Risk of Skeletal-Related Events in Patients with Advanced Prostate Cancer Treated with Pamidronate or Zoledronic Acid

BACKGROUND: Pamidronate and zoledronic acid are used for the prevention of skeletal-related events (SREs) in patients with advanced solid tumors, particularly breast and prostate cancers. There have been no head-to-head clinical trials comparing pamidronate and zoledronic acid among patients with advanced prostate cancer. OBJECTIVE: To estimate the risk of developing an SRE among men with metastatic prostate cancer after being treated with either pamidronate or zoledronic acid. METHODS: A retrospective cohort study was conducted, using data from Kaiser Permanente's Southern California Region. The cohort included men aged >= 18 years diagnosed with prostate cancer from 1998 to 2004 who received at least 1 infusion of either pamidronate or zoledronic acid after their cancer diagnosis. Patients receiving both drugs and those with a documented SRE prior to diagnosis were excluded. The primary outcome of SREs was defined using diagnosis codes for fractures, spinal cord compression, radiation to bone, and hypercalcemia of malignancy. Secondary outcomes were deterioration in renal function, based on serum creatinine laboratory results, and mortality. Multivariate logistic regression was used to predict SREs and mortality risk for pamidronate compared to zoledronic acid. The proportion of patients with renal function deterioration was analyzed using chi(2) tests. RESULTS: The cohort included 118 patients treated with pamidronate and 274 treated with zoledronic acid. Results showed no significant difference in risk of SREs for pamidronate versus zoledronic acid (OR 0.99; 95% Cl 0.59 to 1.67; p = 0.98). No significant difference was found in renal function deterioration (chi(2) 2.08; p = 0.15) or mortality (OR 0.71; 95% Cl 0.43 to 1.17; p = 0.18). CONCLUSIONS: For patients with prostate cancer, the choice between these 2 bisphosphonates must be balanced between the shorter infusion time of zoledronic acid versus its increased costs. We found no evidence for a difference in outcomes; therefore, pamidronate is an effective choice where clinic capacity permits.