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. 2019 Nov 25;180(2):245–253. doi: 10.1001/jamainternmed.2019.5679

Association of Anticoagulant Therapy With Risk of Fracture Among Patients With Atrial Fibrillation

Pamela L Lutsey 1,✉, Faye L Norby 1, Kristine E Ensrud 1,2,3, Richard F MacLehose 1, Susan J Diem 2,3, Lin Y Chen 3, Alvaro Alonso 4
PMCID: PMC6902159  PMID: 31764956

This comparative effectiveness cohort study tests the hypothesis that use of direct anticoagulants is associated with a lower risk of fracture compared with warfarin therapy among patients with atrial fibrillation.

Key Points

Question

Are oral anticoagulants differentially associated with risk of fracture among patients with atrial fibrillation?

Findings

In this comparative effectiveness cohort study of 167 275 patients with atrial fibrillation, direct oral anticoagulants (ie, dabigatran, rivaroxaban, and apixaban) were associated with modestly lower fracture risk compared with warfarin. This protective association was more pronounced among patients with atrial fibrillation who also had a diagnosis of osteoporosis; among the direct oral anticoagulants, fracture risk was lowest among apixaban users.

Meaning

These findings add to speculation that warfarin may be harmful to bone health and suggest that direct oral anticoagulants may be preferred among patients with atrial fibrillation and high fracture risk.

Abstract

Importance

Warfarin is prescribed to patients with atrial fibrillation (AF) for the prevention of cardioembolic complications. Whether warfarin adversely affects bone health is controversial. The availability of alternate direct oral anticoagulant (DOAC) options now make it possible to evaluate the comparative safety of warfarin in association with fracture risk.

Objective

To test the hypothesis that, among patients with nonvalvular AF, use of DOACs vs warfarin is associated with lower risk of incident fracture.

Design, Setting, and Participants

This comparative effectiveness cohort study used the MarketScan administrative claims databases to identify patients with nonvalvular AF and who were prescribed oral anticoagulants from January 1, 2010, through September 30, 2015. To reduce confounding, patients were matched on age, sex, CHA2DS2-VASc (congestive heart failure, hypertension, age [>65 years = 1 point; >75 years = 2 points], diabetes, and previous stroke/transient ischemic attack [2 points], vascular disease) score, and high-dimensional propensity scores. The final analysis included 167 275 patients with AF. Data were analyzed from February 27, 2019 to September 18, 2019.

Exposures

Warfarin and DOACs (dabigatran etexilate, rivaroxaban, and apixaban).

Main Outcomes and Measures

Incident hip fracture, fracture requiring hospitalization, and all clinical fractures (identified using inpatient or outpatient claims) defined by International Classification of Diseases, Ninth Revision, Clinical Modification codes.

Results

In the study population of 167 275 patients with AF (38.0% women and 62.0% men; mean [SD] age, 68.9 [12.5] years), a total of 817 hip fractures, 2013 hospitalized fractures, and 7294 total fractures occurred during a mean (SD) follow-up of 16.9 (13.7) months. In multivariable-adjusted, propensity score–matched Cox proportional hazards regression models, relative to new users of warfarin, new users of DOACs tended to be at lower risk of fractures requiring hospitalization (hazard ratio [HR], 0.87; 95% CI, 0.79-0.96) and all clinical fractures (HR, 0.93; 95% CI, 0.88-0.98), whereas the association with hip fractures (HR, 0.91; 95% CI, 0.78-1.07) was not statistically significant. When comparing individual DOACs with warfarin, the strongest findings were for apixaban (HR for hip fracture, 0.67 [95% CI, 0.45-0.98]; HR for fractures requiring hospitalization, 0.60 [95% CI, 0.47-0.78]; and HR for all clinical fractures, 0.86 [95% CI, 0.75-0.98]). In subgroup analyses, DOACs appeared more beneficial among patients with AF who also had a diagnosis of osteoporosis than among those without a diagnosis of osteoporosis.

Conclusions and Relevance

In this real-world population of 167 275 patients with AF, use of DOACs—particularly apixaban—compared with warfarin use was associated with lower fracture risk. These associations were more pronounced among patients with a diagnosis of osteoporosis. Given the potential adverse effects of warfarin on bone health, these findings suggest that caution should be used when prescribing warfarin to patients with AF at high risk of fracture.

Introduction

An estimated 1 in 3 to 1 in 5 individuals will develop atrial fibrillation (AF) in their lifetime,1,2 and the prevalence of AF in the United States is projected to exceed 12 million by 2030.3 In addition to rhythm and/or rate control, anticoagulant therapy for the prevention of stroke and cardioembolic complications is a mainstay of nonvalvular AF management.4 Oral anticoagulant (OAC) options now include vitamin K antagonists (typically warfarin in the United States) and several direct OACs (DOACs), namely dabigatran etexilate, rivaroxaban, apixaban, and edoxaban tosylate. Direct OACs have been shown to be as effective as warfarin for the prevention of stroke and cardioembolic complications in patients with nonvalvular AF and have been associated with a lower risk of bleeding events in randomized clinical trials5,6,7,8 and large, observational comparative effectiveness studies.9,10

Concerns have been raised about whether warfarin use may be associated with impaired bone quality11 and increased fracture risk, although the existing evidence is inconsistent. This hypothesis was bolstered by a 2017 publication12 that, using a population of patients with AF from Hong Kong, reported that dabigatran was associated with a significantly lower risk of fracture compared with warfarin. However, only 32 events were reported among dabigatran users. Conversely, a 2019 meta-analysis of 4 studies13 found no difference in fracture risk between use of a DOAC vs warfarin. Likewise, findings from comparisons of warfarin users and individuals not prescribed an OAC have been inconsistent.13,14 To our knowledge, no studies have yet conducted comparisons among different DOAC users, although doing so is important15 because prescribers and patients must decide among the various OAC options.

Given present uncertainty regarding whether fracture risk differs according to type of OAC therapy and the need to optimize AF management to avoid unintended consequences and maximize quality of life, we used data from the MarketScan administrative claims databases to test the hypothesis that, among patients with nonvalvular AF, use of DOACs vs warfarin is associated with lower risk of incident clinical fracture. Head-to-head comparisons of individual DOACs were also conducted.

