Persistent hypocalcemia induced by zoledronic acid in a patient with androgen-independent prostate cancer and extensive bone metastases.

Zoledronic acid is a highly potent bisphosphonate that has been shown to reduce skeletal-related events in patients with androgen-independent prostate cancer metastatic to bone. We report a patient with androgen-independent prostate cancer and extensive bone metastases. After receiving a single dose of zoledronic acid, the patient developed hypocalcemia that persisted for approximately 60 days despite intravenous and oral calcium supplementation, likely because of excess unopposed osteoblastic activity. This case underscores the need for calcium and vitamin D monitoring and supplementation to avoid bisphosphonate-induced secondary hyperparathyroidism and highlights the possibility that extensive osteoblastic metastasis alone might lead to hypocalcemia.