Refractory hypophosphatemia following ferric carboxymaltose administration

Hypophosphatemia is a rare side effect of intravenous iron replacement. Urinary phosphate wasting due to increased FGF23 is the most likely mechanism. Here, we present a case of intractable hypophosphatemia in a 32-year-old female patient with history of ulcerative colitis (UC), who was primarily hospitalized due to UC flare-up. Her urinary fractional excretion of phosphate was inappropriately elevated at 70%. A careful history revealed that she had been treated with ferric carboxymaltose 2 weeks prior to hospitalization, leading to a diagnosis of iron-induced hypophosphatemia. She was treated with 5 weeks of intravenous sodium phosphate since she did not tolerate oral supplementation. In conclusion, clinicians should be aware of iron-induced hypophosphatemia and be cautious when prescribing intravenous iron.