Calcitriol as a Therapeutic Strategy for Ferric Carboxymaltose–Induced Hypophosphatemia

We describe an 83-year-old man with idiopathic protein-losing enteropathy on chronic total parenteral nutrition who developed profound, persistent hypophosphatemia after intravenous ferric carboxymaltose (FCM) infusion for anemia. His course was notable for hypophosphatemia refractory to phosphate supplementation, accompanied by hypocalcemia, secondary hyperparathyroidism, suppressed 1,25-dihydroxy vitamin D, and markedly elevated fibroblast growth factor 23 (FGF23). These findings were consistent with FCM-induced hypophosphatemia, a condition increasingly recognized as part of the "6H Syndrome." Initiation of oral calcitriol led to rapid normalization of calcium and phosphate levels and enabled long-term stability without further IV iron exposure. This case underscores the need for heightened clinical awareness of FCM-associated electrolyte disturbances, especially in patients with baseline malnutrition or malabsorptive disorders.