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Pharma ESA4 > Platelets And Clotting > Flashcards

Platelets And Clotting Flashcards

1
Q

What is warfarin’s main mechanism of action

A

Inhibition of vitamin K dependent clotting factors production
(Stops conversion of VitK to active reduced form)

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2
Q

Which clotting factors are affected by warfarin?

A

II (prothrombin), VII, IX, X

Extrinsic pathway

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3
Q

How long does warfarin take to have an effect

A

Days

Rate of platelet turnover dependent. High half life

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4
Q

How is warfarin given?

A

Orally - good GI absorption

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5
Q

How is warfarin’s slow onset ameliorated

A

Heparin used initially to cover the patient until warfarin takes effect

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6
Q

Which anticoagulant is the preferred choice for long term use?

A

Warfarin

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7
Q

Is warfarin protein bound?

A

Yes, heavily bound to albumin

Caution with drugs that will displace it

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8
Q

Can warfarin cross the placenta

A

Yes - do not give in 1st trimester (teratogenic) or 3rd (brain haemorrhage)

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9
Q

How is warfarin monitored?

A

Extrinsic pathway factors, prothrombin time

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10
Q

How do other drugs affect warfarin?

A

Majority increase the effect, but some may decrease.

Check BNF

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11
Q

Which drugs inhibit hepatic metabolism of warfarin?

A

Amiodarone, quinolone, metronidazole, cimetidine, alcohol

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12
Q

Which drug inhibits platelet function?

A

Aspirin

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13
Q

Which drug reduces vitamin K from gut bacteria?

A

Cephalosporin antibiotics

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14
Q

Which drugs inhibit warfarin action?

A

Antiepileptics, rifampicin, St John’s wort

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15
Q

When is warfarin used?

A

DVT, PE, Atrial fibrillation, mechanical prosthetic valve, cardiac thrombus

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16
Q

What are the adverse effects of warfarin?

A

Bleeding, bruising, teratogenic

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17
Q

What is the usual loading dose of warfarin?

A

10mg (when INR is about 1), 10, 5, maintenance dose

18
Q

How long is INR monitored in warfarin patients?

A

1-4 weeks

19
Q

How is warfarin reversed?

A

Stop giving warfarin, IV vitamin K (takes 2/3 days), prothrombin complex concentrate, fresh frozen plasma (both work faster)

20
Q

When is prothrombin complex concentrate/fresh frozen plasma indicated?

A

With major bleeding

21
Q

When is vitamin K indicated?

A

When INR is >8

Need to keep patient on heparin until effects wear off

22
Q

What is the main mechanism of heparin?

A

Activates anti-thrombin III

23
Q

What does ATIII do?

A

Deactivates factor Xa and IIa

Also IXa and possibly some others

24
Q

What are the two kinds of heparin given?

A

Unfractionated (usually IV), low molecular weight (usually subcutaneous)

25
Q

What is the difference between the two kinds of heparin?

A

Unfractionated heparin can deactivate both IIa and Xa (large enough to bind to it and ATIII at the same time), LMW heparin can only deactivate Xa

26
Q

What is the main advantage of using LMW heparin?

A 
It is absorbed more uniformly
highly bioavailable
long half life
does not require monitoring
less likely to cause thrombocytopenia
27
Q

Where is LMW heparin cleared?

A

Renally - take care in patients with renal impairment (reduce dose)

28
Q

Can heparin be given orally?

A

No - poor GI absorption

29
Q

Is UF heparin predictable?

A

No - variable bioavailability and action

30
Q

What anticoagulant is given as prophylaxis in peri-operative patients?

A

LMW heparin at a low dose

31
Q

Is warfarin still given peri-operatively?

A

No - warfarin patients are given heparin instead, as it can be quickly stopped if bleeding occurs

32
Q

Which form of heparin is given to patients with DVT, PE, or atrial fibrillation?

A

LMW heparin to cover initial period of warfarin loading, unless fine control is required (can’t monitor routinely)

33
Q

What is heparin alone given for?

A

Acute coronary syndromes - reduces recurrence/extension of coronary artery thrombosis, MI, unstable angina, pregnancy in place of warfarin (cautiously)

34
Q

What are the adverse effects of heparin?

A

Bruising/bleeding (intracranial, injection sites, GI loss, epistaxis)
Thrombocytopenia (autoimmune, leads to platelet depletion, stop heparin and give hirudin)
Osteoporosis

35
Q

How is heparinisation reversed?

A

Protamine sulphate - dissociates it from ATIII
(Overdose can cause bleeding)
Stop heparin
Give protamine

36
Q

How does aspirin work as an antiplatelet?

A

COX-1 inhibition

37
Q

How does dipyridamole work as an antiplatelet?

A

Phosphodiesterase inhibition

38
Q

How does clopidogrel work as an antiplatelet?

A

ADP antagonist

39
Q

What is the series of platelet action?

A

Platelet adhesion > activation > aggregation

40
Q

What platelet stage do aspirin/NSAIDs inhibit?

A

Activation

Irreversibly inhibits COX-1

41
Q

What is the mechanism of action of Gp IIb/IIIa inhibitors?

A

Prevent platelet cross-linking by targeting GpIIb/IIIa

42
Q

What platelet stage do clopidogrel and dipyridamole inhibit?

A

Platelet aggregation

Pharma ESA4 (8 decks)

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