Background Prolia® (denosumab) has shown to be a safe and efficacious therapy for osteoporotic patients in numerous clinical trials. However, few studies have been performed to determine its effectiveness in real world clinical practice. Currently, best practice guidelines state that Prolia® should be administered every six months. This study explores whether deviation from this recommended subcutaneous injection course would have an impact on patient's bone mineral density (BMD).

Objectives The objective of this study is to assess if a delay in administration of Prolia will have a negative impact on the patient's BMD measured at the lumbar spine and femoral neck, measured 12 months after initiation of Prolia therapy

Methods A retrospective cohort study was conducted from August 2012 to August 2013 for all osteoporotic patients who received a minimum of two subcutaneous injections of Prolia® since May 2010. Patients who have only received their first subcutaneous injection and patients without a corresponding BMD score were excluded from the study. Data obtained included age, sex, injection history (number of days between subsequent injections), and BMD of the femoral neck and lumbar spine. Patients were classified into 3 categories: 1) subsequent injection less than five months, 2) between five to seven months, 3) more than seven months after their initial subcutaneous injection. Changes in BMD from a one-year follow-up were obtained and compared.

Results Of the study population (n=212), the baseline characteristics were: mean (SD) age 68.78±11.56 years, 91.9% female, 8.1% male. After one year of treatment, BMD scores increased in all three groups for both lumbar spine (37.79%, 15.16%, 18.09%) and femoral neck (8.77%, 5.55%, 8.77%) for patients receiving a subsequent injection less than five months, between five to seven months and more than seven months after their initial injection, respectively. The relationship between drug administration and change in BMD was found to be not statistically significant (p>0.05).

Conclusions This study suggest that the efficacy of Prolia® (denosumab), as assessed by BMD measurements at the lumbar spine and femoral neck is not affected by a delay in timing of the subsequent injection. Current best practice is to administer the drug every six months, and although we will continue to strive for this, the preliminary data that we present suggests that there is some flexibility in this timing, especially if a subsequent injection needs to be delayed. A follow-up study with a larger sample size will allow for a more indepth characterization of this relationship.

Disclosure of Interest M. Wong-Pack: None declared, A. Kalani: None declared, J. Hordyk: None declared, G. Ioannidis: None declared, R. Bensen: None declared, W. Bensen: None declared, J. Adachi Grant/research support: Amgen, Speakers bureau: Amgen, Astra Zenica, Eli Lilly, GSK, Merck, Novartis, Nycomed, Pfizer, Proctor and Gamble, Roche, Sanofi-Aventis, Wyeth, BMS, A. Lau Grant/research support: Amgen, Roche, Speakers bureau: Amgen, Roche

DOI 10.1136/annrheumdis-2014-eular.4744