Discontinuation and Nonadherence to Medications for Chronic Conditions after Hematopoietic Cell Transplantation: A 6-Year Propensity Score-Matched Cohort Study

INTRODUCTION

Hematopoietic cell transplantation (HCT) is an established curative option for patients with hematological malignancies and other life-threatening conditions. Evidence on nonpersistence and nonadherence to oral medications for chronic conditions among patients following HCT is lacking.

OBJECTIVES

This study aims to examine patterns of oral medication use for chronic conditions following HCT in the U.S.

POPULATION

METHODS

Nonpersistence and nonadherence to oral medications for diabetes, hypertension, and dyslipidemia among HCT recipients were assessed in a cohort that included 1382 autologous and 650 allogeneic HCT recipients with hematological malignancies using the Truven Health MarketScan Research Database between 2009 and 2014. Recipients of HCT were compared to propensity score-matched cancer patients receiving chemotherapy without transplantation. Multivariable Cox proportional hazards models and generalized estimating equations were used to determine characteristics associated with nonpersistence and nonadherence to oral chronic medications, respectively.

RESULTS

Recipients of HCT had higher risks of discontinuing medication for diabetes mellitus (allogeneic HCT hazard ratio [HR] = 1.93, 95% confidence interval [CI] 1.10-3.39; autologous HCT HR = 1.49, 95% CI 1.04-2.15); hypertension (allogeneic HCT HR = 1.75, 95% CI 1.21-2.53; autologous HCT HR = 1.32, 95% CI 1.07-1.62), and dyslipidemia (allogeneic HCT HR = 2.02, 95% CI 1.39-2.93; autologous HCT, HR = 1.26, 95% CI 0.98-1.61) compared to patients treated with only chemotherapy. Lower odds of adherence to antihypertensive medications (odds ratio [OR] = 0.58, 95% CI 0.38-0.89) and to lipid-lowering medications (OR = 0.38, 95% CI 0.22-0.65) were observed in allogeneic HCT recipients compared with propensity score-matched patients who underwent chemotherapy only.

CONCLUSIONS

Poor medication persistence and adherence to chronic disease medications are common after HCT. Further research to improve long-term outcomes following HCT should include management of medication therapy for chronic comorbid conditions.

High number of newly initiated direct oral anticoagulant users switch to alternate anticoagulant therapy

Real-world evidence focusing on medication switching patterns amongst direct oral anticoagulant (DOACs) has not been well studied. The objective of this study is to evaluate patterns of prescription switching in non-valvular atrial fibrillation (NVAF) patients initiated on a DOAC and previously naïve to anticoagulation (AC) therapy. Data was obtained from Truven Health MarketScan^® Commercial and Medicare Supplemental database (2009-2013). AC naïve (those without prior anticoagulant use) NVAF patients initiated on a DOAC, with 6 months of continuous health plan enrollment before and after treatment initiation and maintained on continuous therapy for a minimum of 6 months were included. Of 34,022 AC naïve NVAF patients initiating a DOAC, 6613 (19.4%) patients switched from an index DOAC prescription to an alternate anticoagulant and 27,409 (80.6%) remained on the DOAC [age: 68.5 ± 11.7 vs. 67.1 ± 12.7 years, p < 0.001; males: 3781 (57.2%) vs. 17,160 (62.6%), p < 0.001]. Amongst those that switched medication, 3196 (48.3%) did so within the first 6 months of therapy. Overall, 2945 (44.5%) patients switched to warfarin, 2912 (44.0%) switched to another DOAC and 756 (11.4%) switched to an injectable anticoagulant. The highest proportion of patients switched from dabigatran to warfarin (N = 2320; 42.5%) or rivaroxaban (N = 2252; 41.3%). The median time to switch from the index DOAC to another DOAC was 309.5 days versus 118.0 days (p < 0.001) to switch to warfarin. In NVAF patients newly initiated on DOAC therapy, one in five patients switch to an alternate anticoagulant and one of every two patients do so within the first 6 months of therapy. Switching from an initial DOAC prescription to traditional anticoagulants occurs as frequently as switching to an alternate DOAC.

