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Extremely elevated international normalized ratio of warfarin in a patient with CYP2C9*1/*3 and thyrotoxicosis

Ji Eun Lee1, Duck Hyun Ryu1, Ho Jung Jeong1

  • 1Department of Medicine, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul, Korea.

Journal of Korean Medical Science
|September 24, 2014
PubMed

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.

Keywords:
GenotypeInternational Normalized RatioThyrotoxicosisWarfarin

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