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van den Besselaar AMHP, Stavelin A, Kitchen S, Bryant M, Tripodi A, Scalambrino E, Clerici M, Herbel P, Jünschke A, Meyer Dos Santos S, Meijer P, Niessen RWLM, Meijers JCM, Thelwell C, Cuker A, Kung C, Cao Z, Zander N, Iwasaki Y, Depasse F, van Rijn C, Baktawar S, Abdoel C, Cobbaert CM. Defining a metrologically traceable and sustainable calibration hierarchy of international normalized ratio for monitoring of vitamin K antagonist treatment in accordance with International Organization for Standardization (ISO) 17511:2020 standard: communication from the International Federation of Clinical Chemistry and Laboratory Medicine-SSC/ISTH working group on prothrombin time/international normalized ratio standardization. J Thromb Haemost 2024; 22:1236-1248. [PMID: 38128762 DOI: 10.1016/j.jtha.2023.12.013] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2023] [Revised: 12/01/2023] [Accepted: 12/07/2023] [Indexed: 12/23/2023]
Abstract
Calibration of prothrombin time (PT) in terms of international normalized ratio (INR) has been outlined in "Guidelines for thromboplastins and plasmas used to control oral anticoagulant therapy" (World Health Organization, 2013). The international standard ISO 17511:2020 presents requirements for manufacturers of in vitro diagnostic (IVD) medical devices (MDs) for documenting the calibration hierarchy for a measured quantity in human samples using a specified IVD MD. The objective of this article is to define an unequivocal, metrologically traceable calibration hierarchy for the INR measured in plasma as well as in whole blood samples. Calibration of PT and INR for IVD MDs according to World Health Organization guidelines is similar to that in cases where there is a reference measurement procedure that defines the measurand for value assignment as described in ISO 17511:2020. We conclude that, for PT/INR standardization, the optimal calibration hierarchy includes a primary process to prepare an international reference reagent and measurement procedure that defines the measurand by a value assignment protocol conforming to clause 5.3 of ISO 17511:2020. A panel of freshly prepared human plasma samples from healthy adult individuals and patients on vitamin K antagonists is used as a commutable secondary calibrator as described in ISO 17511:2020. A sustainable metrologically traceable calibration hierarchy for INR should be based on an international protocol for value assignment with a single primary reference thromboplastin and the harmonized manual tilt tube technique for clotting time determination. The primary international reference thromboplastin reagent should be used only for calibration of successive batches of the secondary reference thromboplastin reagent.
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Affiliation(s)
- Antonius M H P van den Besselaar
- Coagulation Reference Laboratory, Department of Clinical Chemistry and Laboratory Medicine, Leiden University Medical Center, Leiden, the Netherlands.
| | - Anne Stavelin
- The Norwegian Organisation for Quality Improvement of Laboratory Examinations, Bergen, Norway
| | - Steve Kitchen
- Sheffield Haemophilia and Thrombosis Centre, Royal Hallamshire Hospital, Sheffield, UK
| | - Michelle Bryant
- Sheffield Haemophilia and Thrombosis Centre, Royal Hallamshire Hospital, Sheffield, UK
| | - Armando Tripodi
- Fondazione Istituto di Ricovero e Cura a Carattere Scientifico Ca' Granda Ospedale Maggiore Policlinico, Angelo Bianchi Bonomi Hemophilia and Thrombosis Center, Milano and Fondazione Luigi Villa, Milano, Italy
| | - Erica Scalambrino
- Fondazione Istituto di Ricovero e Cura a Carattere Scientifico Ca' Granda Ospedale Maggiore Policlinico, Angelo Bianchi Bonomi Hemophilia and Thrombosis Center, Milano and Fondazione Luigi Villa, Milano, Italy
| | - Marigrazia Clerici
