anticoagulations and antiplatelets Flashcards
what do you need to consider before starting a patient on anticoagulation
are there any contraindications to anticoagulation?
- active bleeding, surgeries, bleeding disorders ect
what is the indication for anticoagulation and is there more than 1?
some require specific types of drug eg warfarin
whats the patients likely bleeding risk?
has-bled
are there any patient related factors that dictate choice of anticoagulant
what drugs require warfarin?
metallic valves
valvar AF
rheumatic mitral stenosis
antiphospholipid syndrome
warfarin
vitamin K reductase inhibitor
decreases activity of vitamin K dependant clotting factors:
- factor II
- factor VII
- factor IX
- factor X
decreases protein C and S
only fully anticoagulated when prothrombin and factor 10 drop - can take a few days
prolongues PT and APTT
what factors does vitamin K act on - therefore warfarin decreases?
2
7
9
10
contraindications warfarin
pregnancy
malignancy
many drug-drug interactions
when is warfarin used
- VTE
- AF
- metallic heart valves
- mitral stebnosis
- thrombosis and renal imparement
- thrombosis and need for extra monitoring
- antiphospholipid syndrome
- recurrent thromboses on current anticoagulations
warfarin half life
36 hours
Heparins how they work and their classes
Boosts the activity of anti-thrombin
- Inhibits thrombin and Xa
- Can’t be orally absorbed
- Derived from porcine intestine
- Be aware of religious objections
Two classes:
- Unfractionated heparin (UFH) inhibits FXa + thrombin
- Low molecular weight heparin (LMWH) - only inhibits FAx
which pathways does heparin act on and whats its effect on the APTT and PT?
Impacts on
-common pathway
UFH - Prolongs PT AND APTT, APTT >PT
LMWH – PT and APTT may be normal or prolonged
which pathways does warfarin act on and whats its effect on the APTT and PT?
Impacts on
-extrinsic
-intrinsic
-common pathways
PROLONGS PT AND APTT, PT first (due to FVII)
when is UH and LMWH used?
UH:
- VTE
- need for anticoag but high bleed risk or severe renal imparement
- bridging pateints on warfarin
- pre-post surgery
LMWH:
- VTE prophylaxis
- VTE treatment
- malignancy or pregnancy
- anticoag w concerns about bleed risk
- patients establishing on warfarin
- pre-post surgery
contraindications of UH + LMWH
UH:
- risk of heparin induced thrombocytopaenia
- drop in platelet count
LMWH:
- lower risk of heparin induced thrombocytopaenia
dosage of heparins
UH - based of APTT ratio
LMWH - based of weight
heparins monitoring
UH - APTT ratio at least once daily
LMWH - not routinely
warfarin monitoring
INR - usual target range 2-3 X higher
DOACS examples and the pathways they act on and PT APTT results
direct oral anticoagulants
Factor Xa inhibitors
Apixaban, rivaroxaban, edoxaban
Direct thrombin inhibitors
Dabigatran
Impacts on
-common pathway
Variable impact on PT and APTT
-may be completely normal!
when are Xa inhibitors (DOACS) used
VTE prophylaxis after orthopaedic surgery
VTE treatment
Non valvular AF
Xa inhibitor contraindications
Contra-indicated - CrCl <15, pregnancy
Be aware of drug interactions
Apixaban - lowest risk GI bleeding
Edoxaban - best evidence in low body weight
monitoring DOACS
nah
whens thrombin inhibitors (DOAC) used?
VTE prophylaxis after orthopaedic surgery
VTE treatment
Non-valvular AF
thrombin inhibitors (DOAC) contraindications
Contra-indicated - CrCl <30, pregnancy
Be aware of drug interactions
how antiplatelets work and common examples
Typically prevent platelet activation or aggregation with other platelets
May be used in combination after acute event
Most commonly used
Aspirin
Clopidogrel
Ticagrelor
Prasugrel
aspirin mechanism
Mechanism
Cyclo-oxygenase inhibitor
-blocks production of thromboxane (TXA2)
-TXA2 facilitates aggregation and stimulates further platelet activation and vasoconstriction
-binds irreversibly for platelet lifespan
p2y12 inhibitors
Inhibit ADP binding to P2Y12
P2Y12 binding stimulates aggregation via GPIIb/IIIa receptors and granule release for further platelet activation
Clopidogrel and prasugrel are prodrugs – converted by liver CYP450 into active form
Clopidogrel and prasugrel bind irreversibly for platelet lifespan, ticagrelor reversible binding
