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Age and gender differences during long-term warfarin anticoagulation monitored with Fiix-prothrombin time or prothrombin time in patients with atrial fibrillation

Maí 2015

Introduction: The prothrombin time (PT, PT-INR) during monitoring of warfarin measures its influence on the activity of coagulation factors (F) II, VII and X. Rapid fluctuations occur in the PT-INR due to FVII´s short half-life but these fluctuations have little effect on the antithrombotic activity of warfarin which is mainly induced by FII and possibly FX. The new Fiix-PT measures only the activity of the longer half-life FII and FX. The Fiix-trial showed that monitoring with Fiix-PT lead to less variability of anticoagulation than monitoring with PT. The objective of this study was to compare if stability of anticoagulation monitored by Quick-PT and Fiix-PT was affected differently by age and gender.
Methods and materials: This study is a part of the prospective, randomized controlled and double-blinded Fiix-trial. Patients were randomized to dosing based on Fiix-PT (Fiix-INR) monitoring (the active Fiix arm) and PT (PT-INR) monitoring (control PT arm). The participants were outpatients over 18 years old with INR 2-3 as a therapeutic range. The current subgroup study analyzed anticoagulation indicators in 815 atrial fibrillation (AF) patients on long-term warfarin therapy. The main outcome parameters were time in therapeutic range (TTR), INR variance growth rate (VGR), frequency of INR monitoring, fraction of tests in defined target INR range and number of dose adjustments.
Results: Patients in the Fiix-PT arm had 65.5% of tests in target range compared to 62.9% in the PT arm (p = 0.0019) and they had proportionally fewer tests with INR < 2 (18.9% vs 20.9%, respectively, p = 0.0061). There were fewer dose changes per monitoring test in the Fiix-PT arm than in the PT arm (0.26 vs 0.28, p = 0.0428). Males in the Fiix-PT group and PT group had 0.26 vs 0.27 median dose changes per monitoring test (p = 0.2707). Females in the Fiix-PT group and PT group had 0.27 and 0.32 dose changes per monitoring test (p = 0.0292). Females in the Fiix-PT group had 64% of tests in target range and females in the PT group had 59% (p = 0.0001). Females in the Fiix-PT group had 20% of tests with INR < 2 and females in the PT group had 24% (p = 0.0002). The median TTR in females in the Fiix-PT group was 80.3% compared to 75.3% in females in the PT group (p = 0.0401) but the median TTR in males was 80.7% vs 80.3% (n.s.). Females in the PT group had higher median daily warfarin dose than females in the Fiix-PT group, 4.2 mg vs 3.4 mg (p = 0.0029). Both the Fiix-PT and the PT-INR variability (VGR) were significantly higher in females than in males. There was a significant difference between the TTR (median) in the Fiix-PT and PT groups in 66-80 years old patients and in 66-74 years old patients in dose changes per test and VGR. The daily dose decreased with increasing age in both groups.
Conclusion: The Fiix-PT test improved the stability of warfarin in females. Females on warfarin monitored with the Fiix-INR had significantly higher TTR and their dose-adjustment need was reduced. Anticoagulation variability (VGR) was higher in females than in males in both groups.


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