Difelikefalin
An FDA-approved peripheral kappa opioid receptor agonist for chronic kidney disease-associated itch, without CNS side effects.
Difelikefalin (brand name Korsuva) is an FDA-approved drug for severe itching in people on hemodialysis. It switches on opioid receptors in the nerves of your skin but cannot reach your brain, so it eases itch without the high, the dependence, or the breathing problems that other opioids cause. A nurse injects it into your dialysis line at the end of each session. It works, but modestly — pooled trial data put it well behind gabapentin-type drugs for itch relief, and every attempt to extend it beyond dialysis has failed.
What is Difelikefalin?
Difelikefalin is a synthetic D-amino acid tetrapeptide that selectively activates peripheral kappa opioid receptors without crossing the blood-brain barrier. It is FDA-approved as Korsuva for moderate-to-severe pruritus (itching) in adults with chronic kidney disease on hemodialysis. Its peripheral selectivity avoids the dysphoria and CNS effects of traditional kappa agonists.
What Difelikefalin Is Investigated For
Difelikefalin has one FDA-approved indication — moderate-to-severe pruritus in adults on hemodialysis — and is the first systemic therapy specifically approved for CKD-associated itch. The strongest evidence is the KALM-1 and KALM-2 Phase 3 trials, which enrolled hemodialysis patients with moderate-to-severe pruritus and demonstrated significant reductions in WI-NRS scores and quality-of-life improvements at week 12, with sustained benefit in the open-label extensions. A 2026 Phase 3 trial extended the evidence to Chinese hemodialysis patients, though more modestly than the KALM cohorts: its primary endpoint was at week 4 (difelikefalin minus placebo −0.81 on the WI-NRS, 95% CI −1.25 to −0.37, P=.0003), and the week-12 >=3-point responder gap (48.7% vs 33.8%) carried only a nominal P value. The broader concept of peripheral kappa-opioid agonism as a novel pain and itch mechanism without CNS side effects or addiction liability is mechanistically interesting and supported by dedicated abuse-liability and respiratory-depression studies, but approved use is narrow, and the attempt to widen it has now failed: the sponsor terminated its Phase 3 programs in non-dialysis/advanced CKD pruritus, its Phase 3 in atopic dermatitis, and its Phase 2/3 in notalgia paresthetica, in each case after an interim analysis showed no meaningful clinical benefit (or, for advanced CKD, a corporate decision to exit). A reader should also know how difelikefalin ranks rather than only that it works: the 2023 Cochrane review of pruritus interventions graded kappa-opioid agonists as reducing itch only slightly versus placebo (VAS mean difference −0.96, 95% CI −1.22 to −0.71; six RCTs, n=1292; certainty of evidence: high), which is a substantially smaller effect than the same review found for GABA-analogues such as gabapentin and pregabalin (MD −5.10, certainty: moderate). Difelikefalin is the only systemic therapy specifically approved for CKD-associated itch — it is not the most effective agent in pooled randomized data. The honest caveat is that Korsuva is exclusively administered via the dialysis circuit by healthcare staff, cannot be self-administered, and has not demonstrated general analgesic efficacy despite earlier development attempts in postoperative pain.
History & Discovery
Difelikefalin (originally CR845) emerged from the targeted drug-discovery effort to develop kappa opioid receptor agonists with reduced central nervous system side effects — a long-standing pharmacological challenge given that traditional kappa opioids produce dysphoria, sedation, and hallucination through CNS-localized receptor activation. Cara Therapeutics, founded in 2004 specifically to advance peripheral opioid pharmacology, designed difelikefalin as a synthetic D-amino acid tetrapeptide whose hydrophilicity and molecular characteristics prevent meaningful blood-brain barrier penetration. The all-D-amino-acid composition also confers protease resistance, supporting parenteral pharmacokinetic stability. Early clinical development explored multiple indications including postoperative pain, but the program crystallized around chronic kidney disease-associated pruritus — a condition whose reported prevalence spans roughly 21% to 55% depending on how it is ascertained — a 2026 Danish multicenter cross-sectional study of 642 patients found 21% (95% CI 18–24%) using a WI-NRS threshold, while DOPPS-era estimates cluster near 40% and a 2026 systematic review cites 55% — with the spread driven mainly by differing severity cut-offs and self-report instruments rather than by true population differences. Across all estimates it is common, and associated with substantially worse quality of life, sleep disruption, and higher mortality. The pivotal Phase 3 KALM-1 (US/Canada/Europe, published in NEJM 2020) and KALM-2 (international) trials enrolled hemodialysis patients with moderate-to-severe pruritus and demonstrated significant reductions in itch intensity (primary endpoint: WI-NRS score) and improvements in itch-related quality of life. The intravenous formulation (Korsuva) received FDA approval in August 2021 for moderate-to-severe pruritus associated with chronic kidney disease in adults undergoing hemodialysis — the first FDA-approved systemic therapy specifically for this indication. The pivotal program is more specific than it is usually described: KALM-1 (NCT03422653, n=378) and KALM-2 (NCT03636269, n=473) were the two placebo-controlled Phase 3 trials, and Study 3105 (NCT03998163, n=222) was the open-label single-arm study that supplies much of the long-term and pooled-analysis data cited in the literature. The EU approved the same molecule as Kapruvia in April 2022, through Vifor Fresenius Medical Care Renal Pharma. The ending of the development story is less triumphant than the beginning. Cara took oral difelikefalin into Phase 3 across non-dialysis and advanced CKD pruritus (NCT05342623, NCT05356403), atopic dermatitis (NCT05387707) and notalgia paresthetica (NCT05978063); every one of those programs was terminated, the dermatologic ones after interim analyses found no meaningful clinical benefit. Two earlier analgesia programs had already been abandoned: a Phase 2/3 in post-abdominal-surgery pain (NCT02542384, n=451) and a Phase 2 of oral difelikefalin in hip and knee osteoarthritis (NCT02944448, n=761). In April 2025 Cara Therapeutics sold difelikefalin development, manufacturing and commercialization rights to CSL Vifor and was itself merged into Tvardi Therapeutics, ending its existence as an independent peripheral-opioid company. The molecule survives as an approved product with a single indication and one active extension program — a Phase 2 in adolescents on hemodialysis (NCT06593392). The peripheral kappa-agonist concept remains mechanistically novel and difelikefalin proved it can work; what the subsequent decade showed is how narrow that proof turned out to be.
