5: Anticoagulant drugs Flashcards
Which clotting times are used to monitor
a) warfarin
b) heparin
activity?
a) INR (which is a standardised method of measuring PT)
b) APTT
What are two indications for anti-coagulant drugs?
Venous thrombosis
Atrial fibrillation (increases likelihood of thrombosis)
Thrombophilia
Atrial fibrillation can cause (venous / arterial) thrombosis.
either
depending on heart chamber where the blood clots
What blood components are activated in
a) venous thrombosis
b) arterial thrombosis?
a) Fibrin
b) Platelets
Because of their short half life, Protein C and S levels drop first when a patient is given anticoagulant drugs.
What is the effect of this?
Increased risk of thrombosis (temporary)
Which anticoagulant drug enhances the activity of antithrombin?
Heparin
What are the two forms and routes of administration of heparin?
Unfractionated heparin (IV)
LMWH (subcut)
Name an example of LMWH?
Dalteparin sodium
Heparin enhances the activity of ___.
antithrombin
Heparin potentiates the activity of antithrombin, a protein which inactivates clotting factors.
Unfractionated heparin enhances the activity of antithrombin against ___.
LMWH enhances the activity of antithrombin against ___.
unfractionated: thrombin
LMWH:Xa
Which anticoagulant drugs are monitored using
a) INR
b) APTT?
a) Warfarin
b) Heparin
Which clotting time is used to monitor the activity of unfractionated heparin?
APTT
Does LMWH require monitoring?
No
But you can using Anti-Xa assay
What is the main side effect of heparin?
Bleeding
Heparin can trigger an autoimmune reaction causing which deficiency?
Thrombocytopaenia
Name three side effects of heparin.
Bleeding
Thrombocytopaenia (autoimmune)
Osteoporosis (long term use)
What happens if you overdose a patient on heparin?
Bleeding
Heparin has a (short / long) half life.
short half life
so if bleeding or requiring a procedure you can just stop it
In emergencies, which drug can be used to reverse the effects of heparin?
Protamine sulphate
Which clotting factors does
a) unfractionated
b) LMW
heparin act on?
a) Thrombin
b) Xa
Which anticoagulant drug inhibits the action of Vitamin K?
Warfarin
What is the mechanism of action of warfarin?
Inhibits action of Vitamin K
REDUCING ACTIVATION FACTORS II, VII, IX AND X
Where are clotting factors produced?
Liver
What is required for the production of factors II, VII, IX and X in the liver?
Vitamin K
Do patients on warfarin still produce clotting factors?
What is the significance of this?
Yes
The clotting factors are non-functional, need to be activated by Vitamin K
Vitamin K can be used to reverse the effects of warfarin
Warfarin has a narrow ___ ___.
therapeutic index
Which family of enzymes metabolises warfarin in the liver?
Cytochrome P450
Warfarin dosage depends on what?
Patient’s INR after first dose of 5 - 10 mg
i.e liver clearance of warfarin by CYP450
When should warfarin be taken?
Same time every day
Which clotting time is used to measure warfarin response?
INR
Which is a different way of measuring PT
Which clotting factors does warfarin affect?
II
VII
IX
X
What is INR?
International normalised ratio
Standardised method of measuring a prothrombin time
since people were using different reagents to do the test
What is the main side effect of warfarin?
Bleeding
Warfarin ___ with other drugs.
interacts
Which substance inhibits the liver’s ability to metabolise warfarin?
Alcohol
Alcohol intake increases bleeding risk in patients on warfarin
What is the half life of warfarin compared to heparin?
What does this mean in the context of bleeding?
T1/2 warfarin > T1/2 heparin
Omitting warfarin won’t control bleeding as effectively as heparin omission
Apart from stopping warfarin, what can be done to reverse warfarin overdose?
Vitamin K PO / IV
Clotting factors (give FFP)
Why is warfarin omission and oral Vitamin K attempted before giving warfarin patients clotting factors via FFP?
Exposure to BBVs (inc. ones we don’t know about)
How long does Vitamin K require to take effect?
6 hours
ish
How long does FFP require to take effect?
Immediate
Which clotting factor does rivaroxaban act on?
Xa
‘xa’ in the name hints that the drug is a Factor Xa inhibitor
Which clotting factor does dabigatran act on?
Thrombin
Which clotting factor do rivaroxaban, apixaban and edoxaban act on?
Xa
‘xa’ in the name
How are NOACs taken?
PO
What is an
a) advantage
b) disadvantage
of using NOACs versus warfarin?
a) Arguably more effective; No monitoring required
b) No antidote
Protamine sulphate is used to reverse (heparin / warfarin) overdose.
heparin overdose
Vitamin K is used to reverse (heparin / warfarin) overdose.
warfarin overdose
