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Pharmacology > Anticoagulants + Antiplatelets > Flashcards

Anticoagulants + Antiplatelets Flashcards

1
Q

When are anticoagulants used

Why

A

Venous thrombosis treatment and prevention

Venous thrombus consist more of fibrin than platelets due to slow flow

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2
Q

What is Thrombosis

A

Formation of solid mass of blood within circulatory system during life

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3
Q

What causes thrombosis

A

Virchows triad:
Abnormal blood flow (stagnation in venous)
Abnormal vessel wall (atheroma in arteries)
Abnormal blood components (post-op)

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4
Q

When are antiplatelets used

Why

A

Arterial thrombosis

Arterial thrombus consists of platelets>fibrin due to high flow

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5
Q

What are the types of anticoagulants

A 
Warfarin
Heparin
Selective FXa inhibitor
Direct thrombin inhibitor 
NOACs
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6
Q

What is the mechanism of action of warfarin

A

Inhibit synthesis of Vitamin K dependent clotting factors: II, VII, IX, X
by competitive antagonism of Vitamin K Reductase

(Inhibit activation of Vitamin K, inhibit carboxylation of glutamate required for CF synthesis)

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7
Q

What are indications of warfarin

A

INR 2-3
DVT
PE
AF

INR 2.5-4.5
Mechanical heart valve
Thrombosis with inherited thrombophilia
Recurrent thrombosis on warfarin

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8
Q

What are PK properties of warfarin

A

Good oral bioavailability (oral admin)
Slow onset/offset (heparin cover, stop 3 days)
Hepatic CYP450 metabolism (DIs)
Heavily protein bound (DIs)
Crosses placenta (teratogenic, brain haemorrhage)

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9
Q

How is warfarin administered

A

Oral - good bioavailability

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10
Q

Why does warfarin have slow onset/offset

How do you manage this

A

It takes several days for already synthesised CF to break down/new CF to be synthesised

Initial heparin cover
Withdraw 3 days prior to surgery

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11
Q

What effects does warfarin crossing the placenta have

A

Teratogenicity in 1st trimester

Brain haemorrhage in 3rd trimester

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12
Q

What drug interactions occur with warfarin

A

CYP450 enzyme inducers/inhibitors

Heavily protein bound drugs

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13
Q

What monitoring is required for warfarin

A

INR: international normalised ratio

To adjust dose

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14
Q

What is INR

A

PT/APTT

Measure of time take for blood to clot compared to average for age+gender

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15
Q

What types of interactions can occur with warfarin

A

Potentiating: Increased anticoagulatory effect
Inhibiting: decreased anticoagulatory effect

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16
Q

What causes potentiating DIs

A

CYP450 inhibitors: amiodarone, quinolone, metronidazole, acute alcohol binge, cimetidine
Heavily protein bound drugs: NSAIDs

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17
Q

What causes inhibiting DIs

A

CYP450 inducers: antiepileptics, rifampicin, St Johns wort, chronic alcohol

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18
Q

What are side effects of warfarin

A

Bleeding: epistaxis, GI bleed (unexplained anaemia), intracranial haemorrhage
Teratogenicity

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19
Q

How do you reverse warfarin

A

INR 3-6, no bleed: stop warfarin, restart when <5 INR

INR 6-8, minor bleed: IV Vitamin K (slow onset)

Major bleed: give FFP or Prothrombin complex (fast onset)

20
Q

What is mechanism of action of heparin

A

Bind + form complex with antithrombin III by binding to pentasacharide sequence
Increase activity of ATIII
Inhibit thrombin and FXa

21
Q

What are the types of heparin

A

Unfractionated heparin

Low molecular weight heparin

22
Q

What is the mechanism of action of UH

A

Inhibit FXa and thrombin

Can bind to AT III and thrombin simultaneously

23
Q

What is the mechanism of LMWH

A

Inhibit FXa only

Cannot bind to thrombin and AT III simultaneously and thrombin requires binding at 2 sites to be inactivated

