Improved sleep quality — by reducing nocturnal pruritus, significantly improves sleep disturbance scores in hemodialysis patientsstrong
  • Quality of life improvement — reduces the profound burden of uremic pruritus on daily functioning, mood, and social activitiesstrong
  • Anti-inflammatory properties — peripheral KOR agonism reduces pro-inflammatory cytokines and may benefit inflammatory skin conditions beyond uremic prurituspreliminary

Dosage Protocols

RouteDosage RangeFrequencyNotes
Intravenous (hemodialysis)0.5 mcg/kg (dry body weight)Three times per week after each hemodialysis sessionAdministered as IV bolus into the venous line of the dialysis circuit at the end of each hemodialysis session. Dose is based on dry body weight. Maximum single dose is 0.5 mcg/kg. No dose adjustment needed for hepatic impairment.
Oral tablet (investigational)0.25–1 mgOnce dailyOral difelikefalin is in phase 3 clinical trials for pruritus associated with CKD (non-dialysis patients), atopic dermatitis, and notalgia paresthetica. If approved, it would greatly expand the treatable population beyond hemodialysis patients.

Medical disclaimer

Dosage information is provided for educational reference only. Always follow your prescriber's instructions and consult a qualified healthcare provider before starting any peptide protocol.

Side Effects

  • Diarrhea — occurs in 9% of patients, the most common adverse event; typically mild and self-limitingcommon
  • Dizziness — reported in 6–7% of patients, generally mild and transientcommon
  • Nausea — occurs in 5% of patients during initial dosingcommon
  • Hyperkalemia — elevated potassium levels in 3–4% of patients (relevant in the CKD population)rare
  • Gait disturbances and somnolence — uncommon CNS-like effects reported in a small percentage; mechanism unclear given peripheral restrictionrare

Frequently Asked Questions

What is CKD-associated pruritus and why is it so difficult to treat?
CKD-associated pruritus (CKD-aP), formerly called uremic pruritus, affects 40–70% of hemodialysis patients and is one of the most distressing symptoms of advanced kidney disease. It is caused by accumulation of uremic toxins, systemic inflammation, imbalanced opioid signaling (mu/kappa ratio), neuropathy, and immune dysregulation — not simple histamine-mediated itch. This is why antihistamines are ineffective. Traditional treatments (moisturizers, UV phototherapy, gabapentin) provide inconsistent relief. Before difelikefalin, there was no FDA-approved treatment specifically for CKD-aP. Severe pruritus is independently associated with higher mortality, depression, and poor quality of life in dialysis patients.
How does difelikefalin avoid the side effects of traditional opioids?
Difelikefalin was engineered with three features to prevent central nervous system penetration: (1) D-amino acid composition — all four amino acids are in the D-configuration, making the peptide resistant to BBB peptide transporters and enzymatic degradation; (2) positive charge at physiological pH — the D-Lys residue provides a permanent positive charge that impedes passive diffusion across the lipophilic BBB; (3) PEGylation — the polyethylene glycol moiety further increases molecular size and hydrophilicity. Additionally, it selectively targets kappa-opioid receptors (anti-pruritic, anti-inflammatory) rather than mu-opioid receptors (responsible for euphoria, respiratory depression, and addiction).
Will oral difelikefalin be available for non-dialysis patients?
An oral formulation of difelikefalin is in advanced clinical development. Phase 2 and phase 3 trials are evaluating oral difelikefalin for: (1) CKD-associated pruritus in non-dialysis patients (CKD stages 3–5); (2) atopic dermatitis (moderate-to-severe); and (3) notalgia paresthetica (localized neuropathic itch). Phase 2 data in atopic dermatitis showed significant itch reduction. If approved, oral difelikefalin would dramatically expand the patient population from the approximately 500,000 US hemodialysis patients to millions with chronic pruritic conditions.
How does kappa-opioid receptor agonism reduce itch?
The body has an endogenous opioid "itch balance" between mu and kappa systems. Mu-opioid receptor activation promotes itching (which is why morphine causes pruritus as a side effect), while kappa-opioid receptor activation suppresses itching. In CKD, there is an imbalance favoring mu-opioid signaling. Kappa agonists like difelikefalin restore this balance by: (1) directly inhibiting peripheral sensory neurons carrying itch signals; (2) reducing release of pruritogenic cytokines (IL-31) from immune cells; (3) decreasing mast cell degranulation; and (4) counteracting the itch-promoting effects of endogenous mu-opioid peptides. This opioid-based mechanism explains why traditional antihistamines fail — CKD-aP is not primarily histamine-mediated.
Is difelikefalin a controlled substance?
No. Despite being an opioid receptor agonist, difelikefalin is not a controlled substance. The DEA determined that difelikefalin has no abuse potential because it does not cross the blood-brain barrier and therefore cannot produce euphoria, psychoactive effects, or physical dependence. Clinical abuse liability studies confirmed no subjective effects distinguishable from placebo. This is a significant practical advantage — it can be prescribed and administered without the regulatory restrictions, monitoring requirements, and stigma associated with controlled opioid medications.

References

  1. 1
    Difelikefalin for moderate-to-severe CKD-associated pruritus: KALM-1 randomized trial results(2021)PubMed ↗
  2. 2
    Difelikefalin in hemodialysis patients with CKD-associated pruritus: KALM-2 phase 3 trial(2022)PubMed ↗
  3. 3
    Peripheral kappa-opioid receptor agonists as novel analgesic and anti-pruritic agents(2017)PubMed ↗

Latest Research

Last updated: 2026-02-19