Methods

Study Population

We used MarketScan Commercial Claims and Encounters and MarketScan Medicare Supplemental and Coordination of Benefits databases (IBM Corporation) from January 1, 2010, through September 30, 2015. The Commercial Claims and Encounters database consists of employer- and health plan–sourced data, whereas the Medicare Supplemental and Coordination of Benefits database includes beneficiaries with Medicare supplemental insurance paid for by employers.16 Missing from these databases are individuals with no insurance, and individuals working at small companies are underrepresented. Because this is a commercially insured population, age at AF is younger than that typically seen in clinical practice. The databases contain individual-level, deidentified health care claims information compliant with the Health Insurance Portability and Accountability Act, inclusive of enrollment records and inpatient, outpatient, ancillary, and drug claims, which are linked via individual-level identifiers. The University of Minnesota institutional review board deemed this analysis exempt from review and informed consent because the data were deidentified. This comparative effectiveness cohort study followed the Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) reporting guideline.

To identify AF, we required at least 1 inpatient claim for AF or 2 outpatient claims for AF from 7 to 365 days apart (International Classification of Diseases, Ninth Revision, Clinical Modification [ICD-9-CM] codes 427.3, 427.31, and 427.32 in any position). The positive predictive value (PPV) of this definition is approximately 90%, and the sensitivity is approximately 80%.17 We excluded patients with ICD-9-CM codes indicating valvular disease or valve repair or replacement owing to the lack of approval of DOACs for valvular AF.

The initial sample included 956 884 patients with nonvalvular AF aged 18 to 99 years. The analytic sample consisted of 546 214 patients once we restricted the population to individuals receiving OACs from January 1, 2010, to September 30, 2015; 217 962 patients after requiring at least 3 months of continuous enrollment before the first OAC prescription; and 212 995 patients after excluding those with fracture codes (any fracture in any position) in the 90-day run-in period. These 212 995 patients were eligible for matching (eFigure 1 in the Supplement).

Anticoagulant Use

New users of OACs (ie, individuals without known prior exposure to OACs) were categorized according to the first OAC they were prescribed. To mimic the intention-to-treat approach of a randomized clinical trial,18 participants remained in this drug category for the entire analysis. Validity of warfarin claims in administrative databases is excellent (sensitivity, 94%; PPV, 99%).19 Validity for DOACs claims has not yet been established.

Initial Matching

We matched each DOAC new user with as many as 3 warfarin-only new users by age (±3 years), sex, time since database enrollment (±90 days), and drug initiation date (±90 days). Matching was performed separately for each DOAC by using an automated greedy matching algorithm.20 The matching process was repeated for each head-to-head DOAC comparison using 1:1 matching.

Fracture Ascertainment

Outcomes of interest were (1) hip fractures (inpatient ICD-9-CM code 820), (2) fractures requiring hospitalization (inpatient codes only), and (3) all clinical fractures (inpatient and outpatient codes). Only fractures in the primary position were counted. The all-clinical and hospitalized fracture outcomes were identified by the presence of ICD-9-CM codes 733.1x, 733.93 to 733.98, or 800 to 829. Fractures associated with E codes (E800-E848) were not included, nor were fractures of toes, fingers, and skull or face (ICD-9-CM codes 733.94, 800, 801, 802, 803, 815, 816, 817, 825, or 826).

Identification of Prespecified Covariates

Prespecified covariates were derived using information before the date of initiation of OAC therapy (minimum, 90 days) obtained from all MarketScan data sources (ie, demographic data, inpatient, outpatient, and pharmacy claims). Validated published algorithms were used to define numerous prespecified comorbidities, prior procedures, and medications (pharmacy prescription fills).21,22 Table 1 lists prespecified covariates; eTable 1 in the Supplement provides details of the codes used to derive these variables. Osteoporosis was defined by ICD-9-CM inpatient or outpatients codes 715 or 733 or by pharmacy claims indicative of osteoporosis treatment (ie, bisphosphonates [alendronate sodium, risedronate sodium, zoledronic acid, and ibandronate sodium], raloxifene hydrochloride, denosumab, and teriparatide). The CHA2DS2-VASc (congestive heart failure, hypertension, age [>65 years = 1 point; >75 years = 2 points], diabetes, and previous stroke/transient ischemic attack [2 points], vascular disease) score23 and a frailty index24 were calculated.

Table 1. Characteristics of Patients With Atrial Fibrillation by Anticoagulant Prescribeda.

