According to a report from MedPage Today, the U.S. Food and Drug Administration (FDA) has added a boxed warning to the label of denosumab after finding that the osteoporosis drug may cause severe hypocalcemia in patients with advanced chronic kidney disease. The FDA’s new warning follows in the wake of a recent study published by Bird et al in JAMA detailing the safety of denosumab in comparison with bisphosphonates among older dialysis-dependent patients. Researchers found that female patients with chronic kidney disease—especially those on dialysis, who may already have had low blood calcium levels—who took denosumab had a 41% risk of developing severe hypocalcemia after 12 weeks of treatment vs 2% among those who received oral bisphosphonates. Patients with chronic kidney disease who develop severe hypocalcemia may experience symptoms such as confusion, weakness, numbness, tingling, irregular heart rhythms, fainting, face twitching, uncontrolled muscle spasms, and seizures, and may be at an increased risk of hospitalization, life-threatening events, and death. The FDA advised physicians to evaluate patients’ kidney function and consider the new boxed warning prior to prescribing denosumab. Among patients newly prescribed denosumab or continuing existing treatment with the agent, the FDA recommended that physicians regularly monitor blood calcium levels. Physicians and patients were urged to report all side effects of denosumab to the FDA’s MedWatch program at accessdata.fda.gov.