Optimum and clinical factors affecting the stable maintenance dose of warfarin at Ratchaburi Hospital


  • Kannika Mueanjanjaem กลุ่มงานเภสัชกรรม โรงพยาบาลราชยุรี


stable maintenance dose of warfarin, factors effecting warfarin dose


Background : Warfarin is the most widely used oral anticoagulant in Thailand. Its indication is the prevention and treatment of thromboembolism. Warfarin has several limitations because of its narrow therapeutic index and the large inter-individual variability in dosing requirement making it a very problematic drug to prescribe. Several factors can affect the patients’ response to warfarin.

Objective : To determine an optimum stable maintenance dose of warfarin in patients and impact factors; gender, age, body weight, comorbidity, and concurrent drugs on warfarin treatment at Ratchaburi hospital.

Methods : The study design was a retrospective cohort study in outpatients who received warfarin during 1st October 2018 to 30th September 2019. All patients in the study were over the age of 18. Data were analyzed using descriptive statistics, Chi-square, and Pearson’s correlations to determine the association and relationship between the factors and the warfarin dose.

Results : The results showed that in 328 patients, 165 use warfarin for atrial fibrillation (50.30%). An average warfarin daily dose for patients with a target international normalized ratio (INR) of 2.0-3.0 was 3.11±1.29 mg/day and with a target INR of 2.5-3.5 was 3.68±0.94 mg/day. The significant factors were age (r=-0.426, p=0.0001) and body weight (r=0.201, p=0.001). The older patients tended to received lower dose, the high body weight patients tended to received higher dose of warfarin.

Conclusion : Age and body weight were found to be the significant factors that affected the warfarin requirement at Ratchaburi Hospital.


Hirsh J, Fuster V, Ansell J, Halperin JL. American Heart Association/American College of Cardiology Foundation guide to warfarin therapy. Circulation 2003; 107: 1692-711.

Jaffer A, Bragg L. Practical tips for warfarin dosing and monitoring. Clev Clin J Med 2003; 70: 361-73.

Carlquist J, Horne B, Muhlestein J, Lappe D, Whiting B, Kolek M, et al. Genotypes of the cytochrome p450 isoform, CYP2C9, and the vitamin K epoxide reductase complex subunit 1 conjointly determine stable warfarin dose: a prospective study. J Thromb Thrombolysis 2006; 22: 191-7.

Cherna H, Uengb T, Fuc Y, Chengd C. CYP2C9 polymorphrism and warfarin sensitivity in Taiwan Chinese. Clin Chim Acta 2006; 367: 108-13.

Mushiroda T, Ohnishi Y, Saito S, Takahashi A, Kikuchi Y, Shimomura H, et al. Association of VKORC1 and CYP2C9 polymorphrisms with warfarin dose requirement in Japanese patients. J Hum Genet 2006; 51: 249-53.

Sconce E, Khan T, Wynne H, Avery P, Monkhouse L, King B, et al. The impact of CYP2C9 and VKORC1 genetic polymorphrism and patient characteristics upon warfarin dose requirements: proposal for a new dosing regimen. Blood 2005; 106: 2329-33.

Yuan H, Chen J, Lee MT, Wung J, chen Y, Charng M, et al. A novel functional VKORC1 promoter polymorphrism is associated with inter-individual and inter-ethnic differences in warfarin sensitivity. Human Molecular Genetics 2005; 14: 1745-51.

Rieder MJ, Reiner AP, Gage BF, Nickerson DA, Eby CS, Mcleod HL, et al. Effect of VKORC1 Haplotypes on the transcriptional regulation and warfarin dose. N Engl J Med 2005; 352: 2285-93.

บุรัสกร ทรัพย์สุพรรณ. ความสัมพันธ์ระหว่างภาวะพหุสัณฐาน CYP2C9และVKORC1 ต่อขนาดยาวาร์ฟารินในผู้ป่วยชาวไทย [วิทยานิพนธ์]. นครปฐม: มหาวิทยาลัยศิลปากร; 2556.