Hydroxycarbamide adherence and cumulative dose associated with hospital readmission in sickle cell disease: a 6-year population-based cohort study

Sickle cell disease (SCD) is a congenital haemoglobinopathy that causes frequent acute care/emergency room visits and hospital admissions for affected individuals. Evidence from population-based studies demonstrating the role of hydroxycarbamide (HC, also termed hydroxyurea) in reducing hospital readmission rates is limited. Our objective was to describe the use of HC and its association with acute care utilization and readmission rates using a large, nationally-representative US health insurance claims database over a 6-year period between 2009 and 2014. We identified 20 721 SCD-related inpatient and acute care encounters. Patients had been exposed to HC within 6 months prior to admission in 4263 (21%) of SCD-related admission events. HC use was more common among children aged 10-17 years and young adults aged 18-29 years. HC was associated with lower 30-day all-cause readmission rates in adults treated with average daily doses ≥1 g (odds ratio [OR], 0·72, 95% confidence interval [CI] 0·52-0·99) and doses of 0·5-1 g (OR, 0·73, 95% CI 0·57-0·93), compared to HC treatment with average daily doses of <0·5 g; adherence to HC with proportion of days covered of ≥0·80 was also associated with significantly lower 30-day all-cause readmission risks (OR, 0·59, 95% CI 0·41-0·84). Optimal therapeutic dosing and adherence to HC treatment significantly reduces 30-day readmissions among patients with SCD.

A New Approach towards Minimizing the Risk of Misdosing Warfarin Initiation Doses

It is a challenge to be able to prescribe the optimal initial dose of warfarin. There have been many studies focused on an efficient strategy to determine the optimal initial dose. Numerous clinical, genetic, and environmental factors affect the warfarin dose response. In practice, it is common that the initial warfarin dose is substantially different from the stable maintenance dose, which may increase the risk of bleeding or thrombosis prior to achieving the stable maintenance dose. In order to minimize the risk of misdosing, despite popular warfarin dose prediction models in the literature which create dose predictions solely based on patients' attributes, we have taken physicians' opinions towards the initial dose into consideration. The initial doses selected by clinicians, along with other standard clinical factors, are used to determine an estimate of the difference between the initial dose and estimated maintenance dose using shrinkage methods. The selected shrinkage method was LASSO (Least Absolute Shrinkage and Selection Operator). The estimated maintenance dose was more accurate than the original initial dose, the dose predicted by a linear model without involving the clinicians initial dose, and the values predicted by the most commonly used model in the literature, the Gage clinical model.

Implementation of inpatient models of pharmacogenetics programs

PURPOSE

The operational elements essential for establishing an inpatient pharmacogenetic service are reviewed, and the role of the pharmacist in the provision of genotype-guided drug therapy in pharmacogenetics programs at three institutions is highlighted.

SUMMARY

Pharmacists are well positioned to assume important roles in facilitating the clinical use of genetic information to optimize drug therapy given their expertise in clinical pharmacology and therapeutics. Pharmacists have assumed important roles in implementing inpatient pharmacogenetics programs. This includes programs designed to incorporate genetic test results to optimize antiplatelet drug selection after percutaneous coronary intervention and personalize warfarin dosing. Pharmacist involvement occurs on many levels, including championing and leading pharmacogenetics implementation efforts, establishing clinical processes to support genotype-guided therapy, assisting the clinical staff with interpreting genetic test results and applying them to prescribing decisions, and educating other healthcare providers and patients on genomic medicine. The three inpatient pharmacogenetics programs described use reactive versus preemptive genotyping, the most feasible approach under the current third-party payment structure. All three sites also follow Clinical Pharmacogenetics Implementation Consortium guidelines for drug therapy recommendations based on genetic test results.

CONCLUSION

With the clinical emergence of pharmacogenetics into the inpatient setting, it is important that pharmacists caring for hospitalized patients are well prepared to serve as experts in interpreting and applying genetic test results to guide drug therapy decisions. Since genetic test results may not be available until after patient discharge, pharmacists practicing in the ambulatory care setting should also be prepared to assist with genotype-guided drug therapy as part of transitions in care.

