Outcomes of patients with prostate cancer receiving zoledronic acid or pamidronate for prevention of skeletal-related events.

Study Objective: To determine the relative effectiveness of two bisphosphonates--pamidronate and zoledronic acid--for preventing skeletal-related events (SREs) in patients with prostate cancer metastatic to bone.

Design: Retrospective cohort study.

Setting: Large, tertiary care cancer center.

Patients: One hundred thirty-seven patients with a diagnosis of prostate cancer who received either pamidronate or zoledronic acid between January 1, 1998, and December 31, 2004, were identified in the electronic medical records; 24 of these patients met all prespecified eligibility criteria, and 105 patients met relaxed eligibility criteria.

Measurements And Main Results: Using a binary logistic regression model, we explored the effect of the bisphosphonate received on development of an SRE. Whether the patient was receiving chemotherapy as of the date of first receipt of a study drug, the number of bisphosphonate doses received, time since the diagnosis of prostate cancer, and the number of previous SREs were included as covariates. The odds ratio for developing an SRE after receiving zoledronic acid was 0.80 (95% confidence interval 0.08-7.50) compared with the reference group that received pamidronate. This difference did not reach statistical significance (p=0.84). Because of the limited number of patients who met all prespecified eligibility criteria, various post hoc analyses were performed in the 105 patients with use of relaxed eligibility criteria. None provided definitive evidence of the superiority of one agent versus the other.

Conclusion: No definitive evidence of a difference in the efficacy for preventing the development of an SRE was found between pamidronate and zoledronic acid, although a smaller-than-expected sample size impairs the interpretability of this finding. In the absence of additional research, it seems reasonable to assume that no clinically important difference exists between the two agents.