Thamwanta S, Muenpa R. Optimum and Factors Predicting Warfarin Maintenance Dose and Factors Affecting the Out of Therapeutic INR Range. Thai Journal of Hospital Pharmacy 2010; 20: 199-209.

Absher RK, Moore ME, Parker MH. Patient-specific factors predictive of warfarin dosage requirements. Ann Pharmacother 2002; 36: 1512-7.

Lee V, You J, Lee K, Chau T, Waye M, Cheng G. Factors affecting the maintenance stable warfarin dosage in Hong Kong Chinese patient. J Thromb Thrombolysis 2005; 20: 33-8.

Miao L, Yang J, Huang C, Shen Z. Contribution of age, body weight, and CYP2C9 and VKORC1 genotype to the anticoagulant response to warfarin: proposal for a new dosing regimen in Chinese patients. Eur J Clin Pharmacol 2007; 63: 1135-41.

Mueller JA, Patel T, Halawa A, Dumitrascu A, Dawson NL. Warfarin dosing and body mass index. Ann Pharmacother 2014; 48: 584-8.

Wallace JL, Reaves AB, Tolley EA, Oliphant CS, Hutchison L, Alabdan NA, et al. Comparison of initial warfarin response in obese patients versus non-obese patients. J Thromb Thrombolysis 2013; 36: 96-101.

Holbrook AM, Pereira JA, Labiris R, McDonald H, Douketis JD, Crowther M, et al. Systematic overview of warfarin and its drug and food interaction. Arch Intern Med 2005; 165:1095-106.

Havrda DE, Mai T, Chonlahan J. Enhanced antithrombotic effect of warfarin associated with low-dose alcohol consumption. Pharmacother 2005; 25: 303-7.

Nathisuwan S, Dilokthornsakul P, Chaiyakunapruk N, Morarai T, Yodting T, Piriyachananusorn N. Assessing evidence of interaction between smoking and warfarin: a systematic review and meta-analysis. Chest 2011; 139: 1130-9.

Yu HCM, Chan TYK, Critchley JAJH, Woo KS. Factors determining the maintenance dose of warfarin in Chinese patients. Q J Med 1996; 89: 127-35.

Routledge PA, Chapman PH, Davies DM, Rawlins MD. Factors affecting warfarin requirements. A prospective population study. Eur J Clin Pharmacol 1979; 15: 319-22.

O´Malley K, Stevenson IH, Ward CA, Wood AJJ, Crooks J, Determinants of anticoagulant control in patients receiving warfarin. Br J Clin Pharmacol 1977; 4: 309-14.

Dobrzanski S, Duncan SE, Harkiss A, Wardlaw A, Age and weight as determinants of warfarin requirements. J Clin Pharm Ther 1983; 8: 75-7.

Redwood M, Taylor C, Jain BJ, Matthews. The association of age and dosage requirement for warfarin . Age Ageing 1991; 20: 217-20.

James AH, Britt RP, Raskino CL, Thompson SG. Factors affecting the maintenance dose of warfarin. J Clin Path 1992; 45: 704-6.

Gurwitz JH, Avorn J, Ross-Degnan D, Choodnovskiy I, Ansell J. Aging and the anticoagulant response to warfarin therapy. Ann Intern Med 1992; 116: 901-4.

สุทธิดา แก้วมุงคุณ, นิตย์สุภา วัฒนชัย, วิจิตรา ทัศนียกุล. ปัจจัยทางคลินิกและปัจจัยทางสิ่งแวดล้อมที่มีผลต่อการรักษาด้วยยาวาร์ฟารินในขนาดคงที่. The National and International Graduate Research Conference 2016; 775-83.




How to Cite

Mueanjanjaem, K. (2020). Optimum and clinical factors affecting the stable maintenance dose of warfarin at Ratchaburi Hospital. Hua Hin Medical Journal, 5(1), 18–29. Retrieved from https://he01.tci-thaijo.org/index.php/hhsk/article/view/240517



Original article