Intravenous Iron Induced Severe Hypophosphatemia

Introduction: Hypophosphatemia is a recently recognized adverse effect of certain intravenous iron formulations. It was previously thought to be asymptomatic and transient, however it can cause severe hypophosphatemia associated with renal phosphate wasting. We present a case of severe hypophosphatemia following intravenous ferric carboxymaltose administration. Clinical Case: A 40-year-old female with history of iron deficiency anemia, Hashimoto’s hypothyroidism and multinodular goiter status post thyroidectomy and obesity status post gastric sleeve presents to the hospital due to dizziness, generalized weakness, bone pain and severe myalgia right after 2(nd) dose of 750 mg of ferric carboxymaltose administration. She received 1(st) dose of 750 mg of ferric carboxymaltose a week ago prior to the presentation. She was found to have severe hypophosphatemia with a phosphorus level 1.0 mg/dl (2.4 - 4.8 mg/dl), hypocalcemia with calcium level at 8.7 mg/dl, normal PTH at 40 pg/ml and normal 25-OH Vitamin D level at 59.1 ng/ml. The fractional excretion of filtered phosphate (FEPO4) was 19.5%, supporting renal phosphate wasting. She was hospitalized for 5 days and received intravenous phosphate 45 mmol on hospitalization day 1, 15 mmol on day 2 and 30 mmol on day 3. She was discharged on K-phos Neutral 250 mg TID, Calcium carbonate/Vitamin D3 600 mg/500 IU 2 tablets TID and Calcitriol 0.5 mcg daily. While she was taking K-phos Neutral, Calcitriol and Calcium carbonate/Vitamin D3, her phosphorous level was down to 1.3 mg/dl, which was 4 weeks after 1(st) dose of ferric carboxymatose administration. She presented to the ED and received intravenous phosphate 15 mmol. She is currently taking K-phos Neutral 250 mg QID, Calcitriol 0.5 mcg daily and Calcium carbonate/Vitamin D3 600 mg/500 IU 2 tablets TID. Her phosphorous levels ranged at 2.5 - 3.0 mg/dl. Her bone pain and myalgia have gradually improved. Conclusion: Clinician should be aware of the side effect of hypophosphatemia following ferric carboxymaltose administration. Recent studies showed that incidence of hypophosphatemia associated with intravenous iron administration was significantly higher in ferric carboxymatose group compared with either iron isomaltoside group or ferumoxytol group. The impact of severe hypophosphatemia should be considered when choosing an intravenous iron medication.