5-7. ANTICOAGULANT AGENTS
a. Anti-platelet agents. Anti-platelet agents are used to prevent a clot from
forming (step I) or prevent the clot from getting larger and occluding the entire vessel.
All patients must be warned of the increased risk of bleeding when taking these drugs.
(1) Aspirin. Aspirin is the most widely used anti-platelet drug. It inhibits
platelet aggregation for the life of the platelet (7-10 days). Because of this effect, aspirin
is prescribed in the setting of acute myocardial infarction and prophylactically to prevent
reinfarction. Always ask the patient if he/she has an allergy to aspirin.
(2) Clopidogrel (Plavix) and Ticlopidine (Ticlid). Clopidogrel and
ticlopidine work by inhibiting platelet aggregation. They are often prescribed for patients
that have an aspirin allergy or are intolerant of aspirin (usually stomach upset). Both
agents may be used in patients with atherosclerotic disease to prevent heart attacks,
prevent stokes, and prevent coronary artery closure in patient undergoing angioplasty.
Ticlopidine is administered twice daily and is associated with a risk of decreased white
blood cells (neutropenia). Clopidogrel is administered once daily and has a much lower
risk of neutropenia. Both agents can cause a rash.
(3) Dipyridomole (Persantine). Dipyridomole works by inhibiting platelets
from adhering to the injured cell wall. Although not used extensively, it may be
prescribed in combination with other anticoagulants. The combination product of
dipyridomole and aspirin is called Aggrenox.
(4) Abciximab (ReoPro), Tirofiban (Aggrastat), and Eptifibatide
(Integrelin). The following agents are known as glycoprotein Ilb/IIIa inhibitors. The
GP Ilb/IIIa receptor is the major receptor on the platelet responsible for platelets
adhering to each other and forming the initial clot. These drugs are administered
intravenously in patients with acute coronary syndromes (unstable angina) or in patients
undergoing angioplasty with or without stent placement in the cardiac catheterization
lab. The agents prevent clots from forming in the coronary arteries of the heart. The
agents are not interchangeable and differ in their respective half-lives and infusion
schedules. The major side effect is thrombocytopenia (low platelet count) occasionally
requiring a platelet transfusion.
b. Heparin products. Heparin is used to prevent the clotting of blood in the
patient and in laboratory samples by inhibiting certain clotting factors (Thrombin/Factor
Ila and Factor Xa). Like anti-platelet drugs, heparin will not dissolve a clot but prevents
it from getting larger. The dosage of this agent is based upon the needs of the patient
(prophylactic vs. treatment doses). It may be administered subcutaneously or
intravenous (IV Push or IV continuous infusion). The major side effect associated with
heparin is possible hemorrhage. Protamine sulfate is used to treat heparin overdose.
Although protamine sulfate is also an anticoagulant, it counteracts the effects of heparin
by binding with the heparin. The net result is removing the effects of the heparin. The