Difelikefalin reaches the clinic by an unusual route. It is a kappa-opioid receptor agonist — and the kappa receptor family is better known for the itch that opioid drugs can provoke. Difelikefalin does the opposite: selective peripheral kappa agonism reduces itch. It is also one of the small set of peptides in this reference that holds a real UK marketing authorisation.
What difelikefalin is
Difelikefalin is a synthetic short-chain peptide built from D-amino acids. The D-configuration and the hydrophilic character are deliberate design choices: they keep the molecule out of the central nervous system so that it acts on kappa-opioid receptors in the periphery rather than in the brain. It is described as a peripherally restricted kappa-opioid receptor (KOR) agonist.
The precise link between KOR activation and relief of itch is still not fully understood. What is established is that kappa agonism attenuates pruritus, while mu-opioid agonism tends to provoke it.
Licensed indication and regulatory history
Difelikefalin is licensed for the treatment of moderate-to-severe pruritus associated with chronic kidney disease in adults undergoing haemodialysis. It is given intravenously by dialysis staff at the point of care, so there is no patient self-administration route.
The regulatory sequence is worth setting out precisely:
- The US FDA approved difelikefalin injection (Korsuva) on 23 August 2021.
- The European Commission granted a marketing authorisation in April 2022 under the brand name Kapruvia, covering all EU member states.
- The UK approval followed in April 2022, also under the brand name Kapruvia.
- Further approvals followed in Switzerland and Singapore (August 2022), Canada (August 2022), Australia (November 2022) and Japan (September 2023).
For the UK reader the important line is that difelikefalin is a licensed prescription-only medicine, not a research chemical. Its authorisation sits under the Medicines Act 1968 and the Human Medicines Regulations 2012, and supply is restricted to the licensed, clinician-administered product.
The evidence base
The two pivotal trials were KALM-1 and KALM-2: randomised, double-blind, placebo-controlled Phase 3 studies in haemodialysis patients with chronic-kidney-disease-associated pruritus. KALM-1 was conducted in the United States; KALM-2 enrolled patients across the United States, Europe and Asia-Pacific. The principal results of KALM-1 were published in the New England Journal of Medicine in 2020, reporting a statistically significant reduction in itch intensity against placebo over the treatment period.
That is a genuine human evidence base — randomised, placebo-controlled, tied to a licensed indication. It is a reminder that "peptide" is not itself an evidence category. Some peptides rest on Phase 3 data and a marketing authorisation; most of the compounds that circulate through the grey-market catalogue do not.
How it sits in the wider peptide picture
Difelikefalin belongs to a small group of peptides with an actual UK licence, alongside the somatostatin analogues, the GnRH analogues, several incretin-based medicines and the conopeptide ziconotide. This reference treats those licensed exceptions as the story precisely because they are exceptions: they show the evidentiary ceiling against which the rest of the field is measured.
After approval
Post-marketing experience is accumulating. A 2025 real-world safety analysis of difelikefalin in chronic-kidney-disease-associated pruritus has been published and is cited below. As with any medicine, suspected adverse reactions should be reported in the UK through the MHRA Yellow Card scheme.
Nothing on this page is consumption, dosing or self-administration guidance. Difelikefalin is described here for research and reference purposes only, and research-use-only framing applies throughout this reference.
This article is AI-researched and editorially reviewed. It is provided for research and educational purposes only and is not medical advice. Research peptides are not licensed for human consumption in the UK.