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Human Pharmacy > Anticoagulant drugs > Flashcards

Anticoagulant drugs Flashcards

1
Q

List the pharmacological classes of the relevant anticoagulants

A

Heparin

Direct thrombin inhibitors

Factor Xa inhibitors

Vitamin K antagonists

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2
Q

What are the type of heparin?

A

Standard/ unfractionated heparin = Heparin

LMWH = enoxaparin, dalteparin, nadroparin

Heparinoid = danaparoid

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3
Q

What is the MOA of Heparin?

A

Heparin binds to antithrombin > elongation of antithrombin binding site > the antithrombin then binds to thrombin > blocks binding of thrombin to fibrin

targets unbound thrombin

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4
Q

Which is more selective for factor Xa, LMWH or Danaparoid?

A

Danaparoid is more selective for factor Xa than LMWH

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5
Q

What do LMWH have the greatest effect on?

A

Greater effect on factor Xa than thrombin

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6
Q

List the ADRs of Heparin

A

Bleeding (dose dependent), bruising, pain in injection site, skin necrosis (injection site)

mild reversible thrombocytopenia

hyperkalaemia (monitor for use of ACEi, ARB, K+ sparring diuretics)

inc liver aminotransferase

Osteoporosis and alopecia (long term)

Allergic reaction (urticaria, anaphylaxis) = the drug is a protein

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7
Q

What is classes as severe thrombocytopenia?

A

Platelet count drops by 30-50% below normal –> heparin use in contraindicated in this circumstance cuz it can further decrease platelet count

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8
Q

When does heparin induced thrombocytopenia usually occur?

A

occurs within 5-10 days of treatment

may be earlier if patient has been exposed to heparin (<100 days)

delayed onset = several weeks after stopping heparin

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9
Q

Compare Heparin with LMWH and Danaparoid

A

In renal impairment, risk of bleeding is greater with LMWH and will require dose adjustment. Conversely, heparin has a lesser risk of bleeding in severe renal failure. With both Danaparoid and LMWH heparin in renal failure, monitor Xa levels.

Danaparoid, less risk of bleeding and used over Heparin or LMWH in heparin induced thrombocytopenia (HIT).

LMWH carry a lesser risk of osteoporosis

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10
Q

What should be monitored with heparin use? How?

A

Heparin in monitored with aPTT or APTT time = activated partial thromboplastin time

APTT time = measures activity of intrinsic coagulation pathway

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11
Q

What is the antidote to heparin?

A

Protamine sulfate

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12
Q

Describe the MOA of protamine sulfate

A

combines with heparin > forms inactive complex - onset 5 mins

*only partially effective in reversing LMWHs, not used for danaparoid

*has anticoagulant effect in overdose or absence of heparin

*Not used fir denaparoid overdose

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13
Q

What are the to sub types of direct thrombin inhibitors?

A

Bivalent = two binding points

Univalent = one binding point

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14
Q

List the drug names of the relevant direct thrombin inhibitors

A

Bivalirudin

Dabigatran etexilate (pro drug) –> dabigatran

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15
Q

What is the MOA of bivalirudin (bivalent direct thrombin inhibitor)?

A

Dabigatran binds to both exosite 1 and exosite 2 of thrombin > prevents the binding of fibrin to thrombin > inhibits platelet aggregation

Both bound and unbound thrombin

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16
Q

What is the MOA of dabigatran (univalent direct thrombin inhibitor)?

A

Bivalirudin binds to thrombin in the fibrin binding site > prevents fibrin from binding to thrombin > prevents platelet aggregation

Both bound and unbound thrombin

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17
Q

What are some characteristics of direct thrombin inhibitors?

A

Reversible inhibition

prevent conversion of fibrinogen to fibrin –> Inhibits thrombus formation

Inhibits thrombus induced platelet aggregation -> stops surface thrombin from binding/rec other platelets

antiplatelet effect = reducing thrombin-mediated activation of platelets

18
Q

What are the ADRs of direct thrombin inhibitors?

A

Bleeding, signs of bleeding (anaemia, hypotension)
GI symptoms - Gastritis, dyspepsia, GI bleeding, oesophageal ulcers

19
Q

What is used to reverse the actions of direct thrombin inhibitors?

