Background/Purpose: Denosumab (Prolia®) has shown to be a safe and efficacious therapy for osteoporotic patients in many clinical trials. Unfortunately, few studies have explored its effectiveness in clinical practice. Currently, best practice guidelines suggest that denosumab should be administered subcutaneously every six months. However, in clinical practice, patients do not always receive subsequent denosumab as prescribed. This non-compliance may have a significant impact on the effectiveness of the drug. The objective of this study is to assess the impact that noncompliance with the regular dosing regimen has on bone mineral density (measured at the lumbar spine [LS] and femoral neck [FN]) compared to patients who receive their scheduled dosing regimen.

Methods: A retrospective cohort study was conducted from August 2012 to August 2013. We included all osteoporotic patients from a single academic center who received a minimum of two injections of denosumab with a follow-up BMD measurement since May 2010 for analysis. Patients who have only received their first subcutaneous injection and patients without a corresponding BMD score were excluded from the study. Patients were classified into 3 categories and analyzed in these groups: 1) subsequent injection less than five months, 2) between five to seven months, 3) more than seven months after their initial subcutaneous injection. Interval changes in BMD (at the LS and FN) over a 1-year follow-up period was analyzed between these three groups.

Results: Of the 924 charts examined, 436 patients met eligibility criteria. Multi-variable regression analysis was conducted comparing the change in BMD after one year of denosumab therapy at both the LS and FN for the three pre-specified groups. The group receiving an injection 7 months after their initial injection was used as a reference. The change in BMD (95% confidence interval) after one year was -0.00008 (-0.01335 to 0.01168) and 0.02073 (-0.00697 to 0.04843) for patients receiving a subsequent injection between 5-7 months later, at LS and FN respectively. The change in BMD (95% confidence interval) after one year was 0.00515 (-0.00619 to 0.01649) and 0.01474 (-0.01042 to 0.03990) for patients receiving a subsequent injection less than 5 months later, at LS and FN respectively. The relationship between the timing of drug administration and change in BMD over 1 year was not statistically significant (p>0.05).

Conclusion: This observational study proposes that the efficacy of denosumab (as measured by BMD measurements at the lumbar spine and femoral neck) has great efficacy in the treatment of osteoporosis especially when patient compliance was maintained. This emphasizes the importance of patient compliance and the need for programs available to patients to help ensure this compliance. However, in the small subset of patients who were unable to receive their subsequent denosumab injection within the 5 to 7 month window, there was no difference in BMD measurements. This suggests that although compliance is essential, a delay in a subsequent injection may be acceptable in extenuating circumstances. A follow-up study with a larger sample size and longer follow-up duration is required to further characterize this relationship.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/how-does-non-compliance-to-prolia-denosumab-impact-the-change-in-bone-mineral-density-bmd-in-osteoporotic-patients/