J Korean Med Sci.  2014 Sep;29(9):1317-1319. 10.3346/jkms.2014.29.9.1317.

Extremely Elevated International Normalized Ratio of Warfarin in a Patient with CYP2C9*1/*3 and Thyrotoxicosis

• Lee JE
• Ryu DH
• Jeong HJ
• Kim JH
• Jun JE
• Kim JS
• Lee SY

• KMID: 1794613
• DOI: http://doi.org/10.3346/jkms.2014.29.9.1317

Abstract

A 73-yr-old Korean man with permanent atrial fibrillation visited outpatient clinic with severely increased International Normalized Ratio (INR) values after taking a usual starting dosage of warfarin to prevent thromboembolism. We found out later from his blood tests that he had hyperthyroidism at the time of treatment initiation. His genetic analysis showed CYP2C9*1/*3 and VKORC1+1173TT genotypes. We suspect that both hyperthyroidism and genetic variant would have contributed to his extremely increased INR at the beginning of warfarin therapy. From this case, we learned that pharmacogenetic and thyroid function test might be useful when deciding the starting dosage of warfarin in patients with atrial fibrillation.

Keyword

Warfarin; International Normalized Ratio; Thyrotoxicosis; Genotype

MeSH Terms

Aged
Anticoagulants/blood/metabolism/therapeutic use
Aspirin/therapeutic use
Atrial Fibrillation/*diagnosis
Chromatography, High Pressure Liquid
Cytochrome P-450 CYP2C9/*genetics
Genotype
Humans
Male
Polymorphism, Single Nucleotide
Tandem Mass Spectrometry
Thromboembolism/prevention & control
Thyrotoxicosis/*diagnosis
Vitamin K Epoxide Reductases/genetics
Warfarin/*blood/metabolism/therapeutic use
Anticoagulants
Aspirin
Cytochrome P-450 CYP2C9
Vitamin K Epoxide Reductases
Warfarin

Figure

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  Fig. 1 Treatment course.

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