Anticoagulation Flashcards
Describe the mechanism of an oral anticoagulant
e.g. warfarin
Warfarin is a vitamin K antagonist
Vitamin K essential for the production of prothrombin + factors VII, IX + X (for post-ribosomal carboxylation of glutamic acid residues of proteins)
Warfarin blocks vitamin K reductase (act as cofactor)
Used to prevent thrombosis (prevent blood clot formation) in atrial fibrillation +:
- artificial heart valve (thrombogenic surface)
- pulmonary embolism
- DVT
Warfarin takes a few days to act
Describe the mechanism of an injectable anticoagulant
e.g. heparin
Unfractionated or LMWHs heparins (e.g. enoxaparin, tinzaparin)
Activates antithrombin III (natural protein)
Antithrombin - inactivates some clotting factors + thrombin by complexing with serine protease of the factor
Immediate action
Used to prevent thrombosis + used to prevent blood clotting on collection
Used whilst warfarin takes effect
Unfractionated heparin monitored via APTT
How do we appropriately monitor unfractionated heparin in pts?
Activated partial thromboplastin time
examines intrinsic pathway
Altered by changes in factors
LMWHs do not require coagulation monitoring
Platelets - >5 days heparin can lead to thrombocytopenia
What is deep vein thrombosis?
What are the signs + symptoms?
How do we diagnose it?
When a patient is immobile for a significant long period of time, venous returin becomes impaired, they can form a clot
Major risk for pulmonary embolism
Signs + symptoms = painful swelling in calf
Diagnosis = ultrasound scan
Blood test = increased levels of D-dimer (breakdown product of thrombosis/fibrinolysis)
How do we appropriately monitor warfarin in pts?
INR - international normalised ratio/Prothrombin time
Time for coagulation following of thromboplastin
Prolonged by abnormalities of factors
The activity of warafrin is monitored by INR with a specific target value + dose is adjusted
- must be 1 (in normal pts)
- INR is increased by impaired clotting (due to liver disease + warfarin - as liver produces coagulation factors)
Wafarin has a lot of drug interaction
Warfarin can cause bleeding:
- gastric
- cerebral
- blood in faeces
- blood in urine
- easy bruising
How do we dose warfarin in pts?
Monitor INR freq. at start (2 x week) then increase interval gradually
Can be reversed with vitamin K:
- if patient is bleeding
- high INR
- warfarin overdose
How do we counsel a patient on the correct use of warfarin?
Warfarin is referred as ‘thinning of the blood’
Pts must stick to their regimen
Take at 6 pm
If miss a dose, then they should not take 2 doses together + inform doctor at next blood test
Must tell HCP they are on warfarin
- interact with OTC eds
Females of child-bearing age should not become pregnant when on warfarin
Alcohol can be consumed in moderation
Avoid excessive consumption of green vegetables (broccoli, spinach)
Changes to diets rich in vit. K as dose change may be required
Why is anticoagulants used in pregnancy?
Pregnancy produces a thrombophilic state in the mother
Prevents post partum haemorrhage
Thrombophilia, decreased venous return due to the gravid uterus + immobility during labour
Pts are swapped to artificial heart valves/LMWH if can’t take warfarin
Warfarin is teratogenic - can cause mental retardation, altered bone growth, optic atrophy (avoided in trimester 1 + 3)
If a patient needs to be immediately on anticoagulants due to artifical heart valves, what needs to be done?
Heparin must be taken immediately as warfarin takes a few days to take effect.
Describe the modes of action and use of newer agents such as thrombin inhibitors
Dabigatran: an oral thrombin inhibitor
- Prevents thromboembolism
- less bleeding than warfarin
- fewer drug interactions
- does not require monitoring
- RE-LY trial : equally effective as warfarin in AF
Rivaroxaban: oral inhibitor of activated factor X
