Anticoagulants Flashcards
What are the common indications for anticoagulation?
venous thrombosis; atrial fibrillation
How are protein C and S activated?
by thrombin bound to thrombomodulin
What is the mechanism of heparin?
potentiates antithrombin by stabilising anti-thrombin:protein complex
how is heparin administered?
parenteral (IV/SC)
What are the 2 forms of heparin?
unfractionated and LMWH
What are the mechanisms of anti-thrombin?
inhibts fibrinogen–fibrin and amplification steps
What protein is bound to anti-thrombin in the complex that unfractionated heparin works on?
thrombin
What is the protein bound to anti-thrombin that LMWH works on?
Xa
How is unfractionated heparin monitored?
APTT
How is LMWH monitored?
anti-Xa assayu
What is the aim for the change to APTT in heparin?
1.5-2x normal
Why is monitoring of LMWH not required?
much more predictive dosing- based on weight, whereas unfractionated isn’t so predictable
What are the complications of heparin thepray?
bleeding; heparin induced thrombocytopenia (with thrombosis); osteoporosis
What bloods should be monitored in patients on heparin?
FBC
What causes heparin induced thrombocytopenia?
develop antibody to platelet factor IV which causes platelets to stick together
Which form of heparin is HITT more likely in?
unfractionated
What is the anti-dote to heparin?
protamine sulphate
Give two examples of coumarin anticoagulants?
warfarin; phenindione
What is the mechanism of coumarin anticoagulants?
inhibition of vitamin K
What are the vitamin k dependent factors?
II; VII; IX and X; protein C and S
What is the function of the carboxylation by vitamin K?
need second carboxyl group to makr chemical bond strong enough
How is warfarin metabolised?
cytochrome P450
How should warfarin be taken?
at same time every day (6pm recommended)
Why does warfarin therapy need to be monitored?
narrow therapeutic window
What is the equation for INR?
(patients PT/mean normal PT)^ISI
What is the ISI?
callibration factors as thromboplastin can be different across labs
What is generalyl the target INR?
2-3
What are the factors that influence bleeding risk on warfarin?
intensity of anticoagulation; comrobidities; drug interactions
What should be done with a patient on warfarin if any other medications are changed?
check INR
What is the mnemonic for drugs that potentiate warfarin?
O! DEVICES
What does O! dEVICES stand for?
Omeprazole Disulfriam Erythromycin Valproate Isoniazide Ciprfloxacin and cimetidine Ethanol (acute) Sulphonamides
What is the mnemonic for drugs that inhibt warfarin?
PC BRAS
What does PC BRAS stand for
?
Phenytoin Carbamazepine Barbiturates Rifampicin Alcohol (chronic) Sulfonylureas
How long does vitamin K take to work?
6 hours
How long does a clotting factor transfusion take to work?
immediate
What is the main new thrombin inhibitor?
dabigatram
What is the difference between the new and old anticoagulants?
new agents bind directly to the coagulation factors
What new agents are Xa inhibitors?
rivaroxaban; apixaban
What are the benefits of the new anticoagulation agents?
oral and no monitoring; less interactions
What is the con of the new anticoagulants?
no specfic antidote
