23 Anticoagulants

Multimedia Directory Slide 17 Mechanism of Action of Heparin Animation Slide 25 Mechanism of Action of Warfarin Animation

Hemostasis: Three Events After Injury Vascular spasms: platelets release serotonin, which causes blood vessel to spasm and decrease blood loss until clotting occurs Platelet plug: platelets become sticky and adhere to vessel lining and each other, forming platelet plug, which is invaded by clotting factors

Hemostasis: Three Events After Injury Coagulation: clot forms through chemical reactions that create netlike structure of fibrin, sealing off opening in injured vessel

Figure 23-1 Hemostasis begins when a blood vessel is damaged and ends when the fibrin threads trap blood cells, forming a clot that seals the injured vessel.

Figure 23-2 Basic steps of hemostasis.

Mechanism of Action: Hemostasis Involves 11 plasma proteins (clotting factors) Most clotting proteins synthesized by liver Prothrombin activator, prothrombin, thrombin, fibrinogen, fibrin

Figure 23-3 The steps in the coagulation cascade.

Anticoagulants Medications that prolong bleeding time Do not dissolve clots already formed, but may prevent clots from becoming larger Used to treat MI, venous thrombosis, pulmonary emboli Primarily used for thrombosis in veins

Table 23-1 Anticoagulants

Heparin: Uses Works by increasing length of coagulation; inhibits thrombi from forming or growing larger Treat emboli, thrombi, MI, and to prevent clotting during open-heart surgery, coronary artery bypass graft, and dialysis

Heparin: Adverse Effects Hemorrhage in urinary or GI tracts, subdural hematomas, hemorrhagic pancreatitis, hemarthrosis, ecchymosis

Heparin: Contraindications Contraindicated in serious and intracranial bleeding, severe liver or kidney disease, malignant hypertension Interacts with aspirin, NSAIDs, anesthetics, valproic acid, thrombolytics, and other drugs

Heparin: Patient Information Teach patients how to administer heparin subcutaneously. Advise patients to protect themselves from injury (e.g., use electric shaver). Warn patients to avoid aspirin and other OTC drugs. Instruct patients to report signs of bleeding.

Heparin in Older Adults Older adults are more susceptible to effects of anticoagulants. Signs of overdose include epistaxis, blood in stool or urine, excessive bruising, and prolonged bleeding. Overdose can be treated by slow infusion of 1% protamine sulfate.

Figure 23-4 Mechanism of action of anticoagulants.

Mechanism of Action of Heparin Animation Click on the screenshot to view an animation showing the mechanism of action of heparin. Back to Directory

LMWH: Uses Greater bioavailability and longer action than heparin More effective in preventing and treating venous thromboembolism Less bleeding and fewer episodes of heparin-induced thrombocytopenia

Table 23-2 Common Low-Molecular-Weight Heparins

Warfarin (Coumadin): Uses Interferes with hepatic synthesis of vitamin K-dependent clotting factors (II, VII, IX, X) Used on inpatient and outpatient basis for long-term anticoagulation

Warfarin: Adverse Effects Hemorrhage Diarrhea Urticaria Alopecia Skin necrosis Dermatitis

Warfarin: Contraindications Contraindicated in active or previous ulceration, hepatic or renal disease, malignant hypertension, bacterial endocarditis, chronic alcoholism, pregnancy Interacts with hepatic enzyme inhibitors, aspirin, NSAIDs, and thrombolytics

Warfarin: Patient Information Instruct patients to report signs of bleeding; chest, abdominal, lumbar, or pelvic pain. Advise patient to stop drug immediately if signs of hepatitis occur. Advise female patients to avoid pregnancy with barrier contraceptive and to avoid breastfeeding.

Warfarin Tips for Patients Advise patients that 5 days prior to dental procedures, warfarin should be stopped. Supplemental intake of vitamin K can potentiate or inhibit oral anticoagulants.

Mechanism of Action of Warfarin Animation Click on the screenshot to view an animation showing the mechanism of action of warfarin. Back to Directory

Antiplatelets: Uses Prevent platelets from binding together Used to prevent clot formation in arteries, in MI and stroke, and in PCTA Aspirin: low doses inhibit platelet aggregation and prolong bleeding time Ticlopidine (Ticlid) and clopidogrel (Plavix) irreversibly inhibit platelet activation

Antiplatelets: Uses Abciximab (ReoPro), eptifibatide (Integrilin) and tirofiban (Aggrastat) interrupt interaction of fibrinogen with clotting factors

Table 23-3 Antiplatelet Agents

Antiplatelets: Adverse Effects Epigastric pain, heartburn, nausea, diarrhea, major or minor bleeding Abciximab: cardiac arrhythmias, abnormal thoughts, dizziness

Antiplatelets: Contraindications Contraindicated in patients with history of peptic ulcer, hypertension, asthma, allergies, nasal polyps Interact with anticoagulants, thrombolytic agents, dextran, and other drugs

Antiplatelets: Patient Information Instruct patients to report nausea, diarrhea, rash, sore throat, or infections; signs of bleeding; signs of hepatitis. Advise patients to avoid aspirin and antacids.

Garlic as Anticoagulant Garlic has been shown to decrease platelet aggregation. Use of garlic with anticoagulants may increase risk of bleeding complications.

Thrombolytics: Uses Used to prevent or treat excessive bleeding from surgical sites Facilitate conversion of plasminogen to plasmin, which hydrolyzes fibrin to dissolve blood clots Also called plasminogen activators

Table 23-4 Thrombolytics

Thrombolytics: Adverse Effects Common: bleeding caused by fibrinogenolysis or fibrinolysis at site of injury Serious: intracranial bleeding

Thrombolytics: Contraindications Contraindicated in active bleeding, pregnancy, lactation, intracranial trauma, vascular disease, and cancer Interact with anticoagulants, aspirin, and herbs such as feverfew, ginger, and ginkgo

Thrombolytics: Patient Information Instruct patients to report signs of bleeding or changes in consciousness. Advise women to avoid breastfeeding.

Thrombocytopenia Platelet deficiency; most common cause of abnormal bleeding Hemophilia applies to several hereditary bleeding disorders that result from lack of factors needed for clotting.