How It Works
Difelikefalin activates itch-relief receptors on nerve endings outside the brain. Because it can't enter the brain, it provides relief without the mood changes, sedation, or addiction risk of traditional opioid drugs.
Difelikefalin is a peripherally restricted kappa opioid receptor (KOR) agonist. D-amino acid composition prevents BBB penetration and confers protease resistance. Peripheral KOR activation on sensory neurons and immune cells modulates itch signaling and inflammation. KOR activation inhibits TRPV1 and substance P release from peripheral nerve terminals. The anti-pruritic effect is mediated through both neuronal and immunomodulatory mechanisms. Beyond neuronal signaling, a retrospective biomarker analysis of two Phase 3 trials (n=851) found that ten inflammatory mediators — CCL2, CCL22, CXCL2, CXCL10, IFNγ, IL-2RA, IL-31, NGF, TNFα and TSLP — declined in difelikefalin responders but not in placebo responders, leading the authors to conclude that an anti-inflammatory mechanism contributes significantly to difelikefalin's efficacy. That matters because IL-31 and TSLP are the central itch cytokines targeted by modern dermatologic biologics, placing difelikefalin partly on the same axis. A 2026 rational-design study adds an important mechanistic qualifier to the 'clean peripheral agonist' story: difelikefalin is a balanced agonist that recruits β-arrestin as well as G protein, and the authors attribute its residual side effects to that arrestin signaling; their engineered analogue beta01 retained antinociceptive and antipruritic efficacy while reducing sedation and anxiety-like behavior. This offers a concrete candidate explanation for the dizziness and somnolence that difelikefalin produces despite peripheral restriction.
Evidence Snapshot
Human Clinical Evidence
Strong. Phase III KALM trials demonstrated significant reduction in itch intensity vs placebo in hemodialysis patients. Post-approval evidence has continued to accumulate — a 2026 dedicated systematic review of real-world effectiveness and safety (Sheldon 2026 Ren Fail), a 12-month observational effectiveness study (Di Giovanni 2026 Int Urol Nephrol), a refractory-subgroup analysis in gabapentinoid-refractory pruritus (Li 2026 J Nephrol), and a FAERS pharmacovigilance signal analysis (Zhao 2026 Nephrol Dial Transplant) collectively broaden the evidence base beyond the pivotal-trial cohorts. The real-world picture is wider and messier than the trials: across real-world settings 35–92.9% of patients achieved a >=3-point WI-NRS reduction versus 51% in pooled KALM-1/KALM-2 data, but the included studies are heterogeneous and at high risk of bias, and the 12-month observational cohort reported that only 60% of patients completed a year of treatment (40% discontinued). The honest comparative framing comes from the 2023 Cochrane review, which graded kappa-opioid agonists as reducing pruritus only slightly versus placebo at high certainty of evidence — a smaller effect than GABA-analogues in the same analysis.
Animal / Preclinical
Extensive. Peripheral kappa opioid pharmacology is well-characterized.
Mechanistic Rationale
Strong. Peripheral KOR biology and itch signaling are well-understood.
Research Gaps & Open Questions
What the current literature has not yet settled about Difelikefalin:
- 01Non-dialysis CKD pruritus — no longer an open question so much as a closed door: two Phase 3 trials of oral difelikefalin in non-dialysis and advanced CKD (NCT05342623, NCT05356403) were terminated on a corporate decision to discontinue work in advanced chronic kidney disease. The unmet need in this population is real and now has no sponsor pursuing it.
- 02Peritoneal dialysis pruritus — KALM trials enrolled hemodialysis patients only; efficacy and dosing in peritoneal dialysis patients are not established.
