The relationship between osteoporosis treatment history and receipt of a second zoledronic acid dose

We examined characteristics of patients in Ontario, Canada, initiating publicly funded zoledronic acid for osteoporosis from 2006 to 2021. Most patients had prior osteoporosis treatments, with those previously using oral bisphosphonates more likely to receive a second dose. Understanding treatment decisions and patient beliefs is key for future research.

Zoledronic acid is a once-yearly intravenous bisphosphonate and is considered a second-line osteoporosis therapy in Ontario, Canada. This regimen was approved using evidence from clinical trials of treatment-naïve patients. However, many patients initiating zoledronic acid have used other osteoporosis medications prior, which may influence the frequency of dosing. We describe the characteristics of patients initiating zoledronic acid and identify if previous osteoporosis pharmacotherapy impacts the receipt of a second dose.

Healthcare administrative data in Ontario were used to identify older patients initiating publicly funded zoledronic acid from 10/2006 to 10/2021 and followed until 10/2022. Patients were categorized based on 5-year osteoporosis treatment look back history in mutually exclusive groups: (1) no history, (2) denosumab, (3) oral bisphosphonates, and (4) other osteoporosis medications. Cox proportional hazards models were used to compare receipt of a second zoledronic acid infusion between patients in treatment history groups.

We identified 3308 patients initiating zoledronic acid; median age = 77, 81% female, 31% received a second infusion of zoledronic acid. Half (49%) had a history of oral bisphosphonates, 37% no history, 11% denosumab, and 3% other medications. Overall, patients having history of oral bisphosphonates were 1.5 times more likely to receive a second dose relative to no history (HR, 95%CI: 1.50 [1.31-1.71]).

In contrast to patients in pivotal trials, most patients receiving zoledronic acid had prior osteoporosis pharmacotherapy. Patients with prior oral bisphosphonate use had higher rates of receiving a second dose. Better understanding of treatment decisions and patient beliefs around receiving a second infusion of zoledronic acid should be further investigated.