Apixaban plasma concentrations in patients with obesity.

PURPOSE: Routine therapeutic drug monitoring of apixaban is currently not recommended but may however be warranted in some situations and for some patient groups to provide better and safer treatment. Due to limited data on apixaban concentrations in different subpopulations, it is still unclear which group of patients could possibly gain from monitoring. The purpose of this study was to examine apixaban exposure in patients with obesity compared with normal-weight patients. METHODS: Forty patients with obesity (mean BMI 39.4 kg/m2) and 40 controls with normal weight (mean BMI 23.4 kg/m2), treated with apixaban 5 mg twice daily were included. The patients were matched for age, sex, and renal function. Trough and peak apixaban concentrations were measured with LC‒MS/MS methodology. RESULTS: The median trough concentrations in patients with obesity (58.7, range 10.7-200.7 ng/ml) were slightly higher than those in patients with normal weight (52.0, range 31.0-150.9 ng/ml) (p < 0.05). Notably, the variability in trough concentration was considerably higher in patients with obesity. Peak concentrations were similar in both groups, with a median of 124.5 ng/ml (range 82.0-277.5) and 113.5 ng/ml (range 75.5-334.6) in patients with obesity and normal weight, respectively. CONCLUSION: Apixaban exposure did not vary substantially between obese and normal weight matched controls, implying that general dose adjustments are not required. However, vast interindividual variability was observed in patients with obesity, suggesting that measuring the concentrations could be valuable for specific patients. Further research is needed to identify which specific patients may benefit from this approach.

Platelets fine-tune effector responses of naïve CD4+ T cells via platelet factor 4-regulated transforming growth factor ß signaling.

BACKGROUND AND AIM: Platelets are an able regulator of CD4+ T cell immunity. Herein, the mechanisms underlying platelet-regulated effector responses of naïve CD4+ T (Tn) cells were investigated. METHODS: Platelet-Tn cell co-cultures of human cells, genetically modified murine models, and high-throughput bioinformatic analyses were combined to elucidate molecular mechanisms of platelet-dependent regulation. RESULTS: Platelets exerted sophisticated regulation on effector responses of type 1, 2, and 17 T helper (Th1/Th2/Th17) and regulatory T (Treg) cells, in time-, concentration-, and organ-dependent manners and with close cooperation of transforming growth factor ß (TGFß) and platelet factor 4 (PF4). PF4 at low concentrations reinforced TGFß signaling by heteromerizing with type III TGFß receptor (TGFBRIII), and subsequently enhanced TGFBRII expression and TGFß signaling. High-concentration PF4 had, however, opposite effects by directly binding to TGFBRII, blocking TGFß-TGFBRII ligation, and thus inhibiting TGFß signaling. Furthermore, platelet depletion markedly hampered Treg and Th17 responses in the spleen but not in the lymph nodes, blockade of platelet-Tn cell contact diminished platelet effects, while spleen injection of PF4-immobilized microparticles in PF4-deficient mice mimicked platelet effects, suggesting the importance of direct platelet-Tn contact and platelet-bound PF4 for the optimal regulatory effects by platelets. CONCLUSION: Platelets exert context-dependent regulations on effector responses of Tn cells via PF4-TGFß duet, suggesting new possibilities of platelet-targeted interventions of T cell immunity.

Platelets enhance CD4+ central memory T cell responses via platelet factor 4-dependent mitochondrial biogenesis and cell proliferation.

Platelets regulate multiple aspects of CD4+ T cell immunity, and may exert distinct regulations among different T cell subsets. Our aim was to investigate how platelets regulate CD4+ central memory T cell (Tcm) responses. αCD3/αCD28-stimulated human CD4+ Tcm cells were cultured without or with platelets or platelet-derived mediators. Polyclonal stimulation induced cell proliferation and Th1 and Treg cell activation of Tcm cells. Platelet factor 4/PF4 neutralization abolished platelet-enhanced Tcm effector responses, whilst TGFß neutralization only partially inhibited platelet-enhanced Treg cell activation. PF4 supplementation mimicked the effects of platelet co-cultures, while PF4 receptor CXCR3 blockade and CXCR3 knockdown with siRNAs inhibited or abolished PF4-enhanced Th1 and Treg cell responses. Platelet co-cultures or PF4-treatment increased Tcm cell proliferation, whilst CXCR3 blockade counteracted. PF4-enhanced Tcm proliferation and effector cell responses were associated with mitochondrial biogenesis. Overexpression of mitochondrial transcription factor A (TFAM) mimicked PF4 effects, and PF4 treatment attenuated Akt phosphorylation of activated Tcm cells, leading to mitochondrial biogenesis. Impacts of platelets and PF4 on Tcm proliferation were further confirmed by that CXCR3 knockdown/blockade counteracted PF4-enhanced Tcm cell proliferation. In conclusion, platelets enhance Th1 and Treg cell responses of CD4+ Tcm cells, via PF4-dependent mitochondrial biogenesis and cell proliferation of Tcm cells.

