Iron infusions and denosumab are commonly co-prescribed medications for medical conditions occurring in the elderly population. Certain iron infusion formulations are known to affect phosphate metabolism by inducing an FGF23 reaction which consequently have downstream effects including a reduction in renal hydroxylation of 25 OH Vitamin D to its active form. The co-administration of denosumab during this time period compounds the effects on phosphate and calcium metabolism which can lead to severe hypocalcaemia and hypophosphataemia. This retrospective study reviews 18 months of intravenous iron infusions administered within one Victorian health service and the co-administration of available anti-resorptives to highlight the scope of the problem in clinical practice.