All-cause and disease-related health care costs associated with recurrent venous thromboembolism

It was the objective of this study to quantify the risk of complications and the incremental health care costs associated with recurrent VTE events. Health care insurance claims from the Ingenix IMPACT database from 01/2004−09/2008 were analysed. Subjects aged ≥18 years on the date of first recurrent VTE diagnosis with ≥12 months of baseline observation prior to the index recurrent VTE were matched 1:1 with no-recurrent VTE patients based on propensity scores. The risk of developing post-thrombotic syndrome (PTS) and other disease-related diagnoses (thrombocytopenia, superficial venous thrombosis, venous ulcer, pulmonary hypertension, stasis dermatitis, and venous insufficiency) was compared between the recurrent and no-recurrent VTE groups for up to one year. All-cause and disease-related costs per patient per year (PPPY) were calculated. The recurrent VTE and no-recurrent VTE cohorts (8,001 subjects in each group) were matched with respect to age, gender, and comorbidities. The risk ratios (RRs) indicated that the risk of developing post-event complications was significantly higher for the recurrent VTE group compared to the no-recurrent VTE group (RR [95% CI]: PTS: 2.7 [2.4 − 2.9], p-value <0.01). Patients with recurrent VTE had significantly higher average PPPY all-cause costs compared to no-recurrent VTE patients ($86,744 versus $37,525, cost difference: $49,219 [€33,617]; 95% CI= 46,253−51,989). Corresponding disease-related health care costs PPPY were also significantly higher for the recurrent VTE group ($11,120 vs $1,262, cost difference: $9,858 [€6,733]; 95% CI= $9,081-$10,476). In conclusion, in this large matched-cohort study, recurrent VTE patients had significantly higher risk of complications and health care costs compared to no-recurrent VTE patients.

Note: Parts of this manuscript were presented at the American College of Clinical Pharmacy (ACCP) Annual Meeting 2012, October 21–24, Hollywood, Florida and at the International Society for Pharmacoeconomics and Outcomes Research (ISPOR) 18th Annual International Meeting 2013, May 18–22, New Orleans, LA, USA.

Multisite Investigation of Outcomes With Implementation of CYP2C19 Genotype-Guided Antiplatelet Therapy After Percutaneous Coronary Intervention

OBJECTIVES

This multicenter pragmatic investigation assessed outcomes following clinical implementation of CYP2C19 genotype-guided antiplatelet therapy after percutaneous coronary intervention (PCI).

BACKGROUND

CYP2C19 loss-of-function alleles impair clopidogrel effectiveness after PCI.

METHODS

After clinical genotyping, each institution recommended alternative antiplatelet therapy (prasugrel, ticagrelor) in PCI patients with a loss-of-function allele. Major adverse cardiovascular events (defined as myocardial infarction, stroke, or death) within 12 months of PCI were compared between patients with a loss-of-function allele prescribed clopidogrel versus alternative therapy. Risk was also compared between patients without a loss-of-function allele and loss-of-function allele carriers prescribed alternative therapy. Cox regression was performed, adjusting for group differences with inverse probability of treatment weights.

RESULTS

Among 1,815 patients, 572 (31.5%) had a loss-of-function allele. The risk for major adverse cardiovascular events was significantly higher in patients with a loss-of-function allele prescribed clopidogrel versus alternative therapy (23.4 vs. 8.7 per 100 patient-years; adjusted hazard ratio: 2.26; 95% confidence interval: 1.18 to 4.32; p = 0.013). Similar results were observed among 1,210 patients with acute coronary syndromes at the time of PCI (adjusted hazard ratio: 2.87; 95% confidence interval: 1.35 to 6.09; p = 0.013). There was no difference in major adverse cardiovascular events between patients without a loss-of-function allele and loss-of-function allele carriers prescribed alternative therapy (adjusted hazard ratio: 1.14; 95% confidence interval: 0.69 to 1.88; p = 0.60).