Bleeding and thromboembolism due to drug-drug interactions with non-vitamin K antagonist oral anticoagulants-a Swedish, register-based cohort study in atrial fibrillation outpatients.

PURPOSE: To study the association between interacting drugs and bleeding or thromboembolism in atrial fibrillation outpatients treated with non-vitamin K antagonist oral anticoagulants (NOACs). METHODS: Population-based cohort study of outpatients treated with NOACs in Sweden from 2008 to 2017. Patients with atrial fibrillation and newly initiated NOAC treatment were identified in the Prescribed Drug Register. Comorbidities and outcome data were retrieved from the Patient Register and the Cause of Death Register. Cox-regression analyses were performed to evaluate the primary endpoints any severe bleed and ischemic stroke/transient ischemic attack/stroke unspecified during the first six months of treatment. Secondary endpoints were gastrointestinal bleeding, intracranial bleeding, ischemic stroke, and venous thromboembolism. RESULTS: Increased risk of any severe bleed was found when NOAC treatment, and drugs with pharmacodynamic effect on bleeding were combined, compared to NOAC only. An increased risk with these combinations was evident for apixaban (hazard ratio (HR) 1.47; 95% CI 1.33-1.63), rivaroxaban (HR 1.7; 95% CI 1.49-1.92), and dabigatran (HR 1.26; 95% CI 1.05-1.52). For apixaban, there was an increased risk of any severe bleed when combined with CYP3A4 and/or P-glycoprotein (P-gp) inhibitors (HR 1.23; 95% CI 1.01-1.5). The use of inducers of CYP3A4 and/or P-gp was low in this cohort, and effects on ischemic stroke/TIA/stroke unspecified could not be established. CONCLUSION: Increased risk of bleeding was seen for pharmacodynamic and pharmacokinetic interactions with NOACs. Prescribers need to be vigilant of the effect of interacting drugs on the risk profile of patients treated with NOACs.

Risk factors for severe bleeding events during warfarin treatment: the influence of sex, age, comorbidity and co-medication.

PURPOSE: To investigate risk factors for severe bleeding during warfarin treatment, including the influence of sex, age, comorbidity and co-medication on bleeding risk. METHODS: Patients initiating warfarin treatment between 2007 and 2011 were identified in the nationwide Swedish Prescribed Drug Register, and diagnoses of severe bleeding were retrieved from the National Patient Register. Hazard ratios (HR) with 95% confidence intervals (CI) for severe bleeding were estimated using multiple Cox regression adjusting for indications and including covariates age, sex, comorbidities and co-medications. Interactions between sex and other covariates were investigated. RESULTS: The study cohort included 232,624 patients ≥ 18 years (101,011 women and 131,613 men). The incidence rate of severe bleeding was 37 per 1000 person-years, lower among women than men with an adjusted HR (95% CI) of 0.84 (0.80-0.88). Incidence of bleeding increased with age, HR 2.88 (2.37-3.50) comparing age ≥ 80 to < 40 years, and comorbidities associated with the highest risk of severe bleeding were prior bleeding, HR 1.85 (1.74-1.97); renal failure, HR 1.82 (1.66-2.00); and alcohol dependency diagnosis, HR 1.79 (1.57-2.05). Other comorbidities significantly associated with bleeding events were hypertension, diabetes, peripheral vascular disease, congestive heart failure, liver failure, stroke/TIA, COPD and cancer. CONCLUSION: Most of the well-established risk factors were found to be significantly associated with bleeding events in our study. We additionally found that women had a lower incidence of bleeding. Potential biases are selection effects, residual confounding and unmeasured frailty.

Intra- and inter- individual rivaroxaban concentrations and potential bleeding risk in patients with atrial fibrillation.

