Anticoagulant Drugs Flashcards
What are indications for anticoagulant drugs?
Venous thrombosis
Atrial fibrillation
Anticoagulant drugs large what?
The formation of fibrin clot
Describe why venous thrombosis can happen
Venous system is a low pressure system
Platelets not activated
Activates coagulation cascade - rich in fibrin clot
What is the mechanism of action of heparin
Potentiates antithrombin
How quick to act is heparin?
Immediate effect
What are the two ways to deliver heparin?
IV or SC
What 2 forms of heparin exist?
Unfractionated
Low molecular weight (LMWH)
Describe what parts of the pathway unfractionated and LMWH affect
How do we monitor heparin?
Activated partial thromboplastin time (APTT) for unfractionated
Anti-Xa assay for LMWH but usually no monitoring of LMWH is required as more predictable response
What are complications of heparin?
Bleeding
Heparin induced thrombocytopenia (with thrombosis) HITT - monitor FBC in patients on heparin
Osteoporosis with long term use
How do we reverse heparin?
Stop the heparin (short t1/2)
Occasionally in severe bleeding
- Protamine sulphate which reverse antithrombin effect (complete reversal for unfractionated; partial reversal for LMWH)
What is the mechanism of action of coumarin anticoagulants?
Inhibition of vitamin K
What are examples of coumarin anticoagulants?
Warfarin
Phenindione
Acenocoumarin
Phenprocoumon
Where is vitamin K absorbed and what does it require for absorption?
Fat soluble vitamin - requires bile salts for absorption
Absorbed in upper intestine
Vitamin K is required for what clotting factors?
Final carboxylation of clotting factors II, VII, IX and X
What are the vitamin K dependent factors?
Factors II (prothrombin), VII, IX and X; protein C and protein S
Where are vitamin K dependent factors synthesised?
In liver
How does vitamin K work?
Carboxylation of glutamic acid residues in factors II, VII, IX, X (as well as protein C and S)
How does warfarin work?
Blocks ability of vitamin K to carboxylate the vitamin K dependent clotting factors, thereby reducing their coagulant activity
What is the INR equation?
What is INR (international normalised ratio)?
A mathematical correction that normalises the PT ratio by adjusting for variability in the sensitivity of different thromboplastin
Allows for comparison of results between labs and standardises reporting of prothrombin time
What is the major adverse effect of warfarin?
Haemorrhage
What mild and severe bleeding complications can occur secondary to warfarin treatment?
Mild - skin bruising, epistaxis, haematuria
Severe- GI, intracerebral, significant drop in Hb
How do you reverse warfarin?
