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ABSTRACT
Objectives
Warfarin exhibits huge inter-individual variability in therapeutic response. We assessed the extent and the factors affecting inter-individual variability in the anticoagulation control using pre-validated pharmacodynamic indices.
Methods
Patients receiving warfarin for at least 6 months were recruited. CHA₂DS₂-VASc, HASBLED, SAMe-TT2R2 scores, warfarin sensitive index (WSI), log-INR variability, and warfarin composite measure (WCM) were assessed. National Institute for Health and Care Excellence (NICE) guideline was adhered for assessing the anticoagulation control using time in therapeutic range (TTR) (TTR < 65%-poor; and TTR ≥ 65%-good). Odds ratio [95% confidence interval] was the effect estimate measure.
Results
Eighty-seven (39.5%) of the patients were poorly anticoagulated. Those with lower HASBLED [OR: 0.3; 0.1, 0.6] and SAMe-TT2R2 scores [OR: 0.2; 0.04, 0.7] and higher CHA₂DS₂-VASc score [OR: 1.8; 1.1, 1.3] predicted good anticoagulation control. Thirty-five (15.9%) patients had high INR variability. Lower TTR, shorter duration of therapy, and higher WSI were observed in patients with high INR variability, and presence of drugs with potential interaction significantly predicted high INR variability.
Conclusion
Significant numbers of our patients on warfarin had poor anticoagulation control and high INR variability. We have identified duration of therapy, CHA₂DS₂-VASc score, and WSI as reliable predictors for anticoagulation control and INR variability.
Acknowledgments
We wish to thank all the staff nurses in the anticoagulation clinic for their immense support while carrying out this study. We are also grateful to Ministry of Health for their kind approval. We also thank the AGU RCSI Steering Committee for their support.
Article highlights
Time in therapeutic range (TTR) is the most common parameter used for assessing anticoagulation control in almost all the studies relevant to pharmacodynamic assessment of warfarin.
However, INR variability is often undermined clinically and has rarely been reported despite the association of high INR variability with thrombotic and bleeding episodes.
Patients with high risk of INR variability were to be closely monitored particularly during initial stages of warfarin therapy.
Declaration of interest
The authors have no relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or pending, or royalties.
Reviewer disclosures
Peer reviewers on this manuscript have no relevant financial or other relationships to disclose.