Study Design and Participants
This was a double-blind, randomized, active-controlled, two-armed, parallel-group, noninferiority, phase 3 study performed from April 2017 to August 2020 in 12 centers in Iran. Postmenopausal women aged between 45 and 75 years were included in the study if they had a T score of ≤ − 2.5 and ≥ − 4 at the lumbar spine (L1–L4), total hip, or femoral neck or were at high risk for fracture based on the Fracture Risk Assessment Tool (FRAX) criteria and needed medical treatment. Key exclusion criteria included conditions affecting the safety and efficacy of drugs such as malignancy, osteonecrosis of the jaw (ONJ) risk factors (e.g., diagnosis of cancer, poor oral hygiene, periodontal and/or dental diseases, having dentures, and comorbid disorders such as anemia with a hemoglobin level less than 11 g/dl, history of diseases with coagulopathy, oral and dental infections), long-lasting untreated hypocalcemia (albumin-adjusted serum calcium level less than 8 mg/dl), history of recent bisphosphonate treatment (parenteral bisphosphonates in the last 12 months, oral bisphosphonates in the last 3 months), corticosteroid treatment (> 5 mg prednisone daily or equivalent for ≥ 3 months), confined to bed (for two weeks during the past three months), and the impossibility of measuring BMD for any reason.
Other exclusion criteria were as follows: hypersensitivity to denosumab or any component of the formulation; malabsorption syndrome; history of thyroid surgery, parathyroid surgery or intestinal resection if causing malabsorption; chronic kidney disease (CKD) stage 4 or 5 (glomerular filtration rate (GFR) < 30 cc/min); 25-hydroxy vitamin D level less than 20 ng/ml (such patients could be enrolled after management of vitamin D deficiency with two tests showing blood levels above 20 ng/ml within a month); untreated hypercalciuria (> 250 mg/24 h) and hypocalciuria (< 100 mg/24 h); severe and active infections; inability to take 1000 mg elemental calcium as a supplement; conditions affecting bone turnover (e.g., hypo- or hyperparathyroidism, hypo- or hyperthyroidism, hypocalcemia, inflammatory rheumatologic diseases such as rheumatoid arthritis, Paget's disease of bone, unresponsive osteomalacia, which means not responding to 1-month administration of vitamin D); one severe (> 50% vertebral height loss) or more than two moderate (25–50% vertebral height loss) vertebral fractures; history of severe bone pain with bisphosphonates; use of parathyroid hormone or its derivatives, systemic hormone-replacement therapy, selective estrogen receptor modulator, calcitonin, or calcitriol within six weeks before study enrollment; use of heparin (more than 20,000 international units/day for ≥ 6 months prior to the study); and patients with chronic conditions such as allergies, asthma, and coagulation disorders who required to use corticosteroids (> 5 mg prednisone daily or equivalent for ≥ 3 months) or heparin (more than 20,000 international units/day for 6 months and longer) during the study period.
Written informed consent was obtained from all study patients. The study was approved by the ethics committees of Tehran University of Medical Sciences and Tabriz University of Medical Sciences. The study was registered at Clinicaltrial.gov (NCT03293108).
Randomization and Blinding
Randomization and treatment allocation occurred after primary screenings and confirmation of patients' eligibility. Randomization was carried out centrally using R-CRAN software version 3.2.3 in a 1:1 ratio, with permuted blocks with lengths of two or four. The physicians, patients, and outcome assessors were masked to treatment assignments to prevent bias.
Patients were randomly assigned to receive 60 mg of either biosimilar or reference denosumab subcutaneously every 6 months, including at baseline, month 6, and month 12. Prior to denosumab administration, vitamin D and calcium levels were corrected in patients with deficiency. All patients were supplemented with daily calcium (1000 mg of elemental calcium) and vitamin D (at least 400 IU) during the study. According to the exclusion criteria, all allowed concomitant medications were continued. Concomitant drugs were recorded at baseline and during periodic visits.
