Background/Purpose: Oral bisphosphonates adherence has been reported as less than 50% at one year. Adherence to denosumab has been reported to be higher than alendronate in several clinical trials. We evaluated adherence rates for denosumab, an anti-osteoporosis medication (AOM) administered in office as an injection every six months, by rheumatologists in a large healthcare system.

Methods: We identified new denosumab users using billing data between June 2010 and October 2013 based on HCPCS code J0897 or J3590 with denosumab as the listed biologic. Patients had at least 183 days (6 months) follow-up and were administratively censored at two years post-denosumab initiation, for death, or on 6/1/2014 (end of study period). These data were linked to electronic medical record data and only included patients who had at least two office visits in a rheumatology clinic. Patient characteristics were assessed prior to first administration. Adherence to denosumab was assessed with proportion of days covered (PDC) based on a 183 day coverage period (dosing interval for denosumab). After initiation, PDC was calculated at a maximum of one and two years or censored at study end. We defined a patient as adherent if they had ≥80% of days covered. Results are presented as mean (standard deviation [SD]) or %.

Results: Five hundred patients met inclusion criteria. Included patients had a mean age of 71.9 (SD 11.0), 92.6% were women, and 88.8% Caucasian. Denosumab was the first AOM in 9.8% of patients. In those with a history of previous therapy, a mean of 2.3 (SD 1.5) AOMs were prescribed. Prevalent fractures were present in 32.8%, mean Charlson Comorbidity score of 2.0 (SD 2.7), and 25% had diagnoses for either gastric ulcers or GERD at first denosumab administration. Eighty-three percent of patients had 12 months follow-up and 26% had 24 months of follow-up. Two denosumab injections were given in 82.3% of patients, 3 in 53% and 4 in 30% of patients. Of those who didn’t receive a second administration 2.6% were prescribed another AOM. Mean 1 year PDC, 85.5% (SD 19.0), and 80.7% (SD 21.6) at 2 years. PDC ≥80% was achieved in 72.8% and 62.0% of patients at 1 and 2 years, respectively.

Conclusion: In patients treated with denosumab 72.8% of patients were adherent at 12 months and 62.0% were adherent at 24 months. Only 9.8% of patients started on denosumab were treatment naïve. Adherence rates were higher than those reported for oral bisphosphonates. Other studies have suggested that higher adherence rates for denosumab may be related to in office administration, patient preference and convenience, and a favorable side effect profile. Since studies have suggested that adherence rates <50% are associated with little anti-fracture effect, the greater adherence with denosumab may have important implications for fracture prevention.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/adherence-to-denosumab-in-a-large-healthcare-system/