The metabolism and disposition of the oral direct thrombin inhibitor, dabigatran, in humans

Incorporating edoxaban into the choice of anticoagulants for atrial fibrillation

The non-vitamin K antagonist oral anticoagulants (NOACs) are replacing warfarin for stroke prevention in many patients with nonvalvular atrial fibrillation. Edoxaban, an oral factor Xa inhibitor, is the newest entrant in this class. Results of the Effective Anticoagulation with Factor Xa Next Generation in Atrial Fibrillation (ENGAGE AF) study demonstrate that edoxaban is noninferior to warfarin for prevention of stroke and systemic embolic events, and is associated with significantly less major bleeding, including intracranial bleeding, and reduced cardiovascular mortality. With a net clinical benefit over warfarin, edoxaban is well positioned as a choice among the NOACs, which include dabigatran, rivaroxaban, and apixaban. But how will clinicians choose amongst them? The purpose of this paper is to (a) place the ENGAGE AF trial results into context with results of the studies with the other NOACs, and (b) aid clinicians in selection of the right anticoagulant for the right atrial fibrillation patient.

BCRP/ABCG2 and high-alert medications: Biochemical, pharmacokinetic, pharmacogenetic, and clinical implications

The human breast cancer resistance protein (BCRP/ABCG2) is an ATP-binding cassette efflux transporter that uses ATP hydrolysis to expel xenobiotics from cells, including anti-cancer medications. It is expressed in the gastrointestinal tract, liver, kidney, and brain endothelium. Thus, ABCG2 functions as a tissue barrier to drug transport that strongly influences the pharmacokinetics of substrate medications. Genetic polymorphisms of ABCG2 are closely related to inter-individual variations in therapeutic performance. The common single nucleotide polymorphism c.421C>A, p.Q141K reduces cell surface expression of ABCG2 protein, resulting in lower efflux of substrates. Consequently, a higher plasma concentration of substrate is observed in patients carrying an ABCG2 c.421C>A allele. Detailed pharmacokinetic analyses have revealed that altered intestinal absorption is responsible for the distinct pharmacokinetics of ABCG2 substrates in genetic carriers of the ABCG2 c.421C>A polymorphism. Recent studies have focused on the high-alert medications among ABCG2 substrates (defined as those with high risk of adverse events), such as tyrosine kinase inhibitors (TKIs) and direct oral anti-coagulants (DOACs). For these high-alert medications, inter-individual variation may be closely related to the severity of side effects. In addition, ethnic differences in the frequency of ABCG2 c.421C>A have been reported, with markedly higher frequency in East Asian (∼30-60%) than Caucasian and African-American populations (∼5-10%). Therefore, ABCG2 polymorphisms must be considered not only in the drug development phase, but also in clinical practice. In the present review, we provide an update of basic and clinical knowledge on genetic polymorphisms of ABCG2.

Influence of proton pump inhibitors on blood dabigatran concentrations in Japanese patients with non-valvular atrial fibrillation

Background

Dabigatran is a direct thrombin inhibitor used to decrease the risk of ischemic stroke in patients with non-valvular atrial fibrillation (NVAF). Its prodrug, dabigatran etexilate (DE) is often co-administrated with a proton pump inhibitor (PPI) because of its adverse effects on the gastrointestinal tract. Drug-drug interactions between DE and PPIs in daily clinical practice have not been fully elucidated.

Methods

Changes in blood dabigatran concentration (DC) were investigated using the dilute thrombin time test in a randomized, open-label, two-period crossover study including 34 Japanese patients with NVAF receiving dabigatran therapy with or without PPI.

Results

The average trough DC was significantly higher without PPI than with PPI (83 ± 42.3 vs. 55.5 ± 24.6 ng/mL, respectively; P < 0.001). Similarly, the average peak DC was significantly higher without PPI than with PPI (184.1 ± 107.7 vs. 124 ± 59.2 ng/mL, respectively; P = 0.0029). The average ratio of DC change at the trough and peak levels did not differ significantly among the three PPI types.

Conclusions

PPI administration significantly decreased the trough and peak DCs in patients with NVAF. Therefore, when prescribing PPIs for patients with NVAF in a clinical setting, the possibility that the bioavailability of dabigatran may decrease should be considered.

Dabigatran-Induced Massive Spontaneous Hemothorax

Spontaneous hemothorax due to anticoagulant use is extremely rare in clinical practice. Dabigatran is a novel anticoagulant to prevent stroke or thromboembolic episodes in patients with nonvalvular atrial fibrillation. We report on an 83-year-old man who received dabigatran therapy (110 mg twice daily) for 7 months and developed massive spontaneous hemothorax and acute renal failure. The patient was admitted to the hospital with complaint of a dull ache in the chest and dyspnea. Chest computed tomography scan revealed massive pleural effusion in the left hemithorax with atelectasis. Acute renal failure was observed 4 days later after admission. Almost 2500 mL of blood was repeatedly drained by ultrasound-guided thoracocentesis, followed by a dramatic decrease in serum red blood cell count, hemoglobin and hematocrit. After excluding other possible causes, diagnostic withdrawal was performed for dabigatran, and plasma transfusion was conducted to supply the lost blood volume. A causal relationship was established, because the patient's renal function gradually improved and no further pleural effusion developed after dabigatran was discontinued. This is a rare case report of massive spontaneous hemothorax caused by dabigatran. Therefore, practitioners should be aware of hemothorax as a potential complication of dabigatran therapy.

