C H A P T E R 4 8
Drugs affecting blood coagulation
755
the needs of the heart muscle and hypoxia develops. If
a vessel becomes so narrow that a tiny clot occludes it
completely, the blood supply to that area is cut off and
anoxia occurs, followed by infarction and necrosis. With
age, many of the vessels in the body can be damaged
and develop similar problems with narrowing and blood
delivery. These disorders are treated with drugs that
interfere with the normal coagulation process to prevent
the formation of clots in the system.
Haemorrhagic disorders
Haemorrhagic disorders
, in which excess bleeding
occurs, are less common than thromboembolic disor
ders. These disorders include haemophilia, in which
there is a genetic lack of clotting factors; liver disease, in
which clotting factors and proteins needed for clotting
are not produced; and bone marrow disorders, in which
platelets are not formed in sufficient quantity to be effec
tive. These disorders are treated with clotting factors
and drugs that promote the coagulation process.
■■
Disorders that are directly related to the clotting
process include thromboembolic disorders, in which
too much clotting can lead to emboli and occlusion of
blood vessels, and haemorrhagic disorders, including
haemophilia, in which lack of efficient clotting can
lead to excessive blood loss.
DRUGS AFFECTING CLOT FORMATION
AND RESOLUTION
Drugs that affect clot formation include
antiplatelet
drugs, which alter platelet aggregation and the forma
tion of the platelet plug; anticoagulants, which interfere
with the clotting cascade and thrombin formation; and
thrombolytic agents, which break down the thrombus
or clot that has been formed by stimulating the plasmin
system (see Table 48.1). Box 48.2 discusses the inter
action of herbal remedies with these agents.
KEY POINT
TABLE 48.1
DRUGS IN FOCUS Drugs affecting clot formation and resolution
Drug name
Dosage/route
Usual indications
Antiplatelet agents
abciximab (ReoPro)
0.25 mg/kg IV bolus 10–60 minutes before
procedure, then continuous infusion of
10 mcg/kg per minute for 12 hours
Angina: 0.25 mg/kg by IV bolus, then
10 mcg/kg per minute IV for 18–24 hours
Prevention of acute cardiac events during
transluminal coronary angioplasty when
used in conjunction with heparin and
aspirin; early treatment of unstable
angina and non-Q-wave myocardial
infarction (MI)
anagrelide (Agrylin)
0.5 mg PO q.i.d. or 1 mg PO b.d., may increase
by 0.5 mg/day each week; maximum dose
10 mg/day or 2.5 mg as a single dose
Treatment of essential thrombocythaemia
to reduce elevated platelet count and
decrease the risk of thrombosis
aspirin (Astrix,
Cardiprin, Solprin)
150 mg/day PO to reduce platelet aggregation
Reduction of the incidence of TIAs and
strokes in men; reduction of the risk of
death or non-fatal MI in people with a
past history of MI or with angina
cilostazol (Pletal)
100 mg PO b.d.
Reduction of symptoms of intermittent
claudication, allowing increased walking
distance in adults
clopidogrel (Plavix)
75 mg/day PO
Treatment of people who are at risk for
ischaemic events; people with a history
of MI, peripheral artery disease, or
ischaemic stroke; and people with acute
coronary syndrome
dipyridamole (Persantin)
50 mg PO t.d.s. for angina; 75–100 mg PO
q.i.d. for heart valve people; 0.142 mg/kg per
minute IV over 4 minutes for diagnosis
Prevention of thromboembolism in people
with artificial heart valves when used in
combination with warfarin; aids diagnosis
of coronary artery disease (CAD) in
people who cannot exercise; may be
used in treatment of angina (found to be
only “possibly effective” by the US FDA)
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