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CASE REPORT
Severe FGF23-based hypophosphataemic osteomalacia due to ferric carboxymaltose administration
  1. Klara Klein1,
  2. Shonda Asaad2,
  3. Michael Econs3,
  4. Janet E Rubin4
  1. 1Department of Medicine, University of North Carolina, Chapel Hill, North Carolina, USA
  2. 2Southeastern Medical Oncology, Jacksonville, North Carolina, USA
  3. 3Department of Endocrinology and Metabolism, Indiana University School of Medicine, Indianapolis, Indiana, USA
  4. 4Department of Medicine/Endocrinology, University of North Carolina, Chapel Hill, North Carolina, USA
  1. Correspondence to Dr Janet E Rubin, jrubin{at}med.unc.edu

Summary

Ferric carboxymaltose (FCM) is a novel iron formulation increasingly prescribed due to its effectiveness and fast infusion time. FCM administration can cause an asymptomatic hypophosphataemia secondary to fibroblast growth factor 23 (FGF23) dysregulation. In patients with chronic iron needs, however, a severe, long-lasting hypophosphataemia can lead to osteomalacia with associated bone pain. Lack of awareness of this complication results in delayed time to diagnosis and significant morbidity. We report a case of a patient with Crohn’s disease and chronic iron-deficiency anaemia receiving multiple doses of FCM who developed severe hypophosphataemic osteomalacia with urinary phosphate loss and increased FGF23. FGF23 excess and osteomalacia resolved only months after FCM discontinuation and aggressive phosphate repletion. Potential mechanisms of FGF23 dysregulation are discussed, with the aim of raising awareness of this significant side effect for prescribers of chronic intravenous iron supplementation, and to help guide future studies to determine the safety of FCM in all patient populations.

  • contraindications and precautions
  • haematology (drugs and medicines)
  • gastrointestinal system
  • calcium and bone

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Footnotes

  • Contributors KK made substantial contributions to the conception, analysis and interpretation of data; drafted the work and gave final approval of submission; and will be accountable for all aspects of work including accuracy and integrity. SA made substantial contributions to the conception, analysis and interpretation of data; reviewed draft and gave final approval of submission; and will be accountable for all aspects of work including accuracy and integrity. ME made substantial contributions to the analysis and interpretation of data, reviewed draft and gave final approval of submission, and will be accountable for aspects of work including accuracy and integrity. JER made substantial contributions to the conception, analysis and interpretation of data; drafted the work and gave final approval of submission; and will be accountable for all aspects of work including accuracy and integrity.

  • Competing interests None declared.

  • Patient consent Obtained.

  • Provenance and peer review Not commissioned; externally peer reviewed.

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