阿司匹林(摘要)

POEM*

Low dose aspirin safely reduced thrombosis in polycythaemia vera

Question Is low dose aspirin safe and effective for the prevention of thrombotic complications in patients with polycythaemia vera?

Synopsis Polycythaemia vera is associated with increased blood viscosity, which in turn leads to thrombotic complications. A previous study with high dose aspirin (900 mg/day) was unsuccessful because of a high risk of gastrointestinal bleeding. In this randomised controlled (double blinded) study, 518 patients with polycythaemia, no contraindication to aspirin, and no other indication for antithrombotic therapy were randomised (allocation concealed) to aspirin 100 mg/day or matching placebo. The average red cell count was 5.9 million cells per microlitre, and most patients had a normal platelet count (range 179 000 to 63 000 cells/mm3). The two primary end points were the combination of nonfatal myocardial infarction (MI), nonfatal stroke, or death from cardiovascular causes, and this combination plus pulmonary embolism (PE) and major venous thrombosis. The groups were balanced at the beginning of the study, analysis was by intention to treat, and patients were followed up for a mean of three years. The study was stopped earlier than intended because of difficulty recruiting patients and lack of funding. Patients were evaluated once a year, and end points were adjudicated by two or more evaluators blinded to the treatment assignment. There was a consistent but not always statistically significant benefit to treatment. The risk of the first (2% v 4.9%; P = 0.09) and second (3.2% v 7.9%; P = 0.03) composite end points was lower in the aspirin group. Thus, you would have to treat 21 patients to avoid one non-fatal myocardial infarction, non-fatal stroke, death from

cardiovascular causes, pulmonary embolism, or major venous thrombosis. There were

trends toward lower all cause mortality and for each of the individual clinical end points.

The risk of major bleeding was similar, with three episodes in the aspirin group and two in

the placebo group, but there was a trend toward more minor bleeding in the aspirin group

(20 v 12 episodes; P = 0.1).

Bottom line Low dose aspirin (100 mg/day) is safe and reduces the risk of thrombotic

complications in patients with polycythaemia vera who have a normal platelet count.

Level of evidence 1b (see /levels.html). Individual randomised controlled

trials (with narrow confidence interval). Landolfi R, Marchioli R, Kutti, et al. Efficacy and

safety of low-dose aspirin in polycythemia vera. N Engl J Med 2004;350:114-24.

.infoPOEMs 1992-2004 /informationmastery.cfm

* Patient-Oriented Evidence that Matters. See editorial (BMJ 2002;325:983)

阿司匹林防中风因人而异

日期：2004-06-29 作者：来源：新民晚报

近日国际中风大会上，芝加哥的研究人员称，通过一个小规模的研究，发现约有47％的中风患者或存在一过性脑缺血发作的患者，对阿司匹林的抗栓疗法不是很敏感，即存在阿司匹林抵抗。

该研究在59名中风患者中进行，他们在患病之前至少服用了3天阿司匹林。结果发现，阿司匹林抵抗主要发生在服用低剂量的患者身上。另外还发现，对于不同剂型的阿司匹林来说，肠溶型阿司匹林比非肠溶剂型更容易发生阿司匹林抵抗，分别为73％和39％。该结果说明，对于不同的患者应该采取不同剂量和剂型的阿司匹林治疗。（上海助医网特约编译）

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/lcsj/xyzl.asp?ID=8792

一．阿司匹林的抗血小板作用

研究表明血小板上的环氧化酶(COX-1)可作用于花生四烯酸，使其生成血栓素A2(TXA2)以及前列腺素，而阿司匹林作用于环氧化酶活化部位附近的丝氨酸-529，使其不可逆的乙酰

化而发生酶的失活。TXA2刺激血小板的聚积并诱发血栓形成。阿司匹林通过COX-1的抑

制而减少TXA2的生成，从而起到抑制血小板功能的作用。在不稳定性心绞痛、心肌梗死、高血压甚至糖尿病患者，其血小板的TXA2合成明显增加，血小板血栓素A2受体(TP受体)

的表达也增加，可见阿司匹林在这些疾病中的应用具有举足轻重的地位。

二．阿可匹林抵抗现象

出现阿司匹林的心血管保护作用的不应答或抵抗现象的确切机理目前尚不十分清楚。有研究