CONCLUSIONS

These data from real-world observations demonstrate a higher risk for cardiovascular events in patients with a CYP2C19 loss-of-function allele if clopidogrel versus alternative therapy is prescribed. A future randomized study of genotype-guided antiplatelet therapy may be of value.

Quality of Pharmacist-Managed Anticoagulation Therapy in Long-Term Ambulatory Settings: A Systematic Review

OBJECTIVE

To perform a systematic review to evaluate the quality of warfarin anticoagulation control in outpatient pharmacist-managed anticoagulation services (PMAS) compared with routine medical care (RMC).

DATA SOURCES

MEDLINE, SCOPUS, EMBASE, IPA, CINAHL, and Cochrane CENTRAL, from inception to May 2017. Search terms employed: ("pharmacist-managed" OR "pharmacist-provided" OR "pharmacist-led" OR "pharmacist-directed") AND ("anticoagulation services" OR "anticoagulation clinic" OR "anticoagulation management" OR "anticoagulant care") AND ("quality of care" OR "outcomes" OR "bleeding" OR "thromboembolism" OR "mortality" OR "hospitalization" OR "length of stay" OR "emergency department visit" OR "cost" OR "patient satisfaction").

STUDY SELECTION AND DATA EXTRACTION

Criteria used to identify selected articles: English language; original studies (comments, letters, reviews, systematic reviews, meta-analyses, editorials were excluded); warfarin use; outpatient setting; comparison group present; time in therapeutic range (TTR) included as a measure of quality of anticoagulant control; study design was not a case report.

DATA SYNTHESIS

Of 177 articles identified, 25 met inclusion criteria. Quality of anticoagulation control was better in the PMAS group compared with RMC in majority of the studies (N = 23 of 25, 92.0%). Clinical outcomes were also favorable in the PMAS group as evidenced by lower or equal risk of major bleeding (N = 10 of 12, 83.3%) or thromboembolic events (N = 9 of 10, 90.0%), and lower rates of hospitalization or emergency department visits (N = 9 of 9, 100%). When reported, PMAS have also resulted in cost-savings in all (N=6 of 6, 100%) of studies.

CONCLUSIONS

Compared with routine care, pharmacist-managed outpatient-based anticoagulation services attained better quality of anticoagulation control, lower bleeding and thromboembolic events, and resulted in lower health care utilization.

Anticoagulation Monitoring Part 1: Warfarin and Parenteral Direct Thrombin Inhibitors

OBJECTIVE:

To review the availability, mechanisms, limitations, and clinical application of point-of-care (POC) devices used in the management of warfarin and parenteral direct thrombin inhibitors.

DATA SOURCES:

Scientific articles were identified through a MEDLINE search (1966–August 2004), manufacturer Web sites, additional references listed in articles and Web sites, and abstracts from scientific meetings.

STUDY SELECTION AND DATA EXTRACTION:

English-language literature from clinical trials was reviewed to evaluate the accuracy, reliability, and clinical application of POC monitoring devices.

DATA SYNTHESIS:

The prothrombin time expressed as the international normalized ratio (PT—INR) is a well-established test for monitoring warfarin anticoagulation. Multiple devices are available for POC testing. Because there is no universally accepted standard, the performance of each device is typically tested against a standard test performed in a reference laboratory. Performance of currently available devices, as measured by correlations to a standard reference laboratory PT—INR, may be considered very good and acceptable for use in patient care. Utilization of patient self-testing and patient self-monitoring of warfarin anticoagulation using POC devices is increasing. Parenteral direct thrombin inhibitors are typically monitored using a standard laboratory activated partial thromboplastin time. Some research has shown that POC monitoring of direct thrombin inhibitors using the ecarin clotting time is helpful for patients undergoing cardiopulmonary bypass surgery, although that test is not readily available.

CONCLUSIONS:

POC testing for anticoagulation therapy has been available for >20 years. Multiple POC devices are available to monitor warfarin. There is some variability in results between devices and between reagents used in the same device. Despite these limitations, POC monitoring of warfarin via the PT—INR is an integral part of clinical practice. Additional research evaluating POC monitoring of direct thrombin inhibitors is necessary.

