Anticoagulation Flashcards
What tends to drive clot formation in:
a) venous and intracardiac systems
b) arterial system
a) coagulation cascade
b) platelet activation
what is used as primary prevention for venous thromboembolism (DVTs and PEs)?
Heparin (usually LMWH)
Name two examples of heparins
enoxaparin
dalteparin
how are heparins administered and what is used to work out the dose?
subcutaenously
use weight to work out dose (200 units/kg)
what is the mechanism of action of heparins?
increase activity of antithrombin which inactivates clotting factors.
what can be used for primary prevention of DVT and PE other than heparins?
fondaparinux or DOACs
in what patients might you use unfractionated heparin to treat DVT or PE?
renal impairment
patients with an increased risk of bleeding
after starting warfarin, why do you have to continue giving a LMWH for 5 days?
warfarin only has effects on coagulation factors that are being newly synthesised so it takes a few days for it to reach a therapeutic level of anticoagulation
what drugs can be used as alternatives to warfarin?
DOACs
what is the main side effect of warfarin?
increased risk of bleeding
why should warfarin be avioded in patients with liver disease?
less able to metabolise it so they risk having too much warfarin in their system
warfarin has a low therapeutic index, what does this mean?
there is a fine line between the dose needed to prevent clotting and the dose that will cause bleeding
name some drugs that interact with warfarin and by doing so will reduce its effect making the person more susceptible to clotting
Rifampicin,carbamazepine (anti-epileptic),phenytoin (anti-epileptic),primidone (barbiturate anti-epileptic)
name some CYP inhibitors that reduce the metabolism of warfarin thus increase bleeding risk
fluconazole, metronidazole, amiodarone, gemfibrozil and sulfamethoxazole
how do some antibiotics cause an increase in the effects of warfarin due to their effects on gut flora?
some kill gut flora that synthesise vitamin K meaning there are even less clotting factors available.
especially cotrimoxazole, metronidazole, macrolides and fluoroquinolones
name the one DOAC that doesn’t have ‘xa’ in its name
dabigatran
when would you use a DOAC?
for secondary prevention of a VTE or as primary prevention in patients undergoing elective hip or knee replacement surgery.
what should you check before starting warfarin?
electrolytes and renal function
how are DOACs metabolised and excreted? what effect does this have on who you should avoid prescribing it to?
cytochorme P450 and eliminated in faeces and urine.
avoid in hepatic or renal disease.
what is the antidote for warfarin?
phytomenadione (vitamin K1), prothrombin complex concentrate, fresh frozen plasma
what is the antidote to dabigatran overdose?
idarucizumab