Effect of direct oral anticoagulants on the risk of delayed bleeding after gastric endoscopic submucosal dissection

BACKGROUND AND AIM

Anticoagulants are used to prevent thromboembolic events. Direct oral anticoagulants (DOAC) are our new choice; however, their effect on bleeding risk for endoscopic treatment has not been reported. We aimed to assess the clinical effect of DOAC compared to warfarin for gastric endoscopic submucosal dissection (ESD).

METHODS

We retrospectively studied 97 patients on anticoagulants and treated 108 gastric neoplasms with ESD in three referral institutes. Twenty-four patients were taking DOAC, including dabigatran (12), rivaroxaban (11), and apixaban (one) and 73 were taking warfarin.

RESULTS

In the DOAC group, delayed bleeding rate was significantly higher in patients on rivaroxaban than in patients on dabigatran (45% vs 0%, P < 0.05) without relation to heparin bridge therapy (HBT). In the warfarin group, 78% of patients underwent HBT, and delayed bleeding rate was significantly higher in patients with HBT than in those without (36% vs 0%, P < 0.05). Delayed bleeding rate increased as intake of antithrombotic agents increased (P < 0.05). HBT period was shorter (P < 0.05) in DOAC because DOAC achieve the maximum effect quicker, and hospitalization period was shorter (P < 0.05), compared with warfarin. Multivariate analysis showed that HBT (OR, 10.7), rivaroxaban (OR, 6.00) and multiple antithrombotic agents (OR, 4.35) were independent delayed bleeding risk factors.

CONCLUSIONS

The DOAC effect differs in each agent. Dabigatran is a feasible alternative to warfarin for shortening the hospitalization period and decreasing delayed bleeding rate, although rivaroxaban has a significantly higher delayed bleeding risk.

Initial anticoagulation in patients with pulmonary embolism: thrombolysis, unfractionated heparin, LMWH, fondaparinux, or DOACs?

The initial treatment of haemodynamically stable patients with pulmonary embolism (PE) has dramatically changed since the introduction of low molecular weight heparins (LMWHs). With the recent discovery of the direct oral anticoagulant drugs (DOACs), initial treatment of PE will be simplified even further. In several large clinical trials it has been demonstrated that DOACs are not inferior to standard therapy for the initial treatment of PE, and because of their practicability they are becoming the agents of first choice. However, many relative contraindications to DOACs were exclusion criteria in the clinical trials. Therefore, LMWHs will continue to play an important role in initial PE treatment and in some cases there still is a role for unfractionated heparin (UFH). In this review we will give an overview of the biophysical, pharmacokinetic and pharmacodynamic properties of anticoagulants currently available for the initial management of PE. In addition, we will provide a comprehensive overview of the indications for the use of UFH, LMWHs and DOACs in the initial management of PE from a pharmacokinetic/-dynamic point of view.

The recommended dose of idarucizumab may not always be sufficient for sustained reversal of dabigatran

Essentials Reversal of anticoagulant effects of dabigatran may occur despite application of idarucizumab. Monitoring of dabigatran level after antidote application is crucial to detect rebound. Repeated doses of idarucizumab may be necessary in cases of massive dabigatran accumulation. Combination of antidote application and renal replacement therapy may offer additional benefit.

SUMMARY

Idarucizumab is a monoclonal antibody fragment designed for reversing the anticoagulant effects of dabigatran. Administration is recommended as two intravenous boluses of 2.5 g within 15 min of each other or as a single 5 g bolus. However, in certain situations a second dose of the drug could be necessary. We report the case of a 77-year-old man, treated with dabigatran for paroxysmal atrial fibrillation. He presented at our department with acute renal failure, concomitant massive dabigatran accumulation and subsequent acute gastrointestinal bleeding. Fifty minutes after the administration of idarucizumab, the dabigatran plasma concentration decreased from a peak of 1630 ng ml-1 to a level below the detection limit of 30 ng ml-1 and bleeding stopped. Eight hours after administration, the dabigatran plasma level started to increase up to 1560 ng ml-1 (96% of the maximum value obtained), accompanied by a further drop in hemoglobin. Concomitant hemodialysis and hemofiltration led to a continuous decrease in dabigatran plasma levels. However, sepsis and multiorgan failure ensued, which led to death. With this case report we raise the question of whether massive dabigatran accumulation requires repeated doses of idarucizumab, or alternatively, if the combination of antidote with hemodialysis/renal replacement therapy is advisable in order to remove circulating levels of dabigatran.

Fexofenadine, a Putative In Vivo P-glycoprotein Probe, Fails to Predict Clearance of the Substrate Tacrolimus in Renal Recipients

Whether the combined use of probe drugs for CYP3A4 and P-glycoprotein can clarify the relative contribution of these proteins to pharmacokinetic variability of a dual substrate like tacrolimus has never been assessed. Seventy renal recipients underwent simultaneous 8-h pharmacokinetic profiles for tacrolimus, the CYP3A4 probe midazolam, and the putative P-glycoprotein probe fexofenadine. Patients were genotyped for polymorphisms in CYP3A5, CYP3A4, ABCB1, ABCC2 and SLCO2B1, -1B1, and 1B3. Carriers of the ABCB1 2677G>A polymorphism displayed lower fexofenadine C_max (-66%; P = 0.012) and a trend toward higher clearance (+157%; P = 0.078). Predictors of tacrolimus clearance were CYP3A5 genotype, midazolam clearance, hematocrit, weight, and age (R² = 0.61). Fexofenadine pharmacokinetic parameters were not predictive of tacrolimus clearance. In conclusion, fexofenadine pharmacokinetics varied considerably between renal recipients but most of this variability remained unexplained, with only minor effects of genetic polymorphisms. Fexofenadine cannot be used to assess in vivo CYP3A4-P-glycoprotein interplay in tacrolimus-treated renal recipients.