Anticoagulation endpoints with clinical implementation of warfarin pharmacogenetic dosing in a real-world setting: A proposal for a new pharmacogenetic dosing approach

Achieving therapeutic anticoagulation efficiently with warfarin is important to reduce thrombotic and bleeding risks and is influenced by genotype. Utilizing data from a diverse population of 257 patients who received VKORC1 and CYP2C9 genotype-guided warfarin dosing, we aimed to examine genotype-associated differences in anticoagulation endpoints and derive a novel pharmacogenetic nomogram to more optimally dose warfarin. We observed significant differences across patients with 0, 1, or ≥2 reduced-function VKORC1 or CYP2C9 alleles, respectively, in time to achieve therapeutic international normalized ratio (INR) (7.8 ± 5.8, 7.2 ± 4.7, and 5.4 ± 4.6 days, P = 0.0004) and mean percentage of time in therapeutic range in the first 28 days (22.2, 27.8, and 32.2%, P = 0.0127) with use of existing pharmacogenetic algorithms. These data suggest that more aggressive dosing is necessary for patients with 0 to 1 VKORC1/CYP2C9 variants to more efficiently achieve therapeutic anticoagulation. Herein, we provide a novel kinetic/pharmacodynamic-derived dosing nomogram optimized for a heterogeneous patient population.

Correlations between the enantio- and regio-selective metabolisms of warfarin

AIM

To clarify whether the activities of multiple CYPs associated with warfarin metabolism would be correlated with each other.

METHODS

Oral clearances (CLpo) of warfarin enantiomers were estimated in 378 Chinese, Caucasians and African-Americans. The partial metabolic clearances (CLm) for 7-hydroxywarfarin enantiomers were also measured. In addition, CLpo and CLm were determined in a patient on warfarin and rifampicin.

RESULTS

Correlations between CLpo for warfarin enantiomers existed across the three populations. In addition, there was a significant correlation between the CLm for 7-hydroxylation of warfarin enantiomers. Under induced conditions by rifampicin, there were significant correlations between the enantio- and regio-selective metabolisms of warfarin.

CONCLUSION

Metabolic activities of CYP2C9, CYP1A2 and CYP3A4 may be regulated by common transcriptional mechanism(s).

Choosing the Appropriate Antithrombotic Agent for the Prevention and Treatment of VTE: A Case-Based Approach

Objective:

To review the risk of venous thromboembolism (VTE) in various patient populations and evaluate the agents available for the prevention and treatment of VTE using a case-based approach.

Data Sources:

A MEDLINE search (1995–July 2006) was conducted to identify relevant literature. Additional references were reviewed from selected articles.

Study Selection and Data Extraction:

Articles related to the prevention of VTE in orthopedic surgery, general surgery, and medically ill patients, as well as the treatment of VTE, were reviewed.

Data Synthesis:

Pharmacologic options for the prevention and treatment of VTE include warfarin, unfractionated heparin (UFH), low-molecular-weight heparins (LMWH), and fondaparinux. Current guidelines support the use of warfarin, LMWH, or fondaparinux for VTE prophylaxis following lower limb major orthopedic surgery. For VTE prophylaxis in hospitalized medical patients or patients undergoing general surgery, use of UFH and LMWH is supported; however, recent data on fondaparinux suggest that it is also effective in these patient populations. The use of UFH or LMWH (both in conjunction with warfarin) for treatment of acute deep venous thrombosis or nonmassive pulmonary embolism is recommended. Recent data suggest that fondaparinux (in conjunction with warfarin) is also effective for the treatment of VTE. A variety of pharmacokinetic, pharmacodynamic, and pharmacoeconomic factors differentiate each agent for the various indications.

Conclusions:

Currently, a “one-size-fits-all” anticoagulant is not available for treatment of VTE. A variety of patient factors, including type of surgery, medical indication, thrombotic risk factors, bleeding risk, history of heparin-induced thrombocytopenia, and a variety of comorbid conditions can affect the safety, efficacy, and selection of appropriate VTE therapy.