BACKGROUND: Routine laboratory monitoring of rivaroxaban and dose adjustment relating to exposure is currently not recommended. However, in certain clinical situations, assessment of rivaroxaban levels is desirable. OBJECTIVES: To examine inter- and intra-subject plasma rivaroxaban variability in patients with atrial fibrillation (AF) and to correlate these results to clinical outcomes. PATIENTS/METHODS: We included 60 patients with AF treated with rivaroxaban: half on 20 mg daily (R20) and half on 15 mg daily (R15). Three trough and peak blood samples were collected with an interval of 6-8 weeks apart. Plasma rivaroxaban concentration was measured directly by liquid chromatography-tandem mass-spectrometry (LC-MS/MS) and indirectly by anti-Xa for rivaroxaban, prothrombin time (PT), and activated partial thromboplastin time (APTT). RESULTS: Patients on R15 were older (76 ± 6 vs 71 ± 6 years), had lower creatinine clearance (60 ± 26 vs 99 ± 32 mL/min), higher CHADS2 (2.5 ± 1.2 vs 1.8 ± 1.3), all p < 0.01, but had similar rivaroxaban concentrations in trough samples to patients on R20. There was no significant intra-individual variability for trough or peak rivaroxaban concentration assessed by LC-MS/MS, anti-Xa, or PT. Trough rivaroxaban levels determined by LC-MS/MS (48 ± 30 vs 34 ± 26, p = 0.02) and anti-Xa, but not with PT and APTT, were higher in patients with bleeding than in patients without it. CONCLUSIONS: There is a pronounced inter-, but not intra-individual variability in the rivaroxaban trough levels in patients with AF. Assessment of trough rivaroxaban concentration with LC-MS/MS or anti-Xa, but not with APTT or PT, may help to identify patients at increased risk of bleeding.

Persistence with dimethyl fumarate in relapsing-remitting multiple sclerosis: a population-based cohort study.

PURPOSE: To describe patients initiating dimethyl fumarate (DMF) and measure persistence with DMF, discontinuation, and switching in treatment-naïve DMF patients and patients switching to DMF from other multiple sclerosis disease-modifying treatments (DMTs). METHODS: A population-based cohort study of all Stockholm County residents initiating DMF from 9 May 2014 until 31 May 2017. All data were derived from a regional database that collects individual-level data on healthcare and drug utilization of all residents. The study outcomes were persistence with DMF and DMF discontinuation and switching to other DMTs. Persistence was measured as the number of days until either DMF discontinuation (treatment gap ≥ 60 days) or switching to another DMT. RESULTS: The study included 400 patients (median follow-up = 2.5 years). The majority had previously been treated with other DMTs (61%). Throughout the follow-up period, 124 patients (31%) discontinued DMF and 114 patients (29%) switched treatment. Overall, 34% of patients initiating DMF stopped treatment within 1 year and only 43% of patients remained on DMF at 2 years from treatment initiation. CONCLUSIONS: DMF had a rapid market uptake likely due to high expectations held by both patients and clinicians. However, persistence with DMF in routine clinical practice was found to be low.

The changing multiple sclerosis treatment landscape: impact of new drugs and treatment recommendations.

PURPOSE: The purpose of this study is to describe the utilization of disease-modifying treatments (DMTs) in relapsing-remitting multiple sclerosis (MS) and assess the impact of both the introduction of new drugs and treatment recommendations (local recommendation on rituximab use issued at the largest MS clinic in Stockholm and regional Drug and Therapeutics Committee (DTC) recommendation on how dimethyl fumarate should be used). METHODS: Interrupted time series analyses using monthly data on all MS patients treated with DMTs in the Stockholm County, Sweden, from January 2011 to December 2017. RESULTS: There were 4765 individuals diagnosed with MS residing in the Stockholm County from 2011 to 2017. Of these, 2934 (62%) were treated with an MS DMT. Since 2011, fingolimod, alemtuzumab, teriflunomide, dimethyl fumarate, peginterferon beta-1a, and daclizumab were introduced. Only fingolimod and dimethyl fumarate significantly impacted MS DMT utilization. In parallel, the use of rituximab off-label increased steadily, reaching 58% of all DMT-treated MS patients by the end of the study period. The local recommendation on rituximab was associated with an increase in rituximab use. The regional DTC recommendation on dimethyl fumarate was associated with a decrease in dimethyl fumarate use. CONCLUSIONS: Three MS DMTs-fingolimod, dimethyl fumarate, and rituximab off-label-impacted MS DMT utilization in the Stockholm County. The associations between the treatment recommendations and the subsequent changes in MS DMT utilization indicate that such interventions can influence the uptake and utilization of new drugs used in the specialized care setting.

