Coagulation Modifier Drugs

Chapter 26: Coagulation Modifier Drugs

Hemostasis

• Definition: General term for any process that stops bleeding.
• Hemostasis involves a complex relationship between substances that:
  • Promote clot formation.
  • Inhibit coagulation or dissolve formed clots.
• Key Terms:
  • Thrombus: Technical term for a blood clot.
  • Embolus: A thrombus that moves through blood vessels.

Coagulation System

• Description of the coagulation system as a "cascade" where:
  • Each activated factor serves as a catalyst that amplifies the next reaction.
  • The final result is fibrin, a clot-forming substance.
• There are two main pathways:
  • Intrinsic pathway
  • Extrinsic pathway

Fibrinolytic System

• Function: Initiates the breakdown of clots to balance the coagulation process.
• Fibrinolysis: The mechanism by which formed thrombi are lysed to prevent excessive clot formation and blockage of blood vessels.

Detailed Mechanics of the Fibrinolytic System

• Process:
  • Fibrin in a clot binds to a circulating protein called plasminogen.
  • This binding converts plasminogen to plasmin.
  • Plasmin is an enzymatic protein that breaks down the fibrin thrombus into fibrin degradation products, which helps keep the thrombus localized and prevents it from becoming an embolus.

Hemophilia

• A rare genetic disorder where natural coagulation and hemostatic factors are limited or absent.
• Patients with hemophilia face a fatal risk if coagulation factors are not provided.
• Types:
  • Factor VII deficiency
  • Factor VIII and/or Factor IX deficiency

Pharmacology Overview

• Coagulation-affecting drugs are considered some of the most dangerous drugs used today due to multiple factors influencing their actions.

Coagulation Modifier Drugs

• Definition: Medications that affect coagulation processes in the body.
• Categories include:
  • Anticoagulants: Prevent or delay blood coagulation by inhibiting action or formation of clotting factors.
  • Antiplatelet drugs: Prevent the formation of platelet plugs or inhibit platelet aggregation.
  • Hemorheologic drugs: Alter platelet function without preventing the platelets' actions.
  • Thrombolytic drugs: Dissolve thrombi by acting akin to tissue plasminogen activator, effectively lyse existing clots.
  • Antifibrinolytic or hemostatic drugs: Prevent lysis of fibrin, promoting blood coagulation.

Anticoagulants

• Characteristics:
  • Classified as antithrombotic drugs.
  • No direct effect on an already formed blood clot.
  • Key for the prevention of:
  • Intravascular thrombosis
  • Clot formation (thrombus)
  • Embolus (dislodged clot)

Thromboembolic Events

• Definitions and examples of events:
  • Myocardial Infarction (MI): Embolus lodged in a coronary artery.
  • Stroke: Embolus obstructs a brain vessel.
  • Pulmonary Emboli: Embolus in the pulmonary circulation.
  • Deep Vein Thrombosis (DVT): Embolus travels to a vein in the leg.

Anticoagulants: Heparins

• Action: Prevent blood from clotting by inhibiting clotting factors IIa (thrombin) and Xa, slowing fibrin formation and preventing new clot development.
• Uses: Prevention and treatment of DVT, PE, and MI.

Unfractionated Heparin (UFH)

• Characteristics:
  • Large, natural molecule derived from animal sources (e.g., pig intestinal mucosa or cow lungs).
  • Effects can be unpredictable, requiring frequent monitoring.
• Action: Inhibits Factors IIa (thrombin) and Xa.
• Monitoring: Requires aPTT with a goal of 1.5-2.5 times control.
• Routes of Administration: IV (for treatment), SQ (for prevention).
• Antidote: Protamine sulfate.
• Heparin Flush: 10-100 units/mL, keeps IV lines open, does not need monitoring.

Low Molecular Weight Heparins (LMWHs)

• Examples: Enoxaparin (Lovenox), Dalteparin (Fragmin).
• Characteristics: Synthetic, smaller molecular structure derived from heparin.
• Advantages include:
  • More predictable anticoagulant response primarily inhibiting Factor Xa.
  • No need for frequent aPTT monitoring.
  • Generally administered subcutaneously and can be used on an outpatient basis.
  • Longer duration of action than unfractionated heparin.

