at San Francisco, California and other locations
study started
estimated completion:
Anthony Portale



UX023-CL203 is a Phase 2b, open-label, long-term extension study. The study will be conducted in adults to assess the safety and pharmacodynamics of KRN23 administered via subcutaneous injections monthly (every 4 weeks) for a total of 68 weeks. The study will enroll approximately 25 adults with XLH who participated in Kyowa Hakko Kirin Pharma, Inc.'s (KHK's) study KRN23-INT-001 or KRN23-INT-002. Subjects will need to discontinue oral phosphate and vitamin D metabolite therapy prior to enrollment and throughout the duration of the study.

Official Title

A Phase 2b, Open-Label, Long-Term Extension Study to Evaluate the Safety and Pharmacodynamics of KRN23 in Adult Subjects With X-Linked Hypophosphatemia (XLH)


X-Linked Hypophosphatemia XLH FGF23 KRN23 Hypophosphatemia Familial Hypophosphatemic Rickets


You can join if…

  1. Have participated in KHK's KRN23-INT-001 or KRN23-INT-002 studies (received at least 2 doses of KRN23)
  2. Estimated glomerular filtration rate (eGFR) ≥60 mL/min at Screening.
  3. Sexually active subjects must be willing to use an acceptable method of contraception(e.g., double barrier method) while participating in the study and for 30 days after receiving the last dose of KRN23.

You CAN'T join if...

  1. Subject experienced a safety-related event in the KRN23-INT-001 or KRN23-INT-002 study that, in the opinion of the investigator and sponsor, precludes resuming KRN23 treatment.
  2. Presence of nephrocalcinosis on renal ultrasound that, in the opinion of the investigator and sponsor, precludes resuming KRN23 treatment.
  3. Pregnant or breastfeeding at Screening or planning to become pregnant (self or partner) at any time during the study.
  4. Participation in an investigational drug or device trial within 30 days of enrollment(other than KRN23-INT-001 or KRN23-INT-002).
  5. Use of a pharmacologic vitamin D metabolite or analog (e.g., calcitriol,doxercalciferol, and paricalcitol), phosphate, or aluminum hydroxide antacids (e.g.,Maalox® and Mylanta®) within 21 days prior to Screening or during the study.
  6. Use of medication to suppress PTH (e.g., Sensipar®, cinacalcet, calcimimetics) within 2 months prior to Screening.


  • University California San Francisco Hospital
    San Francisco California 94143 United States
  • Houston Methodist Reasearch Institute
    Houston Texas 77030 United States

Lead Scientist

  • Anthony Portale
    Professor, Pediatrics. Authored (or co-authored) 43 research publications


in progress, not accepting new patients
Start Date
Completion Date
Ultragenyx Pharmaceutical Inc
Phase 2
Study Type
Last Updated