Anticoagulant drugs Flashcards
anticoagulants are used for arterial/venous thrombosis
venous
what are the main indications for anticoagulants
DVT
atrial fibrillation
venous clots are platelet/fibrin rich
fibrin
what types of anticoagulants are there
heparin
warfarin
DOACs
how does heparin work
enhances the natural anticoagulation system by potentiating the effects of anti thrombin
anti thrombin inhibits thrombin and Xa
heparin has an immediate/delayed effect
immediately effective
the therapeutic index of heparin and warfarin are wide/narrow
narrow
when heparin binds to antithrombin it enhances thrombin/Xa inhibition more
thrombin
when LMWH binds to antithrombin it enhances
thrombin/Xa inhibition more
Xa
how is unfractionated heparin administered
IV
how is LMWH administered
SC
which needs more monitoring, unfractionated heparin or LMWH
unfractionated heparin
how do you monitor unfractionated heparin
APTT
how can you monitor LMWH
anti-Xa assays
why is APTT measured for heparin
heparin will eventually decrease both PTT and APTT but because of the effect thrombin has on factors 8+9 (intrinsic pathway) APTT is more sensitive to change
what are complications of heparin
bleeding
immune reaction: heparin induced thrombocytopaenia with thrombosis HITT
osteoporosis in the long term
how do you reverse heparin
stop heparin
if severe bleeding:
protamine sulphate
heparin has a short/long half life
short
what is the antidote to heparin overdose
protamine sulphate
what group of drugs does warfarin belong to and what is their mechanism of action
Coumarin anticoagulant group
Vit K antagonists
Vit K is fat/water soluble
fat
what are the vitamin K dependent factors and where are they made
2,7,9,10
Protein C+S
produced by the liver
why is it important that carboxylation of clotting factors by vit K occurs
this allows clotting factors to effectively bind to platelet plug
When you start warfarin, levels of which proteins go down
What is a consequence of this
Protein C+S
causes you to become prothrombotic initially
why should you not start warfarin alone immediately after a VTE
what should be given alongside
heparin
because of increased thrombosis risk initially
which enzyme in the body causes the required dose of warfarin to be different in individuals
Cytochrome P450
how is warfarin monitored
INR
internationalised normalised ratio
standardised across the world
what is the ideal target INR
2-3
what are complications of warfarin therapy
bleeding
co-morbidities
DRUG INTERACTIONS
what should be measured if a patient on warfarin starts a new drug
INR
what should be done if a patient on warfarin has a high INR and has bruises
omit doses of warfarin
what can you give to quickly reduce INR
PO vitamin K
what should be done in a patient on warfarin who is bleeding severely
stop warfarin
Vitamin K
clotting factors 2,7,9,10
how fast do Vit K and clotting factors work
vit K - 6 hours
clotting factors - immediately
indications for warfarin
metal heart valves
APLS
what are DOACs
Direct oral anticoagulants
newer agents that directly target Xa or thrombin
how are DOACs administered
PO
why are DOACs more favourable to use
no monitoring required
less drug interactions
give an example of a direct thrombin inhibitor
dabigatran
what is the method of action of dabigatran
inhibits thrombin which means fibrin cannot form from fibrinogen
where is dabigatran metabolised and excreted
kidneys
give examples of direct Xa inhibitors
rivaroxiban, apixaban, edoxiban
how does rivaroxiban work
inhibits factor Xa and so prevents thrombin formation
indications for DOACs
prophylaxis in joint replacement surgery
DVT/PE
stroke prevention in AF
what can potentiate the action of warfarin and what is a consequence
liver disease/cirrhosis
high metabolic activity
drug interactions
Bleeding risk
what can lessen the action of warfarin and what is a consequence
Pregnancy
hypothyroidism
Vitamin K consumption
drug interactions
clot formation
