Diagnosis and Management of Denosumab-Induced Hypocalcemia and Hypophosphatemia in the Setting of Metastatic Prostate Cancer

Denosumab, a receptor activator of nuclear factor kappa-Β ligand (RANK-L) monoclonal antibody used in osteoporosis and various malignancies, has been shown to cause hypocalcemia shortly after initiation of treatment. There have been few case reports of electrolyte abnormalities in patients managed with long-term treatment with this medication. This report presents the case of a 43-year-old male with metastatic prostate cancer who presented with severe hypophosphatemia and hypocalcemia, initially resistant to repletion. After more aggressive and persistent repletion with IV calcium, phosphorus, and vitamin D, as well as time for the denosumab to dissipate, the patient’s electrolytes stabilized and he was able to be discharged with oral replacement and close follow-up. Therefore, long-term monitoring of electrolytes for patients on denosumab should be carefully considered.