Antiplatelet drugs
Antiplatelet drugs are used to prevent arterial
thromboembolism,particularly in patients at risk for MI, stroke, and
arteriosclerosis (hardening of the arteries).
Aspirin, clopidogrel, dipyridamole, sulfinpyrazone,
and ticlopi-dine are examples of oral antiplatelet drugs. Antiplatelet drugs
ad-ministered I.V. include abciximab, eptifibatide, and tirofiban.
When taken orally, antiplatelet drugs are absorbed very quickly and
reach peak concentration in 1 to 2 hours. Aspirin maintains its antiplatelet
effect for about 10 days, or as long as platelets normal-ly survive. The
effects of clopidogrel last about 5 days. Sulfinpyra-zone may require several
days of administration before its anti-platelet effects occur.
After I.V. administration, antiplatelet drugs are quickly distrib-uted
throughout the body. They’re minimally metabolized and ex-creted unchanged in
urine. The effects of these drugs occur within 15 to 20 minutes of
administration and last about 6 to 8 hours.
Elderly patients and patients with renal failure may have de-creased clearance
of antiplatelet drugs, which would prolong the antiplatelet effect.
Antiplatelet drugs interfere with platelet activity
in different drug-specific and dose-related ways.
§ Low doses of aspirin inhibit clot formation
by blocking the syn-thesis of prostaglandin, which in turn prevents formation
of the platelet-aggregating substance thromboxane A2.
§ Clopidogrel inhibits platelet aggregation by
inhibiting platelet-fibrinogen binding.
§ I.V. antiplatelet drugs inhibit the
glycoprotein IIa-IIIb receptor, which is the major receptor involved in
platelet aggregation.
§ Dipyridamole may inhibit platelet aggregation
because it in-creases adenosine, a coronary vasodilator and platelet
aggrega-tion inhibitor.
§ Ticlopidine inhibits the binding of fibrinogen
to platelets during the first stage of the clotting cascade.
§ Sulfinpyrazone inhibits several platelet
functions. It lengthens platelet survival and prolongs the patency of
arteriovenous shunts used for hemodialysis. A single dose rapidly inhibits platelet
ag-gregation.
Antiplatelet drugs have many different uses.
Aspirin is used in patients who have had a previous
MI or who have unstable angina to reduce the risk of death in pa-tients at high
risk for CAD. It’s also prescribed to reduce the risk of transient ischemic
attacks (TIAs) (temporary reduction in circulation to the brain).
Clopidogrel is used to reduce the risk of stroke or
vas-cular death in patients with a history of a recent MI, stroke, or
established peripheral artery disease. Clopido-grel is also used to help treat
acute coronary syndromes, especially in patients undergoing percutaneous
translumi-nal coronary angioplasty (PTCA) or coronary artery by-pass graft.
Eptifibatide may be used for patients with acute
coronary syn-drome and for those undergoing percutaneous coronary interven-tion
(PCI). Abciximab may also be used in combination with PCI. Tirofiban may be
used to treat acute coronary syndrome.
Antiplatelet drugs interfere with platelet activity
in different drug-specific and dose-related ways.
Low doses of aspirin inhibit clot formation by
blocking the syn-thesis of prostaglandin, which in turn prevents formation of
the platelet-aggregating substance thromboxane A2.
Clopidogrel inhibits platelet aggregation by
inhibiting platelet-fibrinogen binding.
I.V. antiplatelet drugs inhibit the glycoprotein
IIa-IIIb receptor, which is the major receptor involved in platelet
aggregation.
Dipyridamole may inhibit platelet aggregation because
it in-creases adenosine, a coronary vasodilator and platelet aggrega-tion
inhibitor.
Ticlopidine inhibits the binding of fibrinogen to
platelets during the first stage of the clotting cascade.
Sulfinpyrazone inhibits several platelet functions.
It lengthens platelet survival and prolongs the patency of arteriovenous shunts
used for hemodialysis. A single dose rapidly inhibits platelet ag-gregation.
Antiplatelet drugs have many different uses.
Aspirin is used in patients who have had a previous
MI or who have unstable angina to reduce the risk of death in pa-tients at high
risk for CAD. It’s also prescribed to reduce the risk of transient ischemic
attacks (TIAs) (temporary reduction in circulation to the brain).
Clopidogrel is used to reduce the risk of stroke or
vas-cular death in patients with a history of a recent MI, stroke, or
established peripheral artery disease. Clopido-grel is also used to help treat
acute coronary syndromes, especially in patients undergoing percutaneous
translumi-nal coronary angioplasty (PTCA) or coronary artery by-pass graft.
Eptifibatide may be used for patients with acute
coronary syn-drome and for those undergoing percutaneous coronary interven-tion
(PCI). Abciximab may also be used in combination with PCI. Tirofiban may be
used to treat acute coronary syndrome.
Dipyridamole is used with a coumarin compound to prevent thrombus
formation after cardiac valve replacement. Dipyri-damole may be administered
with aspirin to prevent blood clots in Hypersensitivity
reactions, particularly anaphylaxis, can occur. Bleeding is the most common
ad-verse reaction when I.V. antiplatelet drugs are administered.
Ticlopidine is used to reduce the risk of thrombotic
stroke in high-risk patients, such as those with a history of frequent TIAs or
a previous thrombotic stroke.
Antiplatelet medications taken with NSAIDs,
heparin, oral anti-coagulants, or another antiplatelet medication increase the
risk of bleeding.
Sulfinpyrazone taken with aspirin and oral
anticoagulants in-creases the risk of bleeding.
§ Aspirin increases the risk of toxicity of
methotrexate and val-proic acid.
§ Aspirin and ticlopidine may reduce the
effectiveness of sulfin-pyrazone to relieve signs and symptoms of gout.
§ Antacids may reduce the plasma levels of
ticlopidine.
§ Cimetidine increases the risk of ticlopidine
toxicity and bleed-ing.
Because guidelines haven’t been established for
administrating ticlopidine with heparin, oral anticoagulants, aspirin, or
fibrinolyt-ic drugs, these drugs should be discontinued before ticlopidine
therapy begins. (See Adverse reactions to
antiplatelet drugs.)
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