Renal safety and efficacy of intravenous bisphosphonates in patients with skeletal metastases treated for up to ten years

Introduction. Bisphosphonates (BPs) delay the onset or reduce the incidence of skeletal complications in patients with bone metastases. However, there are few data on the renal safety and activity of i.v. BPs beyond 2 years of administration. Materials and Methods. We retrospectively analyzed serum creatinine (SCr) levels and skeletal-related events (SREs) in cancer patients receiving i.v. BPs for >= 24 months. All patients received 90 mg pamidronate every 3-4 weeks. Pre- and post-treatment SCr levels and the peak levels attained were recorded. A notable SCr increase was defined as: an increase > 0.5 mg/dl for patients with baseline SCr < 1.4 mg/dl; an increase > 1 mg/dl for patients with baseline SCr > 1.4 mg/dl; or doubling over baseline. The following parameters were also analyzed: the proportion of patients with at least one SRE, the distribution of each type of SRE, the time to first SRE, and the skeletal morbidity rate (SMR). Results. Fifty-seven patients with bone metastases resulting from breast cancer (BC) (n = 48), multiple myeloma (n = 7), renal cell carcinoma (n = 1), and prostate cancer (n = 1) were evaluated. The median age at the start of treatment was 57 years (range, 27-81); 25% of the patients were > 70 years old. Forty-three patients received pamidronate then switched to zoledronic acid. The median overall duration of BP administration was 34 months (range, 24+ to 131+), with a median duration of zoledronic acid therapy of 25 months (range, 2-40). Twenty-seven of 48 BC patients received different chemotherapy regimens (median number of lines, 2; range, 1-6). The median SCr levels were: baseline, 0.82 mg/dl (range, 0.4-1.4); time of analysis, 0.89 mg/dl (0.4-2); highest level, 1.0 mg/dl (0.5-2). A notable SCr increase was observed in seven patients (12.2%; all grade 1). Twenty-six patients (45.6%) experienced SREs after starting BP treatment. The median time to first SRE was 911 days (95% confidence interval, 731; 1,023). The SMR was 0.20 events per year. Ten patients ceased treatment because of: an SCr level of 2 mg/dl (n = 1) physician decision (n = 6) and jaw osteonecrosis (n = 3). Ten patients died of progressive disease. Conclusion. i.v. BPs are safe and active during prolonged treatment administration, and renal function is maintained in patients receiving multiple cytotoxic therapies. Jaw osteonecrosis occurred in 5% of the study population, and its causal relationship with BP treatment requires further observation and study.