Participants underwent periodic assessments at months 0, 1, 3, 6, 9, 12, 15, and 18 of the study. The BMD of the lumbar spine (L1–L4), total hip, and femoral neck were measured by dual-energy X-ray absorptiometry (DXA) scan (Hologic 4500 or higher) at the screening and last (month 18) visits with the same device. Necessary training for BMD measurement was given to staff before the start of the trial, based on the same guideline approved by the principal investigator and careful monitoring during the trial. To ensure precision, a standard quality control program that involved training, certification, and recertification of DXA operators was implemented in all BMD measurement centers periodically. In addition, DXA devices were assessed and calibrated before and periodically during the study. The same physician and radiologist assessed lateral spine X-ray radiography (T4–L4) at the screening visit and month 18. The evaluation of bone turnover markers (BTMs), including bone-specific alkaline phosphatase (BSAP), osteocalcin (OC), procollagen type 1 N-terminal pro-peptide (P1NP), serum C-terminal telopeptide (CTX), and serum N-terminal telopeptide (NTX), was performed on fasting blood samples at baseline and during periodic visits. The immunogenicity assessment was performed by ELISA at months 0, 6, 12, and 18.
During this study, adverse events (AEs) were monitored at each scheduled visit. Any clinically significant change in physical examination, vital signs, and laboratory data of clinical interest was considered an AE. All AEs were classified based on the Medical Dictionary for Regulatory Activities (MedDRA) terms. The MedDRA terms were also used for addressing the AEs throughout this paper. All the reported events were graded according to the National Cancer Institute Common Terminology Criteria for Adverse Events (CTCAE) v5.0. The causality relation was assessed based on the World Health Organization (WHO) criteria.
Infections and infestations, eczema, ONJ, atypical femoral fracture (AFF), bone fracture, cardiovascular disorder, neoplasm benign, malignant and unspecified (including cysts and polyps), and pancreatitis acute were considered adverse events of special interest (AESIs).
The primary endpoint was the noninferiority of the biosimilar denosumab to the reference denosumab in improving the percentage change in BMD at the lumbar spine (L1–L4), total hip, and femoral neck over 18 months of the study. The secondary endpoints included the incidence of new vertebral fractures, adverse events, immunogenicity, and changes in biochemical markers of bone metabolism during the study.
The sample size was calculated using a one-sided independent sample t-test with a 2.5% significance level. A sample size of 95 patients per intervention arm was required to achieve a power of 80% to establish noninferiority for the lumbar spine (L1–L4) BMD change from baseline at month 18 by considering a drop-out rate of 10% during the trial. In one study, the efficacy of Prolia® in comparison with placebo for lumbar spine BMD improvement was reported to be 7.1%. The margin of noninferiority was set at − 1.78 based on calculation and clinical considerations. The populations were assumed to have equal standard deviations of 4.116. The biosimilar denosumab would be noninferior to the reference product if the lower limit (LL) of the 95% confidence interval (95% CI) of the between-group difference in the percent BMD change after 18 months, calculated by a two-sample t-test, was greater than the predetermined noninferiority margin of − 1.78.
To conduct sensitivity analysis for the primary endpoint (percent change in BMD), an ANCOVA model was performed considering baseline BMD values and treatment groups as covariates. The least-square means and 95% CIs were calculated based on the ANCOVA model. All primary analyses were performed using both per-protocol (PP) and intention-to-treat (ITT) sets. The missing BMD values at the 18-month timepoint were imputed based on a linear regression model including BMD and serum NTX baseline values, and patients with missing values for baseline serum NTX were not imputed in ITT analysis. The PP set was defined as all patients with no major protocol violations. The ITT set was defined as all randomized patients who received at least one dose of the study drug.
The incidence of new vertebral fractures was analyzed by the chi-square test, and the trends of the BTMs were compared with the longitudinal analysis using the GEE model (with an exchangeable working correlation matrix) adjusting corresponding values at baseline as covariates. The safety set included all randomized patients who received at least one dose of the study drug. Safety evaluation was reported as the incidence rate of AEs, and between-group differences in incidence rates were assessed by the chi-squared test. All statistical analyses were conducted using STATA version 14.0 and R Version 3.2.3 or later.
Arthritis Res Ther. 2022;24(161) © 2022 BioMed Central, Ltd.
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