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BSc module 3 > Anticoagulants > Flashcards

Anticoagulants Flashcards

1
Q

What is an anticoagulant?

A

Reduces the tendency of blood to coagulate
Usually considered distinct from antiplatelet agents

All anticoagulants reduce thrombin generation

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2
Q

Why anticoagulate?

A

To reduce risk of thrmobosis in people suseptible/after suseptible events
In some cases, risk of thrombosis outweighs risk of anticoagulation

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3
Q

Ways to use anticoagulant therapy

A

Prophylactic - low dose

Therapeutic - high dose

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4
Q

Effect of surgery on VTE

A

in-patient surgery – risk increased by 100% and this lasts for weeks
Increases for outpatient too but much less

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5
Q

VT recurrence

A

After people have a thrombosis - define themselves as prone to thrmobosis

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6
Q

Why are we interested in venous thombosis

A

Common
Significant sequelae

PE is the cause of 5-10% of hospital deaths
25000 deaths pa from hospital related VTE
Difficult to reverse and leads to morbidity
Preventable

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7
Q

Natural procoagulant factors

A 
V
VIII 
XI 
IX
X
II 
Fibrinogen
Platelets
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8
Q

Natural anticoagulant factors

A 
TFPI
Protein C
Protein S
Thrombomodulin
EPCR
Antithrombin

Fibrinolysis

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9
Q

Approach to anticoagulation

A

Reduce procoagulant factors
Enhance natural anticoagulant pathways
Inhibit procoagulant factors

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10
Q

How to reduce procoagulant factors?

A
  1. Vitamin K antagonists (warfarin)

2. Inhibition of FXI synthesis

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11
Q

How does warfarin work

A

Pro coagulant factors need carboxylation - this requires vit K
Warfarin is vit k antagonist. Makes people a bit vit K deficient but it doesn’t do much else in body so it’s fine

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12
Q

Warfarin structure

A

Similar to vit K - blocks recycling of Vit K.

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13
Q

Vit K dependent factors

A

FVII
FIX
FX
FII

Protein C
Protein S
Protein Z

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14
Q

How long does warfarin action take

A

Days - because indirect effect on anticoagulation

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15
Q

Why is initial effect of warfarin procoagulant?

A

Rapid fall in protein C

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16
Q

How do avoid initial procoagulation effect of warfarin

A

Combination with immediate immediate acting acting

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17
Q

Warfarin effect between people

A

Therapeutic effect of warfarin is a balacne of how much you give them and how much vit k they are taking in.
The amount of warfarin needed to achieve desired effect can vary quite sgnificantly person to person
Consequence is that it needs monitoring.

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18
Q

Warfarin dose sensitive to…

A

diet (Fat and Vitamin K intake)
other drugs (+/-)
ethnicity (polymorphisms)
age

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19
Q

Measure of warfarin

A

INR

20
Q

Action of warfarin

A

Reduces thrombin generation

21
Q

When INR goes up, means…

A

more anticoagulant with warfarin

22
Q

Downside of warfarin

A

major bleeding rate of 3.8%

23
Q

Why is there a therapeutic window of warfarin

A

Ischaemic stroke risk decreases significantly with warfarin
Intracranial bleeding risk increases with warfarin
SO you need to be in the therapeutic range INR: 2-3

24
Q

Risk of poor INR control

A

Increases stroke risk

25
Q

Why do we need warfarin reversal

A
  1. Active bleeding (esp ICH): Therapeutic INR, Elevated INR

2. Likelihood of bleeding: High INR ± other factors, Surgery, Trauma

26
Q

Underlying thrombotic risk of warfarin reversal

A

Atrial Fibrillation
VTE
Prosthetic valve

27
Q

How to do warfarin reversal

A

Stop warfarin

Give vit K

28
Q

Why can’t you just stop warfarin in warfarin reversal

A

Will take several days to resynthesises the coagulation factors

29
Q

If correction in <12-24 hrs required for warfarin reversal

A

Replace factors:

  • FFP
  • Prothrombin complex concentrate (PCC) contains Factors II, VII, IX, X
30
Q

What is FXI-ASO

A

a factor XI targeted second-generation antisense oligonucleotide

31
Q

Outcomes of FXI suppresion

A

High dose is better and don’t bleed more

but takes weeks

32
Q

Augmenting natural anticoagulants

A
  1. Unfractionated heparin (UFH)
  2. Low molecular weight heparin (LMWH)
  3. Fondaparinux (pentasaccharide)
33
Q

Action of heparin suplhate

A

enhances inhibitory activity of Antithrombin

- causes AT to adopt active conformation

34
Q

Where is heparin synthesised

A

Synthesised in mast cells. Not found in vasculature physiologiclaly (collected from gut mucosa)

Related to heparin sulphate

35
Q

What is heparin sulphate

A

on proteoglycans present on the vascular endothelium.

The essential pentasaccharide can be synthesised for therapeutic use (fondaparinux)

36
Q

2 effects of heparin on antithrombin

A
  1. The pentasaccharide “activates” AT. This is all that is required for the enhancement of anti-FXa activity. This only marginally enhances anti-thrombin activity
  2. Longer heparins (>18 saccharide units) stimulates
    anti-thrombin activity by ~2000 fold by bridging antithrombin
37
Q

Mechanism of action of heparin

A

1) The pentasccharide sequence is necessary
for any anticoagulant activity
2) The length of the heparin chain is important
For anticoagulant activity:

-for inhibition of factor Xa, a pentasaccharide
is minimum sequence (MW ~1500) required

  • for thrombin inhibition, there must be 18 saccharides (MW ~5000) at least – and possibly more
  • LMWH is made by degradation of UFH (mean MW~7000
38
Q

LMWH effect vs UFH effect

A

More effect on Xa than IIa

39
Q

Monitoring of UFH vs LMWH

A

UFH necessary.

Not for LMWHN

40
Q

What reverses UFH and LMWH

A

Protaimine
Complete reversal of UFH
Incomplete reversal of LMWH

41
Q

Biggest benefit of LMWH over FH

A

No complex dose response

42
Q

What is protamine

A

Protamine is positively charged. Binds and neutralises heparin

Less effective for LMWH

43
Q

Coagulation inhibitors

A

Direct acting oral anticoagulants (DOACs)
anti – IIa
anti - Xa

44
Q

DOAC for IIa

A

Dabigatran

45
Q

DOAC for Xa

A

Rivaroxaban
Apaxiban
Edoxaban

46
Q

Pros of DOACs

A 
Oral
Immediate acting
Direct action
No monitoring
Fewer drug/lifestyle interactions
Short half life of effect
47
Q

Cons of DOACs

A 
Lack of experience 
side effects, safety
Adherence less certain
Single therapeutic range
Unable to tailor intensity
No antidote/reversal 
Some renal dependence
Cost

BSc module 3 (10 decks)

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