In a patient with hypercalcemia due to malignancy, what is the SINGLE most appropriate initial step in treatment?

In the scenario of hypercalcemia due to malignancy, the correct initial step in treatment is the administration of intravenous (IV) 0.9% saline. The primary objective in the management of hypercalcemia, especially in cases related to malignancy, is to enhance renal excretion of calcium. Dehydration can exacerbate the hypercalcemic state, and rehydration with normal saline not only helps to dilute the serum calcium but also promotes diuresis, which further aids in calcium excretion.

IV fluids are particularly important in this context because they help to restore intravascular volume and improve kidney perfusion. With better renal blood flow, the kidneys can work more efficiently to eliminate excess calcium from the body.

Other treatment options, like calcitonin and bisphosphonates, have their roles in the management of hypercalcemia but are usually not the first step. Calcitonin can reduce serum calcium levels, but its effects are transient and are not as effective as fluid resuscitation in severely elevated cases. Bisphosphonates are effective in treating hypercalcemia due to malignancy by inhibiting bone resorption, but they take time to act and are typically used after initial hydration has been established. IV