Background
Reports have highlighted a potential interaction between denosumab and intravenous iron infusion, leading to severe hypophosphatemia, hypocalcemia, and secondary hyperparathyroidism. Research suggests maintaining a three-month interval between these treatments to minimize electrolyte imbalances (1).
Case Presentation
MT, a chemo@home (c@h) patient receiving trastuzumab, pertuzumab, and denosumab, under an oncologist, every three weeks, was referred for an iron infusion by her GP on November 19, 2024. To mitigate the potential interaction, denosumab was withheld on November 21, 2024, and the iron infusion was rescheduled to November 26 where she was admitted to hospital with close electrolyte monitoring.
Pre-iron infusion blood results showed normal phosphate (1.32 mmol/L; NR: 0.75-1.5) and corrected calcium levels (2.5 mmol/L; NR: 2.1-2.6). Post-iron infusion results on November 27, 2024 revealed lower phosphate (1.13 mmol/L) but stable corrected calcium (2.54 mmol/L). MT proceeded with her routine treatment, including denosumab, on December 12, 2024, with planned post-infusion monitoring.
On December 17, 2024, blood tests revealed critical phosphate depletion (<0.32 mmol/L), reduced corrected calcium (2.06 mmol/L), and elevated PTH (38.7pmol/L; NR: 1.90-8.5). Following review of these results by the c@h clinical pharmacist, contact was made with MT’s oncologist, who admitted her for intravenous electrolyte replacement. This resulted in partial recovery by December 23, 2024, with a phosphate (0.63 mmol/L) and corrected calcium levels (1.93 mmol/L).
Outcome
MT’s denosumab was withheld multiple times, and she is scheduled for resumption on March 6, 2025, following continuous monitoring.
Conclusion
This case highlights the importance of scheduling and proactive electrolyte checks to avoid severe complications in patients receiving both denosumab and IV iron therapy.