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3 HAEM > anti-coagulants/anti-platelets > Flashcards

anti-coagulants/anti-platelets Flashcards

1
Q

indications for anticoagulant drugs

A

venous thrombosis

atrial fibrillation

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2
Q

which factors does anti-thrombin work against

A

mostly thrombin and Xa

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3
Q

what is the mechanism of action of heparin

A

potentiates anti-thrombin

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4
Q

how long does it take for heparin to take effect

A

immediately

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5
Q

what is the difference between the two forms of heparin

A

unfractionated
mostly affects thrombin

LMWH
mostly affects Xa

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6
Q

which blood test is used to monitor heparin

A

APTT

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7
Q

which the of heparin needs monitoring

A

unfractionated

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8
Q

what are the complications of heparin

A

bleeding
heparin induced thrombocytopaenia with thrombosis (HITT)
osteoporosis

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9
Q

describe the mechanism of HITT

A

body recognises heparin as non-self
produces antibodies which create a complex with heparin and platelets
consumptive thrombocytopenia

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10
Q

how does heparin cause osteoporosis

A

interferes with osteoclasts

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11
Q

how long is the half life of heparin

A

unfractionated = 30 mins

LMWH = 12-24 hours

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12
Q

which drug can be given to reverse the effects of heparin and how effective is it against the to types of heparin

A

protamine sulphate

unfractionated = complete reversal

LMWH = partial reversal

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13
Q

what is the mechanism of action of warfarin

A

vitamin K antagonist

prevents carboxylation of factors II, VII, IX and X making them non-functional

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14
Q

what is needed for the absorption of vitamin K

A

bile salts

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15
Q

as well as factors II, VII, IX and X, which other substances involved in the clotting system are dependent of vitamin K

A

protein C and S

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16
Q

why does warfarin have a brief pro-coagulation phase at the start of treatment

A

it inhibits the action of protein C and S which are naturally occurring anti-coagulants

17
Q

what is used to monitor warfarin levels

A

INR

18
Q

why is INR (modified PT) used to monitor warfarin and not APTT

A

factor VII has a shorter half life than the other factors affected, so the extrinsic pathway is more acutely changed by changes to warfarin levels

19
Q

what is the INR

A

a mathematical correction for differences in the sensitivity of thromboplastin reagent in different centres

20
Q

what factors influence the risk of haemorrhage in warfarin therapy

A

intensity of coagulation (increasing INR)
concomitant clinical disorders
drug interactions (including alcohol)
quality of management (reactivity to INR)

21
Q

examples of mild bleeding on warfarin therapy

A

skin bruising
epistaxis
haematuria

22
Q

examples of severe bleeding on warfarin therapy

A

GI bleeding
intracerebral haemorrhage
significant drop in BP

23
Q

how long does it take warfarin to leave the system

A

up to 7 days

24
Q

how can warfarin therapy be reverse in the event of a bleed

A

oral vitamin K (6 hours)

IV factor concentrates (immediate effect)

25
Q

what is the mechanism of action of the NOACs

A

direct thrombin inhibition (dabigatran)
direct Xa inhibition
(rivaroxaban, apixaban)

26
Q

what monitoring is required for the NOACs

A

none

27
Q

when are NOACs used

A

post-op thromboprophylaxis
stroke prevention in AF
treatment of DVT/PE

28
Q

what is the mechanism of action of aspirin

A

it inhibits cyclo-oxygenase
block production of prostaglandins
prostaglandins needed to produce thromboxane A2 (platelet agonist)

29
Q

side effects of aspirin

A

bleeding (nose bleeds, GI bleeding, mucosal membranes)

blocks production of prostaglandins (GI ulceration and bronchospasm)

30
Q

what is the mechanism of action of clopidogrel/prasugrel

A

antagonises ADP receptors (prevents platelet aggregation)

31
Q

which is more potent: aspirin or clopidogrel?

A

clopidogrel

32
Q

what is the mechanism of action of dipyramidole

A

phosphodiesterase inhibitor

reduces production of cAMP which is a secondary messenger in platelet activation

33
Q

what is the mechanism of action of abciximab

A

GPIIaIIIb inhibitor

switches off platelet aggregation completely

34
Q

when is abciximab used

A

given before heart surgery

35
Q

how long before an operation should antiplatelet therapy by stopped

A

7 days

36
Q

how to reverse anti platelets

A

platelet transfusion

3 HAEM (20 decks)

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