Study Population
This study used administrative claims data from the Truven Health MarketScan® Commercial Claims and Encounters Database and the Medicare Supplemental and Coordination of Benefits Database (Truven Health Analytics Inc., Ann Arbor, MI) [17]. The MarketScan Commercial database included claims data covering individuals enrolled in commercial health insurance plans in the United States. The Medicare Supplemental and Coordination of Benefits database provided additional data on individuals with Medicare supplemental plans. The databases provide comprehensive information on patients’ enrollment data, inpatient and outpatient claims, and outpatient pharmaceutical dispensings. The institutional review board at Emory University reviewed and approved this study and waived the need for patient consent.
In this analysis, we included individuals enrolled in the MarketScan databases between 2007 and 2015. We selected individuals with a prior diagnosis of nonvalvular AF receiving OAC therapy (either warfarin or DOAC), initiating an antidepressant after receiving OAC therapy, and having at least 180 days of continuous enrollment without antidepressant prescription filling after OAC initiation. AF patients’ OAC initiation was captured based on their first OAC prescription filling after AF diagnosis. The index date for our analysis was defined as the first antidepressant prescription filling date no less than 180 days after enrollment. AF history was defined as the presence of International Classification of Disease Ninth Revision Clinical Modification (ICD-9 CM) code 427.31 or 427.32 on any position in at least one inpatient claim or two consecutive outpatient claims, 7 days to 1 year apart, and without any inpatient history of mitral stenosis (ICD-9 CM code 394.0) or mitral valve disorders (ICD-9 CM code 424.0) [18]. This study was reviewed and approved by the Institutional Review Board at Emory University.
Oral Anticoagulant and Antidepressant Use
MarketScan outpatient pharmaceutical claims database included individual prescription filling date and the National Drug Code. Based on this information, all eligible study enrollees’ OAC (warfarin, dabigatran, rivaroxaban, apixaban) prescriptions between 2007 and 2015 were identified. We excluded all edoxaban users since it was not approved on the market by the US Food and Drug Administration until 2015.
As with the selection of OAC prescriptions, we identified all eligible patients’ antidepressant prescription information using the pharmaceutical claims data. For this analysis, we included all drugs coded under the category of antidepressants in the claims database. Antidepressants were categorized as SSRI, serotonin/norepinephrine reuptake inhibitors (SNRIs), serotonin reuptake inhibitors (SRIs), tricyclic antidepressants (TCAs), and other (tetracyclic antidepressant, alpha-2 antagonist, and dopamine/norepinephrine reuptake inhibitor). A list of generic drug names under each category is included in supplemental Table S1 (see the electronic supplementary material).
Bleeding Outcome Definition
The primary outcome of interest was the first hospitalization for hemorrhage and bleeding after initiation of antidepressant among AF patients on oral anticoagulation. Bleeding was defined by the presence of ICD-9 CM diagnostic codes for hemorrhage including organ-specific hemorrhage and all-cause bleeding, using a previously published algorithm by Fang et al. [19].
Covariates
We selected the following covariates as potential confounders for the association between antidepressant initiation and risk of bleeding: sex, age at antidepressant initiation, comorbidities (heart failure, hypertension, diabetes mellitus, myocardial infarction, peripheral arterial diseases, kidney failure, stroke, bleeding, anemia, coagulopathy, cancer, mood disorders, cognitive impairment, liver disease, chronic obstructive pulmonary disease, alcohol use), other medication use prior to index date (antiplatelet, diuretics, digoxin, lipid-lowering medications, antiarrhythmics, beta-blockers, angiotensin-converting-enzyme inhibitors, angiotensin II receptor blockers, calcium channel blockers), CHA2DS2-VASc score, and HAS-BLED score [20]. All covariate definitions were created using inpatient, outpatient, and pharmaceutical claims data. Diagnostic codes used to define comorbidities are presented in supplemental Table S2 (see the electronic supplementary material).
Statistical Analysis
Primary analyses compared the risk of bleeding hospitalization across five categories of antidepressants (TCA [reference group], SSRI, SNRI, SRI, and other) among AF patients on OAC. Follow-up time started at the time of the initial antidepressant prescription and ended when the patient had a bleeding event or disenrolled from the database. Cox proportional hazard models using time to first bleeding hospitalization as the outcome variable were used to estimate hazard ratios (HRs) and 95% confidence intervals (CIs). Regression models adjusted for all potential confounders described previously. All analyses followed an intention-to-treat approach and, therefore, did not take into consideration switching or discontinuation of the initial antidepressant regime.
We conducted additional analyses performing pairwise comparisons of all combination of SSRI, SNRI, SRI, and TCA among eligible populations after propensity-score (PS) matching. We calculated PSs for initiating a certain type of antidepressant treatment for each comparison, using logistic regression models including all previously described covariates as predictors. For each comparison, eligible patients were matched 1:1 by treatment group with a caliper of 0.2 standard deviations of the PS using the gmatch macro [21]. We did not include the “other” antidepressant category in the pairwise analyses due to the small number of antidepressant users among each sub-category within that group. We ran Cox proportional hazard models to calculate HRs and 95% CIs in PS-matched cohorts. In the full model, we adjusted for all covariates listed previously to address potential residual confounding after PS matching.
Finally, we evaluated whether associations of antidepressant type with bleeding differed by OAC treatment, age, and sex, performing stratified analyses and including multiplicative terms in the models to test for interactions. In addition, we assessed the presence of additive interaction by calculating the relative excess risk due to interaction (RERI) [22].