- 03Other pruritic conditions — the expansion attempt has been made and has failed. The atopic dermatitis Phase 3 (NCT05387707) and the notalgia paresthetica Phase 2/3 (NCT05978063) were both terminated after interim analyses showed no meaningful clinical benefit, and a cholestatic-pruritus study closed for slow enrollment. Whether the failures reflect an oral-formulation exposure problem or a genuine absence of effect outside the uremic-pruritus context is the real unresolved question, and no sponsor is currently positioned to answer it. Case-series use of IV difelikefalin in refractory CKD-associated pruritus — including one report of benefit in a patient on conservative kidney management without chronic hemodialysis — remains anecdotal.
- 04Long-term beyond-2-year safety — open-label extension data extends to roughly 2 years; longer-duration safety, including any cumulative cardiovascular or metabolic effects, requires ongoing pharmacovigilance.
- 05Mortality benefit signal — observational data suggests CKD pruritus is associated with worse mortality outcomes, raising the question of whether effective pruritus treatment translates to survival benefit; adequately powered mortality trials are not yet available.
- 06Mechanism of dizziness/somnolence despite peripheral restriction — a 2026 rational-design study (PMID 41980950) supplies a candidate answer the field had been missing: difelikefalin is a balanced agonist that recruits β-arrestin alongside G protein, and an engineered biased analogue retained efficacy while reducing sedation and anxiety-like behavior. Whether β-arrestin recruitment is in fact the source of difelikefalin's clinical dizziness and somnolence in humans has not been tested directly.
- 07Beyond-pruritus indications for peripheral KOR agonism — a 2026 sepsis-associated acute kidney injury model (PMID 42013153) raises the possibility of organ-protective applications, but this is early-stage and has not entered controlled human evaluation. The analgesic direction is less promising than it first appears: difelikefalin's own postoperative-pain and osteoarthritis programs were discontinued, and 2026 work in chemotherapy-induced neuropathy found that peripheral KOR agonism actually worsened cold hypersensitivity while a KOR antagonist attenuated it — so peripheral KOR agonism may be the wrong direction for at least some pain phenotypes.
Forms & Administration
IV injection administered after hemodialysis sessions (0.5mcg/kg). Given by healthcare professionals 3 times per week.
Dosing & Protocols
The ranges below reflect protocols commonly discussed in the literature and by clinicians — not a prescription. Actual dosing for any individual should be determined by a qualified healthcare provider who knows the patient.
Typical Range
0.5 micrograms/kg administered as an intravenous bolus into the venous line of the dialysis circuit at the end of each hemodialysis session.
Frequency
Three times weekly, dosed at the end of each hemodialysis session — corresponding to the standard thrice-weekly dialysis schedule. Patients on more or less frequent dialysis dose accordingly with each session.
Timing Considerations
No specific timing requirements: can be administered at any time of day, with or without food, and is not tied to exercise timing. Consistency matters more than the specific clock — dose at roughly the same time each day (or same day each week, for weekly protocols) to keep exposure steady.
Cycle Length
Chronic indefinite for as long as the patient remains on hemodialysis and continues to derive benefit. There is no fixed treatment duration limit. Long-term open-label extension data (52+ weeks) supports sustained efficacy and tolerability.
Protocol Notes
Administration is exclusively by healthcare professionals during the dialysis session — patients do not self-administer. The IV bolus is delivered into the venous return line of the dialysis circuit, typically over a few seconds at the end of treatment. This route ensures rapid distribution and avoids the need for separate venous access. Dose adjustment is not required for hepatic impairment (peptide proteolytic clearance dominates) or for variations in dialysis efficiency. Pharmacokinetics in dialysis patients are well-characterized: difelikefalin is partially cleared by dialysis itself, but the end-of-session timing is designed around the post-dialysis pharmacokinetic profile. Dizziness, somnolence, and gait disturbance are reported in clinical trials despite the peripheral restriction — likely reflecting either small residual CNS exposure or peripheral-vagal effects on autonomic tone — and patients should be counseled. Falls risk is a particular concern in elderly dialysis patients; dosing is at the end of dialysis (when patients are typically being discharged) so post-dose ambulation should be supervised initially. Hyperkalemia signal in trial data warrants attention given that hyperkalemia is already a major management concern in dialysis patients. Serum potassium should be monitored as part of routine dialysis care; difelikefalin should be used cautiously in patients with persistently elevated potassium despite dialysis optimization. Handling specifics from the label matter in practice: Korsuva must not be mixed or diluted before administration, and must be given within 4 hours of syringe preparation. The label also carries explicit guidance for a missed hemodialysis treatment, and a warning on driving and operating machinery — patients should be advised not to drive or operate dangerous machinery until they know how difelikefalin affects them. Difelikefalin does not produce traditional opioid effects (euphoria, dysphoria, respiratory depression, addiction) at therapeutic doses, supported by dedicated abuse-liability and respiratory-depression studies in recreational polydrug users and in hemodialysis patients respectively.
Korsuva is FDA-approved only for moderate-to-severe pruritus associated with chronic kidney disease in adults undergoing hemodialysis. Use in non-dialysis CKD pruritus, peritoneal dialysis pruritus, or other pruritic conditions is not approved and is investigational. The IV formulation requires dialysis-circuit administration and is not appropriate for outpatient or non-dialysis settings.
