Prescriptions for vitamin D among patients taking antiresorptive agents in Canada

Abstract

Background: Data on the rate of concomitant vitamin D use with antiresorptive medications are limited. Such information is important because vitamin D is indicated in patients with osteoporosis, including those receiving bisphosphonates, and there is evidence of inadequate use by these patients.

Objective: To examine prescription vitamin D utilization patterns.

Research design and methods: A retrospective analysis of patients aged > or = 65 years was conducted in a Canadian pharmacy-insurance organization (RAMQ) who received at least one prescription for an antiresorptive agent (i.e., alendronate, risedronate, raloxifene) from January 1, 1996, through December 31, 2003, and did not switch to any other agent during the 1-year post period. Data on prescriptions of vitamin D formulations on the RAMQ formulary (e.g., alfacalcidol, calcitriol, cholecalciferol, doxercalciferol, ergocalciferol) were also captured. No data on generic or over-the-counter vitamin D preparations were available. A vitamin D and antiresorptive agent possession ratio (R(P)) was computed as: R(P) = SigmaD(SPVD) / SigmaD(SARR) where SigmaD(SPVD) = the sum of the days of supply with prescription vitamin D and SigmaD(SARR) = the sum of days of supply with alendronate, risedronate, or raloxifene A vitamin D and antiresorptive agent overlap ratio (R(0)) was computed as: R(0) = SigmaD(SPVDOARR) / SigmaD(SARR) where SigmaD(SPVDOARR) = the sum of days of supply of prescription vitamin D overlapping with alendronate, risedronate, or raloxifene, and SigmaD(SARR) = the sum of the days of supply with alendronate, risedronate, or raloxifene.

Results: A total of 46,226 antiresorptive treatment users were identified, > 90% of whom were women. A total of 17,151 (37.1%) had concomitant vitamin D prescriptions. The average duration of prescription therapy with alendronate, risedronate, or raloxifene was 247 days; and the mean duration of prescription vitamin D therapy was 83 days. Patients had a supply of vitamin D for 55% of days of antiresorptive agents therapy (R(P) = 0.55) and a vitamin D supply overlapping with 24% of their days on antiresorptive agents (R(o) = 0.24). Possession and overlap ratios were significantly higher in patients receiving once-weekly bisphosphonate prescriptions compared with once-daily regimens (bisphosphonates or raloxifene). Vitamin D prescriptions were also significantly more likely in patients receiving prescriptions for once-weekly bisphosphonates (odds ratio (OR) = 4.65; 95% CI = 4.29-5.05; p < 0.0001) and once-daily bisphosphonates (OR = 1.91; 95% CI = 1.76-2.07; p < 0.0001) compared with once-daily raloxifene.

Conclusions: Despite the benefits of vitamin D for osteoporosis, most patients ( approximately 63%) receiving prescriptions for antiresorptive agents were not taking vitamin D, indicating a substantial treatment gap. The study is limited by including data only on (1) pharmacy claims, which do not equate to patient behaviors, such as filling or refilling prescriptions and/or taking the medications; and (2) prescription (but not generic or over-the-counter) vitamin D formulations.