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Is there a circannual variation in the anticoagulation control of warfarin?
  1. Kannan Sridharan1,
  2. Rashed Al Banna2,
  3. Aysha Husain2
  1. 1Department of Pharmacology & Therapeutics, College of Medicine & Medical Sciences, Arabian Gulf University, Manama, Kingdom of Bahrain
  2. 2Department of Cardiology, Salmaniya Medical Complex, Ministry of Health, Manama, Kingdom of Bahrain
  1. Correspondence to Dr Kannan Sridharan, Department of Pharmacology & Therapeutics, College of Medicine & Medical Sciences, Arabian Gulf University, Manama 329, Bahrain; skannandr{at}gmail.com

Abstract

Background The literature regarding the seasonal variation in the therapeutic response to warfarin is somewhat contradictory, with several discrepancies. We assessed the influence of seasons on various pharmacodynamic indices of warfarin.

Methods A retrospective study was carried out in adults receiving warfarin for at least 6 months. Details of their demographic characteristics, duration and dose of warfarin therapy and values of prothrombin time international normalised ratio (PT-INR) were retrieved. Standard definitions were followed for defining various seasons, time in therapeutic range (TTR), log-INR variability and warfarin sensitivity index (WSI). National Institute for Health and Care Excellence (NICE) criteria were used for defining TTR into good (≥65%) and poor (<65%) anticoagulation control.

Results Two hundred and four patients were recruited. Only a subtle statistically significant difference was observed between the numbers of patients in the various PT-INR categories. However, no significant intra-individual differences were observed in mean TTR. Similarly, the proportion of patients with poor anticoagulation control, high INR variability and high WSI was not significantly different between summer, transition period 1, winter and transition period 2.

Conclusion No clinically significant seasonal variations were observed in the therapeutic response to warfarin.

  • clinical medicine
  • anticoagulants
  • cardiology
  • pharmacology
  • thromboembolism

Data availability statement

Data are available upon reasonable request. The data will be shared upon a reasonable request.

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Data availability statement

Data are available upon reasonable request. The data will be shared upon a reasonable request.

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