Timeline of Effects
Onset
Reduction in itch intensity is typically observed within the first 1–2 weeks of three-times-weekly dosing. Sleep-quality improvements (often reflecting reduced nocturnal scratching) are reported in similar timeframes.
Peak Effect
Both pivotal trials assessed response at week 12. The primary endpoint was a reduction of at least 3 points on the 24-hour Worst Itching Intensity Numerical Rating Scale (WI-NRS): 49.1% of difelikefalin patients vs 27.9% of placebo patients in KALM-1 (imputed; P<0.001) and 54.0% vs 42.2% in KALM-2. The more stringent >=4-point reduction was a secondary endpoint and the rates are correspondingly lower — 37.1% vs 17.9% in KALM-1 and 41.2% vs 28.4% in KALM-2. The high placebo response typical of pruritus trials is visible in both, and is most pronounced in KALM-2. Quality-of-life improvements (5-D itch scale, Skindex-10) and sleep improvements were sustained through long-term extension follow-up.
After Discontinuation
Pharmacokinetics differ sharply by renal status, and the dialysis figure is the one that matters clinically. In the dedicated [14C]difelikefalin mass-balance study (Stark 2023 Clin Pharmacokinet), mean plasma half-life was 38.0 hours in hemodialysis subjects versus 2.6 hours in subjects with normal renal function, with total exposure (AUC) roughly 11-fold higher in the dialysis group — difelikefalin is cleared renally in healthy people but accumulates and is removed largely by dialysis and the fecal route in end-stage disease. Despite that long terminal half-life, pruritic symptoms typically return within days to a few weeks of stopping therapy, because the drug suppresses itch signaling rather than modifying the underlying CKD-pruritus pathophysiology, which persists. There is no dependency or withdrawal phenomenon: the kappa-receptor pharmacology is peripherally restricted, and a dedicated physical-dependence study in hemodialysis patients plus an abuse-potential study in recreational polydrug users both support the absence of central reinforcement.
Monitoring & Measurement
Bloodwork & Labs
- •Serum potassium — the one lab that genuinely changes management; hyperkalemia appeared as a trial signal and is already a central concern in dialysis care, so it is tracked as part of routine pre-dialysis bloodwork
- •Complete blood count and peripheral blood smear — not for difelikefalin itself, but standard dialysis surveillance that distinguishes uremic pruritus from other causes of itch
- •Serum calcium, phosphate and intact PTH — secondary hyperparathyroidism and mineral-bone disorder are competing drivers of CKD-associated itch, and uncontrolled values predict a poor response to any anti-pruritic
- •Kt/V or urea reduction ratio — dialysis adequacy is the first thing to optimize before attributing persistent itch to a drug failure
Functional & Performance Tests
- •24-hour Worst Itching Intensity Numerical Rating Scale (WI-NRS), 0–10, recorded daily — this is the actual trial endpoint and the only measure that maps onto the published response rates
- •5-D Itch Scale — captures duration, degree, direction, disability and distribution rather than intensity alone
- •Skindex-10 — the itch-specific quality-of-life instrument used in KALM-1 and KALM-2
- •A simple sleep log or validated sleep questionnaire — nocturnal scratching is often what patients actually want fixed, and it improved alongside itch in the trials
When to Test
Record WI-NRS daily from a baseline week before the first dose. The trials read out at week 12, so judge response at 12 weeks rather than earlier, while expecting the first change within 1–2 weeks. Serum potassium follows the routine dialysis schedule; 5-D Itch and Skindex-10 at baseline and week 12.
Interpretation & Notes
Difelikefalin is unusual among the peptides on this site in that its response measure is a validated patient-reported score rather than a lab value, and the relevant threshold is published: a >=3-point drop in the 24-hour WI-NRS was the primary endpoint in both pivotal trials, with a >=4-point drop as the more stringent secondary. Because placebo response in pruritus trials is high (28–42% achieved the 3-point threshold on placebo), a single patient's improvement cannot be confidently attributed to the drug — which is an argument for recording a genuine pre-treatment baseline week rather than a retrospective impression. Note also the real-world discontinuation rate: in a 12-month observational cohort only 60% of patients completed a year, so a structured reassessment at 12 weeks and again at 6 months is more realistic than assuming indefinite continuation. All of this monitoring happens inside an existing dialysis unit with thrice-weekly clinical contact and routine labs, so it adds essentially no testing burden.
Common Questions
Is difelikefalin addictive like other opioids?
No. Because it doesn't cross the blood-brain barrier, it doesn't produce the euphoria, dysphoria, or addiction associated with central opioid receptor activation. Dedicated abuse-liability testing in recreational polydrug users supported the peripheral-restriction pharmacology, and the FDA did not place Korsuva under Controlled Substances Act scheduling.
How quickly does difelikefalin reduce itch in hemodialysis patients?
Reductions in itch intensity are typically observed within the first 1-2 weeks of three-times-weekly dosing. The pivotal KALM-1 and KALM-2 trials measured their primary endpoint at week 12, defined as a reduction of at least 3 points on the 24-hour Worst Itching Intensity Numerical Rating Scale (WI-NRS); a >=4-point reduction was a pre-specified secondary endpoint, not the primary one. Sleep-quality improvements often track alongside reduced itch in similar timeframes.