- Fondazione Istituto di Ricovero e Cura a Carattere Scientifico Ca' Granda Ospedale Maggiore Policlinico, Angelo Bianchi Bonomi Hemophilia and Thrombosis Center, Milano and Fondazione Luigi Villa, Milano, Italy
| | | | | | | | - Piet Meijer
- External quality Control of diagnostic Assays and Tests (ECAT) Foundation, Voorschoten, the Netherlands
| | | | - Joost C M Meijers
- Department of Molecular Hematology, Sanquin Research, Amsterdam, the Netherlands; Department of Experimental Vascular Medicine, Amsterdam Cardiovascular Sciences, Amsterdam University Medical Center, University of Amsterdam, Amsterdam, the Netherlands
| | - Craig Thelwell
- Therapeutic Reference Materials, Medicines and Healthcare Products Regulatory Agency, National Institute for Biological Standards and Control, Potters Bar, UK
| | - Adam Cuker
- Department of Medicine, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA; Department of Pathology and Laboratory Medicine, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania, USA
| | | | | | | | | | | | - Claudia van Rijn
- Coagulation Reference Laboratory, Department of Clinical Chemistry and Laboratory Medicine, Leiden University Medical Center, Leiden, the Netherlands
| | - Shanti Baktawar
- Coagulation Reference Laboratory, Department of Clinical Chemistry and Laboratory Medicine, Leiden University Medical Center, Leiden, the Netherlands
| | - Charmane Abdoel
- Coagulation Reference Laboratory, Department of Clinical Chemistry and Laboratory Medicine, Leiden University Medical Center, Leiden, the Netherlands
| | - Christa M Cobbaert
- Coagulation Reference Laboratory, Department of Clinical Chemistry and Laboratory Medicine, Leiden University Medical Center, Leiden, the Netherlands
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Hollestelle MJ, Kristoffersen AH, Idema RN, Meijer P, Sandberg S, de Maat MPM, Aarsand AK. Systematic review and meta-analysis of within-subject and between-subject biological variation data of coagulation and fibrinolytic measurands. Clin Chem Lab Med 2023; 61:1470-1480. [PMID: 36810291 DOI: 10.1515/cclm-2022-1207] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2022] [Accepted: 02/10/2023] [Indexed: 02/24/2023]
Abstract
OBJECTIVES The diagnosis and monitoring of bleeding and thrombotic disorders depend on correct haemostatic measurements. The availability of high-quality biological variation (BV) data is important in this context. Many studies have reported BV data for these measurands, but results are varied. The present study aims to deliver global within-subject (CVI) and between-subject (CVG) BV estimates for haemostasis measurands by meta-analyses of eligible studies, by assessment with the Biological Variation Data Critical Appraisal Checklist (BIVAC). METHODS Relevant BV studies were graded by the BIVAC. Weighted estimates for CVI and CVG were obtained via meta-analysis of the BV data derived from BIVAC-compliant studies (graded A-C; whereby A represents optimal study design) performed in healthy adults. RESULTS In 26 studies BV data were reported for 35 haemostasis measurands. For 9 measurands, only one eligible publication was identified and meta-analysis could not be performed. 74% of the publications were graded as BIVAC C. The CVI and CVG varied extensively between the haemostasis measurands. The highest estimates were observed for PAI-1 antigen (CVI 48.6%; CVG 59.8%) and activity (CVI 34.9%; CVG 90.2%), while the lowest were observed for activated protein C resistance ratio (CVI 1.5%; CVG 4.5%). CONCLUSIONS This study provides updated BV estimates of CVI and CVG with 95% confidence intervals for a wide range of haemostasis measurands. These estimates can be used to form the basis for analytical performance specifications for haemostasis tests used in the diagnostic work-up required in bleeding- and thrombosis events and for risk assessment.