Sex differences in spontaneous reports on adverse drug events for common antihypertensive drugs.

PURPOSE: To explore sex differences in spontaneously reported adverse drug events (ADEs) for antihypertensives in routine care. METHODS: A cross sectional analysis combining number of reports from the national pharmacovigilance database with data from the Swedish Prescribed Drug Register, from 2005 to 2012 for ACE inhibitors (ACE-I) and angiotensin receptor blockers (ARB), with or without thiazide, diuretics (thiazides, potassium-sparing agents, sulfonamides, aldosterone antagonists), selective betablockers, and dihydropyridine calcium-channel-blockers (DHPs). The total number of reports was adjusted to exposed patients and dispensed DDDs among women and men. Dose exposures, co-medications, and co-prescriptions were also analyzed. RESULTS: In women, a higher prevalence of ADE-reports was seen in ACE-I (odds ratio, OR 1.21; 95% CI 1.09-1.35), ACE-I-combinations (OR 1.61; 1.44-1.79), ARB-combinations (OR 2.12; 1.47-3.06), thiazides (OR 1.78; 1.33-2.39), diuretics and potassium-sparing agents (OR 1.62; 1.22-2.17), and DHPs (OR 1.40; 1.17-1.67), with a potential linkage to dose exposure. For aldosterone antagonists, we observed a higher prevalence of ADE reports in men (OR 0.75; 0.59-0.97) but without any sex difference in dose exposure. CONCLUSIONS: This ecological study of reported ADEs showed a higher prevalence of reports in women in six out of ten groups of antihypertensive drugs, and this may potentially be linked to dose exposure. Aldosterone antagonists was the only group with a higher prevalence of ADE-reports in men with a similar dose exposure between women and men.

Patients' knowledge and attitudes to the Wise List - a drug formulary from the Stockholm Drug and Therapeutic committee.

BACKGROUND: Involving patients in decisions about their pharmacotherapy is crucial for a satisfactory treatment outcome. Information and opinions about medicines are available from a variety of sources. The Wise List is the drug formulary of recommended essential medicines for the Stockholm healthcare region and is issued by the Drug and Therapeutics Committee (DTC). To inform the public about treatment for common diseases and the concept of recommended medicines, a patient edition of the Wise List was developed. The aim of this study was to explore patients' knowledge, needs and attitudes to the Wise List, DTC and information about medicines in general. METHODS: To examine patient knowledge about recommended medicines a survey (n = 312) was carried out at four large primary healthcare centres in Stockholm, Sweden. To further elucidate the patients' needs of the information on recommended medicines and medicines in general, three focus group discussions (FGDs) were performed. RESULTS: Of the respondents 57% did not recognise the Wise List, 26% recognised but did not use it and 17% used it. A total of 63% reported that they search for information about medicines. The most common information source was "asking their doctor" (36%) followed by searching the internet (31%). The FGDs revealed that the patients were not interested in medicines in general, only in the medicines they use themselves. They did not understand the aim of the Wise List or how they could benefit from information about recommended medicines. The patients expressed a wish to access all information they need about their own care as well as public healthcare information at one location. CONCLUSION: The intended aim of the DTC with providing information to the public was not achieved as the patients have difficulties to understand the information and how they should use it. The patients were not interested in medicines in general, they wanted information tailored to their specific needs. The findings highlight the importance of creating tools for patients in collaboration with them and evaluate the concept continuously.

Clinical evaluation of laboratory methods to monitor exposure of rivaroxaban at trough and peak in patients with atrial fibrillation.

