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Prescribing Pattern and Risk Analysis of Potential Significant Drug Interactions among Warfarin Users in Taiwan: A National Health Insurance Research Database Study
warfarin,prescribing pattern,drug interaction,drug adverse event,National Health Insurance Research Database,
|Publication Year :||2010|
使用1997∼2004年臺灣100萬人健保資料庫承保抽樣歸人檔，進行回溯性世代研究，研究族群為1997年3月31日以後開始服用warfarin的新使用者（new-users）。Warfarin處方型態分析包含每日使用劑量、平均PT/INR (prothrombin time/international normalized ratio)值監測頻率等。
有六成以上（63.8%）的warfarin使用者曾暴露於一級交互作用之下。前五名常見之一級交互作用藥品為aspirin (34.5%)、noscapine (11.1%)、amiodarone (9.4%)、ketoprofen (7.4%)、和naproxen (7.2%)，且近七成（67.7%）是來自同位醫師，約一半（54.4%）是來自醫學中心。並且，有無一級交互作用時的warfarin劑量無統計上顯著差異（p=0.114），且有近五成（44.6%）的病人在交互作用期間無監測PT/INR值，且當交互作用來自不同醫師時，有更高比例（66.7%）無監測。
Warfarin exhibits narrow therapeutic range and high protein binding. It is metabolized via cytochrom P450 enzyme system. Therefore, patients treated with warfarin are prone to serious drug-drug interactions (DDIs) and major adverse events (AEs). DDI of warfarin is significantly associated with 1.2~4.5 times increased risk of major hemorrhage, hospital admission, and prolonged length of stay. However, the occurrence of DDIs and AEs during warfarin therapy has not been studied extensively among Asian population. Few studies used national database, and definitions and lists of DDIs varied in the literature.
Using Taiwan’s National Health Insurance Research Database to analyze the prescription pattern of warfarin, prevalence rate of potential significant DDIs, incidence rate (IR) of major AEs (i.e., hemorrhage and thromboembolism) among warfarin users in Taiwan.
The National Health Insurance Research Database with one million randomly selected individuals in Taiwan was used in this retrospective cohort study. New users started warfarin between April 1997 and December 2004. Prescribing pattern, including prescribed daily warfarin dose and average PT/INR (prothrombin time/international normalized ratio) monitoring frequency, were analyzed.
DDIs were defined as prescriptions from outpatient clinics with at least one day overlap with warfarin treatment episodes. Significance grade one DDIs were defined as DDIs with major severity and established documentation. A total of 56 grade one DDIs were evaluated in this study. In addition, dose of warfarin and PT/INR monitoring frequency when DDIs occurred were compared with those without grade one DDIs.
Major adverse events were defined as the first emergency room visits and/or hospitalizations with a diagnosis of hemorrhage or thromboembolism, identified by International Classification of Disease, Ninth Revision, Clinical Modification (ICD9-CM), during the treatment episode. Moreover, all thromboembolism events were confirmed by antithrombotic agents and primary indications for warfarin.
Among 4047 new-users, mean age was 63.4 years old. More than half (56.3%) of new-users were female. Warfarin was prescribed mainly for ischemic heart disease (23.2%). The most common comobidity was hypertension (36.4%). Average daily dose of warfarin was 2.8 ±1.2 mg. There were 29.1% of patients never received PT/INR monitoring during warfarin treatment. Other patients monitored PT/INR every 40.5 days.
A total of 2582 warfarin users (63.8%) were concurrently prescribed drugs with grade 1 DDIs. The most frequently prescribed medicines were aspirin (34.5%), noscapine (11.1%), amiodarone (9.4%), ketoprofen (7.4%), and naproxen (7.2%). Approximately 70% of these prescriptions were from the same physicians. About half of DDIs (54.4%) were from the medical centers. Doses of warfarin with or without DDIs were similar (p = 0.114). About half of patients (44.6%) had no PT/INR monitoring orders during DDIs. Fewer patients checked PT/INR when DDIs were involved different physicians.
There were 412 patients developing hemorrhage with an incidence rate of 10.9% per person-year, and the majority was gastrointestinal hemorrhage (40.8%). On the other hand, 474 patients experiencing thromboembolism with an incidence rate of 12.8% per person-year, and the most common diagnosis was ischemic stroke (31.4%).
Average daily warfarin dose was 2.8 mg. Approximately 30% of patients had no PT/INR monitoring during treatment. PT/INR was ordered about every 6 weeks. Prevalence of grade one DDIs were more than 60%. The most prevalent DDIs were aspirin, noscapine, amiodarone. Almost half of patients had no PT/INR monitoring orders during DDIs. Moreover, IRs of hemorrhage and thromboembolism were 10.9%, 12.8% per person-years, respectively. The most common major AEs were gastrointestinal hemorrhage and ischemic stroke. In Taiwan, medical records from different physicians have not yet been completely retrieved through medical insurance cards. Computerized DDI alert systems are uncommon in hospitals. It is essential to establish a computerized electronic alert system on DDIs along with continuing educations for physician and pharmacist to safeguard patients’ safety.
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