Summary: Comparison of Heparins

Nursing Considerations for Heparins

• Monitor for signs of bleeding including:
  • Bruising
  • Hematuria (blood in urine)
  • Melena (black stools)
  • Nosebleeds
• Educate patients about signs of bleeding and injury prevention.
• Avoid concurrent use with NSAIDs, aspirin, or other anticoagulants.
• Rotate subcutaneous injection sites and do not aspirate or massage.
• Keep protamine sulfate available for overdose situations.

Mechanism of Action: Warfarin

• Inhibits vitamin K–dependent clotting factors: Factors II, VII, IX, and X.
• Specifically, warfarin inhibits vitamin K synthesis by:
  • Bacteria in the gastrointestinal tract.
  • Liver production, leading to decreased synthesis of vitamin K–dependent clotting factors.
• The final effect is prevention of clot formation.
• Note: Coumadin (warfarin) name brand was discontinued in 2020 due to non-cost-effective manufacturing issues.

Anticoagulants: Factor Xa Drugs

• Factor Xa Inhibitors include:
  • Fondaparinux (Arixtra) - Direct
• Direct Oral Anticoagulants:
  • Rivaroxaban (Xarelto)
  • Apixaban (Eliquis)
  • Edoxaban (Savaysa)
  • Betrixaban (Bevyxxa)
• All these drugs inhibit thrombosis specifically via Factor Xa.

Anticoagulants: Direct Thrombin Inhibitors

• Action: Directly inhibit thrombin (Factor IIa).
• Drugs:
  • Natural: Human antithrombin III (Thrombate)
  • Synthetic:
  • Lepirudin (Refludan)
  • Argatroban (Argatroban)
  • Bivalirudin (Angiomax)
  • Dabigatran (Pradaxa) (oral)

Indications for Anticoagulants

• Used to prevent clot formation in scenarios likely to cause clotting, including:
  • MI
  • Unstable angina
  • Atrial fibrillation
  • Indwelling devices (mechanical heart valves)
  • Major orthopedic surgery

Contraindications for Anticoagulants

• Conditions where anticoagulants should not be used include:
  • Drug allergy
  • Any acute bleeding process or high risk for such occurrences.
  • Warfarin is strongly contraindicated in pregnancy, other anticoagulants vary in pregnancy risk ratings (B or C).
  • LMWHs are contraindicated in patients with indwelling epidural catheters due to the risk of epidural hematoma.

Adverse Effects of Anticoagulants

• Risks increase with dosage:
  • Bleeding: Can be localized or systemic.
  • Heparin-induced thrombocytopenia (HIT).
  • General side effects: Nausea, vomiting, abdominal cramps, and thrombocytopenia.
  • Warfarin may cause skin necrosis and purple toes syndrome.

Heparin-Induced Thrombocytopenia (HIT)

• Type I:
  • Gradual reduction in platelets; heparin therapy can be continued.
• Type II:
  • Acute fall in platelets (> 50% reduction from baseline); not safe to continue heparin.
  • Considered a medical emergency.

Toxic Effects of Heparin

• Symptoms to watch for include:
  • Hematuria
  • Melena
  • Petechiae
  • Ecchymoses
  • Gum or mucous membrane bleeding.
• The drug should be stopped immediately.
• Treatment: Administer intravenous protamine sulfate; 1 mg of protamine can reverse 100 units of heparin.

Toxic Effects of Warfarin

• Reversal:
  • Discontinue warfarin, liver may need 36 to 42 hours to synthesize enough clotting factors to reverse its effects.
  • High doses of vitamin K1 (phytonadione) (10 mg IV) can hasten the return to normal coagulation within 6 hours.
• Caution: Vitamin K administration can lead to warfarin resistance for up to 7 days.
• Severe bleeding may require transfusions of plasma or clotting factor concentrates. In life-threatening bleeding situations, Kcentra and Profiline may be used.
  • Risk of anaphylaxis with IV vitamin K; minimize risk by diluting and administering slowly over 30 minutes.

Idarucizumab (Praxbind)

• Specific antidote for dabigatran.
• Reverses anticoagulant effects of dabigatran for emergency surgery or in life-threatening/uncontrolled bleeding situations.