Erratum to: Pharmacology of anticoagulants used in the treatment of venous thromboembolism

Anticoagulant drugs are the foundation of therapy for patients with VTE. While effective therapeutic agents, anticoagulants can also result in hemorrhage and other side effects. Thus, anticoagulant therapy selection should be guided by the risks, benefits and pharmacologic characteristics of each agent for each patient. Safe use of anticoagulants requires not only an in-depth knowledge of their pharmacologic properties but also a comprehensive approach to patient management and education. This paper will summarize the key pharmacologic properties of the anticoagulant agents used in the treatment of patients with VTE.

Upper-Extremity Deep-Vein Thrombosis: A Retrospective Cohort Evaluation of Thrombotic Risk Factors at a University Teaching Hospital Antithrombosis Clinic

BACKGROUND

Upper-extremity deep-vein thrombosis (UEDVT) causes significant morbidity and mortality and is not well characterized in the existing literature, particularly in underrepresented minorities such as African Americans.

OBJECTIVE

To describe the characteristics of a cohort of patients with UEDVT seen at an urban academic medical center.

METHODS

This was a retrospective cohort study among patients with a confirmed UEDVT at the University of Illinois Hospital and Health Sciences System between 1996 and 2011. Patients were identified by ICD-9 code for UEDVT. Variables collected include thrombotic risk factors and outcomes, including recurrent thrombosis and bleeding.

RESULTS

We identified 229 patients with UEDVT; 71% were African American, and 11% were diagnosed with sickle cell disease. The average number of UEDVT risk factors was 4.40 ± 1.5, the most common being central venous catheter (CVC) use (178, 78%). In the year following UEDVT, 13% experienced recurrent thrombosis, and 6% experienced major bleeding. Of 181 patients receiving warfarin after an UEDVT, 36% of international normalized ratio (INR) values were therapeutic. Patients with sickle cell disease had a lower proportion of INRs within the target range (25% vs 38%, P < 0.01), and were more likely to be lost to follow-up (67% vs 46%, P = 0.05) and experience a recurrent thrombotic event (29% vs 11%, P = 0.02).

CONCLUSION

A CVC is the most common risk factor for UEDVT; however, patients with sickle cell disease demonstrate additional unique demographics and risk factors. Patients included in this underrepresented demographic cohort had a low quality of anticoagulation control, particularly those with sickle cell disease.

Pharmacology of anticoagulants used in the treatment of venous thromboembolism

Anticoagulant drugs are the foundation of therapy for patients with VTE. While effective therapeutic agents, anticoagulants can also result in hemorrhage and other side effects. Thus, anticoagulant therapy selection should be guided by the risks, benefits and pharmacologic characteristics of each agent for each patient. Safe use of anticoagulants requires not only an in-depth knowledge of their pharmacologic properties but also a comprehensive approach to patient management and education. This paper will summarize the key pharmacologic properties of the anticoagulant agents used in the treatment of patients with VTE.

Factors influencing pharmacokinetics of warfarin in African-Americans: implications for pharmacogenetic dosing algorithms

AIM

This study attempted to identify predictors of S-warfarin clearance (CL[S]) and to make a pharmacokinetic evaluation of genotype-based dosing algorithms in African-Americans.

METHODS

Using plasma S-warfarin concentration (Cp[S]) at a steady state and eight SNPs previously shown to influence warfarin dose in African-Americans, CL(S) and its predictors were estimated by population pharmacokinetic analysis in 60 African-Americans. The time courses of Cp(S) following either the loading dose or maintenance dose were simulated using the population pharmacokinetic estimates.

RESULTS

CYP2C9*8 and body surface area or body weight were predictors of CL(S) (-30 and -5% per -0.1 m(2)/-10 kg reduction in CL[S], respectively) in African-Americans. Simulations of Cp(S) showed that Cp(S) at steady state was 1.4-times higher in patients with CYP2C9*8 than in those with CYP2C9*1/*1, irrespective of the algorithm for loading dose or maintenance dose.

