Severe and prolonged hypophosphatemia after intravenous iron administration in a malnourished patient

Introduction: Intravenous iron administration has been reported to induce hypophosphatemia via an increase of FGF 23, an inhibitor of renal phosphate reabsorption and 1,25-(OH)₂ vitamin D production. This serious and potentially life threatening side effect is not widely acknowledged and little is known about the effects of intravenous iron on phosphate homeostasis in the setting of malnutrition.

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Results: We report a case of severe and prolonged hypophosphatemia associated with intravenous iron administration in a 24-year-old malnourished woman (anorexia/bulimia nervosa, BMI variable between 14 – 19 kg/m²). Due to chronic fatigue attributed to iron deficiency she received an intravenous infusion of 2 × 500 mg iron carboxymaltose (Ferinject). Seven days after the iron administration, she presented with a generalized weakness and persistent fatigue. Severe hypophosphatemia (0.18 mM; normal range 0.8 – 1.4) associated with mild hypocalcemia and inappropriately high urine phosphate levels were detected without evidence of hyperparathyroidism or 25-OH vitamin D deficiency. Intravenous phosphate infusions in parallel with oral supplements were initiated and had to be pursued for 4 weeks in order to reach phosphate levels of 0.4 mM. Not until 2 month after iron administration, normal serum phosphate levels could be achieved by maintaining oral substitution therapy. In parallel with the normalisation of phosphate levels, clinical symptoms improved slowly.

Conclusion: Our case demonstrates that, in the setting of malnutrition, an underlying phosphate deficit can be unmasked and severely aggravated by intravenous iron administration. Thus, parenteral iron administration should be used with caution, especially in the context of pre-existing malnutrition.

References: Schouten BJ, Hunt PJ, Livesey JH, Frampton CM, Soule SG. FGF23 elevation and hypophosphatemia after intravenous iron polymaltose: a prospective study. J Clin Endocrinol Metab. 2009 Jul;94(7): 2332 – 7.

Disclosure of Interest: None Declared