Characteristic Treatment Group
Warfarin (n = 82 625) Dabigatran (n = 31 647) Rivaroxaban (n = 35 252) Apixaban (n = 17 751)
Age, mean (SD), y 70.2 (12.3) 67.0 (12.4) 67.7 (12.3) 69.1 (12.6)
Aged ≥75 y 41.1 30.3 31.7 36.6
Female 38.8 34.9 38.1 39.9
Comorbidities
Hypertension 75.5 72.5 75.7 79.6
Diabetes 33.2 27.7 28.2 30.3
Myocardial infarction 11.2 7.2 8.2 9.2
Heart failure 33.0 23.8 24.6 27.9
Ischemic stroke or TIA 22.8 17.1 17.2 19.9
Hemorrhagic stroke 1.2 0.6 0.7 0.9
PAD 18.6 12.4 13.6 15.4
Dementia 1.8 0.8 1.1 1.2
Renal disease 14.6 7.0 8.2 11.9
Chronic pulmonary disease 28.3 22.2 24.9 26.5
Liver disease 5.0 3.9 4.8 5.0
Malignant neoplasm 14.0 11.1 12.4 13.0
Depression 10.0 7.3 9.2 9.9
Hematological disorders 13.8 7.3 8.8 9.8
Metastatic cancer 2.3 1.3 1.9 1.6
Alcohol abuse 0.5 0.4 0.5 0.5
GI tract bleed 6.9 5.2 5.5 6.1
Other bleed 5.0 2.8 3.3 3.8
CHA2DS2-VASc score, mean (SD) 3.6 (2.0) 3.0 (1.9) 3.1 (1.9) 3.4 (2.0)
Osteoporosis 29.9 26.1 29.8 28.2
Previous fracture 4.3 3.4 4.0 4.2
Frailty 21.2 13.7 15.4 18.8
Frailty proportion, mean (SD)b 0.14 (0.10) 0.12 (0.09) 0.13 (0.10) 0.14 (0.10)
Prior procedures
Cardiac 69.9 66.0 67.2 67.3
Vascular 10.8 3.8 5.1 5.6
GI tract 28.6 26.1 27.0 28.5
Neurological 13.9 12.7 16.0 14.3
Medications
Digoxin 9.3 9.6 7.2 7.4
Clopidogrel 11.4 11.3 10.2 12.0
Antiplatelets 2.1 1.9 1.9 2.4
Angiotensin-converting enzyme inhibitors 32.8 31.5 30.2 32.1
Angiotensin receptor blockers 20.5 21.4 22.5 23.9
β-Blockers 56.6 59.1 58.1 63.9
Calcium channel blockers 34.3 34.7 34.9 37.8
Antiarrhythmic agents 12.9 19.1 17.0 19.1
Statins 50.1 49.1 48.6 52.1
Diabetes medications 23.6 20.8 20.2 21.8
Osteoporosis medications 5.1 5.3 4.0 3.6
Clinical fractures, No.
Hip fractures, first position 461 182 130 44
Inpatient fractures, first position 1150 447 315 101
All fractures, first position 3944 1771 1160 419
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Abbreviations: CHA2DS2-VASc, congestive heart failure, hypertension, age (>65 years = 1 point; >75 years = 2 points), diabetes, and previous stroke/transient ischemic attack (2 points), vascular disease; GI, gastrointestinal; PAD, peripheral arterial disease; TIA, transient ischemic attack.

a

Analytic sample is matched initially on age (±3 years), sex, time since database enrollment (±90 days), and drug initiation date (±90 days) and again on high-dimensional propensity score. Data are from the MarketScan Commercial Claims and Encounters and Medicare Supplemental and Coordination of Benefits databases from January 1, 2010, through September 30, 2015. Unless otherwise indicated, data are expressed as percentage of patients.

b

Number of frailty components divided by 27, with higher scores indicating greater frailty.

Creation of High-Dimensional Propensity Scores and Rematching

Separate high-dimensional propensity scores (HDPS)25 were calculated for each of the 6 main comparisons (individual DOACs vs warfarin or vs other DOACs) using the following steps25:

  1. MarketScan information was categorized into 5 domains: inpatient diagnostic codes, inpatient procedure codes, outpatient diagnostic codes, outpatient procedure codes, and medications. Within each domain, we selected the 200 most prevalent conditions, resulting in 1000 covariates.

  2. Covariates were then empirically ranked based on their potential for controlling confounding (ie, strength of the covariate-outcome association and prevalence of the covariate).26 The top 500 covariates were selected based on this ordering.

  3. The 500 covariates along with the prespecified covariates (also listed in Table 1) were included in a regression model to calculate the probability of exposure (ie, receiving a specific DOAC vs warfarin or the reference DOAC).

As noted above, for the purpose of defining an index date and collecting covariate information at the time of initiation of drug therapy, we initially matched OAC users by age, sex, enrollment date, and OAC therapy initiation date. After computing the HDPSs, we rematched patients according to each outcome-specific HDPS to make the participant characteristics even more similar at the time of therapy initiation. A greedy matching technique with a caliper of 0.25 SD of each HDPS was used,20 with patients matched with 1 comparison patient (ie, users of warfarin or the reference DOAC).

Statistical Analysis

Data were analyzed from February 27, 2019 to September 18, 2019. Cox proportional hazards regression was used to compare the OACs according to risk of incident fracture. Follow-up began at the date of the first OAC prescription, and person-time accrued until incident fracture, health plan disenrollment (including due to death), or the end of study follow-up (September 30, 2015), whichever came first. Models were adjusted for age (continuous), sex, CHA2DS2-VASc score, HDPS, and frailty. Separate models also compared DOACs by dosage. Multiplicative interactions were evaluated by sex, age (<75 vs ≥75 years), and whether the claims indicated a diagnosis of osteoporosis (yes vs no). The Cox proportional hazards regression assumption was checked using Schoenfeld residuals, and there was no evidence of violations.

Sensitivity analyses were also conducted by (1) adjusting for prevalent fracture (claims indicating fracture before the 90-day run-in period), (2) adjusting for diagnosis of osteoporosis, (3) excluding those with any prevalent fracture, (4) requiring at least 180 days (compared with 90 days in the primary analysis) of continuous enrollment before the first OAC prescription, and (5) censoring participants on evidence of nonadherence (ie, a gap in prescription refills). E values were also calculated to gauge the likelihood that unmeasured confounding explained our findings.27,28 Statistical analyses were performed with SAS, version 9.3 (SAS Institute Inc).

Results

Among the 212 995 patients with AF eligible for initial matching, a total of 167 275 patients were matched (38.0% women and 62.0% men; mean [SD] age, 68.9 [12.5] years), initially and by HDPS, and are included in the present analysis (eFigure 1 in the Supplement). Of these, 18.9% were prescribed dabigatran; 21.1%, rivaroxaban; 10.6%, apixaban; and 49.4%, warfarin. Table 1 displays characteristics of these matched participants by OAC initially prescribed. Individuals prescribed warfarin (mean [SD] age, 70.2 [12.3] years) and apixaban (mean [SD] age, 69.1 [12.6] years) tended to be older than patients prescribed dabigatran (mean [SD] age, 67.0 [12.4] years) and rivaroxaban (mean [SD] age, 67.7 [12.3] years). The mean (SD) CHA2DS2-VASC scores followed a similar pattern: 3.6 (2.0) for warfarin, 3.4 (2.0) for apixaban, 3.0 (1.9) for dabigatran, and 3.1 (1.9) for rivaroxaban.

