Anticoagulant and antiplatelet drugs Flashcards by Adele Atkins

Describe the coagulation cascade

Extrinsic pathway - Tissue factor (3), 7
Intrinsic pathway - 12, 11, 9, 8

Prothrombin (2) - Thrombin (2a)

Fibrinogen (1) - Fibrin monomer - 13 - fibrin clot formation

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Name some anticoagulants

Warfarin
Heparin
Direct oral anticoagulants 
Antiplatelets
Antifibrinolytics

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List the two types of heparin

Unfractionated

Low molecular weight

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List some direct oral anticoagulants and state what they inhibit

Dabigatran - Thrombin (2a)

Rivaroxaban - 10a

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What is warfarin?

Vitamin K antagonist
Prevents gamma carboxylation of factors 2, 7, 9 and 10
Prolongs the extrinsic pathway

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How is warfarin use monitored?

International normalised ration (INR)

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What is the target INR for DVT/PE/AF?

2.5

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What is the target INR for recurrent VTE or metal heart valves?

3.5

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Describe how warfarin is metabolised

Hepatically metabolised by CYP2C9

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How many days does it take warfarin to reach therapeutic levels?

> 3 days

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What does warfarin inhibit?

Natural anticoagulants - Protein C and protein S

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What is the half life of clotting factor 7?

6 hrs

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What is the half life of clotting factor 9?

24 hrs

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What is the half life of clotting factor 10?

40 hours

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What is the half life of clotting factor 2?

60 hours

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Describe how warfarin is prescribed?

Patient usually loaded with LMW heparin cover
10mg, 10mg, 5mg

Fall in protein C and S within hours may result in a temporary pro-coagulant state

LMW heparin continued till INR> 2.0 for 2 consecutive days

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Why does warfarin interact with other drugs?

Cytochrome P450

Beware of interaction with alcohol

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List some enzyme inhibitors that potentiate warfarin

Carbamezepine 
Azathioprine
Allopurinol 
Erythromycin 
Ciprofloxacin 
Metronidazole 
Fluconazole

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List some enzyme inducers which inhibit warfarin

Rifampicin
Amiodarone
Citalopram
Phenytoin

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List some side effects of warfarin

Haemorrhage risk - intracranial bleeds, increased risk in elderly
Skin necrosis
Alopecia

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Is warfarin safe to use in pregnancy?

teratogenic effects

Which anticoagulant is used in pregnancy?

LMW heparin

How do you reverse warfarin?

If life threatening bleed - give activated prothrombin complex (octaplex) containing factors 2, 7, 9 and 10 (25-50 units per kg)

Give vitamin K 2-10mg iv/po depending on INR level

Fresh frozen plasma can also be used

Describe heparin

Mucopolysaccharide that potentiates antithrombin

Irreversibly inactivates factors 2a (thrombin) and 10a

How is heparin administered?

Parentally LMW - Sc injections Unfractionated - iv infusion

Describe the use of unfractionated heparin

Given with iv 5000bolus and 1000U/hour infusion

How is unfractionated heparin monitored?

APTT

What is the APTT target range of unfractionated heparin?

1.5-2.5 x normal

Is unfractionated heparin safe in renal failure?

Yes

How can unfractionated heparin be partially reversed?

Protamine sulphate

List two rare complications of using unfractionated heparin

Thrombocytopenia | VTE

Describe the use of low molecular weight heparin

Once daily sc injections Prescribed according to the patients weight Not usually monitored - can use Xa assay Patient must have creatinine clearance of over 30ml/minute

List the LMW heparin formulations

Tinzaparin 175U/Kg Enoxaparin 1.5mg/Kg Dalteparin

What is LMW heparin commonly used for in hospital patients?

Thromboprophylaxis

Describe the dose of LMW heparin used in thromboprophylaxis in hosptial patients

3500 U or 4500 U Tinzaparin | 20 or 40mg Enoxaparin

Describe a Hirudin and give an example

Snake venom derived Argatroban - direct thrombin inhibitor Used in place of heparin in patients with HIT

Describe a heparinoid and give an example

Danaparoid - heparin like compound

Describe a fondaparinux and ive an example

Arixtra - potentiates anti thrombin - inhibits factor Xa

Give the two classes of direct oral anticoagulant and Give examples

``` Direct thrombin (2a) inhibitor - dabigatran Direct factor 10a inhibitor - rivaroxaban ```

Give the indications of rivaroxaban

VTE prophylaxis Treatment of DVT and PE Stroke prevention in AF

Give the dosing of rivaroxaban

15mg bd for 3 weeks | then 20mg od

Give the indications for dabigatran

VTE prophylaxis Treatment of DVT and PE Stroke prevention in AF

Give the dosing of dabigatran

Treatment dose - 150mg bd | Prophylactic dose 110mg bd

What must you do before prescribing dabigatran?

Confirm creatinine clearance > 30ml/min

How can dabigatran be reversed?

Praxbind

List the types of antiplatelet drugs

``` Aspirin Clopidogrel Dipyridamole Prostacyclin Glycoprotein 2b/3a inhibitors ```

How does aspirin work?

Cyclooxygenase inhibitor

How does clopidogrel work?

ADP receptor blocker

How does dipyridamole work?

Inhibits phosphodiesterase

How does Prostacyclin work?

Stimulates adenylate cyclase

Name some glycoprotein 2a/3b inhibitors

Abciximab - monoclonal antibody Eptifibatide - snake venom derivative Tirofiban - blocks platelet aggregation

Describe fibrinolytic agents

Thrombolytic agents used to lyse fresh thrombi (arterial) by converting plasminogen to plasmin Tissue plasminogen activator (alteplase, tap) and streptokinase Administered systemically in acute MI, recent thrombotic stroke, major PE or iliofemoral thrombosis Aim to use within 6 hrs