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Antithrombotic Trialists' Collaboration Correspondence
to: Antithrombotic Trialists' Secretariat, Clinical Trial Service
Unit, Radcliffe Infirmary, Oxford OX2 6HE www.ctsu.ox.ac.uk
Objective:
To determine the effects of antiplatelet
therapy among patients at high risk of occlusive vascular events.
What is already known on this topic
Long term treatment is beneficial for patients who have had a
myocardial infarction, stroke, or transient ischaemic attack Daily aspirin doses of 75-325 mg are effective What this study adds
Antiplatelet therapy can be started promptly during acute presumed
ischaemic stroke and continued long term Daily aspirin doses of 75-150 mg seem to be as effective as higher
doses for long term treatments (and clopidrogel is an appropriate
alternative for patients with a contraindication to aspirin) Short term addition of a glycoprotein IIb/IIIa antagonist to aspirin
prevents vascular events in patients having percutaneous coronary
intervention and those with unstable angina but causes increased
bleeding
Design:
Collaborative meta-analyses (systematic overviews).
Inclusion criteria:
Randomised trials of an
antiplatelet regimen versus control or of one antiplatelet regimen
versus another in high risk patients (with acute or previous vascular
disease or some other predisposing condition) from which results were
available before September 1997. Trials had to use a method of
randomisation that precluded prior knowledge of the next treatment to
be allocated and comparisons had to be unconfounded
that is, have
study groups that differed only in terms of antiplatelet regimen.
Studies reviewed:
287 studies involving 135 000
patients in comparisons of antiplatelet therapy versus control and
77 000 in comparisons of different antiplatelet regimens.
Main outcome measure:
"Serious vascular event":
non-fatal myocardial infarction, non-fatal stroke, or vascular death.
Results:
Overall, among these high risk patients,
allocation to antiplatelet therapy reduced the combined outcome of any
serious vascular event by about one quarter; non-fatal myocardial
infarction was reduced by one third, non-fatal stroke by one quarter,
and vascular mortality by one sixth (with no apparent adverse effect on
other deaths). Absolute reductions in the risk of having a serious
vascular event were 36 (SE 5) per 1000 treated for two years among
patients with previous myocardial infarction; 38 (5) per 1000 patients
treated for one month among patients with acute myocardial infarction;
36 (6) per 1000 treated for two years among those with previous
stroke or transient ischaemic attack; 9 (3) per 1000 treated for three
weeks among those with acute stroke; and 22 (3) per 1000 treated for
two years among other high risk patients (with separately significant
results for those with stable angina (P=0.0005), peripheral arterial
disease (P=0.004), and atrial fibrillation (P=0.01)). In each of these
high risk categories, the absolute benefits substantially outweighed
the absolute risks of major extracranial bleeding. Aspirin was the most
widely studied antiplatelet drug, with doses of 75-150 mg daily at
least as effective as higher daily doses. The effects of doses lower
than 75 mg daily were less certain. Clopidogrel reduced serious
vascular events by 10% (4%) compared with aspirin, which was similar
to the 12% (7%) reduction observed with its analogue ticlopidine.
Addition of dipyridamole to aspirin produced no significant further
reduction in vascular events compared with aspirin alone. Among
patients at high risk of immediate coronary occlusion, short term
addition of an intravenous glycoprotein IIb/IIIa antagonist to aspirin prevented a further 20 (4) vascular events per 1000 (P<0.0001) but
caused 23 major (but rarely fatal) extracranial bleeds per 1000.
Conclusions:
Aspirin (or another oral antiplatelet
drug) is protective in most types of patient at increased risk of
occlusive vascular events, including those with an acute myocardial
infarction or ischaemic stroke, unstable or stable angina, previous
myocardial infarction, stroke or cerebral ischaemia, peripheral
arterial disease, or atrial fibrillation. Low dose aspirin (75-150 mg
daily) is an effective antiplatelet regimen for long term use, but in acute settings an initial loading dose of at least 150 mg aspirin may
be required. Adding a second antiplatelet drug to aspirin may produce
additional benefits in some clinical circumstances, but more research
into this strategy is needed.
Antiplatelet therapy is effective for short term treatment of patients
with suspected acute myocardial infarction and unstable
angina
Antiplatelet therapy protects against vascular events among patients
with stable angina, intermittent claudication, and (if oral
anticoagulants are unsuitable) atrial fibrillation
© BMJ 2002
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