During a mean (SD) follow-up of 16.9 (13.7) months, 817 hip fractures, 2013 fractures requiring hospitalization, and 7294 clinical fractures occurred. The incidence per 1000 person-years was 3.7 for hip fracture, 9.3 for hospitalized fracture, and 35.7 for any clinical fracture. Adjusted hazard ratios (HRs) and 95% CIs for incident fracture according to DOACs vs warfarin are shown in Table 2. Relative to warfarin, being prescribed a DOAC was generally associated with lower risk of fractures requiring hospitalization (HR, 0.87; 95% CI, 0.79-0.96), all clinical fractures (HR, 0.93; 95% CI, 0.88-0.98), and hip fractures (HR, 0.91; 95% CI, 0.78-1.07). When comparing dabigatran with warfarin, there was some evidence of lower risk of fractures requiring hospitalization with dabigatran (HR, 0.88; 95% CI, 0.78-1.00), although for hip and all clinical fractures, the estimates were near the null. Rivaroxaban use compared with warfarin use was associated with lower risk of fractures requiring hospitalization (HR, 0.80; 95% CI, 0.69-0.93) and all clinical fractures (HR, 0.82; 95% CI, 0.76-0.89), although the estimate for hip fractures (HR, 0.89; 95% CI, 0.71-1.12) was not statistically significant. Apixaban use was associated with lower risk of all fracture outcomes compared with warfarin, including hip fractures (HR, 0.67; 95% CI, 0.45-0.98), fractures requiring hospitalization (HR, 0.60; 95% CI, 0.47-0.78), and all clinical fractures (HR, 0.86; 95% CI, 0.75-0.98). These findings were robust to a number of sensitivity analyses, including adjusting for prevalent fracture, adjusting for the diagnosis of osteoporosis, excluding those with prevalent fracture, and requiring a 6-month run-in (eTable 2 in the Supplement). Likewise, findings were similar when we censored participants at evidence of nonadherence; with a mean (SD) follow-up of 7.1 (8.0) months, there were 220 hip fractures, 525 fractures requiring hospitalization, and 2232 clinical fractures. The HRs for DOAC users vs matched warfarin users were 0.91 (95% CI, 0.70-1.19) for hip fracture, 0.81 (95% CI, 0.69-0.97) for inpatient fracture, and 0.91 (95% CI, 0.84-0.99) for all fractures.

Table 2. Adjusted HRs for Incident Fracture Comparing New Users of DOACs vs Warfarin Among Patients With Nonvalvular Atrial Fibrillationa.

Outcomes by Prescribed DOAC No. of Events HR (95% CI)b P Value
DOAC Users Matched Warfarin Users
Any DOACc
Hip fractures, first position 293 312 0.91 (0.78-1.07) .27
Inpatient fractures, first position 697 791 0.87 (0.79-0.96) .007
All fractures, first position 2685 2829 0.93 (0.88-0.98) .009
Dabigatrand
Hip fractures, first position 182 186 0.98 (0.80-1.20) .86
Inpatient fractures, first position 447 510 0.88 (0.78-1.00) .06
All fractures, first position 1764 1803 0.96 (0.90-1.03) .23
Rivaroxabane
Hip fractures, first position 128 170 0.89 (0.71-1.12) .33
Inpatient fractures, first position 307 445 0.80 (0.69-0.93) .003
All fractures, first position 1124 1493 0.82 (0.76-0.89) <.001
Apixabanf
Hip fractures, first position 41 70 0.67 (0.45-0.98) .04
Inpatient fractures, first position 92 174 0.60 (0.47-0.78) <.001
All fractures, first position 396 521 0.86 (0.75-0.98) .02
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Abbreviations: DOAC, direct oral anticoagulant; HR, hazard ratio.

a

Data are from the MarketScan Commercial Claims and Encounters and Medicare Supplemental and Coordination of Benefits databases from January 1, 2010, through September 30, 2015.

b

Adjusted for age, sex, CHA2DS2-VASc (congestive heart failure, hypertension, age [>65 years = 1 point; >75 years = 2 points], diabetes, and previous stroke/transient ischemic attack [2 points], vascular disease) score, high-dimensional propensity score, and frailty.

c

Compares 55 826 DOAC users and 55 826 warfarin users.

d

Compares 31 612 dabigatran users and 31 612 warfarin users.

e

Compares 32 440 rivaroxaban users and 32 440 warfarin users.

f

Compares 15 645 apixaban users and 15 645 warfarin users.

In analyses stratified by subgroups of interest (Figure 1 and eTable 3 in the Supplement), risk of hip fracture associated with DOAC use was lower among patients with AF who had claims indicating an osteoporosis diagnosis (HR, 0.74; 95% CI, 0.58-0.96) compared with those without osteoporosis (HR, 1.06; 95% CI, 0.86-1.30) (P = .03 for interaction). This finding was similar when evaluating fractures requiring hospitalization (HR for no osteoporosis, 0.97 [95% CI, 0.85-1.11]; HR for osteoporosis, 0.75 [95% CI, 0.64-0.88]; P = .59 for interaction) (Figure 2 and eTable 3 in the Supplement). Although interactions were not always significant, some evidence suggested that the lower risk associated with DOAC use was more pronounced in women than in men. Subgroup analyses for the all clinical fractures outcome are provided in eTable 3 and eFigure 2 in the Supplement. Table 3 provides head-to-head comparisons of the specific DOACs associated with fracture risk. Little evidence suggested that fracture risk varied according to type of DOAC prescribed.

Figure 1. Adjusted Hazard Ratios (HRs) for Incident Hip Fracture Among Matched Direct Oral Anticoagulant (DOAC) Users.

Figure 1.

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Patients were identified by initial oral anticoagulant therapy for the treatment of atrial fibrillation and stratified by subgroups of interest from the MarketScan Commercial Claims and Encounters and Medicare Supplemental and Coordination of Benefits databases from January 1, 2010, through September 30, 2015. Models were adjusted for age, sex, CHA2DS2-VASc (congestive heart failure, hypertension, age [>65 years = 1 point; >75 years = 2 points], diabetes, and previous stroke/transient ischemic attack [2 points], vascular disease) score, high-dimensional propensity score, and frailty.

Figure 2. Adjusted Hazard Ratios (HRs) for Incident Hospitalized Fracture Among Matched Direct Oral Anticoagulant (DOAC) Users.

Figure 2.

