Anticoagulants Flashcards
What are the main types of anticoagulants?
Heparin
Warfarin
DOACs
What is the indication of heparin?
- VTE - prophylaxis and rx
2. ACS
What are the two types of heparin?
- LMWH
2. Unfractionated heparin.
What are examples of LMWH?
Dalteparin
Enoxaparin
Tinzaparin
Give the mechanism of action of heparin
inhibit function of thrombin and factor Xa which are key to formation of fibrin clot
How does unfractionated heparin work?
Binds antithrombin, increases ability to inhibit thrombin, factor Xa and IXa
How does LMWH work?
similar to UFH but preferentially inhibit factor Xa
Why is LMWH generally preferred to UFH?
- response is more predictable
- lab monitoring not required
- only needs to be given OD or BD
what are SEs of heparin?
- ↑ bleeding
- heparin induced thrombocytopenia (mainly UFH)
- osteoporosis (long term)
- hyperkalaemia (beware)
What are the CIs of heparin?
- Bleeding disorders
- Platelets <60
- Previous HIT
- Peptic ulcer
- Cerebral haemorrhage
- Severe HTN
- Neurosurgery
When should LMWH be used at a lower dose and why?
renal impairment
may accumulate
(can use UFH instead)
What drug is similar to heparin and what does it act on?
fondaparinux
inhibits factor Xa only
What is the indication of fondaparinux?
VTE prophylaxis
Rx of unstable angina and NSTEMI/STEMI - ACS
Rx of DVT + PE
How is UFH administered
IV
How is LMWH administered?
SC
When is UFH more useful?
- Situations where there is a high risk of bleeding as anticoagulation can be terminated rapidly
- Renal failure
What is an antidote for heparin?
protamine sulphate
How does warfarin work?
Inhibits vitamin K epoxide reductase preventing reactivation of vitamin K and coagulation factor synthesis
Clotting factors II, VII, IX, X (1972) + protein C
What are the indications of warfarin?
- VTE - prevent clot extension + recurrence
- AF
- Prevent heart valve replacement complications
What is warfarin NOT used for? Why?
to prevent arterial thrombosis e.g. MI, thrombotic stroke
This is driven by platelet aggregation so is prevented by anti platelets e.g. aspirin, clopidogrel
When is the target INR 2.5-3?
VTE
AF
Cardioversion
Antiphospholipid syndrome
When is target INR 3.5?
recurrent VTE whilst on anticoagulants
What is INR?
Ratio of prothrombin time for the patient over the normal prothrombin time
What factors make warfarin more active?
Liver disease
P450 enzyme inhibitors - amiodarone, ciprofloxacin
Cranberry juice
What are SEs of warfarin?
Bleeding e.g. with peptic ulcers, minor trauma Skin necrosis (rare)
What factors increase risk of bleeding in those on warfarin?
Those at increased risk of haemorrhage:
- > 65yrs
- Prev. bleeding episode
- Recent ischaemic stroke, HTN etc
- Regular NSAIDs
- XS alcohol, falls
- Recent or imminent surgery, trauma
How is warfarin administered?
orally
What INR indicates increased bleeding risk?
increased INR
What test measures how well the coagulation factors in the extrinsic pathway work?
PT
What test measures the clotting factors of the intrinsic and common pathways?
PTT
What is PT?
Prothrombin time
measures number of seconds it takes for a clot to form
What is PTT
Partial thromboplastin time (aPTT), partial as absence of tissue factor
What is INR?
calculation that adjusts for changes in the PT reagents and allows for results from different labs to be compared
When should target INR be higher?
if there is a higher risk of a blood clot
What is the management of major bleeding on warfarin?
- Stop warfarin
- Give IV vit K 5mg
- Prothrombin complex concentrate
What is the management of minor bleeding with an INR >8
stop warfarin
IV vit K 1-3mg
Restart warfarin when INR <5
What is the management of INR >8 w no bleeding
Stop warfarin
Vit K 1-5mg PO
Restart warfarin when INR <5
What is the management of INR 5-8 w minor bleeding?
same as >8 w minor bleeding
What is the management of INR 5-8 w no bleeding?
withhold 1 or 2 doses of warfarin
reduce subsequent maintenance dose
What things can lower INR (increase risk of clotting)
P450 inducers:
- AEDs
- barbiturates
- rifampicin
- chronic alcohol
- St Johns Wort
- Smoking
What things can increase INR (increase risk of bleeding)
P450 inhibitors: (decrease W metabolism)
- abx: ciprofloxacin, erythromycin (macrolide)
- fluconazole
- isoniazid
- protease inhibitors
- omeprazole
What are rivaroxaban and apixaban examples of? how do they work?
Direct oral anticoagulants (DOAC)
factor Xa inhibitors, in the NAME lol
How does dabigatran work? what is it an example of?
DOAC
direct thrombin inhibitor
What is the administration route of DOAC?
oral
What are DOACs used for?
Alternative to warfarin
- prevention of VTE following hip/knee surgery
- Rx of DVT/PE
- prevention of stroke in non-valvular AF
How should warfarin be given initially?
5-10mg given at 18:00 on days 1 and 2
Check INR on day 3
Adjust subsequent doses according to INR
