Hypophosphatemia in Patients Receiving Intravenous Iron Supplementation for Iron-Deficiency Anemia: A Narrative Review

Intravenous (IV) iron is used to replenish iron stores in patients with iron-deficiency anemia (IDA) who do not benefit from oral iron supplementation. Hypophosphatemia is an increasingly recognized adverse event associated with certain IV iron formulations. Mild/moderate hypophosphatemia may be asymptomatic or present with symptoms similar to those seen in patients with IDA, including fatigue, malaise, and muscle weakness. Persistent hypophosphatemia can cause osteomalacia due to reduced bone mineralization, leading to bone pain and pseudofractures. Ferric carboxymaltose (FCM) can impact phosphate homeostasis through an increase in fibroblast growth factor 23, leading to increased urinary phosphate excretion and hypophosphatemia. In clinical trials, rates of hypophosphatemia were significantly higher in patients receiving FCM compared with other IV iron formulations, such as ferric derisomaltose and ferumoxytol. Treatment guidelines recommend monitoring serum phosphate levels in patients receiving FCM who are at risk for low phosphate or who require repeat infusions, and alternative iron formulations should be considered in at-risk patients. This narrative review summarizes current evidence regarding IV iron-induced hypophosphatemia in individuals with IDA and examines the underlying pathophysiology and clinical evidence for IV iron-induced hypophosphatemia, particularly with FCM, the populations most at risk, and the clinical consequences of persistent hypophosphatemia.