• Weerayuth Saelim Department of Pharmacy, Faculty of Pharmacy, Silpakorn University, Sanam Chandra Palace Campus, Nakhon Pathom
  • Pornwalai Boonmuang Department of Pharmacy, Faculty of Pharmacy, Silpakorn University, Sanam Chandra Palace Campus, Nakhon Pathom
  • Juthathip Suphanklang Department of Pharmacy, Faculty of Pharmacy, Silpakorn University, Sanam Chandra Palace Campus, Nakhon Pathom
  • Parnrada Nualsopaphon Department of Pharmacy, Phramongkutklo Hospital, Bangkok
Keywords: warfarin, factors, prosthetic valve, international normalized ratio (INR)


Warfarin is oral anticoagulant that has been used for prevention of systemic thromboembolism in valve replacement patients. There are many factors that can change the international normalized ratio (INR) in warfarin users. This study aimed to determine the influence of factors that related to the target range of INR among warfarin users who underwent heart valve replacement. This study is a retrospective study. The data were collected in patients who underwent valve replacement in warfarin clinic, Phramongkutklao Hospital, Thailand from January 2007 to December 2015. Demographic data including gender, age, type of prosthetic valve, co-morbidities, other medications used with warfarin, herbs or dietary supplements used with warfarin, laboratory data, warfarin initial dosing regimen and INR value were collected. The demographic data and the risk factors were analyzed via descriptive statistics and Fisher's exact test consecutively by using R-program. One hundred and nineteen patients were included. Sixty-four cases were male (53.78%) and mean (±SD) age was 55.09±14.78 years old. The mean (±SD) of body weight was 61.48±13.97 kilograms. Of those, 96 cases (80.67%) had mechanical valve replacement. Only sixteen of warfarin users (13.45%) had INR values with in target range. The results of the present study showed that drug interaction was one of the important factors that was associated with out-of-range INR target (OR 10.17, 95%CI 0.59-175.77) (p=0.051). Drug interaction including drug-drug, drug-herbs and drug-dietary supplement interaction were concerned in patients who received warfarin underwent heart valve replacement.


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