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Patients were identified by initial oral anticoagulant therapy for the treatment of atrial fibrillation and stratified by subgroups of interest from the MarketScan Commercial Claims and Encounters and Medicare Supplemental and Coordination of Benefits databases from January 1, 2010, through September 30, 2015. Models were adjusted for age, sex, CHA2DS2-VASc (congestive heart failure, hypertension, age [>65 years = 1 point; >75 years = 2 points], diabetes, and previous stroke/transient ischemic attack [2 points], vascular disease) score, high-dimensional propensity score, and frailty.

Table 3. Adjusted HRs for Incident Fracture Comparing New Users of DOACs Among Patients With Nonvalvular Atrial Fibrillationa.

Outcomes by Comparison of DOACs No. of Events HR (95% CI)b P Value
DOAC Users Matched DOAC Users
Dabigatran vs matched rivaroxaban usersc
Hip fractures, first position 48 54 0.88 (0.60-1.30) .52
Inpatient fractures, first position 121 140 0.87 (0.68-1.11) .25
All fractures, first position 543 510 1.08 (0.95-1.22) .24
Apixaban vs matched rivaroxaban usersd
Hip fractures, first position 41 42 0.98 (0.63-1.50) .91
Inpatient fractures, first position 96 116 0.82 (0.62-1.08) .15
All fractures, first position 394 401 0.99 (0.86-1.13) .84
Apixaban vs matched dabigatran userse
Hip fractures, first position 17 18 0.95 (0.49-1.86) .88
Inpatient fractures, first position 42 38 1.06 (0.68-1.65) .80
All fractures, first position 160 153 1.05 (0.84-1.31) .66
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Abbreviations: DOAC, direct oral anticoagulant; HR, hazard ratio.

a

Data are from the MarketScan Commercial Claims and Encounters and Medicare Supplemental and Coordination of Benefits databases from January 1, 2010, through September 30, 2015.

b

Adjusted for age, sex, CHA2DS2-VASc (congestive heart failure, hypertension, age [>65 years = 1 point; >75 years = 2 points], diabetes, and previous stroke/transient ischemic attack [2 points], vascular disease) score, high-dimensional propensity score, and frailty.

c

Includes 12 572 users of each drug.

d

Includes 16 621 users of each drug.

e

Includes 5112 users of each drug.

Precision was poorer for analyses comparing the association of different DOAC doses and warfarin with fracture risk (eTable 4 in the Supplement). Nevertheless, we found some evidence of dose response, whereby risk (vs warfarin) was lower for standard doses than for reduced doses of rivaroxaban. For example, the standard dose of rivaroxaban (20 mg) had an HR of 0.78 (95% CI, 0.58-1.05), while for the 15 mg dose, the HR was 1.02 (95% CI, 0.74-1.40).

E values were calculated to evaluate how strong unmeasured confounding would have to be to negate the observed results. For the association of DOACs vs warfarin with fractures requiring hospitalization, the E value was 1.56, indicating that residual confounding could explain the observed association if an unmeasured covariate had a relative risk association at least as large as 1.56 with OAC choice (DOACs vs warfarin) and fractures requiring hospitalization. For all clinical fractures and hip fractures, the E values were 1.36 and 1.43, respectively. To put these results in context, in a model adjusted for Table 1 covariates, hypertension was associated with an HR for fracture of 0.79 (95% CI, 0.69-0.91), diabetes with an HR for fracture of 1.16 (95% CI, 1.02-1.31), and ischemic stroke with an HR for fracture of 1.09 (95% CI, 0.92-1.28). Even established risk factors for fracture, such as dementia (HR, 1.43; 95% CI, 1.08-1.91), had an association weaker than the E value, although the upper limit of the confidence interval exceeds the E value.

Discussion

Use of the DOACs, and particularly apixaban, was associated with lower incidence of clinical fracture relative to warfarin in this retrospective analysis of patients with AF who had health care insurance coverage. Although the lower risk in DOAC users vs warfarin users did not reach statistical significance for the outcome of hip fracture, precision was poorer for this outcome. In general, associations were more pronounced among patients with AF with a diagnosis of osteoporosis relative to those without. The strongest effect estimates were observed when comparing apixaban and warfarin; this finding was not hypothesized and, as such, warrants further scrutiny. We found no apparent differences in fracture risk in head-to-head DOAC comparisons. Collectively, our findings support the notion that warfarin may be harmful to bone health.

Speculation that long-term warfarin use might increase fracture risk stems from warfarin’s role as a vitamin K antagonist.29 Vitamin K is important in posttranslational glutamination of osteocalcin, the major noncollagenous bone matrix protein. Warfarin interferes with this process and consequently inhibits the activation of bone matrix proteins.30 Experimental rat models31 and observational human studies32,33 have suggested that warfarin reduces blood osteocalcin levels and may impair bone quality. Few studies have directly compared the effects of DOACs vs warfarin on indicators of bone health. Switching from warfarin to rivaroxaban was associated with an increase in bone formation markers and a decrease in bone resorption markers in a study of 21 patients with AF.11 An animal study also found dabigatran to be advantageous over warfarin on numerous markers of bone health.34

Our findings that warfarin is associated with greater fracture risk relative to DOACs is consistent with the evaluation of patients with AF from Hong Kong12 that showed greater fracture risk with use of warfarin than dabigatran. Conversely, a smaller study of patients with AF in the Florence, Italy, metropolitan area35 identified no difference in fracture risk by OAC. In post hoc analysis of the Effective Anticoagulation With Factor Xa Next Generation in Atrial Fibrillation–Thrombolysis in Myocardial Infarction 48 trial,36 findings suggested that edoxaban vs warfarin lowered fracture risk (HR, 0.88; 95% CI, 0.75-1.03) among participants at increased risk of falls but not among those at low fall risk. The present findings enhance the current literature in that we had far more fracture events among DOAC users (ie, 356 hip, 863 requiring hospitalization, and 3350 all clinical) than previous analyses and therefore reasonable precision to evaluate subgroups of interest.