Can difelikefalin be taken at home or as a pill?
Not for the approved hemodialysis-pruritus indication. Korsuva is administered intravenously into the venous return line of the dialysis circuit by healthcare professionals at the end of each session. An oral difelikefalin formulation was investigated for non-dialysis CKD pruritus, but those Phase 3 programs were terminated in 2023–2024 and no oral product is in development.
Can adolescents on dialysis receive difelikefalin?
Not yet as approved therapy — the label states that safety and effectiveness in pediatric patients have not been established — but this is the one area where difelikefalin is actively advancing rather than retreating. A 2026 pharmacokinetic study gave a single 0.5 mcg/kg dose to 12-to-17-year-olds at the end of dialysis and found systemic exposure comparable to adults with no serious adverse events, which supports using the adult dose in this age group. A Phase 2 safety and tolerability trial in adolescents on hemodialysis (NCT06593392) began recruiting in August 2026.
Does difelikefalin work for itch outside chronic kidney disease?
No — and this question now has a firmer answer than it used to. FDA approval is limited to moderate-to-severe pruritus in adults on hemodialysis. Every attempt to extend difelikefalin beyond dialysis has been discontinued after failing an interim efficacy analysis: notalgia paresthetica (Phase 2/3, terminated because oral difelikefalin 'did not demonstrate a meaningful clinical benefit at any dose compared to placebo'), atopic dermatitis as an add-on to topical corticosteroids (Phase 3, terminated for the same reason), and non-dialysis/advanced CKD pruritus (two Phase 3 trials, terminated on a corporate decision to discontinue work in advanced chronic kidney disease). A small cholestatic-pruritus study was also terminated, for slow COVID-era enrollment. The one genuinely active extension program is in adolescents on hemodialysis, not a new disease.
Who Difelikefalin Is NOT For
- •Use in patients not undergoing hemodialysis — IV difelikefalin is dialysis-circuit administered and approved only for hemodialysis-associated pruritus. The Phase 3 programs in non-dialysis and advanced CKD pruritus were terminated, so this is not merely unapproved but unsupported by the trials that were run.
- •Peritoneal dialysis — this is a labeled Limitation of Use, not an open question: Korsuva has not been studied in patients on peritoneal dialysis and is explicitly not recommended in that population.
- •Pregnancy — limited safety data; should be used only if benefit outweighs risk.
- •Breastfeeding — limited data; clinical decisions are individualized.
- •Pediatric use — not established; safety and efficacy in patients under 18 years are not adequately characterized.
- •Known hypersensitivity to difelikefalin or formulation excipients.
- •Persistent significant hyperkalemia despite dialysis optimization — relative contraindication given the trial-observed hyperkalemia signal.
- •Concurrent CNS depressants (high-dose opioids, sedating antihistamines, benzodiazepines) — additive somnolence/dizziness risk warrants caution and possible dose timing adjustments; not absolute contraindication but warrants clinical monitoring.
Drug & Supplement Interactions
Difelikefalin has a relatively limited drug-interaction profile due to its peptide proteolytic clearance (no significant CYP-mediated metabolism) and peripheral restriction. Central nervous system depressants (opioids, benzodiazepines, sedating antihistamines, anticonvulsants, alcohol): although difelikefalin itself has minimal CNS penetration, the dizziness and somnolence signals observed in clinical trials may be additive with concurrent CNS depressants. Patients on chronic opioid therapy in particular should be monitored carefully, especially during initiation. A pooled exploratory analysis of KALM-1, KALM-2 and Study 3105 put numbers on this: nonfatal serious treatment-emergent adverse events were more common among concomitant opioid users on difelikefalin (44.7% vs 19.0% in non-users) — but the same gap appeared on placebo (38.0% vs 15.9%), so the signal tracks opioid use and its associated comorbidity rather than an interaction with difelikefalin specifically. The practical implication is heightened monitoring of a frailer population, not avoidance of the combination. Kappa opioid antagonists (naltrexone, naloxone): theoretically could attenuate difelikefalin's anti-pruritic effect, though peripheral-restriction-specific data is limited. Clinical relevance is modest given naltrexone's primary indications. Medications that affect serum potassium (ACE inhibitors, ARBs, potassium-sparing diuretics, potassium supplementation, certain antibiotics): should be monitored given the trial hyperkalemia signal, though many dialysis patients are already on these agents and integrated potassium management is standard. As a peptide cleared partly by dialysis itself, dose timing relative to dialysis is built into the labeled administration (end of session). No formal dose adjustment for hepatic or renal function beyond dialysis context is required. As with any chronic specialty therapy in dialysis patients, all medications including OTC supplements should be disclosed to the dialysis care team.
Safety Profile
Common Side Effects
Cautions
- • Only approved for CKD patients on hemodialysis — the label explicitly states Korsuva has not been studied in peritoneal dialysis patients and is not recommended in that population
- • Administered by healthcare professionals into the dialysis circuit; not self-administered
- • Labeled warning on driving and operating machinery — may impair mental or physical abilities; patients should not drive or operate dangerous machinery until they know how difelikefalin affects them
- • Falls and gait disturbance, particularly in elderly dialysis patients; dosing occurs at the end of dialysis, when patients are being discharged
- • Monitor serum potassium as part of routine dialysis care given the trial hyperkalemia signal
- • FAERS pharmacovigilance has flagged disproportionate reporting of mental status change, disorientation and electric-shock sensation — some not seen in Phase 3 — concentrated in patients aged 65 and over
What We Don't Know
Use outside of CKD-associated pruritus is still being studied.