Andexxa

• Drugs Involved: Factor Xa inhibitors such as Rivaroxaban (Xarelto) and Apixaban (Eliquis).
• Antidote/Reversal Agent: Used for life-threatening or uncontrolled bleeding from these anticoagulants.
• Works by binding and inactivating Factor Xa inhibitors, reversing their anticoagulant effects and restoring normal clotting.
• Black Box Warning: Abrupt discontinuation can lead to:
  • Myocardial infarction (MI)
  • Ischemic stroke
  • Cardiac arrest
  • Sudden death.
• Nursing Implications:
  • Closely monitor for signs of thrombosis post-reversal.
  • Use only during severe/life-threatening bleeding conditions.
  • Avoid sudden discontinuation without a new anticoagulant plan.
  • Educate patients on symptoms to report such as chest pain, shortness of breath, and neurological deficits.

Drug Interactions: Anticoagulants

• Mechanism of Interactions:
  • Enzyme Inhibition of Metabolism: Some drugs may inhibit liver enzymes that metabolize anticoagulants (e.g., warfarin), increasing their levels and bleeding risk.
  • Displacement from Protein-Binding Sites: Drugs that bind to plasma proteins can displace anticoagulants, leading to enhanced effects and increased bleeding risk.
  • Decrease in Vitamin K Absorption or Synthesis: Antibiotics or GI disturbances can hinder vitamin K production by gut bacteria, leading to increased anticoagulant effects because of diminished clotting factor production.
  • Alteration in Platelet Count or Activity: Certain drugs (e.g., aspirin, NSAIDs) impair platelet function or reduce platelet count, magnifying bleeding risks when combined with anticoagulants.

Clinical Significance of Drug Interactions

• Essential to monitor INR/PT levels closely.
• Always look out for signs of bleeding such as bruising, hematuria, and gum bleeding.
• Exercise caution when introducing new medications into anticoagulant therapy.

Common Drug Interactions with Warfarin (Coumadin)

1. Increased Anticoagulant Effect (↑ Bleeding Risk):
   • Antibiotics (e.g., sulfonamides, metronidazole) reduce vitamin K synthesis and inhibit warfarin metabolism.
   • Amiodarone: inhibits warfarin metabolism.
   • NSAIDs/Aspirin: inhibit platelet function and cause mucosal damage.
   • Cimetidine (Tagamet): inhibits hepatic metabolism.
   • Herbal products: Garlic, ginkgo, ginseng, feverfew.
2. Decreased Anticoagulant Effect (↓ Warfarin Activity):
   • Barbiturates, Carbamazepine, Rifampin induce hepatic enzymes leading to faster warfarin breakdown.
   • Vitamin K-rich foods (broccoli, spinach) can counteract warfarin efficacy.
   • Oral contraceptives increase synthesis of clotting factors.

Nursing Considerations for Warfarin (Coumadin)

• Regular monitoring of PT/INR is crucial.
• Teach patients to maintain a consistent diet regarding vitamin K intake (avoid large variations).
• Advise against new OTC or herbal medications without provider approval.
• Monitor for signs of bleeding or clotting.

Argatroban

• A synthetic direct thrombin inhibitor indicated for use in active HIT and during percutaneous coronary intervention procedures in at-risk patients.
• Administration is only via IV.

Dabigatran (Pradaxa)

• The first oral direct thrombin inhibitor approved for stroke prevention and thrombosis in patients with non-valvular atrial fibrillation.
• Functions as a prodrug activated in the liver; binds to free and clot-bound thrombin reversibly.
• Adverse Effects: Includes bleeding and GI complications; does not require coagulation monitoring.

Enoxaparin (Lovenox)

• A prototypical LMWH with greater affinity for Factor Xa than for Factor IIa.
• Higher bioavailability, longer half-life, and no routine lab monitoring required.
• Administered via injection; use pre-filled syringes without expelling air bubbles and give at least 2 inches from the umbilicus.

Fondaparinux (Arixtra)

• A selective factor Xa inhibitor used for DVT or PE prophylaxis.
• Adverse reactions may include bleeding, anemia, and others; caution is advised post-surgery to avoid complications.