Head-to-head DOAC comparisons yielded no statistically significant differences in fracture risk, although findings suggested that apixaban was the most advantageous. The lack of robust association in comparisons of DOACs is not surprising given the hypothesis that warfarin has a detrimental effect on bone health and the lack of known pathways by which DOACs may influence bone metabolism. To our knowledge, no previous studies have yet evaluated head-to-head comparisons of DOACs and fracture risk.

The hypothesis that warfarin is deleterious to bone health is not without controversy. Comparisons of warfarin users with individuals not prescribed an OAC have provided inconsistent results,14 with some studies reporting a link between warfarin and fracture37,38 and others showing no association.13,39,40 An alternate hypothesis is that perhaps instead of warfarin being harmful, DOACs may be beneficial. Although the mechanism is unclear, DOACs may influence the likelihood of fracture by reducing fall risk.12,15,36

Our findings were robust to numerous sensitivity analyses, including when censoring at evidence of nonadherence, which is important given high OAC discontinuation rates among patients with AF.41 Some evidence suggests a dose-response association, although this effect may be due to uncontrolled confounding because patients prescribed reduced doses tend to be older and have more comorbidities.4 In subgroup analyses, a significant interaction occurred whereby DOACs were more beneficial among participants with diagnosed osteoporosis than those without. Differential effects of DOACs by osteoporosis status were not expected and should be evaluated in independent populations.

Strengths and Limitations

Strengths of the present analysis are the novel head-to-head DOAC comparisons, the large sample of patients with AF who had insurance coverage and consequent relatively large number of fracture events, and evaluation of the risks associated with these OACs in a real-world population that may be more generalizable across patients with AF and health care professionals than a randomized clinical trial population. Uncontrolled confounding is a chief potential limitation; as such, we used a multipronged approach to minimize confounding (ie, initially matching on key patient characteristics, creating and then rematching on empirically derived HDPS, and finally adjusting for the HDPS and other key patient characteristics). Misclassification is also an important consideration. Unfortunately, we were unable to locate a fracture definition that had been validated in a US population. As such, our definition was based on codes identified in a Taiwanese validation study (PPV, 100% for hip fracture, 86% for vertebral fracture, 100% for wrist and forearm fracture, and 100% for humerus fracture)12 and expert opinion. Last, edoxaban was not included in the present analysis because there were few users in our database.

Conclusions

Optimizing care of patients with AF is paramount. In the present study, use of DOACs, and particularly apixaban, was associated with lower fracture risk than use of warfarin. Furthermore, some evidence suggested that this association was more pronounced among patients with AF who had a diagnosis of osteoporosis. Given the detrimental effects of fracture in the elderly,42,43,44 caution should be used when prescribing warfarin to patients with AF at elevated fracture risk.

Supplement.

eFigure 1. Exclusions Flowchart

eFigure 2. Adjusted Hazard Ratios (95% Confidence Intervals) of Incident Fracture, According to Initial Oral Anticoagulant Therapy for the Treatment of Patients With Atrial Fibrillation, Stratified by Subgroups of Interest

eTable 1. ICD-9-CM Codes Used to Define Comorbidities

eTable 2. Sensitivity Analyses Evaluating the Association Between DOACs vs Warfarin on Risk of Hip and Inpatient Fractures Among Patients With Atrial Fibrillation Patients

eTable 3. Adjusted Hazard Ratios (95% Confidence Intervals) for Incident Fracture Comparing New Users of Oral Anticoagulants Among Patients With Nonvalvular AF

eTable 4. Adjusted Hazard Ratios (95% Confidence Intervals) for Incident Fracture Comparing New Users of Oral Anticoagulants by Dose of Direct Oral Anticoagulant to Warfarin, Among Patients With Nonvalvular AF

Click here for additional data file. (268.3KB, pdf)