Major Gastrointestinal Bleeding Often Is Caused by Occult Malignancy in Patients Receiving Warfarin or Dabigatran to Prevent Stroke and Systemic Embolism From Atrial Fibrillation

BACKGROUND & AIMS

Gastrointestinal (GI) bleeding in patients receiving anticoagulation agents can be caused by occult malignancies. We investigated the proportions and features of major GI bleeding (MGIB) events related to occult GI cancers in patients receiving anticoagulation therapy.

METHODS

We analyzed data from the Randomized Evaluation of Long Term Anticoagulant Therapy study (conducted between December 2005 and March 2009 in 951 clinical centers in 44 countries worldwide), which compared the abilities of dabigatran vs warfarin to prevent stroke and systemic embolism in 18,113 patients with atrial fibrillation. Two blinded gastroenterologists independently reviewed source documents of MGIB events (n = 595) that occurred during the study period. We collected data on MGIB events caused by previously unidentified GI malignancies, and compared characteristics of MGIB events in patients who received dabigatran vs warfarin (primary end point), and in patients with bleeding from cancer, vs patients bleeding from a nonmalignant or unidentified source.

RESULTS

Of 546 unique MGIB events, 44 (8.1%) were found to be from GI cancers (34 of 398 MGIB events in dabigatran users and 10 of 148 MGIB events in warfarin users; P = .60). Colorectal cancer accounted for 35 of 44 of all cancers identified. There were more colorectal cancer-associated MGIB events in the dabigatran group (30 of 34) than in the warfarin group (5 of 10) (P = .02), but more gastric cancer-associated MGIB events in the warfarin group (5 of 10) than in the dabigatran group (1 of 34) (P = .001). There were no differences in the short-term outcomes of cancer-related MGIB events in the dabigatran vs the warfarin group, but 75% of all cancer-related MGIB events required at least 1 blood transfusion and the mean hospital stay was 10.1 days. Compared with MGIB events from a nonmalignant or unidentified source, MGIB from cancer occurred sooner (343.0 vs 223.1 d; P = .003), but the bleeding was more likely to be chronic (for >7 d) (27.3% vs 63.6%; P < .001).

CONCLUSIONS

In evaluating data from a study of the effects of anticoagulation therapy, we found approximately 1 of every 12 MGIB events to be related to an occult cancer. Approximately two thirds of cancer-related MGIB presents with chronic bleeding, and morbidity, and resource utilization is high.

Evolving Treatments for Arterial and Venous Thrombosis: Role of the Direct Oral Anticoagulants

The direct oral anticoagulants (DOACs) represent a major advance in oral anticoagulant therapy and have replaced the vitamin K antagonists as the preferred treatment for many indications. By simplifying long-term anticoagulant therapy and improving its safety, the DOACs have the potential to reduce the global burden of thrombosis. Postmarketing studies suggest that the favorable results achieved with DOACs in the randomized controlled trials can be readily translated into practice, but highlight the need for appropriate patient, drug and dose selection, and careful follow-up. Leveraging on their success to date, ongoing studies are assessing the utility of DOACs for the prevention of thrombosis in patients with embolic stroke of unknown source, heart failure, coronary artery disease, peripheral artery disease, antiphospholipid syndrome, and cancer. The purpose of this article is to (1) review the pharmacology of the DOACs, (2) describe the advantages of the DOACs over vitamin K antagonists, (3) summarize the experience with the DOACs in established indications, (4) highlight current challenges and limitations, (5) highlight potential new indications; and (6) identify future directions for anticoagulant therapy.

Novel Anticoagulant Agents in the Perioperative Setting

An increasing number of oral anticoagulants have become available over the past decade. Each of these agents has differing implications on both regional and neuraxial anesthetic techniques. This article describes the pharmacology, pharmacokinetics, and pharmacodynamics of the most commonly used novel oral anticoagulants (NOACs). It also outlines recent guidelines for the use of NOACs in the perioperative setting, especially with regard to neuraxial anesthesia.

Gastrointestinal bleeding in patients on novel oral anticoagulants: Risk, prevention and management

Novel oral anticoagulants (NOACs), which include direct thrombin inhibitor (dabigatran) and direct factor Xa inhibitors (rivaroxaban, apixaban and edoxaban), are gaining popularity in the prevention of embolic stroke in non-valvular atrial fibrillation as well as in the prevention and treatment of venous thromboembolism. However, similar to traditional anticoagulants, NOACs have the side effects of bleeding, including gastrointestinal bleeding (GIB). Results from both randomized clinical trials and observations studies suggest that high-dose dabigatran (150 mg b.i.d), rivaroxaban and high-dose edoxaban (60 mg daily) are associated with a higher risk of GIB compared with warfarin. Other risk factors of NOAC-related GIB include concomitant use of ulcerogenic agents, older age, renal impairment, Helicobacter pylori infection and a past history of GIB. Prevention of NOAC-related GIB includes proper patient selection, using a lower dose of certain NOACs and in patients with renal impairment, correction of modifiable risk factors, and prescription of gastroprotective agents. Overt GIB can be managed by withholding NOACs followed by delayed endoscopic treatment. In severe bleeding, additional measures include administration of activated charcoal, use of specific reversal agents such as idarucizumab for dabigatran and andexanent alfa for factor Xa inhibitors, and urgent endoscopic management.