PURPOSE: The one-dose daily regime of rivaroxaban could cause a pronounced variability in concentration and effect of which a deeper knowledge is warranted. This study aimed to evaluate the typical exposure range and effect of the direct factor Xa (FXa)-inhibitor rivaroxaban in a cohort of well-characterized patients with atrial fibrillation (AF). METHODS: Seventy-one AF patients (72 ± 8 years, 55 % men) were treated with rivaroxaban 15 mg/20 mg (n = 10/61) OD. Trough (n = 71) and peak (n = 30) plasma concentrations determined by liquid chromatography-tandem mass-spectrometry (LC-MS/MS) were compared to the coagulation assays anti-FXa for rivaroxaban, prothrombin time-international normalized ratio (PT-INR) (venous samples and point-of-care assay (POC) CoaguChek XS Pro), and aPTT. RESULTS: Median rivaroxaban plasma concentrations by LC-MS/MS were 34 (range 5-84) and 233 ng/ml (range 120-375) at trough and peak, respectively. A strong correlation between LC-MS/MS and the anti-FXa assay was found (p < 0.001) for both trough (r (2) = 0.92) and peak (r (2) = 0.91) samples. PT-INR results from the POC assay, but not from the conventional PT assay, correlated significantly with LC-MS/MS in peak samples exclusively (r (2) = 0.41, p < 0.001). CONCLUSIONS: In "real-life" AF patients treated with rivaroxaban, we observed a pronounced variability in plasma concentrations at trough and to a lesser extent at peak measured by LC-MS/MS. The anti-FXa assay performed well upon rivaroxaban levels in a normal exposure range, although LC-MS/MS remains the only method that covers the whole concentration range with accuracy. Interestingly, the POC assay for PT-INR could be useful to indicate high exposure to rivaroxaban in emergency situations although further validation is required.

Sex differences in spontaneous reports on adverse bleeding events of antithrombotic treatment.

PURPOSE: To explore if sex differences are found in spontaneously reported adverse events for clopidogrel, low-dose aspirin and warfarin treatment in routine care. METHODS: A cross-sectional analysis combining data on bleeding events from the Swedish Spontaneous Adverse Drug Event Reporting System (SWEDIS) with data from the National Prescribed Drug register. Bleeding event reports from 1999 to 2010 and 2005 to 2010 were adjusted to the number of prescriptions and the number of exposed patients respectively among women and men. Co-medication and co-prescription were analysed. RESULTS: More men were dispensed clopidogrel although the reported bleeding event risk after adjustment for number of patients exposed was higher in women (RR 1.40; 95 % CI, 1.00-1.96). The difference disappeared when adjusting for the number of prescriptions (RR 0.99; 95 % CI, 0.71-1.39). The reported bleeding event risk with low-dose aspirin was lower in women, adjusted for patients exposed (RR 0.80; 95 % CI, 0.66-0.97). For warfarin, no sex difference in bleeding event reports could be found (RR 1.01; 95 % CI, 0.87-1.17). CONCLUSIONS: This ecological comparison of bleeding reports and dispensed prescriptions showed a signal towards a higher prevalence of bleeding reports in women on clopidogrel treatment while the opposite was found for low-dose aspirin. For warfarin, no significant sex difference was seen regarding bleeding event reports, suggesting individualised dosing being an important factor. Men were more commonly prescribed antithrombotic combinations, and this was reflected by a larger proportion of bleeding reports including more than one antithrombotic agent.

Personalizing health care: feasibility and future implications.

Considerable variety in how patients respond to treatments, driven by differences in their geno- and/ or phenotypes, calls for a more tailored approach. This is already happening, and will accelerate with developments in personalized medicine. However, its promise has not always translated into improvements in patient care due to the complexities involved. There are also concerns that advice for tests has been reversed, current tests can be costly, there is fragmentation of funding of care, and companies may seek high prices for new targeted drugs. There is a need to integrate current knowledge from a payer's perspective to provide future guidance. Multiple findings including general considerations; influence of pharmacogenomics on response and toxicity of drug therapies; value of biomarker tests; limitations and costs of tests; and potentially high acquisition costs of new targeted therapies help to give guidance on potential ways forward for all stakeholder groups. Overall, personalized medicine has the potential to revolutionize care. However, current challenges and concerns need to be addressed to enhance its uptake and funding to benefit patients.

Therapeutic drug monitoring for tomorrow.

Therapeutic drug monitoring (TDM) represents an early approach to personalised medicine. It helps the clinician to individualise drug treatment and guide dosage to reach systemic drug concentrations associated with therapeutic efficacy and/or to reduce the risk of concentration-dependent adverse effects. Well into the fifth decade of TDM as a service to healthcare, this concept is still expanding, and new areas for clinical implementation continue to emerge. The aim of this overview is to discuss promising new therapeutic areas in future TDM services, how to improve the clinical interpretation of single drug measurements and how recent technology development opens the doors to research and new applications.

