Parenteral Anticoagulation Flashcards
Why are anticoagulants used? (2)
- To prevent thrombus formation
- To prevent extension of existing thrombus in the slow-moving venous circulation (where clots are mainly composed of fibrin and some platelets and red cells)
(Notably, NOT to break down pre-existing thrombi)
*anticoagulants are of less use in preventing thrombus formation in arteries because in faster-flowing vessels, thrombi are composed mainly of platelets (with little fibrin)
What information should be given to patients taking anticoagulants?
Patients should be provided with verbal AND written information about their treatment, including how and when to seek medical attention
Immediate medical attention is required in certain patients (such as in those with bleeding that is severe, does not stop or recurs, or who have other signs or symptoms of concern); in particular, patients who have sustained a heated injury should be referred to the hospital emergency department
What are the main parenteral anticoagulants? (7)
- Heparin (‘standard’ or unfractionated)
- Low molecular weight heparins (dalteparin, enoxaparin, tinzaparin)
- Heparinoids (danaparoid)
- Argatroban
- Hirudins (bivalirudin)
- Epoprostenol (prostacyclin)
- Fondaparinux
What is the main difference between standard heparin and LMWH?
Standard heparin acts rapidly but has a short duration of action whereas LMWH has a longer duration of action
Although a low molecular weight heparin is generally preferred for routine use, heparin (unfractionated) can be used in those at high risk of bleeding because its effect can be terminated rapidly by stopping the infusion
What is the main advantage of LMWH over standard heparin?
Lower risk of heparin-induced thrombocytopenia
Is monitoring required when administering LMWH?
No
What are the indications of LMWH?
- Treatment of DVT
- Treatment of PE
- Prevention of clotting in extracorporeal circuits
- Unstable coronary artery disease (other agents are preferred)
What is the mechanism of action of standard heparin?
Inactivation of thrombin (II) and activated X (Xa) through an antithrombin-dependent mechanism (AT III)
What is the mechanism of action of LMWH?
Activation of antithrombin III to accelerate inactivation of activated factor X (Xa)
*does not act directly on thrombin (II), unlike UFH
What are the indications of danaparoid (a heparinoid)? (2)
- Prophylaxis of DVT in patients undergoing surgery
2. Treatment of thromboembolic disease in patients with a history of HIT
What is the main indication of argatroban?
Anticoagulation in patients with HIT who require parenteral antithrombotic treatment
What is the mechanism of action of argatroban?
Inhibition of thrombin
What is the mechanism of action of hirudins?
Inhibition of thrombin (only the activated form)
What are the indications of bivalirudin?
- Unstable angina or NSTEMI in patients scheduled for urgent or early intervention
- Anticoagulant for patients undergoing PCI
What is the mechanism of action of epoprostenol (prostacyclin)?
Inhibition of platelet aggregation
Also a potent vasodilator with a short half-life (~3 min) so must be administered by continuous IV infusion
What are the indications of epoprostenol (prostacyclin)? (2)
- Renal dialysis when heparins are unsuitable or contra-indicated
- Primary pulmonary HTN resistant to other treatment
What is the mechanism of action of Fondaparinux?
Inhibition of factor X
What are the side effects of all heparins? (3)
- Hemorrhage
- HIT
- Skin reactions
In cases of hemorrhage due to heparin administration, what is the recommended course of action?
Usually sufficient to withdraw unfractionated or LMWH BUT if rapid reversal is required, protamine sulfate is a specific antidote (but only partially reverses the effects of LMWH)
Protamine sulfate completely reverses the effect of _______ but only partially reverses the effect of _______.
Standard (unfractionated) heparin /
LMWH
What are the signs of HIT? (3)
- 30% reduction of platelet count
- Thrombosis
- Skin allergy
What is the management of HIT? (3)
If heparin-induced thrombocytopenia is strongly suspected or confirmed:
- heparin should be stopped
- alternative anticoagulant, such as danaparoid, should be given
- ensure platelet counts return to normal range in those who require warfarin
What electrolyte imbalance is associated with heparin?
Hyperkalemia
Inhibition of aldosterone by unfractionated heparin or LMWH can result in hyperkalemia
patients with diabetes mellitus, chronic renal failure, acidosis, raised plasma potassium or those taking potassium-sparing drugs seem to be more susceptible; the risk appears to increase with duration of therapy
What are the contraindications of heparins? (10)
- Major trauma
- Epidural anesthesia
- Hemophilia or other hemorrhagic disorders
- Peptic ulcer
- Recent cerebral hemorrhage
- Recent eye surgery
- Recent nervous system surgery
- Spinal anesthesia
- Thrombocytopenia (including history of HIT)
- Acute bacterial endocarditis