Recent progress in prodrug design strategies based on generally applicable modifications

The development of prodrugs has progressed with the aim of improving drug bioavailability by overcoming various barriers that reduce drug benefits in clinical use, such as stability, duration, water solubility, side effect profile, and taste. Many conventional drugs act as the precursors of an active agent in vivo; for example, the anti-HIV agent azidothymidine (AZT) is converted into its corresponding active triphosphate ester in the body, meaning that AZT is a prodrug in the broadest sense. However prodrug design is generally difficult owing to the lack of general versatility. Thus, these prodrugs, broadly defined, are often discovered by chance or trial-and-error. Recently, many prodrugs that could release the corresponding parent drugs with or without enzymatic action under physiological conditions have been reported. These prodrugs can be easily designed and synthesized because of their generally applicable modifications. This digest paper provides an overview of recent development in prodrug strategies for drugs with a carboxylic acid or hydroxyl/amino group on the basis of a generally applicable modification strategy, such as esterification, amidation, or benzylation.

Dental management of patients taking novel oral anticoagulants (NOAs): Dabigatran

Background

A new group of oral anticoagulants (dabigatran, rivaroxaban, apixaban and edoxaban) with clear advantages over classic dicoumarin oral anticoagulants (warfarin and acenocoumarol) has been developed in recent years. Patients being treated with oral anticoagulants are at higher risk for bleeding when undergoing dental treatments.

Material and Methods

A literature search was conducted through April 2016 for publications in the ISI Web of Knowledge, PubMed and Cochrane Library using the keywords “dabigatran”, “rivaroxaban”, “apixaban”, “edoxaban”, “new oral anticoagulants”, “novel oral anticoagulants”, “bleeding” and “dental treatment”.

Results

There is no need for regular coagulation monitoring of patients on dabigatran therapy. Whether or not to temporarily discontinue dabigatran must be assessed according to the bleeding risk involved in the dental procedure to be performed.

Conclusions

The number of patients under treatment with new oral anticoagulants will increase in the coming years. It is essential to know about the pharmacokinetics and pharmacodynamics of new oral anticoagulants and about their interactions with other drugs. It is necessary to develop clinical guidelines for the perioperative and postoperative management of these new oral anticoagulants in oral surgical procedures, and to carefully evaluate the bleeding risk of dental treatment, as well as the thrombotic risk of suppressing the new oral anticoagulant.

Key words:Dabigatran, rivaroxaban, apixaban, edoxaban, novel oral anticoagulants, bleeding.

Patient compliance with new oral anticoagulants after major orthopaedic surgery: rivaroxaban and dabigatran compared with subcutaneous injection of fondaparinux

PURPOSE

the main purpose of our study was to compare patient compliance with the orally administered new oral anticoagulants (NOCs) dabigatran and rivaroxaban compared with subcutaneously injected fondaparinux after major orthopaedic surgery, and to assess patient preference for the oral vs subcutaneous administration route.

METHODS

prophylactic antithrombotic drug therapy with dabigatran (group D; GD, n=32 patients), rivaroxaban (group R; GR, n=38 patients) or fondaparinux (group F; GF, n=30 patients), to prevent deep vein thrombosis, was started immediately after surgery in 100 patients submitted to total hip arthroplasty.

RESULTS

the patients had a mean age of 68.7±11 years and 62% were female. In GD, 87.5% of patients indicated that they preferred oral intake of medications to subcutaneous injection (12.5%). In GR, 84.2% declared a preference for oral administration over subcutaneous injection (15.8%). In GF, a surprisingly high proportion of patients (73.3%; p < 0.001) declared that they preferred subcutaneous administration of medications over the oral route (26.7%). Overall, the rate of compliance with antithrombotic drug therapy was very high, at 99%.

CONCLUSIONS

intake of the NOAs dabigatran and rivaroxaban following hospital discharge is entirely the responsibility of the patient; a high level of patient compliance with these drugs must therefore be demonstrated in order for them to become well accepted within the medical community. The results of this study showed a very high level of compliance both with orally and subcutaneously administered drugs.

LEVEL OF EVIDENCE

Level I, randomized clinical study.

Old and new oral anticoagulants: Food, herbal medicines and drug interactions

The most commonly prescribed oral anticoagulants worldwide are the vitamin K antagonists (VKAs) such as warfarin. Factors affecting the pharmacokinetics of VKAs are important because deviations from their narrow therapeutic window can result in bleedings due to over-anticoagulation or thrombosis because of under-anticoagulation. In addition to pharmacodynamic interactions (e.g., augmented bleeding risk for concomitant use of NSAIDs), interactions with drugs, foods, herbs, and over-the-counter medications may affect the risk/benefit ratio of VKAs. Direct oral anticoagulants (DOACs) including Factor Xa inhibitors (rivaroxaban, apixaban and edoxaban) and thrombin inhibitor (dabigatran) are poised to replace warfarin. Phase-3 studies and real-world evaluations have established that the safety profile of DOACs is superior to those of VKAs. However, some pharmacokinetic and pharmacodynamic interactions are expected. Herein we present a critical review of VKAs and DOACs with focus on their potential for interactions with drugs, foods, herbs and over-the-counter medications.

