Risk factors contributing to the development of hypocalcemia after zoledronic acid administration in patients with bone metastases of solid tumor.

Zoledronic acid (ZDA) is commonly prescribed to treat and prevent skeletal complications in patients with multiple myeloma or bone metastases. Although hypocalcemia often develops by ZDA, there is little information about the risk factors for hypocalcemia mediated by ZDA. This study was conducted to assess the risk of ZDA-mediated hypocalcemia. We retrospectively reviewed the records of patients receiving ZDA in Mie University Hospital. The subjects were divided into two groups on the basis of whether hypocalcemia developed (19 patients) or not (30 patients). We compared patients' baseline characteristics between the two groups. The patients with hypocalcemia had lower albumin-adjusted serum calcium concentrations (median 9.2 mg/dl) before ZDA administration than the patients without hypocalcemia (median 9.8 mg/dl) (p< 0.01). Multivariate analysis revealed that an adjusted serum calcium concentration lower than 9.5 mg/dl before ZDA administration was an independent risk factor significantly contributing to the development of hypocalcemia (odds ratio 22.0, p< 0.01). Furthermore, the patients receiving corticosteroid had increased risk of ZDA mediated hypocalcemia (odds ratio 11.9, p<0.05). On the other hand, the patients with prostate cancer had a reduced risk for hypocalcemia after ZDA administration (odds ratio 0.06, p<0.05). In conclusion, a lower serum calcium concentration and co-administration of corticosteroid increased the risk of hypocalcemia after ZDA administration, while patients with prostate cancer might have a small risk of this incidence. These findings should provide useful information regarding the monitoring of serum calcium concentration in cancer patients receiving ZDA.