CONCLUSION

African-Americans possess independent predictors of CL(S), possibly leading to a prediction error of any dosing algorithm that excludes African-specific variant(s). Original submitted 3 September 2014; Revision submitted 3 November 2014.

Integrating electronic health records in the delivery of optimized anticoagulation therapy

Integration of accepted practice standards into electronic health record systems can facilitate standardization of anticoagulation care delivery and result in improved anticoagulation safety. However, the majority of commonly used electronic health record systems are lacking the specialized features necessary for optimal anticoagulation management. The Task Force on Electronic Health Records of the New York State Anticoagulation Coalition provides such a Consensus Statement in this issue of the journal. The Anticoagulation Forum endorses these recommendations and advises the electronic health record industry and health information technology programmers at the institutional level to adopt these recommendations in a comprehensive and timely manner.

The evolving role of dabigatran etexilate in clinical practice

INTRODUCTION

Stroke and venous thromboembolism (VTE) affect millions of patients. The vitamin K antagonist, warfarin, has been the main oral anticoagulant used to treat these conditions despite many limitations associated with its use. Recently, multiple novel oral anticoagulants have been approved and are reshaping how patients with atrial fibrillation (AF) at risk of stroke and patients with VTE are treated. The direct thrombin inhibitor, dabigatran etexilate , is among these novel agents that have been developed to overcome limitations with warfarin.

AREAS COVERED

In this article, authors describe the pharmacokinetic and pharmacodynamic properties of dabigatran etexilate and summarize the clinical evidence and controversy surrounding its use in the US, Canada and Europe.

EXPERT OPINION

Dabigatran has demonstrated similar efficacy and safety to enoxaparin for VTE prevention in patients undergoing hip and knee arthroplasty, and to warfarin for the treatment of VTE. Dabigatran (110 mg) is noninferior and dabigatran (150 mg) is superior to warfarin for stroke prevention in patients with nonvalvular AF, with a lower rate of intracranial hemorrhage reported at both doses. Apixaban, rivaroxaban and edoxaban provide alternate anticoagulant options to dabigatran. While there are many similarities, there are also significant differences to consider in agent selection based on patient-specific characteristics.

Risk of recurrent venous thromboembolism among deep vein thrombosis and pulmonary embolism patients treated with warfarin

OBJECTIVE

Guidelines for warfarin treatment of venous thromboembolism (VTE) recommend targeting an international normalized ratio (INR) level of 2-3. This study examines the association between INR levels and VTE recurrence among warfarin-treated patients.

METHODS

A retrospective cohort study in the MedMining electronic health record database included adults treated with warfarin for VTE in 2004-2011. INR levels during warfarin use were categorized as below therapeutic range (<2), in range (2-3), or above range (>3), with time in each category estimated using the Rosendaal method. Recurrent VTE was noted from 30 days after the initial VTE to end of follow-up, which ranged up to 8 years. The incidence of recurrent VTE was calculated, and association with time-varying INR levels estimated using Cox models.

RESULTS

Of 1753 qualifying patients, 867 had deep vein thrombosis, and 886 had pulmonary embolism. Mean age was 58 years, and 50.7% were female. Across all follow-up time, VTE recurrences were observed in 134 (7.6%) patients, at a rate of 3.2 (95% confidence interval [CI]: 0.7-9.1) events per 100 person-years. The risk of VTE recurrence was greater during time spent with INR <2 than with INR in the therapeutic range (hazard ratio [HR]: 3.37; 95% CI: 2.16-5.27). Low platelet counts also predicted greater risk of VTE recurrence (HR: 2.13; 95% CI: 1.24-3.67).

LIMITATIONS

Exposure to warfarin and other anticoagulants was estimated based on prescription data and may be inaccurate. The study data include care within a single health system; thus, care received outside of the health system may be missing, and results may not be generalizable to the broader US population.

CONCLUSIONS

Approximately 8% of patients experienced a recurrent VTE during follow-up. Subtherapeutic INR levels were associated with a more than three-fold increased risk of VTE recurrence.