Paramagnetic micro-particles as a tool for rapid quantification of apixaban, dabigatran, edoxaban and rivaroxaban in human plasma by UHPLC-MS/MS

Background:

Assessment of the anticoagulant activity of direct oral anticoagulants (DOACs) is justified in special clinical situations. Here, we evaluated two independent extraction methods and developed a multi-analyte ultra-high performance liquid chromatography tandem mass (UHPLC-MS/MS) method for the quantification of apixaban, dabigatran, edoxaban and rivaroxaban in human plasma.

Methods:

Routine extraction based on protein precipitation with acetonitrile and subsequent centrifugation was compared to sample clean-up using commercial paramagnetic micro-particles and subsequent magnetic depletion. Stable isotope-labeled analogs of all analytes were employed as internal standards. The method was validated according to international guidelines in terms of linearity, precision, trueness, sensitivity, recovery and matrix effects. The performances of both extraction methods were assessed in clinical samples obtained from patients treated with either apixaban or rivaroxaban. Additionally, we report on a patient with nonadherence to rivaroxaban treatment and fulminant pulmonary embolism.

Results:

The method was linear from 2 to 500 ng/mL for all analytes, and quantification of DOACs was established within a run time of 2.0 min. Based on MS/MS analyte responses, relative matrix effects were better controlled for dabigatran after extraction with paramagnetic micro-particles. Internal standards fully compensated for recovery and matrix effects in all assays, yielding equivalent results for both methods. Apixaban and rivaroxaban concentrations determined in clinical samples after extraction with both methods were in good agreement (R

Conclusions:

A rapid and accurate multi-component UHPLC-MS/MS method for the quantification of four DOACs in human plasma was established. Paramagnetic micro-particles appear suitable for clean-up of plasma samples for LC-MS/MS-based therapeutic drug monitoring purposes.

Real life dabigatran and metabolite concentrations, focused on inter-patient variability and assay differences in patients with atrial fibrillation

Background:

Dabigatran is prescribed to increasing numbers of patients with atrial fibrillation (AF). Although routine monitoring is not considered to be useful, measuring drug concentrations can be clinically relevant in specific situations. The aim of this study was the comparison of different functional and non-functional assays for determination of dabigatran concentrations at different timepoints in a real-life patient population with AF. We focused on the differences between assays in identifying patients with low drug concentrations. Furthermore, we studied the effect of glucuronidation on the established concentration as determined with different assays.

Methods:

This study established dabigatran concentration ranges in 40 real-life AF patients by an ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) reference method and compared these with results from coagulation assays (Hemoclot dTT, LD-dTT and ECA). Samples were taken just before and 2 and 4 h after taking the drug.

Results:

A wide range of concentrations at different time points was found in this patient group. Coagulation assays correlate best with UPLC-MS/MS results that include the glucuronidated metabolites, showing that the pharmacologically active glucuronides are also measured in coagulation testing. The LD-dTT has the best agreement with UPLC-MS/MS and combines good sensitivity with high specificity. Several patients show consistently low or high drug concentrations, implying that drug exposure differs between patients.

Conclusions:

Based on the association of dabigatran concentrations with bleeding and thromboembolic risk, we believe that dabigatran monitoring could be beneficial for further optimizing anticoagulation therapy in AF.

Dabigatran overdose: a case report of acute hepatitis. Extracorporeal treatment

Dabigatran is an oral, direct thrombin inhibitor approved by international regulatory agencies for stroke prevention in patients with paroxysmal or persistent non-rheumatic atrial fibrillation (AF). The benefits of dabigatran are widely described, but its use in the geriatric population is not without risk. Chronic kidney disease is a common comorbidity with AF, and thus frequent checks of renal function in elderly patients are recommended. We report a case of dabigatran intoxication in an elderly man affected by heart failure and worsening renal function, who developed acute hepatitis and coma, which was successfully treated with continuous veno-venous hemodiafiltration. Although extracorporeal therapy has been suggested as a strategy for clearing dabigatran during acute bleeding, this approach may be useful in other dabigatran-related, life-threatening conditions, such as that described in this report.

New frontiers in anticoagulation: non vitamin-K oral anticoagulants in stroke prevention

INTRODUCTION

Non vitamin-K oral anticoagulants (NOACs) are direct and specific inhibitors of the coagulation factors IIa (dabigatran) and Xa (apixaban, rivaroxaban, edoxaban) which share many pharmacokinetic properties. However, indications are lacking regarding the use of NOACs during thrombolysis, surgery and bleeding events. Areas covered: In this paper, the authors retrospectively analyzed the relevant literature on the NOACs using the PubMed and Google Scholar databases. Expert commentary: Although warfarin is effective in cardioembolic stroke prevention, easier handling and more favorable risk-benefit profile often render NOACs a more preferable therapy choice for neurologists. New evidences have suggested their use in treatment of elderly people, in patients with renal insufficiency or with antiphospholipid antibody syndrome. In addition, the use of antidotes, which rapidly reverse the anticoagulant effect of the NOACs, could be useful in bleeding, during emergency procedures, or in case of overdose.

