Denosumab is a human monoclonal antibody with affinity and specificity for receptor activator of nuclear factor kappa-B ligand (RANKL). In postmenopausal women with osteoporosis, denosumab reduces the risk of vertebral, nonvertebral, and hip fractures. No dose adjustment is necessary in patients with renal impairment. The most common adverse reactions reported with denosumab are back pain, pain in extremity, and musculoskeletal pain. Severe symptomatic hypocalcemia is a rare but potentially life-threatening adverse event. We report the case of a 94-year-old woman with chronic kidney disease who received a single dose of denosumab for treatment of osteoporosis. Twenty-three days later, she developed severe hypocalcemia associated with prolonged QT interval. She was treated with intravenous calcium chloride, and her serum calcium level returned to normal range after five days of hospitalization. Hypocalcemia following injection of denosumab is a significant risk in patients with severe renal impairment. Calcium and vitamin D supplementation is an important component of prevention of hypocalcemia. Monitoring of calcium level is highly recommended within 14 days of denosumab injection. Clinicians should be aware of the possibility of severe hypocalcemia after denosumab administration, and patients must notice the symptoms of hypocalcemia.