Legal Status
United States
Korsuva (difelikefalin) is FDA-approved (NDA 214916, approved 23 August 2021, priority review; a supplement followed in March 2025) for moderate-to-severe pruritus associated with chronic kidney disease in adults undergoing hemodialysis. It is a prescription-only specialty medication, not a controlled substance (despite being a kappa opioid agonist — formal scheduling assessment supported non-control given peripheral restriction). Distribution is through specialty channels integrated with dialysis center workflows rather than standard retail pharmacies. The NDA is now held by Vifor (International), Inc.: originator Cara Therapeutics sold difelikefalin development, manufacturing and commercialization rights to CSL Vifor and was itself merged into Tvardi Therapeutics in April 2025, so the molecule has no remaining independent sponsor pursuing new indications.
International
Approved by the EMA as Kapruvia (April 2022) for the same dialysis-pruritus indication. UK MHRA, Health Canada, and Australian TGA approvals followed. Approval and reimbursement vary by jurisdiction; uptake has been slower in some markets than in the US dialysis system.
Sports & Competition
Difelikefalin is not named on the 2026 or 2027 WADA Prohibited List, and — unlike most peptides on this site — that absence is genuinely dispositive rather than a loophole. Two sections could in principle reach it, and neither does. S7 (Narcotics) is a closed, enumerated list of named opioids (buprenorphine, dextromoramide, diamorphine, fentanyl and its derivatives, hydromorphone, methadone, morphine, nicomorphine, oxycodone, oxymorphone, pentazocine, pethidine, tramadol), prohibited in-competition only; difelikefalin is not among them and the list carries no 'including but not limited to' clause. S0 (Non-Approved Substances) catches any pharmacological substance with no current approval by any governmental regulatory health authority for human therapeutic use — and difelikefalin holds both FDA and EMA marketing authorisation, so S0 is excluded by its approval status. The honest framing on performance is narrower than 'no effect': difelikefalin has never demonstrated general analgesic efficacy in humans, with its postoperative-pain and osteoarthritis programs both discontinued, so there is no established ergogenic or analgesic benefit to misuse — not a positive finding that it has none. Athletes using it therapeutically for dialysis-associated pruritus should still document the indication through standard medical-use channels.
Regulatory status changes over time. Verify current local rules with a qualified professional.
Myths & Misconceptions
Myth
Difelikefalin is addictive because it activates opioid receptors.
Reality
Difelikefalin is a peripherally-restricted kappa opioid receptor agonist that does not meaningfully cross the blood-brain barrier. It does not produce the central reinforcement, euphoria, or dysphoria associated with addictive opioids. Dedicated abuse-liability studies in recreational polydrug users supported the peripheral-restriction pharmacology, and the FDA scheduling assessment did not place it under Controlled Substances Act control.
Myth
Difelikefalin works by sedating you so you don't notice the itch.
Reality
Anti-pruritic effect is mediated through peripheral kappa opioid receptors on sensory neurons and immune cells, modulating itch signaling at the source. Although dizziness and somnolence are reported side effects, they are not the mechanism of action. The peripheral pharmacology means itch reduction is direct rather than achieved through CNS suppression.
Myth
Korsuva can be used at home like other anti-itch medications.
Reality
Korsuva is exclusively administered IV via the dialysis circuit at the end of each hemodialysis session by healthcare professionals. There is no oral or self-injectable approved formulation for the dialysis indication. Patients undergoing hemodialysis receive the medication as part of their standard dialysis care.
Myth
All CKD patients with pruritus can use difelikefalin.
Reality
Korsuva is FDA-approved only for adults undergoing hemodialysis. Non-dialysis CKD patients have no approved formulation available to them, and the oral program intended to serve them was terminated rather than approved. For peritoneal dialysis the label goes further than silence: it states that Korsuva has not been studied in this population and is not recommended — a labeled Limitation of Use, not merely an evidence gap.
Myth
An oral version of difelikefalin is coming soon.
Reality
It is not. Oral difelikefalin was taken into Phase 3 and failed. The sponsor terminated the atopic dermatitis trial because oral difelikefalin as an add-on to topical corticosteroids 'did not demonstrate meaningful clinical benefit compared to TCS alone,' and terminated the notalgia paresthetica trial because oral difelikefalin 'did not demonstrate a meaningful clinical benefit at any dose compared to placebo.' The advanced-CKD oral program was closed on a corporate decision to exit that area. Compounding the finality, originator Cara Therapeutics sold the asset to CSL Vifor and was merged into Tvardi Therapeutics in 2025 — there is no sponsor developing an oral formulation.
Myth
Difelikefalin is the most effective treatment for dialysis-related itch.