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Affiliation(s)
- Martine J Hollestelle
- ECAT Foundation (External Quality Control for Assays and Tests), Voorschoten, The Netherlands
| | - Ann Helen Kristoffersen
- Department of Medical Biochemistry and Pharmacology, Haukeland University Hospital, Bergen, Norway
- Norwegian Organization for Quality Improvement of Laboratory Examinations (Noklus), Haraldsplass Deaconess Hospital, Bergen, Norway
| | - René N Idema
- Result Laboratory, Amphia Hospital, Breda, The Netherlands
| | - Piet Meijer
- ECAT Foundation (External Quality Control for Assays and Tests), Voorschoten, The Netherlands
| | - Sverre Sandberg
- Department of Medical Biochemistry and Pharmacology, Haukeland University Hospital, Bergen, Norway
- Norwegian Organization for Quality Improvement of Laboratory Examinations (Noklus), Haraldsplass Deaconess Hospital, Bergen, Norway
- European Federation of Clinical Chemistry and Laboratory Medicine (EFLM) Working Group on Biological Variation and Task Group for the Biological Variation Database, Milan, Italy
| | - Moniek P M de Maat
- Department of Hematology, Erasmus MC, University Medical Center Rotterdam, Rotterdam, The Netherlands
| | - Aasne K Aarsand
- Department of Medical Biochemistry and Pharmacology, Haukeland University Hospital, Bergen, Norway
- Norwegian Organization for Quality Improvement of Laboratory Examinations (Noklus), Haraldsplass Deaconess Hospital, Bergen, Norway
- European Federation of Clinical Chemistry and Laboratory Medicine (EFLM) Working Group on Biological Variation and Task Group for the Biological Variation Database, Milan, Italy
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Dimmitt SB, Floyd CN, Ferner RE. Antithrombotic dose: Some observations from published clinical trials. Br J Clin Pharmacol 2019; 85:2194-2197. [PMID: 31050833 DOI: 10.1111/bcp.13968] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2019] [Revised: 03/31/2019] [Accepted: 04/03/2019] [Indexed: 12/12/2022] Open
Abstract
The clinical doses of antithrombotics-antiplatelet and anticoagulant agents-need to balance efficacy and safety. It is not clear from the published literature how the doses currently used in clinical practice have been derived from preclinical and clinical data. There are few large randomised controlled trials (RCTs) that compare outcomes with different doses vs placebo. For newer antithrombotics, RCT doses appear to have been chosen to maximise the probability of demonstrating noninferiority when compared to established agents such as warfarin or clopidogrel. Data from RCTs show that aspirin is an effective antithrombotic at doses below 75 mg daily, and that direct oral anticoagulants reduce the risk of stroke in patients with coronary disease at doses 1/4 of those recommended in atrial fibrillation. Lower doses than those currently recommended are safer and still maintain substantial efficacy.
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Affiliation(s)
- Simon B Dimmitt
- Division of Internal Medicine, Medical School, Faculty of Health and Medical Sciences, University of Western Australia, Crawley, Australia.,School of Medicine & Public Health, University of Newcastle, UK
| | - Christopher N Floyd
- School of Cardiovascular Medicine and Sciences, Department of Clinical Pharmacology School of Cardiovascular Medicine and Sciences, King's College London British Heart Foundation Centre, London, UK.,Biomedical Research Centre, Clinical Research Facility, Guy's and St Thomas' NHS Foundation Trust, London, UK
| | - Robin E Ferner
- West Midlands Centre for Adverse Drug Reactions, City Hospital, Birmingham, UK.,Institute of Clinical Sciences, University of Birmingham, UK
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van den Besselaar AMHP, Biedermann JS, Kruip MJHA. Point-of-care testing and INR within-subject variation in patients receiving a constant dose of vitamin K antagonist. Thromb Haemost 2015. [PMID: 26202616 DOI: 10.1160/th15-02-0128] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
Many patients treated with vitamin K antagonists (VKA) determine their INR using point-of-care (POC) whole blood coagulation monitors. The primary aim of the present study was to assess the INR within-subject variation in self-testing patients receiving a constant dose of VKA. The second aim of the study was to derive INR imprecision goals for whole blood coagulation monitors. Analytical performance goals for INR measurement can be derived from the average biological within-subject variation. Fifty-six Thrombosis Centres in the Netherlands were invited to select self-testing patients who were receiving a constant dose of either acenocoumarol or phenprocoumon for at least six consecutive INR measurements. In each patient, the coefficient of variation (CV) of INRs was calculated. One Thrombosis Centre selected regular patients being monitored with a POC device by professional staff. Sixteen Dutch Thrombosis Centres provided results for 322 selected patients, all using the CoaguChek XS. The median within-subject CV in patients receiving acenocoumarol (10.2 %) was significantly higher than the median CV in patients receiving phenprocoumon (8.6 %) (p = 0.001). The median CV in low-target intensity acenocoumarol self-testing patients (10.4 %) was similar to the median CV in regular patients monitored by professional staff (10.2 %). Desirable INR analytical imprecision goals for POC monitoring with CoaguChek XS in patients receiving either low-target intensity acenocoumarol or phenprocoumon were 5.1 % and 4.3 %, respectively. The approximate average value for the imprecision of the CoaguChek XS, i. e. 4 %, is in agreement with these goals.
