The most appropriate next step in treatment for this patient with malignancy-associated hypercalcemia is an intravenous bisphosphonate. Initial therapy for hypercalcemia is high-volume normal saline hydration, and in those with kidney failure, forced diuresis with a loop diuretic such as furosemide. This helps restore intravascular volume and decreases serum calcium levels acutely. For tumors that are glucocorticoid-sensitive, such as multiple myeloma and some types of lymphoma, glucocorticoids are indicated to decrease tumor-associated osteoclast activation. Bisphosphonates are powerful inhibitors of osteoclast-mediated bone resorption with an onset of effect occurring several days after administration and a duration of up to several weeks depending on the specific agent used, which allows longer-term control of calcium levels. Hypercalcemia is usually a manifestation of advanced disease, is associated with poor prognosis, and occurs in up to 10% of patients with cancer. Hypercalcemia is most common among patients with multiple myeloma and breast, renal, and lung cancer. Patients initially present with nausea, vomiting, constipation, and polyuria. Polydipsia, diffuse muscle weakness, and confusion follow.

Cinacalcet is a calcimimetic agent that is used to lower the calcium level in patients with primary and tertiary hyperparathyroidism associated with chronic kidney disease. It is not effective or approved for use in malignancy-associated hypercalcemia.

Dialysis is an effective method for lowering serum calcium levels, although it is generally reserved for patients with severe, symptomatic hypercalcemia who have not responded to acute treatment with hydration and other measures or patients in whom aggressive hydration is contraindicated. Dialysis would not be appropriate in this patient whose response to hydration and other initial therapies has not been assessed.

Treatment with chemotherapy or disease-specific targeted agents would be appropriate for long-term control of hypercalcemia but would not be effective for short-term therapy of hypercalcemia.