References

  • 1.Weng L-C, Preis SR, Hulme OL, et al. . Genetic predisposition, clinical risk factor burden, and lifetime risk of atrial fibrillation. Circulation. 2018;137(10):1027-1038. doi: 10.1161/CIRCULATIONAHA.117.031431 [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 2.Mou L, Norby FL, Chen LY, et al. . Lifetime risk of atrial fibrillation by race and socioeconomic status: ARIC study (Atherosclerosis Risk in Communities). Circ Arrhythm Electrophysiol. 2018;11(7):e006350. doi: 10.1161/CIRCEP.118.006350 [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 3.Colilla S, Crow A, Petkun W, Singer DE, Simon T, Liu X. Estimates of current and future incidence and prevalence of atrial fibrillation in the US adult population. Am J Cardiol. 2013;112(8):1142-1147. doi: 10.1016/j.amjcard.2013.05.063 [DOI] [PubMed] [Google Scholar]
  • 4.January CT, Wann LS, Alpert JS, et al. ; American College of Cardiology/American Heart Association Task Force on Practice Guidelines . 2014 AHA/ACC/HRS guideline for the management of patients with atrial fibrillation: a report of the American College of Cardiology/American Heart Association Task Force on Practice Guidelines and the Heart Rhythm Society. J Am Coll Cardiol. 2014;64(21):e1-e76. doi: 10.1016/j.jacc.2014.03.022 [DOI] [PubMed] [Google Scholar]
  • 5.Connolly SJ, Ezekowitz MD, Yusuf S, et al. ; RE-LY Steering Committee and Investigators . Dabigatran versus warfarin in patients with atrial fibrillation. N Engl J Med. 2009;361(12):1139-1151. doi: 10.1056/NEJMoa0905561 [DOI] [PubMed] [Google Scholar]
  • 6.Patel MR, Mahaffey KW, Garg J, et al. ; ROCKET AF Investigators . Rivaroxaban versus warfarin in nonvalvular atrial fibrillation. N Engl J Med. 2011;365(10):883-891. doi: 10.1056/NEJMoa1009638 [DOI] [PubMed] [Google Scholar]
  • 7.Granger CB, Alexander JH, McMurray JJV, et al. ; ARISTOTLE Committees and Investigators . Apixaban versus warfarin in patients with atrial fibrillation. N Engl J Med. 2011;365(11):981-992. doi: 10.1056/NEJMoa1107039 [DOI] [PubMed] [Google Scholar]
  • 8.Giugliano RP, Ruff CT, Braunwald E, et al. ; ENGAGE AF-TIMI 48 Investigators . Edoxaban versus warfarin in patients with atrial fibrillation. N Engl J Med. 2013;369(22):2093-2104. doi: 10.1056/NEJMoa1310907 [DOI] [PubMed] [Google Scholar]
  • 9.Bengtson LGS, Lutsey PL, Chen LY, MacLehose RF, Alonso A. Comparative effectiveness of dabigatran and rivaroxaban versus warfarin for the treatment of non-valvular atrial fibrillation. J Cardiol. 2017;69(6):868-876. doi: 10.1016/j.jjcc.2016.08.010 [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 10.Norby FL, Bengtson LGS, Lutsey PL, et al. . Comparative effectiveness of rivaroxaban versus warfarin or dabigatran for the treatment of patients with non-valvular atrial fibrillation. BMC Cardiovasc Disord. 2017;17(1):238. doi: 10.1186/s12872-017-0672-5 [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 11.Namba S, Yamaoka-Tojo M, Kakizaki R, et al. . Effects on bone metabolism markers and arterial stiffness by switching to rivaroxaban from warfarin in patients with atrial fibrillation. Heart Vessels. 2017;32(8):977-982. doi: 10.1007/s00380-017-0950-2 [DOI] [PubMed] [Google Scholar]
  • 12.Lau WC, Chan EW, Cheung CL, et al. . Association between dabigatran vs warfarin and risk of osteoporotic fractures among patients with nonvalvular atrial fibrillation. JAMA. 2017;317(11):1151-1158. doi: 10.1001/jama.2017.1363 [DOI] [PubMed] [Google Scholar]
  • 13.Fiordellisi W, White K, Schweizer M. A systematic review and meta-analysis of the association between vitamin K antagonist use and fracture. J Gen Intern Med. 2019;34(2):304-311. doi: 10.1007/s11606-018-4758-2 [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 14.Veronese N, Bano G, Bertozzo G, et al. . Vitamin K antagonists’ use and fracture risk: results from a systematic review and meta-analysis. J Thromb Haemost. 2015;13(9):1665-1675. doi: 10.1111/jth.13052 [DOI] [PubMed] [Google Scholar]
  • 15.Sugiyama T. Osteoporotic fractures associated with dabigatran vs warfarin. JAMA. 2017;318(1):90-91. doi: 10.1001/jama.2017.6908 [DOI] [PubMed] [Google Scholar]
  • 16.IBM Watson Health IBM MarketScan research databases for health services researchers (white paper). https://www.ibm.com/downloads/cas/6KNYVVQ2. Published April 2019. Accessed May 2, 2019.
  • 17.Jensen PN, Johnson K, Floyd J, Heckbert SR, Carnahan R, Dublin S. A systematic review of validated methods for identifying atrial fibrillation using administrative data. Pharmacoepidemiol Drug Saf. 2012;21(suppl 1):141-147. doi: 10.1002/pds.2317 [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 18.Hernán MA, Alonso A, Logan R, et al. . Observational studies analyzed like randomized experiments: an application to postmenopausal hormone therapy and coronary heart disease. Epidemiology. 2008;19(6):766-779. doi: 10.1097/EDE.0b013e3181875e61 [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 19.Garg RK, Glazer NL, Wiggins KL, et al. . Ascertainment of warfarin and aspirin use by medical record review compared with automated pharmacy data. Pharmacoepidemiol Drug Saf. 2011;20(3):313-316. doi: 10.1002/pds.2041 [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 20.Division of Biomedical Statistics and Informatics, Mayo Clinic Research. Biomedical Statistics and Informatics [computer program]. http://bioinformaticstools.mayo.edu/research/gmatch/. Updated July 23, 2018. Accessed August 1, 2019.
  • 21.Cunningham A, Stein CM, Chung CP, Daugherty JR, Smalley WE, Ray WA. An automated database case definition for serious bleeding related to oral anticoagulant use. Pharmacoepidemiol Drug Saf. 2011;20(6):560-566. doi: 10.1002/pds.2109 [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 22.Quan H, Sundararajan V, Halfon P, et al. . Coding algorithms for defining comorbidities in ICD-9-CM and ICD-10 administrative data. Med Care. 2005;43(11):1130-1139. doi: 10.1097/01.mlr.0000182534.19832.83 [DOI] [PubMed] [Google Scholar]
  • 23.Lip GY, Nieuwlaat R, Pisters R, Lane DA, Crijns HJ. Refining clinical risk stratification for predicting stroke and thromboembolism in atrial fibrillation using a novel risk factor-based approach: the Euro Heart Survey on atrial fibrillation. Chest. 2010;137(2):263-272. doi: 10.1378/chest.09-1584 [DOI] [PubMed] [Google Scholar]
