Hypocalcemia Following Pamidronate Administration for Bone Metastases of Solid Tumor

Bisphosphonates, such as pamidronate, are a new class of drugs, initially described for treatment of neoplasic hypercalcemia. Currently, they also may be used in the treatment of bone metastases from solid tumor, even without hypercalcemia. Hypocalcemia is a potential adverse effect of these drugs, which is considered infrequent and rarely symptomatic. We describe three cases of severe hypocalcemia following one injection of pamidronate. The three patients had bone metastases from solid tumors (breast in two cases, prostate in one), at least partially osteoblastic, and none had hypercalcemia. The induced hypocalcemia was rapid in onset, severe, and durable. The mechanism seems to be multiple and may include both the expected reduction of osteolysis and also a rapid and direct action on parathyroid glands followed by resistance to parathormone. Some elements could amplify the phenomenon, such as latent hypoparathyroidism after surgery, cervical radiotherapy, hypomagnesemia, or low 25 hydroxy vitamin D (25OH D). For patients who have such risk factors, it may be useful to check calcium several days after the first injection.