A 63-year-old man with metastatic squamous cell carcinoma has persistent thirst, vomiting and confusion. After intravenous saline, his serum calcium concentration remains 3.45 mmol/L (2.10–2.60), and his estimated glomerular filtration rate is 18 mL/min/1.73 m². Calcitonin has provided only transient benefit. Which one of the following is the most appropriate antiresorptive treatment?