Anticoagulant drugs Flashcards Preview

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Flashcards in Anticoagulant drugs Deck (32)
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1
Q

what does warfarin target

A

vitamin K synthesis

vit k needed to produce clotting factors 2,7,9 and 10

2
Q

what does heparin target

A

anti-thrombin - makes it stronger

3
Q

what are the indications for anticoagulant drugs

A

Venous thrombosis

Atrial fibrillation

(to prevent clot forming in the left atrium (which isn’t contracting properly leading to stasis and pooling of blood) and the clot could break off into LV through carotids to the brain causing stroke).

4
Q

treatment of cardioembolic strokes vs atheroembolic

A

cardioembolic - anticoagulants bc its coming from AF in the heart, pooling of blood and fibrin clot

atheroembolic - anti platelets, due to atheroma in situ

5
Q

what are the naturally occurring anticoagulants

A

Serine protease inhibitors - anti thrombin

Protein C (factor V)

Protein S (Factor VIII)

6
Q

what natural anticoagulants are vitamin K reliant

A

protein C

protein S

so warfarin immediately drops protein C and protein S levels increasing risk of thrombosis

7
Q

what does heparin do

A

has an immediate effect to increase the action of anti-thrombin

given IV or SC

IV = unfractionated (needs a lot of monitoring for right does).

SC= low molecular weight heparin (more predictable and given on a weight basis)

8
Q

how does heparin increase the effect of antithrombin

A

joins antithrombin and thrombin together and stabilises them

also joints antithrombin and factor X to prevent prothrombin being converted to thrombin

9
Q

when is unfractionated heparin used

A

complicated patients with thrombosis but also risk of bleeding

can stop it quickly as it has a v short half life

10
Q

what is the predominant target for LMWH vs unfractionated

A

LMWH - more factor Xa

Unfractionated -more thrombin

11
Q

which test is most sensitive for monitoring heparin

A

APTT - activated partial thromboplastin time

Thrombin feeds back to activate factors VIII and IX making this test more sensitive than prothrombin time

12
Q

complications of heparin

A

Bleeding

heparin induced thrombocytopenia (with thrombosis) antibodies to the heparin and platelets - platelets tend to aggregate

osteoporosis with long term use

13
Q

what to do if bleeding on heparin

A

stop heparin - v short half life

can give antidote to heparin - Promatine sulphate

complete reversal for unfractionated and partial for LMWH because it only reverses binding to thrombin not factor Xa

14
Q

what oral agents do you use if a patient needs long term anticoagulation

A

Warfarin

3-6 months for first venous thrombosis

if more than one event = lifelong

15
Q

How does warfarin work

A

inhibits vitamin K

used for carboxylation of clotting factors 2,7,9 and 10

also used for protein C and protein S (so when you first give warfarin you make risk of thrombosis worse)

16
Q

where are vitamin K dependent clotting factors made

A

Liver

17
Q

how is vit K absorbed

A

fat soluble vitamin (ADEK)

absorbed in proximal intestine

needs bile salts to be absorbed

18
Q

what is the action of vitamin K

A

carboxylation of glutamic acid residues in factors II, VII, IX and X and protein C and S

leads to synthesis of non-functional clotting factors

19
Q

why does heparin need to be prescribed with warfarin

A

because of the initial decrease in protein C and S so makes you more thrombotic

20
Q

when would you not need to give heparin with warfarin

A

if you start giving it v slowly so the decrease in protein C and S is not as rapid

has a narrow therapeutic window so need to monitor therapy

dose should be given at the same time every day

21
Q

how do you monitor warfarin

A

prothrombin time - most sensitive as factor VII has the shortest half life

will also effect X and IX so also prolongs APTT but not as much as PT

22
Q

what is the INR

A

score used for monitoring warfarin therapy

international normalised ration

a mathematical correction of normal PT and mean PT

23
Q

risk factors for bleeding on warfarin

A

intensity of coagulation
contaminant clinical disorders
contaminant use of other medicines
quality of management

24
Q

what is the INR which is aimed for in warfarin monitoring

A

2-3

25
Q

types of bleeding complication on warfarin

A

Mild

  • skin bruising
  • epitaxes
  • haematuria

Severe

  • gastro-intestinal
  • intraverebral
  • significant drop in Hb
26
Q

how do you reverse the action of warfarin in bleeding

A

No action - if INR is normal and mild bleeding

omit some doses - if INR high and some mild bleeding

if INR high and not going down - administer oral vitamin K (takes about 6 hours for INR to come back down)

If major severe bleeding - administer clotting factors

27
Q

why dont you give clotting factors immediately

A

risk of infection (blood product)

expensive

28
Q

how quickly do vitamin k and clotting factors work

A

vit K - 6 hours

clotting factors - immediate

29
Q

where do clotting factors bind to to form the fibrin clot

A

surface of platelets in the platelet plug

30
Q

what do new anticoagulants target

A

Thrombin inhibitors (dabigatran) - directly inhibits thrombin (not through antithrombin like heparin)

Xa inhibitors (edoxaban, rivaroxiban, apixaban) - oral and dont need as much monitoring

31
Q

why are new anticoagulants better

A

less monitoring

oral

less risk of bleeding

less drug interactions

dont effect protein C and S so can go straight onto them

32
Q

what are new anticoagulants used for

A

prophylaxis for hip and knee replacement surgery

used for treatment of DVT/PE

Introduced for stroke prevention in Atrial Fib