24
Q

What are PK properties of UH

A

Poor GI absorption - IV
Dose-response - non-linear
Oral bioavailability - unpredictable
Monitoring - required, APTT

25
Q

What are PK properties of LMWH

A 
Poor GI absorption - SC
Dose-response - linear
Oral bioavailability - predictable
Monitoring - not required 
Metabolism - renal
26
Q

What are indications of heparin

A 
Prevention of thromboembolism: surgery, immobility 
Periop warfarin cover 
Initial warfarin cover:DVT, PE, AF
MI, unstable angina
Pregnancy (instead of warfarin)
27
Q

What are side effects of heparin

A

Haemorrhage: epistaxis, GI bleed, intracranial haemorrhage

Thrombocytopenia:
heparin binds to pF4, complex cause IgG production and to form immune complex, cause platelet aggregation, thrombosis and depletion of platelets

28
Q

How do you reverse heparin

A

Stop heparin

Give protamine

29
Q

What is protamine

A

Positive-amine containing molecule
Binds to and neutralise sulphate group on heparin (-ve)
Dissociate heparin from at iii

30
Q

What are selective FXa inhibitors

A

Synthetic pentasaccharide that bind to AT III with high specificity for FXa

31
Q

Give examples of selective Fxa inhibitors

A

Fondaparinux

32
Q

What are direct thrombin inhibitors

A

Binds directly to thrombin and inhibits Without binding to AT III

33
Q

Give examples of direct thrombin inhibitors

A

Bivalirudin

Desirudin

34
Q

When are antiplatelets used

Why

A

Arterial thrombosis

Arterial thrombi consists of platelets >fibrin due to high flow

35
Q

What are indications of antiplatelets

A

Prevention and treatment of arterial thrombotic disease:
Acute coronary syndrome
Stroke

(Arterial thrombosis can occur due to atheroma rupture)

36
Q

What are types of antiplatelets

A

Aspirin
Glycoprotein IIb/IIIa inhibitors
Platelet ADP receptor antagonist
Dipyridamol

37
Q

What are NOACs

Why are they preferred

A

New oral anticoagulants

No monitoring required, rapid onset/offset

38
Q

Give examples of NOACs

A

Apixaban - FXa inhibitor
Dabigatran - thrombin inhibitor
Rivaroxaban - FXa inhibitor

39
Q

Why is LMWH preferred to UH

A

Lower risk of thrombocytopenia
No monitoring required
Only Single daily dose required (longer T1/2)

40
Q

What is mechanism of action of aspirin

A

Irreversible inhibition of COX1
Inhibit Thromboxane A2 synthesis
(binds to TXA2 receptors to cause intracellular Ca increase and activation of GP IIb/IIIa receptors to allow fibrin binding+aggregation)
Inhibit platelet aggregation

41
Q

What is mechanism of action of GLYcoprotein IIa/IIIb inhibitors

A

Inhibit platelet aggregation by binding to GLYcoprotein IIa/IIIb receptors on platelets
(Receptors on platelets that binds to fibrinogen for platelet aggregation)

42
Q

Give examples of GLYcoprotein IIa/IIIb inhibitors

A

Abciximab
Tirofiban
Eptifibatide

43
Q

What is mechanism of action of platelet ADP receptor antagonists

A

Inhibit platelet aggregation by inhibiting adp binding to its receptors on platelets
(ADP binding causes rise in [Ca]i, activation of GP IIa/IIIb, fibrinogen binding, aggregation)

44
Q

Give examples of platelet adp receptor antagonists

A

Clopidogrel
Prasugrel
Ticagrelor

45
Q

What is dipyridamol

What is its mechanism of action

A

Phosphodiesterase inhibitor
Inhibit platelet aggregation by increasing cAMP levels
(PDE breaks down cAMP. cAMP inhibits rise in intracellular Ca)

Pharmacology (19 decks)

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