Estimated glomerular filtration rate calculated using different creatinine and cystatin based formulas in prediction of trough plasma Dabigtran concentration

BACKGROUND

In this paper we evaluated the relationship between trough DAB concentration with eGFR calculated using CRE and CYS based formulas.

MATERIALS AND METHODS

We considered 100 patients. eGFR was calculated using CKD-EPIcreat, CG, MDRD, CKD-EPIcys and CKD-EPIcombined equations. DAB dosage was selected on the basis of CKD-EPIcreat and relationship between trough DAB concentration and eGFRs was evaluated.

RESULTS

Trough DAB concentration roughly correlates with eGFR calculated using various formulas. CKD-EPIcreat eGFR was higher than CKD-EPIcys. In patients receiving a DAB dosage considered adequate using CKD-EPIcreat eGFR but considered excessive using CKD-EPIcys, we observed higher DAB trough concentration and an increased prevalence of subjects with drug concentration >200ng/mL.

CONCLUSION

These results suggest that eGFR alone was unable to fully explain trough DAB plasma concentration. Therefore a drug's prescription schedule based on eGFR only should be inadequate. We observed a better correlation between trough DAB concentration and CKD-EPIcys rather than CKD-EPIcreat eGFR. Thus, in patients chronically treated with DAB for thromboprophylaxis in nonvalvular atrial fibrillation evaluation of eGFR using a cystatin base formula should be considered.

Association between statin use and ischemic stroke or major hemorrhage in patients taking dabigatran for atrial fibrillation

BACKGROUND

Dabigatran etexilate is a prodrug whose absorption is opposed by intestinal P-glycoprotein and which is converted by carboxylesterase to its active form, dabigatran. Unlike other statins, simvastatin and lovastatin are potent inhibitors of P-glycoprotein and carboxylesterase, and might either increase the risk of hemorrhage with dabigatran etexilate or decrease its effectiveness.

METHODS

We conducted 2 population-based, nested case-control studies involving Ontario residents 66 years of age and older who started dabigatran etexilate between May 1, 2012, and Mar. 31, 2014. In the first study, cases were patients with ischemic stroke; in the second, cases were patients with major hemorrhage. Each case was matched with up to 4 controls by age and sex. All cases and controls received a single statin in the 60 days preceding the index date. We determined the association between each outcome and the use of simvastatin or lovastatin, relative to other statins.

RESULTS

Among 45 991 patients taking dabigatran etexilate, we identified 397 cases with ischemic stroke and 1117 cases with major hemorrhage. After multivariable adjustment, use of simvastatin or lovastatin was not associated with an increased risk of stroke (adjusted odds ratio [OR] 1.33, 95% confidence interval [CI] 0.88 to 2.01). In contrast, use of simvastatin and lovastatin were associated with a higher risk of major hemorrhage (adjusted OR 1.46, 95% CI 1.17 to 1.82).

INTERPRETATION

In patients receiving dabigatran etexilate, simvastatin and lovastatin were associated with a higher risk of major hemorrhage relative to other statins. Preferential use of the other statins should be considered in these patients.

Selecting antithrombotic therapy for patients with atrial fibrillation

When considering anticoagulant therapy for patients with atrial fibrillation, one must balance the reduction in risk of thromboembolism that this therapy offers against the risk of bleeding that it poses. The American Heart Association, American College of Cardiology, and Heart Rhythm Society updated their atrial fibrillation guidelines in 2014. This review outlines a rationale for clinical decision-making based on the new guidelines and summarizes the currently approved drugs.

Use of Direct-Acting Oral Anticoagulants in Nonagenarians: A Call for More Data

The prevalence and embolic risk of atrial fibrillation (AF) increase with age. Vitamin K antagonists (VKAs) or direct-acting oral anticoagulants (DOACs) reduce the risk of stroke or embolism. The aim of this review was to summarize the paucity of information regarding the safety and efficacy of DOACs in AF patients aged 90 years or older. The maximum age of included patients is not listed in any of the available DOAC investigating trials and registries, thus it is unclear if nonagenarians were included. Additionally, we could not find any subgroup analysis addressing this issue. There is an urgent need to collect more information on the safety and efficacy of oral anticoagulants in nonagenarians, especially regarding the role of DOACs, which are increasingly prescribed to this group of patients despite the lack of data. The best solution to this problem would be a prospective, randomized trial in this group of patients, however that would require a large investment of time, effort, and funds. In the meantime, we suggest subgroup analyses addressing the effects and safety of VKAs versus DOACs in nonagenarians, in case they have been included in previously completed or ongoing trials or registries. This could be feasible and would be desirable in view of the large amount of data already accumulated. Irrespective of age, anemia in patients receiving DOACs should be carefully investigated to rule out occult blood loss. With their known interaction profile and the possibility of monitoring these drugs, VKAs should be favored over DOACs in nonagenarians until more data are available regarding the safety of DOACs.

