Evaluating the safety of difelikefalin for itchy skin in adolescents on dialysis

Inclusion Criteria:

* Participant must be ≥12 to \<18 years of age at the time of informed consent.
* Participants with CKD on HD 3 times weekly for at least 12 weeks prior to the informed consent procedure who can continue HD without changing its frequency or method.
* Participants whose WI-NRS score in the 7-day run-in period (meets both of the below:

  1. WI-NRS scores have been recorded for at least 4 days through a 7-day run-in period.
  2. The mean value of the recorded WI-NRS scores is \>4.0
* Over the last 3 months prior to screening, the participant has had at least 1 of the following:

  1. At least 2 single-pool Kt/V measurements ≥1.2 on different dialysis days
  2. At least 2 urea reduction ratio measurements ≥65% on different dialysis days
  3. 1 single-pool Kt/V measurement ≥1.2 and 1 urea reduction ratio measurement ≥65% on different dialysis day
* Prescription dry body weight ≥20 kg
* Contraceptive use by men and women should be consistent with local regulations regarding the methods of contraception for those participating in clinical studies.
* Participant and/or legal guardian (as required) is capable of providing the appropriate signed informed consent and where appropriate, assent.

Exclusion Criteria:

* Known to be non-compliant with HD treatments and deemed unlikely by the Investigator to complete the study
* Planned to receive a kidney transplant during the study. Note: being listed on a kidney transplant list is not an exclusion criterion.
* Participants with itching caused by conditions other than chronic renal failure or complications of chronic renal failure, which could in the opinion of the Investigator affect the efficacy evaluation (e.g., atopic dermatitis, chronic urticaria).
* Participants with localised itch restricted to the palms of the hands.
* Participants with pruritus only during the dialysis session (by participant report).
* Participants with known concurrent hepatic cirrhosis or severe hepatic impairment (e.g., Child-Pugh Class C).
* Significant systolic or diastolic heart failure (e.g., New York Heart Association Class IV congestive heart failure).
* Participants with concurrent malignancy except excised basal cell or squamous cell carcinoma of the skin, or carcinoma in situ that has been excised or resected completely.
* Severe mental illness or cognitive impairment (e.g., dementia) or other concurrent mental disorder that, in the opinion of the Investigator, would compromise the validity of study measurements.
* Conditions associated with clinically important disruptions to the blood brain barrier (for example, primary brain malignancies, CNS metastases or other inflammatory conditions, active multiple sclerosis, advanced Alzheimer's disease) that in the Investigator's opinion may be associated with unacceptable risk for CNS effects.
* Acute or unstable medical condition(s) that in the Investigator's opinion, may be associated with increased risk to the participant, or may interfere with study assessments, outcomes, or the ability to provide written informed consent or comply with study procedures.
* Participant is receiving ongoing ultraviolet B treatment and anticipates receiving such treatment during the study.
* New or change of treatment received for itch including antihistamines and corticosteroids (oral, IV, or topical) within 14 days prior to screening.
* New or change of prescription for opioids, gabapentin, or pregabalin within 14 days prior to screening.
* Participant is receiving prohibited medication (e.g., nalfurafine hydrochloride, opioid antagonists) that cannot be stopped at least 14 days before enrolment in the study.
* Participant has known hypersensitivity to the study intervention or any components of the difelikefalin formulation.
* Known or suspected history of alcohol, narcotic, or other drug abuse or substance dependence within 12 months prior to screening or participant with any alcoholic beverage intake of more than two units per day more than once per week.
* Participation in any other investigational device or drug study \<30 days prior to screening, or current treatment with other investigational agent(s).
* Serum ALT, AST greater than 3× the reference ULN.