| Abstract: | The short-term effects of acute mithramycin therapy on calcium homeostasis and strontium-85 kinetics were studied in four patients with metastatic cancer. Fecal calcium content increased after therapy while urinary calcium excretion decreased, but there was no net change in total calcium excretion. Mithramycin lowered the serum calcium level in three patients with either obvious osseous metastasis or hypercalcemia, but no change was observed in a fourth patient without osseous pathology and normal serum levels. The strontium-85 (Sr85) kinetic data revealed an increase in the skeletal clearance (“accretion”) in three patients and no change in the fourth. There was no change in the extrinsic (excretory) clearance rate in any patient. These data suggest that acute mithramycin therapy lowered serum calcium by promoting non-excretory removal from blood (internal skeletal clearance) rather than by increasing calcium excretion. |