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Affiliation(s)
- A M H P van den Besselaar
- A. M. H. P. van den Besselaar, Department of Thrombosis and Hemostasis, Leiden University Medical Center, P. O. Box 9600, 2300 RC Leiden, The Netherlands, Tel.: +31 71 5261894, Fax: +31 71 5266868, E-mail: a. m. h.
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Swarna Nantha Y. Anticoagulant management of atrial fibrillation: the influence of dosing algorithm and recall schedule on time in therapeutic range. Fam Pract 2015; 32:514-9. [PMID: 26251026 DOI: 10.1093/fampra/cmv066] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
BACKGROUND The quality of anticoagulation management in atrial fibrillation patients is reflected by the concept of time spent in therapeutic range (TTR). In a primary care setting, the implementation of a dose nomogram could help increase the mean TTR among these patients. OBJECTIVE This study compares the influence of a dose algorithm with an integrated recall on TTR prior to standard care and after the implementation of the protocol. PATIENTS AND METHODS In a purposive sample of patients with AF, an uncontrolled 'before' and 'after' study design was utilized to measure the effects of the protocol on TTR. Demographic data, TTR levels, frequency of international normalized ratio (INR) within therapeutic range, clinician adherence to dose nomogram and warfarin dose changes were captured from consultations at the anticoagulation clinic. RESULTS A total of 152 patients with AF were entered into the final analysis. The increment in mean TTR in the 'after' intervention phase (2.9%) was not statistically significant (57.5-60.4%, P=0.252). The increase in the frequency of INR values within therapeutic range in the 'after' intervention phase was significant (50.0-56.0%, P<0.05) but with a very low effect size (r=0.04). CONCLUSIONS The implementation of a dose nomogram has the potential of reducing unnecessary dose changes for minor fluctuations in INR levels. The findings in this study needs to be confirmed in a future study involving other indications for anticoagulation, various regional primary care clinics and a larger population size.
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Affiliation(s)
- Y Swarna Nantha
- Primary Care Research Initiative and Methods Education Department (PRIMED), Seremban Primary Care Clinic, Jalan Rasah, 70300 Seremban, Negeri Sembilan Darul Khusus, Malaysia.