  • 24.Kim DH, Schneeweiss S. Measuring frailty using claims data for pharmacoepidemiologic studies of mortality in older adults: evidence and recommendations. Pharmacoepidemiol Drug Saf. 2014;23(9):891-901. doi: 10.1002/pds.3674 [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 25.Schneeweiss S, Rassen JA, Glynn RJ, Avorn J, Mogun H, Brookhart MA. High-dimensional propensity score adjustment in studies of treatment effects using health care claims data. Epidemiology. 2009;20(4):512-522. doi: 10.1097/EDE.0b013e3181a663cc [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 26.Bross ID. Spurious effects from an extraneous variable. J Chronic Dis. 1966;19(6):637-647. doi: 10.1016/0021-9681(66)90062-2 [DOI] [PubMed] [Google Scholar]
  • 27.VanderWeele TJ, Ding P. Sensitivity analysis in observational research: introducing the E-value. Ann Intern Med. 2017;167(4):268-274. doi: 10.7326/M16-2607 [DOI] [PubMed] [Google Scholar]
  • 28.Mathur MB, Ding P, Riddell CA, VanderWeele TJ. Web Site and R package for computing E-values. Epidemiology. 2018;29(5):e45-e47. doi: 10.1097/EDE.0000000000000864 [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 29.Watts NB. Adverse bone effects of medications used to treat non-skeletal disorders. Osteoporos Int. 2017;28(10):2741-2746. doi: 10.1007/s00198-017-4171-4 [DOI] [PubMed] [Google Scholar]
  • 30.Sugiyama T, Kugimiya F, Kono S, Kim YT, Oda H. Warfarin use and fracture risk: an evidence-based mechanistic insight. Osteoporos Int. 2015;26(3):1231-1232. doi: 10.1007/s00198-014-2912-1 [DOI] [PubMed] [Google Scholar]
  • 31.Sugiyama T, Takaki T, Sakanaka K, et al. . Warfarin-induced impairment of cortical bone material quality and compensatory adaptation of cortical bone structure to mechanical stimuli. J Endocrinol. 2007;194(1):213-222. doi: 10.1677/JOE-07-0119 [DOI] [PubMed] [Google Scholar]
  • 32.Rey-Sanchez P, Lavado-Garcia JM, Canal-Macias ML, Rodriguez-Dominguez MT, Bote-Mohedano JL, Pedrera-Zamorano JD. Ultrasound bone mass in patients undergoing chronic therapy with oral anticoagulants. J Bone Miner Metab. 2011;29(5):546-551. doi: 10.1007/s00774-010-0250-8 [DOI] [PubMed] [Google Scholar]
  • 33.Namba S, Yamaoka-Tojo M, Hashikata T, et al. . Long-term warfarin therapy and biomarkers for osteoporosis and atherosclerosis. BBA Clin. 2015;4:76-80. doi: 10.1016/j.bbacli.2015.08.002 [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 34.Fusaro M, Dalle Carbonare L, Dusso A, et al. . Differential effects of dabigatran and warfarin on bone volume and structure in rats with normal renal function. PLoS One. 2015;10(8):e0133847. doi: 10.1371/journal.pone.0133847 [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 35.Lucenteforte E, Bettiol A, Lombardi N, Mugelli A, Vannacci A. Risk of bone fractures among users of oral anticoagulants: an administrative database cohort study. Eur J Intern Med. 2017;44:e30-e31. doi: 10.1016/j.ejim.2017.07.022 [DOI] [PubMed] [Google Scholar]
  • 36.Steffel J, Giugliano RP, Braunwald E, et al. . Edoxaban versus warfarin in atrial fibrillation patients at risk of falling: ENGAGE AF-TIMI 48 analysis. J Am Coll Cardiol. 2016;68(11):1169-1178. doi: 10.1016/j.jacc.2016.06.034 [DOI] [PubMed] [Google Scholar]
  • 37.Gage BF, Birman-Deych E, Radford MJ, Nilasena DS, Binder EF. Risk of osteoporotic fracture in elderly patients taking warfarin: results from the National Registry of Atrial Fibrillation 2. Arch Intern Med. 2006;166(2):241-246. doi: 10.1001/archinte.166.2.241 [DOI] [PubMed] [Google Scholar]
  • 38.Rejnmark L, Vestergaard P, Mosekilde L. Fracture risk in users of oral anticoagulants: a nationwide case-control study. Int J Cardiol. 2007;118(3):338-344. doi: 10.1016/j.ijcard.2006.07.022 [DOI] [PubMed] [Google Scholar]
  • 39.Mamdani M, Upshur REG, Anderson G, Bartle BR, Laupacis A. Warfarin therapy and risk of hip fracture among elderly patients. Pharmacotherapy. 2003;23(1):1-4. doi: 10.1592/phco.23.1.1.31922 [DOI] [PubMed] [Google Scholar]
  • 40.Misra D, Zhang Y, Peloquin C, Choi HK, Kiel DP, Neogi T. Incident long-term warfarin use and risk of osteoporotic fractures: propensity-score matched cohort of elders with new onset atrial fibrillation. Osteoporos Int. 2014;25(6):1677-1684. doi: 10.1007/s00198-014-2662-0 [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 41.Zalesak M, Siu K, Francis K, et al. . Higher persistence in newly diagnosed nonvalvular atrial fibrillation patients treated with dabigatran versus warfarin. Circ Cardiovasc Qual Outcomes. 2013;6(5):567-574. doi: 10.1161/CIRCOUTCOMES.113.000192 [DOI] [PubMed] [Google Scholar]
  • 42.Cummings SR, Melton LJ. Epidemiology and outcomes of osteoporotic fractures. Lancet. 2002;359(9319):1761-1767. doi: 10.1016/S0140-6736(02)08657-9 [DOI] [PubMed] [Google Scholar]
  • 43.Rachner TD, Khosla S, Hofbauer LC. Osteoporosis: now and the future. Lancet. 2011;377(9773):1276-1287. doi: 10.1016/S0140-6736(10)62349-5 [DOI] [PMC free article] [PubMed] [Google Scholar]
  • 44.Virnig B, Durham SB, Folsom AR, Cerhan J. Linking the Iowa Women’s Health Study cohort to Medicare data: linkage results and application to hip fracture. Am J Epidemiol. 2010;172(3):327-333. doi: 10.1093/aje/kwq111 [DOI] [PMC free article] [PubMed] [Google Scholar]

Associated Data

This section collects any data citations, data availability statements, or supplementary materials included in this article.

Supplementary Materials

Supplement.

eFigure 1. Exclusions Flowchart

eFigure 2. Adjusted Hazard Ratios (95% Confidence Intervals) of Incident Fracture, According to Initial Oral Anticoagulant Therapy for the Treatment of Patients With Atrial Fibrillation, Stratified by Subgroups of Interest

eTable 1. ICD-9-CM Codes Used to Define Comorbidities

eTable 2. Sensitivity Analyses Evaluating the Association Between DOACs vs Warfarin on Risk of Hip and Inpatient Fractures Among Patients With Atrial Fibrillation Patients

eTable 3. Adjusted Hazard Ratios (95% Confidence Intervals) for Incident Fracture Comparing New Users of Oral Anticoagulants Among Patients With Nonvalvular AF

eTable 4. Adjusted Hazard Ratios (95% Confidence Intervals) for Incident Fracture Comparing New Users of Oral Anticoagulants by Dose of Direct Oral Anticoagulant to Warfarin, Among Patients With Nonvalvular AF

Click here for additional data file. (268.3KB, pdf)

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