Cost-effectiveness of zoledronic acid vs. pamidronate in the management of hormone refractory prostate cancer (HRPC) patients with bone metastases

Abstract

14660 Background: Canadian guidelines recommend zoledronic acid (ZA) (4 mg every 3 weeks) in patients with hormone HRPC and asymptomatic or minimally symptomatic bone metastases to reduce skeletal-related events (SRE). However, IV pamidronate (90 mg every 3 weeks) (PA) is also routinely used in this setting in spite of no significant improvement in occurrence of SRE or pain compared to NT. Objectives: To assess the cost effectiveness of ZA, PA, or no bisphosphonate therapy (NT) in the management of prostate cancer patients with bone metastases in Canada. Methods: A literature-based decision analytic model was developed to estimate the incremental cost and quality-adjusted life years (QALY) associated with the 3 treatment options. The model included assumptions about SREs, mortality, drug and administration costs, cost of SREs, reduced quality of life due to SRE and bone pain, and therapy duration. Sensitivity analyses considered several scenarios in which various assumptions were used regarding treatment efficacy and QALY gains due to pain relief and SRE prevention. All costs were expressed in Canadian dollars (2004). Results: The cumulative number of SREs over a patient’s remaining lifetime (1.9 years) was estimated at 2.69 for PA and NT patients and 1.76 for ZA. Total discounted costs were $11,918 for NT, $17,593 for PA, and $19,312 for ZA. Compared with patients receiving NT or PA, quality-adjusted survival increased by 0.094 (range depending on scenario considered: 0.072 to 0.106) QALY per patient for those on ZA compared to PA or NT. Compared to NT, ZA resulted in a cost per QALY gained of $78,366 (range: $50,717 to $101,831). Compared to PA, ZA resulted in a cost per QALY gained of $18,343 (range: $2917 to $23,835) per QALY gained. PA was more expensive than NT but did not improve patient-related outcomes. Conclusions: For HRPC patients with bone metastasis, zoledronic acid appears to be the only clinically valuable and economically acceptable option in Canada with a cost effectiveness likely better than previously reported. No significant financial relationships to disclose.