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Kubitza D, Becka M, Mück W, Krätzschmar J. Pharmacodynamics and pharmacokinetics during the transition from warfarin to rivaroxaban: a randomized study in healthy subjects. Br J Clin Pharmacol 2015; 78:353-63. [PMID: 24528331 PMCID: PMC4137827 DOI: 10.1111/bcp.12349] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2013] [Accepted: 12/03/2013] [Indexed: 12/01/2022] Open
Abstract
AIMS This study investigated relevant pharmacodynamic and pharmacokinetic parameters during the transition from warfarin to rivaroxaban in healthy male subjects. METHODS Ninety-six healthy men were randomized into the following three groups: warfarin [international normalized ratio (INR) 2.0-3.0] transitioned to rivaroxaban 20 mg once daily (od; group A); warfarin (INR 2.0-3.0) followed by placebo od (group B); and rivaroxaban alone 20 mg od (group C) for 4 days. Anti-factor Xa activity, inhibition of factor Xa activity, prothrombin time (PT), activated partial thromboplastin time, HepTest, prothrombinase-induced clotting time, factor VIIa activity, factor IIa activity, endogenous thrombin potential and pharmacokinetics were measured. RESULTS An additive effect was observed on the PT and PT/INR during the initial transition period. The mean maximal prolongation of PT was 4.39-fold [coefficient of variation (CV) 18.03%; range 3.39-6.50] of the baseline value in group A, compared with 1.88-fold (CV 10.35%; range 1.53-2.21) in group B and 1.57-fold (CV 9.98%; range 1.37-2.09) in group C. Rivaroxaban had minimal influence on the PT/INR at trough levels. Inhibition of factor Xa activity, activated partial thromboplastin time and endogenous thrombin potential were also enhanced, but to a lesser extent. In contrast, the effects of rivaroxaban on anti-factor Xa activity, HepTest and prothrombinase-induced clotting time were not affected by pretreatment with warfarin. CONCLUSIONS Changes in pharmacodynamics during the transition from warfarin to rivaroxaban vary depending on the test used. A supra-additive effect on PT/INR is expected during the initial period of transition, but pretreatment with warfarin does not influence the effect of rivaroxaban on anti-factor Xa activity.
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van den Besselaar AMHP, van der Meer FJM, Abdoel CF, Witteveen E. Analytical accuracy and precision of two novel Point-of-Care systems for INR determination. Thromb Res 2015; 135:526-31. [PMID: 25596767 DOI: 10.1016/j.thromres.2014.12.022] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2014] [Revised: 11/07/2014] [Accepted: 12/23/2014] [Indexed: 11/28/2022]
Abstract
BACKGROUND Portable point-of-care (POC) instruments for determination of the whole blood prothrombin time (PT) have been available for the last three decades. Recently, two novel POC instruments for PT and International Normalized Ratio (INR) determination in whole blood have been manufactured. The purpose of this study was to compare INR values obtained with the novel instruments (microINR® and ProTime InRhythm™) to the INR determined with the international standard for thromboplastin rTF/09. MATERIALS AND METHODS In 60 patients treated with vitamin K-antagonists, venous whole blood was analysed with four different types of POC instruments including the novel ones. In the same patients, citrated plasma was analysed with the international standard rTF/09 and the manual tilt tube technique for clotting time determination. We assessed the bias of the INR read from the POC instruments relative to the international standard. To study the imprecision of the two novel POC instruments, duplicate INR determinations were performed. RESULTS The results obtained with the two novel POC instruments were positively correlated with those of the international standard rTF/09. However, there was a significant bias between INR read from the novel instruments and the INR determined with rTF/09 (P < 0.001). The mean bias was -13.7% (MicroINR) and -9.3% (InRhythm). The imprecision coefficient of variation in venous blood was 5.0% and 5.1%, respectively. CONCLUSION The imprecision of the two novel instruments is acceptable with respect to the average within-subject variation of the INR. The accuracy of the systems is borderline and should be improved by the manufacturers.