Interface management of pharmacotherapy. Joint hospital and primary care drug recommendations.

PURPOSE: In September 2012 an interactive course on the "Interface Management of Pharmacotherapy" was organized by the Stockholm Drug and Therapeutics Committee in cooperation with Department of Clinical Pharmacology at Karolinska Institutet and at Karolinska University Hospital in Stockholm, Sweden, in collaboration with the WHO. The basis for the course was the "Stockholm model" for the rational use of medicines but also contained presentations about successful models in interface management of pharmacotherapy in other European countries. METHODS: The "Stockholm model" consists of 8 components: 1) Independent Drug and Therapeutics Committee with key role for respected drug experts with policy for "interest of conflicts", 2) The "Wise List", recommendations of medicines jointly for primary and hospital care, 3) Communication strategy with continuous medical education, 4) Systematic introduction of new expensive medicines, 5) E-pharmacological support at "point of care", 6) Methods and tools for follow-up of medicines use, 7) Medicines policy strategy and 8) Operative resources. RESULTS: The course highlighted the importance of efficient and targeted communication of drug recommendations building on trust among prescribers and patients for the guidelines to achieve high adherence. Trust is achieved by independent Drug and Therapeutics Committees with a key role for respected experts and a strict policy for "conflicts of interest". Representations of GPs are also crucial for successful implementation, being the link between evidence based medicine and practice. CONCLUSION: The successful models in Scotland and in Stockholm as well as the ongoing work in Catalonia were considered as examples of multifaceted approaches to improve the quality of medicine use across primary and hospital care.

Evaluation of coagulation assays versus LC-MS/MS for determinations of dabigatran concentrations in plasma.

BACKGROUND: Dabigatran is an oral direct thrombin inhibitor for which routine laboratory monitoring is currently not recommended. However, there are situations in which measurements of the drug and its effect are desirable. We therefore compared and validated different coagulation methods for assessments of dabigatran in clinical samples in relation to measurements of plasma dabigatran, without the purpose of establishing effective and safe concentrations of dabigatran in plasma. METHODS: Samples were obtained from 70 atrial fibrillation patients treated with dabigatran etexilate. Plasma concentrations were measured using liquid chromatography-tandem mass spectrometry (LC-MS/MS) and were compared with coagulation methods Hemoclot thrombin inhibitors (HTI) and Ecarin clotting assay (ECA), as well as with prothrombin time-international normalized ratio (PT-INR) and activated partial thromboplastin time (aPTT). RESULTS: A wide range of dabigatran concentrations was determined by LC-MS/MS (<0.5-586 ng/mL). Correlations between LC-MS/MS results and estimated concentrations were excellent for both HTI and ECA overall (r(2) = 0.97 and 0.96 respectively, p < 0.0001), but the precision and variability of these assays were not fully satisfactory in the low range of dabigatran plasma concentrations, in which ECA performed better than HTI. aPTT performed poorly, and was normal (<40 s) even with dabigatran levels of 60 ng/mL. PT-INR was normal even at supratherapeutic dabigatran concentrations. CONCLUSION: LC-MS/MS is the gold standard for measurements of dabigatran in plasma. Alternatively, either HTI or ECA assays may be used, but neither of these assays is dependable when monitoring low levels or to infer total absence of dabigatran. The aPTT assay is relatively insensitive to dabigatran, and normal aPTT results may be observed even with therapeutic dabigatran concentrations.

Biological Variation in Rotational Thromboelastometry in Patients with Atrial Fibrillation Receiving Rivaroxaban.

Rotational thromboelastometry (ROTEM) is a viscoelastic hemostasis test used primarily in the management of bleeding after trauma or in cardiac surgery. To allow safe and valid clinical interpretation of test results, objective specifications for analytical performance are needed, which are generally based on biological variation within (CVI) and between (CVG) individuals. The aim of this study was to evaluate biological variation in ROTEM in patients receiving rivaroxaban. Sixty patients with atrial fibrillation on stable rivaroxaban therapy were included, from whom blood was collected on six occasions: three times at trough and three at peak rivaroxaban concentrations. ROTEM® Extem and LowTF were measured as well as rivaroxaban concentration, PT, APTT, and anti-Xa. Within- (CVI) and between-subject (CVG) biological estimates were calculated. Knowledge of these biological variation components will help to establish the appropriate objective analytical performance specifications for ROTEM analysis.