Characterization of the Fluorescent Spectra and Intensity of Dabigatran and Dabigatran Etexilate: Application to HPLC Analysis with Fluorescent Detection†

There is considerable interest in dabigatran etexilate (Pradaxa) and its major metabolite, dabigatran, which has been shown to be an important inhibitor of thrombin and clotting. In this study, the fluorescent excitation and emission spectra of dabigatran and dabigatran etexilate were characterized. In addition, a ultra performance liquid chromatography (UPLC) and high performance liquid chromatography (HPLC) method using fluorescent detection was developed for the analysis of dabigatran. Dabigatran and dabigatran etexilate were found to have excitation and emission maxima of 310 and 375 nm and 335 and 400 nm, respectively. UPLC analysis of dabigatran standards and plasma dabigatran samples were analyzed on a reversed phase C-18 column with methanol-water (70:30, v/v) as the mobile phase. The lower limit of quantitation for dabigatran was 10.0 ng/mL for both the standards and plasma samples. Standard curves were linear from 10.0 to 1000.0 ng/mL (R2 = 0.995). Within-day coefficient of variations of the fluorometric method at 50.0, 100.0 and 500.0 ng/mL were 1.38%, 4.83% and 2.31%, respectively. The intense fluorescent properties of dabigatran permit the sensitive and specific UPLC or HPLC fluorescent analysis of dabigatran.

Laboratory Monitoring: A Turning Point in the Use of New Oral Anticoagulants

Large clinical trials have demonstrated that new oral anticoagulants (NOACs) are at least as efficient as vitamin K antagonists (VKAs) in preventing thromboembolic events, while providing a better safety profile. The relatively stable pharmacokinetics and pharmacodynamics, the reduced reports on food and drug interactions, and the wide therapeutic windows of NOACs appear to provide a more predictable anticoagulant effect than that observed with VKAs, enabling the use of fixed doses without the need for monitoring. However, the safe implementation of NOACs may require additional judgment, and one should not have the erroneous impression that NOACs are free from interactions or that inter- and intra-individual variability is absent with NOACs. In fact, a consensus seems to have been reached concerning the usefulness of "circumstantial" testing in certain clinical scenarios. Recent data also suggest that factors such as intercurrent diseases, drug interactions, and inexplicable variability may occasionally alter the anticoagulant effect of NOACs. Furthermore, the issue of nonadherence, already high in VKA-treated patients, may represent an even greater clinical concern with NOACs, given their short half-lives. This review aims to underline the main arguments that support the need for NOAC monitoring, at least in selected categories of patients. Additionally, an overview of classic coagulation assays and novel laboratory techniques that may provide a tool for NOAC monitoring is also provided.

Atrial fibrillation management in older heart failure patients: a complex clinical problem

BACKGROUND

Atrial fibrillation (AF) and heart failure (HF), two problems of growing prevalence as a consequence of the ageing population, are associated with high morbidity, mortality, and healthcare costs. AF and HF also share common risk factors and pathophysiologic processes such as hypertension, diabetes mellitus, ischemic heart disease, and valvular heart disease often occur together. Although elderly patients with both HF and AF are affected by worse symptoms and poorer prognosis, there is a paucity of data on appropriate management of these patients.

METHODS

PubMed was searched for studies on AF and older patients using the terms atrial fibrillation, elderly, heart failure, cognitive impairment, frailty, stroke, and anticoagulants.

RESULTS

The clinical picture of HF patients with AF is complex and heterogeneous with a higher prevalence of frailty, cognitive impairment, and disability. Because of the association of mental and physical impairment to non-administration of oral anticoagulants (OACs), screening for these simple variables in clinical practice may allow better strategies for intervention in this high-risk population. Since novel direct OACs (NOACs) have a more favorable risk-benefit profile, they may be preferable to vitamin K antagonists (VKAs) in many frail elderly patients, especially those at higher risk of falls. Moreover, NOACs are simple to administer and monitor and may be associated with better adherence and safety in patients with cognitive deficits and mobility impairments.

CONCLUSIONS

Large multicenter longitudinal studies are needed to examine the effects of VKAs and NOACs on long-term cognitive function and frailty; future studies should include geriatric conditions.

The Role of Nonvitamin K Antagonist Oral Anticoagulants (NOACs) in Stroke Prevention in Patients with Atrial Fibrillation

Anticoagulation is important in stroke prevention in patients with atrial fibrillation. Until recently, heparins and vitamin K antagonists were the only available therapy for stroke reduction in atrial fibrillation (AF) patients. Non-vitamin K antagonist oral anticoagulants (NOACs) including direct thrombin inhibitor (dabigatran) and direct factor Xa inhibitors (rivaroxaban, apixaban and edoxaban) are now available and offer new options for stroke prevention. This article reviews the available data on the use of NOACs for primary and secondary stroke prevention in AF patients and describes specific patient populations to guide clinician in making the informed decision regarding appropriate use of those agents. It also addresses the use of NOACs early after acute stroke and use of thrombolysis while on NOAC.

Generation of an anti-Dabigatran Monoclonal Antibody and Its Use in a Highly Sensitive and Specific Enzyme-Linked Immunosorbent Assay for Serum Dabigatran

BACKGROUND

Dabigatran (DT) is a direct thrombin inhibitor used to prevent venous and arterial thromboembolism due to atrial fibrillation. DT is the active form of the commercially available prodrug DT etexilate. Although DT has many clinical advantages over warfarin, it increases the incidence of bleeding in patients with renal dysfunction. Circulating levels of DT are increased in such patients because it is mainly eliminated by renal excretion. Therapeutic drug monitoring may therefore help to prevent adverse DT effects, but no method for measuring circulating DT levels has been reported, except for an analysis by liquid chromatography-tandem mass spectrometry. This study sought to develop a novel enzyme-linked immunosorbent assay (ELISA) to measure DT concentrations.