Reality
It is the only systemic therapy specifically approved for it, which is not the same claim. The 2023 Cochrane review of pruritus interventions found that kappa-opioid receptor agonists as a class reduced itch only slightly versus placebo (VAS mean difference −0.96, 95% CI −1.22 to −0.71; six RCTs, n=1292) at high certainty of evidence, while GABA-analogues such as gabapentin and pregabalin achieved a substantially larger reduction in the same review (MD −5.10, moderate certainty). Difelikefalin's advantages are a specific approval, a dialysis-circuit route requiring no patient adherence, and the absence of the sedation and dose-adjustment burden that gabapentinoids carry in renal failure — not superior raw efficacy.
Myth
Difelikefalin will replace opioids for general pain management.
Reality
Difelikefalin's anti-pruritic effect is well-established in CKD pruritus, but its analgesic efficacy in general pain populations has not been demonstrated to justify approval. Earlier development efforts in postoperative pain did not result in approved indications. The peripheral kappa pharmacology is a promising mechanistic concept for non-CNS-acting analgesics, but difelikefalin specifically is currently a focused anti-pruritic agent rather than a broad analgesic alternative to opioids.
Published Research
41 studiesThe pharmacokinetics of a single intravenous dose of difelikefalin in adolescents aged 12 to 17 years on hemodialysis
Mourani and colleagues, Pediatric Nephrology 2026. The first difelikefalin pharmacokinetic data in adolescents: a single 0.5 mcg/kg dry-body-weight dose at the end of dialysis in 12–17-year-olds produced systemic exposure comparable to adults, with no serious adverse events. Directly addresses the page's long-standing pediatric gap and supports the dose selection in the currently recruiting adolescent Phase 2 (NCT06593392).
Chronic Kidney Disease-Associated Pruritus in Danish Dialysis Patients: A Cross-Sectional Multicenter Study of Prevalence, Disease Burden, and Current Treatment Practices
Real-world effectiveness and safety of difelikefalin for chronic kidney disease-associated pruritus: a systematic review.
Sheldon and colleagues, Renal Failure 2026. First dedicated systematic review of post-approval real-world evidence for difelikefalin — an important complement to the KALM-1/KALM-2 trial evidence base that shifts the file's evidence discussion from pivotal-trial-anchored to including verified real-world outcomes across multiple settings.
The neuroimmune architecture of uremic pruritus: mechanisms and therapeutic targeting
Difelikefalin-associated adverse drug event signals: a real-world pharmacovigilance study from the FAERS database.
Zhao and colleagues, Nephrology Dialysis Transplantation 2026. The disproportionality analysis that fills out difelikefalin's safety picture beyond the pivotal trials, and the source of the neurologic signals now reflected in this page's cautions: reporting odds ratios of 85.65 for mental status changes, 33.62 for disorientation, 32.09 for electric shock sensation, 21.06 for fracture, 16.25 for somnolence and 8.46 for falls, with risk concentrated in patients aged 65 and over. Several of these — notably electric shock sensation and disorientation — were not reported in the Phase 3 program at all. Disproportionality signals are hypothesis-generating rather than causal, but the falls-and-fracture cluster is coherent with the labeled gait-disturbance warning.
Difelikefalin in gabapentinoid-refractory CKD-associated pruritus: real-world experience from Australia.
Refractory Chronic Kidney Disease-Associated Pruritus: Old Remedies and Novel Agents
A kappa opioid receptor agonist, difelikefalin, improves acute kidney injury in experimental sepsis models
Rational design of a Kappa opioid receptor peptide agonist with attenuated β-arrestin signaling
Difelikefalin in Chinese patients with chronic kidney disease-associated pruritus
Association of pruritus with comorbidities and survival in chronic kidney disease: a narrative review of the pre-difelikefalin era literature
The Efficacy and Safety of Intravenous Difelikefalin for the Treatment of Pruritus in Patients Undergoing Hemodialysis: A Systematic Review and Meta-Analysis of Randomized Controlled Trials
Real-world effectiveness and tolerability of difelikefalin over 12 months for hemodialysis-associated pruritus.
Influence of Concomitant Opioids on Difelikefalin Treatment Outcomes in Adults with Moderate-to-Severe Pruritus on Maintenance Hemodialysis: Exploratory Analyses
Systemic Inflammatory Markers Correlate with Chronic Kidney Disease-Associated Pruritus and Response to Treatment
Influence of Baseline Itch Severity on Treatment Outcomes With Difelikefalin in Adults With Moderate-to-Severe Pruritus Receiving Maintenance Haemodialysis: An Exploratory Analysis
Difelikefalin [LiverTox: Clinical and Research Information on Drug-Induced Liver Injury]
Difelikefalin in the treatment of hemodialysis patients with pruritus: a systematic review and meta-analysis
Impact of renal impairment on the pharmacokinetic profile of intravenous difelikefalin, a kappa opioid receptor agonist for the treatment of pruritus
The efficacy and safety of difelikefalin for pruritus in hemodialysis patients: a systematic review and meta-analysis of randomized controlled trials
Difelikefalin for Hemodialysis Patients with Pruritus in Japan
Efficacy and safety of difelikefalin in the treatment of hemodialysis patients with pruritus: A meta-analysis and systematic review
Difelikefalin in Black/African American Hemodialysis Patients with Moderate-to-Severe Pruritus: Post hoc Analysis of KALM-1 and KALM-2
Impact of Difelikefalin on the Health-Related Quality of Life of Haemodialysis Patients with Moderate-To-Severe Chronic Kidney Disease-Associated Pruritus: A Single-Arm Intervention Trial
Difelikefalin improves itch-related sleep disruption in patients undergoing haemodialysis
Intravenous difelikefalin for the treatment of hemodialysis pruritus
Pharmacokinetics, Metabolism, and Excretion of Intravenous [14C]Difelikefalin in Healthy Subjects and Subjects on Hemodialysis
Stark and colleagues, Clinical Pharmacokinetics 2023. The radiolabelled mass-balance study and the source of the numbers most often misquoted about this drug: mean plasma half-life was 38.0 hours in hemodialysis subjects versus 2.6 hours in subjects with normal renal function, with AUC roughly 11-fold higher in the dialysis group. Over 99% of circulating drug was unchanged parent compound (minimal metabolism); excretion was primarily urinary in healthy subjects but fecal plus dialysate in hemodialysis patients.