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Affiliation(s)
| | - F J M van der Meer
- Department of Thrombosis and Hemostasis, Leiden University Medical Center, Leiden, The Netherlands
| | - C F Abdoel
- Department of Thrombosis and Hemostasis, Leiden University Medical Center, Leiden, The Netherlands
| | - E Witteveen
- Department of Thrombosis and Hemostasis, Leiden University Medical Center, Leiden, The Netherlands
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Sølvik UØ, Røraas T, Petersen PH, Stavelin A, Monsen G, Sandberg S. The influence of coagulation factors on the in-treatment biological variation of international normalized ratio for patients on warfarin. Scandinavian Journal of Clinical and Laboratory Investigation 2014; 74:470-6. [PMID: 24724577 DOI: 10.3109/00365513.2014.902098] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
BACKGROUND Biological variation is usually estimated in healthy individuals during steady-state conditions. The aim of this study was to estimate the in-treatment biological variation of the International normalised ratio (INR) and to investigate to what extent the different levels of coagulation factors could explain this variation. METHODS Blood samples were collected from randomly included patients on warfarin treatment. INR was determined on a laboratory instrument (STA Compact(®)) and on three point-of-care instruments (Simple Simon(®)PT, CoaguChek(®)XS and INRatio(™)). The level of fibrinogen, and the activity of coagulation factors II, V, VII and X were determined. RESULTS The in-treatment within- and between-subject coefficients of variation of INR were dependent on the method and varied between 18 and 24% and 13 and 19%, respectively, and were reduced to 3.9-5.1% and 2.3-5.8%, after correction for coagulation factors which could explain 91-95% of the variance of INR. CONCLUSIONS The in-treatment biological variation of INR was higher than reported for healthy individuals as well as patients in a steady-state condition, but by correcting for appropriate coagulation factors it was reduced. The association between INR and coagulation factors was different for the different PT methods mainly due to different sensitivity towards FII and FVII.
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Affiliation(s)
- Una Ø Sølvik
- Department of Global Public Health and Primary Care, University of Bergen , Norway
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Computational design of an enantioselective molecular imprinted polymer for the solid phase extraction of S-warfarin from plasma. J Chromatogr A 2014; 1338:9-16. [DOI: 10.1016/j.chroma.2014.02.055] [Citation(s) in RCA: 51] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2013] [Revised: 02/14/2014] [Accepted: 02/18/2014] [Indexed: 11/17/2022]
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Santos PCJL, Dinardo CL, Schettert IT, Soares RAG, Kawabata-Yoshihara L, Bensenor IM, Krieger JE, Lotufo PA, Pereira AC. CYP2C9 and VKORC1 polymorphisms influence warfarin dose variability in patients on long-term anticoagulation. Eur J Clin Pharmacol 2012; 69:789-97. [PMID: 22990331 DOI: 10.1007/s00228-012-1404-5] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2012] [Accepted: 09/02/2012] [Indexed: 01/24/2023]
Abstract
OBJECTIVES The main aim of this study was to determine whether CYP2C9 and VKORC1 polymorphisms influence warfarin dose variability during initial dose-finding phase and during maintenance treatment after 360 days. METHODS Two hundred and six consecutive patients who were beginning warfarin therapy were selected. They were assessed for general and clinical characteristics; prescribed warfarin dose; response to therapy on days 7-10, 30, 60, 180, and 360; adverse events; and CYP2C9 2, 3, 5, 6, 8, 11, and VKORC1 1639G >A assays. RESULTS During the first 30 days of anticoagulation, the relative variability of warfarin dose was significantly associated with CYP2C9*2 and CYP2C9*3 polymorphisms (p = 0.02) and with VKORC1 1639G >A genotypes (p = 0.04). Warfarin variability was also statistically different according to predicted metabolic phenotype and to VKORC1 genotypes after 360 days of treatment, and in the phase between 180 and 360 days (long-term dose variability). Both CYP2C9 and VKORC1 polymorphisms were associated with the international normalized ratio (INR) made between 7 and 10 days/initial dose ratio, adjusted for covariates (p < 0.01 and p = 0.02, respectively). Patients carrying VKORC1 and CYP2C9 variants presented lower required dose (at the end of follow-up of 360 days) compared to patients carrying wild-type genotypes (p = 0.04 and p = 0.03, respectively). CONCLUSIONS Genetic information on CYP2C9 and VKORC1 is important both for the initial dose-finding phase and during maintenance treatment with warfarin.
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Affiliation(s)
- Paulo Caleb Junior Lima Santos
- Laboratory of Genetics and Molecular Cardiology, Heart Institute (InCor), University of Sao Paulo Medical School, Av. Dr. Eneas de Carvalho Aguiar, 44 Cerqueira Cesar, Sao Paulo, SP, CEP 05403-000, Brazil.
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