McKenna's Pharmacology for Nursing, 2e

755

C H A P T E R 4 8 Drugs affecting blood coagulation

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.

KEY POINT

■■ 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.

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 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 150 mg/day PO to reduce platelet aggregation

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) Treatment of essential thrombocythaemia to reduce elevated platelet count and decrease the risk of thrombosis 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 Reduction of symptoms of intermittent claudication, allowing increased walking distance in adults 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 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) Continued on following page

anagrelide (Agrylin)

aspirin (Astrix, Cardiprin, Solprin)

cilostazol (Pletal)

100 mg PO b.d.

clopidogrel (Plavix)

75 mg/day PO

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