Pharmacological interventions for pruritus in adult palliative care patients
Cochrane review, 2023. The most important comparative-efficacy context on this page, and the one most often omitted elsewhere: kappa-opioid receptor agonists as a class (difelikefalin, nalbuphine, nalfurafine) reduced pruritus only slightly versus placebo (VAS mean difference −0.96, 95% CI −1.22 to −0.71; six RCTs, n=1292) at high certainty of evidence — a markedly smaller effect than GABA-analogues achieved in the same review (MD −5.10, moderate certainty). Difelikefalin's distinction is being the only systemic agent approved for this indication, not being the most effective one.
Assessment of the physical dependence potential of difelikefalin: Randomized placebo-controlled study in patients receiving hemodialysis
A phase 2 study of oral difelikefalin in subjects with chronic kidney disease and moderate-to-severe pruritus
Difelikefalin for the treatment of moderate-to-severe pruritus associated with chronic kidney disease on hemodialysis
Phase 2 Trial of Difelikefalin in Notalgia Paresthetica
Kim and colleagues, NEJM 2023. The Phase 2 that prompted the notalgia paresthetica program — and a cautionary example of reading a positive headline too confidently. The trial met its primary endpoint but the authors noted that results for secondary outcomes 'generally did not support those of the primary analysis.' The confirmatory Phase 2/3 (NCT05978063) was subsequently terminated because oral difelikefalin did not show meaningful clinical benefit at any dose.
Difelikefalin for pruritus associated with renal disease
Difelikefalin in the Treatment of Chronic Kidney Disease-Associated Pruritus: A Systematic Review
Difelikefalin: A New κ-Opioid Receptor Agonist for the Treatment of Hemodialysis-Dependent Chronic Kidney Disease-Associated Pruritus
Efficacy and Safety of Difelikefalin in Japanese Patients With Moderate to Severe Pruritus Receiving Hemodialysis: A Randomized Clinical Trial
Evaluation of the abuse potential of difelikefalin, a selective kappa-opioid receptor agonist, in recreational polydrug users
The dedicated human abuse-liability study underpinning difelikefalin's non-scheduled status. Tested in recreational polydrug users — the population most likely to detect reinforcing opioid effects — and supported the peripheral-restriction pharmacology. Together with the respiratory-depression trial, this is why an opioid-receptor agonist reached market without Controlled Substances Act scheduling.
Difelikefalin: First Approval
Effect of difelikefalin, a selective kappa opioid receptor agonist, on respiratory depression: A randomized, double-blind, placebo-controlled trial
The companion safety study to the abuse-liability trial: a dedicated, placebo-controlled assessment showing difelikefalin does not produce the respiratory depression that defines mu-opioid risk. Mechanistically expected — respiratory depression is a mu-receptor and central effect, and difelikefalin is a peripherally restricted kappa agonist — but demonstrating it directly was necessary for the regulatory package.
An evaluation of difelikefalin as a treatment option for moderate-to-severe pruritus in end stage renal disease
A Phase 3 Trial of Difelikefalin in Hemodialysis Patients with Pruritus
Fishbane and colleagues, New England Journal of Medicine 2020 — KALM-1 (NCT03422653), the pivotal trial behind the FDA approval. 378 hemodialysis patients with moderate-to-severe pruritus randomized to IV difelikefalin 0.5 mcg/kg or placebo three times weekly for 12 weeks. Primary endpoint was a >=3-point drop in the 24-hour WI-NRS: 49.1% vs 27.9% (imputed, P<0.001). The >=4-point secondary endpoint was 37.1% vs 17.9%. Note the threshold carefully — the widely-quoted ~49% figure is the 3-point rate, not the 4-point rate.
Quick Facts
- Class
- Peripheral Kappa Opioid Agonist
- Tier
- B
- Evidence
- Strong
- Safety
- Well-Studied
- Updated
- Oct 2026
- Citations
- 41PubMed
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Clinical Trials
View Clinical TrialsLinks to ClinicalTrials.gov for reference. Listing does not imply endorsement.