Anticoagulants, Antithrombotics And Thrombolytics Flashcards
What does heparin consist of?
Sulphanated GAGs of variable length
What drugs are used in vitro to prevent coagulation?
Citrate
EDTA
Heparin
What drugs are used in vivo to prevent coagulation?
Heparin
Warfarin
Rivaroxuban
Dabigatran
How does heparin function as an anticoagulant?
It binds to and enhances the action of endogenous antithrombin III to ihibit clotting factors 2,9,10,11 and 12
Which clotting factor does low molecular weight heparin predominantly inhibit?
Factor 10
What are the advantages of using low molecular weight heparin as opposed to unfractured heparin?
High bioavailability of subcutaneous route
Lower incidence of HIT
No need to monitor PTIdeal agent during pregnancy
What are the disadvantages of using low molecular weight heparin as opposed to unfractured heparin?
Requires dosage adjustment in renal insufficiency
Cannot be used in patients once HIT develops
Only partially reversible
Expensive
Longer half life may prolong the risk of bleeding
Why is heparin not orally active?
Its absorption is prevented by high molecular weight and charge
Heparin can cross the placenta and blood brain barrier. T/F?
False
What are the side effects of heparin?
Allergic reactions
Haemorrhage
Heparin induced thrombocytopenia
How can heparin induced thrombocytopenia be reduced?
By the heparin antagonist protamine
How does warfarin function as an anticoagulant?
It blocks vitamin K reductase and so blocks carboxylation of the gamma carboxyglutamate residues of the N terminal of factors 2,7,9 and 10
Why does warfarin take 1-3 days to take effect?
It takes this time for the existing pool of clotting factor to be replaced by dysfunctional factors
Most of warfarin in the blood is bound to which protein?
Albumim
Why should aspirin never be coadministered with warfarin?
Aspirin displaces warfarin from binding sites on albumin which increases plasma warfarin levels leading to an increased risk of haemorrhage
Why is warfarin not used in pre-eclampsia?
It can cross the placenta and blood brain barrier
How are the effects of warfarin reversed?
It is transfused with plasma or coagulation factor concentrates
What measurement, derived from the patient’s PT, is used to carefully monitor clotting time due to the high incidence of haemorrhage of warfarin? And what is the target range of this measurement?
International normalised ratio
Target range 2.0-3.0
Why are dabigatran and rivaroxuban useful compared to heparin and warfarin for use as anticoagulants?
There is no need to monitor patients
What clotting factor does dabigatran inhibit?
Thrombin
What clotting factor does rivaroxuban directly inhibit?
Factor 10
How does aspirin work as an anticoagulant?
It irreversibly inhibits the COX pathway to inhibit platelet synthesis of thromboxane A2 and endothelium production of prostacyclin. This inhibits platelet activation
How does dipridamole function as a antithrombitic?
It inhibits cyclic nucleotide phosphodiesterases to increase cAMP and cGMP which increases the action of prostacyclin and nitric oxide to inhibit platelet activation
How does epoprtenol work as a qntithrombitic?
It is a stabilised prostacyclin so inhibits platelet activation
