Case report: Dose adjustment of warfarin using genetic information and plasma concentration monitoring

T. Aomori, Y. Fujita, K. Obayashi, H. Sato, K. Kiyotani, K. Nakamura, T. Nakamura, K. Yamamoto

Research output: Contribution to journalArticle

Abstract

What is known and objective Carbamazepine is known to interact with warfarin. We report on a case of this interaction and on its management using the patient's genetic information. Case summary The case concerns a 74-year-old Japanese woman with a mood disorder and a central retinal vein occlusion. She was on therapy that included carbamazepine and had started to take warfarin. However, the patient's prothrombin time expressed as the international normalized ratio (PT-INR) was 1·40 despite taking a dose three times higher than the average. The patient's S-warfarin concentration was 0·15 μg/mL and R-warfarin was 0·52 μg/mL. Her cytochrome P450 2C9 (CYP2C9) and vitamin K epoxide reductase complex, subunit 1 (VKORC1), genotypes were1/1 and -1639GA, respectively. The VKORC1 genotype indicated that she would require an even higher dose. We proposed a further increase in dose and the patient's PT-INR rose to 1·99. What is new and conclusion The patient required a high warfarin dose because of the VKORC1 genotype, and induction of CYP2C9 by carbamazepine. We improved the patient's pharmacotherapy based on her genetic information.

Original languageEnglish
Pages (from-to)319-321
Number of pages3
JournalJournal of Clinical Pharmacy and Therapeutics
Volume39
Issue number3
DOIs
Publication statusPublished - 2014 Jun

Keywords

  • Japanese patient
  • carbamazepine
  • cytochrome P450 2C9
  • pharmacogenetics
  • pharmacy practice
  • therapeutic drug monitoring
  • vitamin K epoxide reductase complex, subunit 1
  • warfarin

ASJC Scopus subject areas

  • Pharmacology
  • Pharmacology (medical)

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