Mechanism of treatment-emergent hypophosphatemia. Following the administration of some intravenous iron formulations is a sharp rise in the plasma iFGF23, triggering a pathophysiological cascade of renal phosphate wasting, calcitriol deficiency, and secondary hyperparathyroidism. This frequently culminates in hypophosphatemia even after iFGF23 levels have normalized. PTH, parathyroid hormone.