Treatment of cancer-related hypercalcemia: the role of gallium nitrate.

Hypercalcemia is a common, life-threatening metabolic disorder that can be associated with cancer. Its pathophysiology includes enhanced osteoclastic bone resorption and decreased renal excretion of extracellular calcium. Symptoms of hypercalcemia include nausea, vomiting, bone pain, polyuria, renal insufficiency, bradycardia, and arrhythmia. The goals of medical therapy are to inhibit bone resorption and promote renal calcium excretion. Hydration is the first step in management. Treatments for hypercalcemia include phosphates, calcitonin, bisphosphonates, and gallium nitrate. Although intravenous phosphates prevent intestinal calcium absorption and inhibit mineral and bone matrix resorption, serious adverse events include renal failure, hypotension, extraskeletal calcification, and severe hypocalcemia. Calcitonin has a rapid onset of action and can lower serum calcium concentrations within hours, but its usefulness is limited by its short duration of effect and the development of tachyphylaxis. Bisphosphonates are effective inhibitors of bone resorption but appear to have decreased response rates in hypercalcemic patients with high levels of parathyroid-related protein. Gallium nitrate, an antitumor agent noncytotoxic to osteoclasts and bone cells, appears to be more effective than pamidronate, etidronate, and calcitonin in the treatment of cancer-related hypercalcemia. Importantly, unlike bisphosphonates, gallium nitrate is effective in both parathyroid-related protein-mediated and non-parathyroid-related protein-mediated hypercalcemia.