Using a low-molecular weight heparin-calibrated anti-factor Xa assay to assess the concentration of apixaban and rivaroxaban.

INTRODUCTION: Direct oral anticoagulant (DOAC)-inhibiting factor Xa (FXa-DOAC) are being increasingly used as prophylaxis of venous thromboembolism and for prevention of stroke in patients with atrial fibrillation. In contrast to vitamin K antagonists, DOACs do not require monitoring in general. However, it is sometimes of value in the acute setting, for instance when considering a reversal agent in uncontrolled bleeding in patients on DOAC. METHODS: We evaluated if a low-molecular weight heparin (LMWH)-calibrated anti-factor Xa assay could be used to estimate FXa-DOAC concentration in the concentration range <100 ng/mL by spiking known concentrations of FXa-DOAC and from those result calculate the FXa-DOAC concentration from the response of the LMWH assay. This procedure was then evaluated by comparing the result with a drug-calibrated chromogenic assay and liquid chromatography tandem mass spectrometry (LC-MS/MS) on clinical plasma samples from patients treated with apixaban or rivaroxaban. RESULTS: Although the measuring range was narrower for the LMWH-calibrated assay, concentrations recalculated from the LMWH assay was comparable with those measured by the drug-calibrated method when compared with LC-MS/MS. CONCLUSION: We suggest that an LMWH-calibrated anti-factor Xa assay can be used after characterization of the response of FXa-DOACs to give guidance on the concentration of apixaban and rivaroxaban. Shorter turnaround time than LC-MS/MS and the greater availability than drug-calibrated chromogenic assays could make this a valuable option in the acute setting.

The in vitro addition of idarucizumab to plasma samples from patients increases thrombin generation.

Dabigatran interferes with many coagulation tests. To overcome this obstacle the use of idarucizumab as an in vitro antidote to dabigatran has been proposed. The aim of this study was to test the effect of idarucizumab as an in vitro antidote to dabigatran in ex vivo plasma samples from routine clinical patients examined by a thrombin generation assay (TGA). From 44 patients with atrial fibrillation five blood samples were collected. Thrombin generation was measured in all samples before and after the addition of idarucizumab. When idarucizumab was added to baseline plasma (no dabigatran), it caused a significantly shorter Lag Time and Time to Peak Thrombin, and a higher Peak Thrombin and Endogenous Thrombin Potential (ETP) of TGA. Similar results were obtained when idarucizumab was added to dabigatran-containing plasma, with TGA parameters comparable to baseline + idarucizumab plasma, but not to baseline plasma. In summary, our study showed that in vitro addition of idarucizumab to plasma samples from patients increases thrombin generation. The use of idarucizumab to neutralize dabigatran in patient plasma samples as well as the clinical relevance of in vitro increased thrombin generation induced by idarucizumab needs further investigation.

Apixaban concentration variability and relation to clinical outcomes in real-life patients with atrial fibrillation.

In some clinical situations, measurements of anticoagulant effect of apixaban may be needed. We investigated the inter- and intra-individual apixaban variability in patients with atrial fibrillation and correlated these results with clinical outcome. We included 62 patients receiving either 5 mg (A5, n = 32) or 2.5 mg (A2.5, n = 30) apixaban twice-daily. We collected three trough and three peak blood samples 6-8 weeks apart. Apixaban concentration was measured by liquid chromatography-tandem mass-spectrometry (LC-MS/MS) and by anti-Xa. Patients on A2.5 were older, had lower creatinine clearance, higher CHA2DS2VASc (4.7 ± 1.0 vs. 3.4 ± 1.7) and lower trough (85 ± 39 vs. 117 ± 53 ng/mL) and peak (170 ± 56 vs. 256 ± 91 ng/mL) apixaban concentrations than patients on A5 (all p < 0.01). In patients on A5, LC-MS/MS showed a significant difference between through levels and between peak levels (p < 0.01). During apixaban treatment, 21 patients suffered bleeding (2 major). There was no association between bleeding and apixaban concentrations or variability. Four patients who suffered thromboembolic event had lower peak apixaban concentrations than patients without it (159 ± 13 vs. 238 ± 88 ng/mL, p = 0.05). We concluded, that there was a significant intra- and inter-individual variability in apixaban trough and peak concentrations. Neither variability nor apixaban concentrations were associated with clinical outcomes.