Rivaroxaban (Xarelto)

• First oral factor Xa inhibitor used for stroke prevention in patients with a-fib and for treatment of DVT and PE.
• Notable adverse reactions consist of peripheral edema, dizziness, and bleeding.

Warfarin (Coumadin)

• The most commonly prescribed oral anticoagulant.
• Monitoring of PT/INR is vital for safe administration.
• Normal INR is approximately 1.0; therapeutic INR (under warfarin therapy) varies from 2 to 3.5, depending on the indication.
• Variations due to genetic factors such as CYP2CP and VKORC1 that may influence drug interactions.

Nursing Implications for Warfarin (Coumadin)

• Many herbal products can interact and increase bleeding risks, including:
  • Capsicum pepper
  • Garlic
  • Ginger
  • Ginkgo
  • St. John’s wort
  • Feverfew
  • Dong quai

Antiplatelet Drugs

• Function: Prevent platelet adhesion at sites of vascular injury, where normally platelets flow through vessels without adhering.
• Common agents include:
  • Aspirin
  • Cilostazol (Pletal)
  • Clopidogrel (Plavix)
  • Prasugrel (Effient)
  • Ticagrelor (Brilinta)
  • Dipyridamole (Persantine)
  • Vorapaxar (Zontivity)

Antiplatelet Drugs: Indications and Adverse Effects

• Mechanism: Vary according to drug performed.
• Common adverse reactions include a tendency for abnormal bleeding.

Aspirin

• Available in various formulations, often combined with other drugs.
• Contraindications: Avoid giving to children with flulike symptoms due to the risk of Reye’s syndrome.

Clopidogrel (Plavix)

• The most widely used ADP inhibitor taken orally.
• Prasugrel (Effient) carries a black-box warning about increased bleeding risk in the elderly or stroke history.
• Ticagrelor (Brilinta) has a black-box warning regarding aspirin dosage exceeding 100 mg.

Thrombolytic Drugs

• Function to break down preformed clots.
• Examples:
  • Older: Streptokinase, Urokinase.
  • Current: t-plasminogen activators (tPA) like Alteplase (Activase, Cathflo Activase) and Tenecteplase (TNKase).
• Action: Activate the fibrinolytic system to quickly digest the clot and reestablish blood flow to organs.

Thrombolytic Drugs: Indications

• Utilized in:
  • Acute myocardial infarction (MI)
  • Arterial thrombolysis
  • Deep vein thrombosis (DVT)
  • Occluded shunts or catheters
  • Pulmonary embolism
  • Acute ischemic stroke

Thrombolytic Drugs: Adverse Effects

• Potential bleeding risks (internal and superficial).
• Other effects may include nausea, vomiting, hypotension, anaphylactoid reactions, and cardiac dysrhythmias.

Nursing Implications for Thrombolytic Drugs

• Important to carefully follow administration guidelines.
• Monitor IV injection sites for bleeding and signs of internal bleeding (changes in blood pressure, increased pulse).

Antifibrinolytic Drugs

• Function: Prevent lysis of fibrin, promoting clot formation.
• Indications: Used for treating excessive bleeding due to hyperfibrinolysis or surgical complications.
• Key agents include:
  • Aminocaproic acid (Amicar)
  • Tranexamic acid (Cyklokapron)
  • Desmopressin (DDAVP)

Nursing Considerations for Antifibrinolytic Drugs

• Generally mild and uncommon adverse effects with rare thrombotic events.

Special Considerations for Heparin and Warfarin

• Ensure IV doses of heparin are double-checked with a second nurse.
• Administer subcutaneous doses carefully, avoiding muscular injections.
• Laboratory values (such as APTT for heparin) should be monitored daily to ensure efficacy and safety.

Case Study Considerations

• Watch for potential for conversions between heparin and warfarin and consider overlap during treatment to maintain anticoagulation coverage.

Educational Implications for Patients

• Ensure patients comprehend the importance of laboratory testing and recognizing signs of abnormal bleeding.
• Provide guidance on dietary consistency concerning vitamin K and advise on the risks associated with specific drug interactions, particularly with herbal and OTC medications.
• Educate on the use of medical alert bracelets and adherence to prescribed anticoagulant regimens.