METHODS

Mice were immunized with a DT-keyhole limpet hemocyanin conjugate to generate an anti-DT antibody. Immunized mouse splenocytes and myeloma cells (SP2/0) were fused to obtain an anti-DT monoclonal antibody (DT-mAb). DT-mAb and DT solutions were added to microplate wells coated with a DT-human serum albumin conjugate. DT concentrations were determined based on the principles of ELISA.

RESULTS

DT-mAb was successfully purified from a hybridoma, and the competitive ELISA developed using this DT-mAb could evaluate DT concentrations ranging from 7.8 to 125 ng/mL. The ELISA signal was not linear using DT-spiked serum; however, it was linear when serum ultrafiltrate was used. Weak cross-reactivity with DT etexilate was detected, but no cross-reactivity was observed with other structurally related drugs or drugs commonly used for the treatment of atrial fibrillation.

CONCLUSIONS

The developed competitive ELISA is a valuable and specific tool to analyze free DT in serum ultrafiltrate for therapeutic drug monitoring and pharmacokinetic studies.

Dabigatran etexilate activation is affected by the CES1 genetic polymorphism G143E (rs71647871) and gender

The oral anticoagulant prodrug dabigatran etexilate (DABE) is sequentially metabolized by intestinal carboxylesterase 2 (CES2) and hepatic carboxylesterase 1 (CES1) to form its active metabolite dabigatran (DAB). A recent genome-wide association study reported that the CES1 single nucleotide polymorphisms (SNPs) rs2244613 and rs8192935 were associated with lower DAB plasma concentrations in the Randomized Evaluation of Long-term Anticoagulation Therapy (RE-LY) study participants. In addition, gender differences in exposure to DAB were observed in clinical studies. The aim of this study was to examine the effect of CES1 genetic polymorphisms and gender on DABE activation using several in vitro approaches. The genotypes of the CES1 SNPs rs2244613, rs8192935, and the known loss-of-function CES1 variant rs71647871 (G143E), and the activation of DABE and its intermediate metabolites M1 and M2 were determined in 104 normal human liver samples. DABE, M1, and M2 activations were found to be impaired in human livers carrying the G143E variant. However, neither rs2244613 nor rs8192935 was associated with the activation in human livers. The incubation study of DABE with supernatant fractions (S9) prepared from the G143E-transfected cells showed that the G143E is a loss-of-function variant for DABE metabolism. Moreover, hepatic CES1 activity on M2 activation was significantly higher in female liver samples than male. Our data suggest that CES1 genetic variants and gender are important contributing factors to variability in DABE activation in humans. A personalized DABE treatment approach based on patient-specific CES1 genotypes and sex may have the potential to improve the efficacy and safety of DABE pharmacotherapy.

Drug-drug interactions of non-vitamin K oral anticoagulants

INTRODUCTION

The approval of non-vitamin K oral anticoagulants (NOACs) as antithrombotic alternatives to vitamin K antagonists (VKAs) has changed clinical practice. However, the efficacy and safety of the four most commonly used NOACs (dabigatran, rivaroxaban, apixaban and edoxaban) might be compromised by co-administration of other medications used for various major comorbidities. Dose adjustment of the NOACs may be needed to avert cases of concomitant medication affecting NOACs absorption, metabolism and coagulation. Areas covered: This review summarizes the current knowledge regarding drug-drug interactions of NOACs in order to guide health professionals regarding the dose modification required if the NOACs are co-administered with other medication with potential significant interactions. The data were acquired from searches of PubMed and also from the NOAC reports to the European Medicines Agency and Food and Drug Administration Agency. Expert opinion: Most of the studies in this field have been organized by pharmaceutical companies. Independent research and registries will provide more information in the near future about the drug-drug interactions of NOACs. P-glycoprotein transporter and cytochrome P450 enzyme complexes appear to be the main pathways where the most drug-drug interactions with NOACs occur.

Cytochrome P450 and Non-Cytochrome P450 Oxidative Metabolism: Contributions to the Pharmacokinetics, Safety, and Efficacy of Xenobiotics

The drug-metabolizing enzymes that contribute to the metabolism or bioactivation of a drug play a crucial role in defining the absorption, distribution, metabolism, and excretion properties of that drug. Although the overall effect of the cytochrome P450 (P450) family of drug-metabolizing enzymes in this capacity cannot be understated, advancements in the field of non-P450-mediated metabolism have garnered increasing attention in recent years. This is perhaps a direct result of our ability to systematically avoid P450 liabilities by introducing chemical moieties that are not susceptible to P450 metabolism but, as a result, may introduce key pharmacophores for other drug-metabolizing enzymes. Furthermore, the effects of both P450 and non-P450 metabolism at a drug's site of therapeutic action have also been subject to increased scrutiny. To this end, this Special Section on Emerging Novel Enzyme Pathways in Drug Metabolism will highlight a number of advancements that have recently been reported. The included articles support the important role of non-P450 enzymes in the clearance pathways of U.S. Food and Drug Administration-approved drugs over the past 10 years. Specific examples will detail recent reports of aldehyde oxidase, flavin-containing monooxygenase, and other non-P450 pathways that contribute to the metabolic, pharmacokinetic, or pharmacodynamic properties of xenobiotic compounds. Collectively, this series of articles provides additional support for the role of non-P450-mediated metabolic pathways that contribute to the absorption, distribution, metabolism, and excretion properties of current xenobiotics.