The Lowest Effective Intensity of Anticoagulation for Patients with Atrial Fibrillation and the Predictor Factors of Maintenance Dose Requirement at a Medical Center
Date Issued
2006
Date
2006
Author(s)
Chou, Guann-Miaw
DOI
zh-TW
Abstract
The pharmacokinetic profile of warfarin is complex. Monitoring is required to avoid both thromboembolic events associated with low intensity anticoagulation and hemorrhagic complications associated with high intensity. Target levels of oral anticoagulation are disease- specific and measured with the international normalized ratio (INR). To attain applicable INR values, patients are routinely monitored and their doses are adjusted when necessary. In practice, it is difficult to maintain a stable and optimal INR because of unexpected fluctuations of the INR values. This can be attributed to many factors including changes in diet, poor compliance with medication, alcohol consumption, and drug-drug interactions.
It has been suggested to keep Asian patients at a lower intensity of anticoagulation because Asians seem to be less vulnerable to thrombotic diseases than White people.Although evidence to support the practice is lacking, most clinicians are cautious to keep at a lower INR. The gudeline of the American College of Chest Physicians (ACCP) recommended the optimal INR for patients with atrial fibrillation at 2-3. However, this range for Europeans and Americans has been questioned as being excessively high for Taiwanese with atrial fibrillation. We performed a retrospective study in National Taiwan University Hospital (NTUH) on patients with atrial fibrillation taking warfarin for storke prevention from January 1, 2004,to September 30,2005.Patients were excluded if they had any a histiry of mechanical heart valve replacement before the recorded AF diagnosis because the target INR range is higher for this indication.We systemically collected the records of warfarin use, comorbid diseases, and all INR results. Thromboembolic episodes included ischemic stroke, transient ischemic attack ,arterial embolism and thrombosis and myocardial infarction .Major bleeding episodes included intracranial hemorrhage and gastrointestinal bleeding .The INR at the time of events or defined temporally related within the past 7 days of the thromboembolic and bleeding episodes were recorded. The INR range was divided into 6 categories: <1.5, 1.5-1.9, 2.0-2.5, 2.6-3.0,3.1-3.5,>3.5.The number of events was recorded for each catogories and this formed the numerator.The denominator was the summation of time each patients stayed in each category of INR.The event rate was calculated for each INR category.
Six hundreds and sixty nine patients were included in the analysis , which constituted 867 patient -years. The time spent in INR=2-3 was 34%. Most time(70.8%) was spent in INR=1.5-3.0. The overall event rate was lowest in the range from 1.5-2.5(3.96%), compared to INR<1.5(10%) or INR>2.5(16.9), p=0.038. This supports the clinical feasibility of lower intensity anticoagulant therapy for Taiwanese patients with atrial fibrillation. Among these patients, coronary artery disease was a risk factor for thromboembolism in univariate analysis. However,older age(≧75 years)was a risk factor for bleeding in multivariate analysis.Among patients taking warfarin longer than 4 weeks,age correlated negatively with the maintenance dose of warfarin (γ=-0.32,p=0.004).
In conclusion, our retrospective study showed that an INR between 1.5-2.5 was associated with lower complications in Taiwanese patients treated with warfarin.
Subjects
心房纖維顫動患
最低有效抗凝血強度
維持劑量
Atrial Fibrillation
The Lowest Effective Intensity of Anticoagulation
Maintenance Dose
Type
text
File(s)![Thumbnail Image]()
Loading...
Name
ntu-95-R93451006-1.pdf
Size
23.31 KB
Format
Adobe PDF
Checksum
(MD5):0d93ac869c190061f6a255d587f8e8ca