A

Idarucizumab

It is a humanised monoclonal antibody fragment

20
Q

Describe the MOA of idarucizumab

A

Binds to dabigatran and metabolites > forms stable inactive complex

immediate effect

21
Q

List the relevant factor Xa inhibitors

A

Rivaroxaban (oral), apixaban (oral), fondaparinux (IV)

22
Q

What is the MOA of direct Xa inhibitors?

A

Bind and inhibit factor Xa > prevents the conversion for factor II (prothrombin) to factor IIa (thrombin) > preventing the conversion of fibrinogen to fibrin > prevents platelet aggregation and coagulation

23
Q

List the ADRs of factor Xa inhibitors

A

Bleeding (signs of bleeding = anaemia, tachycardia, hypotension)

24
Q

What are some concerns with factor Xa inhibitor use?

A

No method to guide dosing

No antidote

25
Q

List the relevant vit k antagonist

A

Warfarin (also phenidione)

26
Q

What is the MOA of warfarin?

A

Warfarin inhibits VKORC (vitamin K epoxide reductase) > inhibits formation of Vit K epoxide to active Vit KH2 > inhibition of vit K dependent clotting factor synthesis

27
Q

Knowing that warfarin is a racemic mixture, which isoform is more potent?

A

S isomer of warfarin is 5 times more potent anticoagulant

28
Q

What P450 enzyme inactivates warfarin?

A

CYP2C9 = highly polymorphic

29
Q

Discuss some facts about warfarin

A

Effect of warfarin dependent on clearance of preformed clotting factors

Initial INR inc occurs 24-36 hrs after first dose, this is not associated with antithrombotic effect

Takes 2 half-lives to express antithrombotic effect (up to 5 days), max effect 48 hrs after administration, can last for next 5 days

30
Q

When is warfarin use indicated?

A

Prevention/treatment of VTE

Prevention of thromboembolism in patient with prosthetic hear valve

Prevention of stroke in people with hx of MI, inc embolic risk

non-valvular AF and high risk of stroke or systemic emboli

31
Q

TRUE or FALSE

Warfarin is not a narrow therapeutic index drug

A

FALSE

Warfarin is a narrow therapeutic index drug, completely orally absorbed

peak action - after 4 hrs

Mostly hepatically cleared

t1/2= 20 to 60 hrs (mean 40hrs)

32
Q

What is used to monitor warfarin?

A

Prothrombin time (PT) = determines prothrombin ratio (PR) and international normalised ratio (INR)

PT = responds to reduction of three of the four vit K clotting factors (II, VII, X)

33
Q

Discuss the INR for warfarin

A

INR = 5 - high chance of bleeding
INR = 0.5 - high chance of clotting

Normal INR range = 0.9 - 1.3

34
Q

What are the INR targets for warfarin therapy?

A

Less intense range INR = 2.0-3.0

High intense range INR = 2.5-3.5 (bigger clot risk)

35
Q

What factors influence warfarin?

A

drug interactions

elderly = exaggerated response due to less vit k

Heavy alcohol = inc liver metabolism, less Vit K, inc risk of falls, poor diet, poor compliace

Amount of Vit K in diet = watch for dark green veggies high in vit K

36
Q

When should monitoring be done for warfarin?

A

INR tested = after starting, after stopping/changing dose of other meds, other situations that could affect INR

INR: measure once a week after change in med to reflect clinically sig interaction

37
Q

When is bleeding rate doubled for warfarin use?

A

INR increase from 2.0-2.9 to 3.0-4.4

50% bleeding = INR <4.0

38
Q

What are some bleeding risk factors for warfarin?

A

> 65 y/o
Uncontrolled hypertension
Hx GI haemorrhage, active peptic ulcer, hepatic insufficiency

Thrombocytopaenia
HX stroke, cognitive, psychological impairment
Renal insufficiency
recent trauma, hx falls

excessive alcohol, mediations

39
Q

What is used to reverse wrafarin?

A

Phytomenadione (Vit K1) is used to reverse warfarin = delayed

Fresh frozen plasma with clotting factors

40
Q

List some ADRs with warfarin use

A

skin necrosis

purple discolouration of toes

alopecia, fever, rash

nausea, vomiting, diarrhoea

hepatic dysfunction, allergic reaction

41
Q

What are the considerations for warfarin in pregnancy?

A

Category D = risk of teratogenicity, foetal or placental haemorrhage

May be used in tri2 = may be more effective than heparins in women with prosthetic heart valves

Human Pharmacy (11 decks)

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