Symptomatic hypophosphataemia after intravenous iron therapy: an underrated adverse reaction

Summary: Iron (ferric carboxymaltose) infusion therapy is used to treat severe iron deficiency which is not responding to the first-line oral iron therapy. However, it can also cause severe renal wasting of phosphate resulting in severe hypophosphataemia in some patients. Despite the growing number of case reports, this side effect is not well known to healthcare professionals. The product labelling information sheet does mention that hypophosphataemia can be a side effect, but also says that this side effect is usually transient and asymptomatic. We report a challenging case of a patient who developed severe, symptomatic and prolonged hypophosphataemia after an intravenous iron infusion for severe iron deficiency. Learning Points: Clinicians prescribing ferric carboxymaltose (Ferinject®) should be aware of the common side effect of hypophosphataemia, which could be mild, moderate or severe. Patients receiving iron infusion should be educated concerning this potential side effect. Pre-existing vitamin D deficiency, low calcium levels, low phosphate levels or raised parathyroid hormone levels may be risk factors, and these should be evaluated and corrected before administering intravenous iron. Patients may require phosphate and vitamin D replacement along with monitoring for a long period after iron infusion-induced hypophosphataemia. Every incident should be reported to the designated body so that the true prevalence and management thereof can be ascertained.