Anticoagulants and antiplatlets

Question 1

What Clotting factors does warfarin inhibit?

Answer 1

• it inhibits vitamin K dependent clotting factors II, VII, IX, X

Question 2

What is the function of warfarin?

Answer 2

Blocks the vKORC1 which is the enzyme responsible for activation of vitamin K as well as protein C&S which adjusts rate of clot formation

Question 3

What is the function of heparin?

Answer 3

It activates anti thrombin III which inactivated factor Xa thrombin preventing thrombin formation and therefore fibrin deposition

Question 4

What are the 3 NOACs?

Answer 4

Dabigatran
Rivaroxaban
Apixaban

Question 5

What is the function of Dabigatran?

Answer 5

Direct thrombin inhibitor

Question 6

What is the function of Rivaroxaban and Apixaban?

Answer 6

Direct factor Xa inhibitor

Question 7

How is a patients warfarin levels measured prior to extraction?

Answer 7

• INR which should be between 2.5-3.5. Ideally below 4 no more than 24hrs before procedure or if stable for past 3 months no more than 72hrs prior to surgery.
  Patients should have bloods monitored weekly.
  If above 4 delay treatment or refer for secondary care if urgent.

Question 8

If a patient is on NOAC and requiring high risk bleeding procedure, how would you manage the medications?

Answer 8

Apixaban and dabigatran:
- miss morning dose on day of Tx and take normal dose at usual time at night as long as 4hrs post haemostasis.

Rivaroxaban:
- delay morning dose and can take 4hrs post haemostasis or if patient takes medication at night this can be taken as normal.

Question 9

What are the main interactions with warfarin that we should look out for?

Answer 9

Metronidazole, antifungals (azoles), NSAIDs

Question 10

What is the role of anticoagulants ?

Answer 10

Blood thinners used to prevent and reduce coagulation of the blood, prolonging the clotting time.
They interfere with the coagulation cascade.
Pts with AF, CAD, MI, DVT, stroke, PE, HD and hyper coagulated states (factor V Leiden).

Question 11

What is the role of antiplatlets?

Answer 11

Reduce platelet aggregation and inhibits thrombus formation - effective in arterial circulation.
They decrease ability of blood clots to form by interfering with platelet activation process.

Question 12

What is dual antiplatelet therapy?

Answer 12

This is when aspirin and an ADP/P2Y (clopidogrel) medication are used in conjunction to obtain a greater effectiveness in preventing platelet aggregation

Question 13

What is the action of aspirin?

Answer 13

It is a irreversible cyclo-oxygenase inhibitor which irreversible inhibits enzyme COX, resulting in reduced platelet production of thromboxane which lowers cyclic AMP and initiates platelet release.
It inhibits platelet aggregation, thromboxane A2 and prostacyclin for lifespan of platelet (10days).

Question 14

What is the action of clopidogrel?

Answer 14

It is an ADP receptor inhibitor which inhibits the ADP induced platelet aggregation dependent activation of factor IIb/IIIa complex via the P2Y12 sub-receptor

Question 15

What is the action of Dipyridamole?

Answer 15

It is a nucleoside transport inhibitor which inhibits platelet phosphodiesterase PDE3 reducing platelet functionality.

Question 16

Name and describe a NOAP?

Answer 16

Prasugrel:
- irrerversibly binds to P2Y12 receptor but has faster, more potent impact with few ever interactions than clopidogrel but higher incidence of bleeding

Ticagrelor:
- reversibly binds to P2Y12 receptor allowing rapid onset of effects

Question 17

What medications can increase bleeding risk?

Answer 17

Anticoagulants and antiplatlets
Cytotoxic drugs associated with bone marrow suppression (reduces platelet numbers and impairs liver function)
NSAIDs (impaired platelet function)
Drugs affecting nervous System - SSRIs, Carbamazepine (impairs platelet aggregation and bone marrow production of platelets)

Question 18

What medical conditions can increase bleeding risk?

Answer 18

Chronic renal failure
Liver disease
Haematological malignant or myelodysplastic disorders 
Recurrent or current chemo 
Advanced heart failure 
Inherited bleeding disorders 
Idiopathic thrombocytopenia purpura

Question 19

Name the most common inherited bleeding disorders?

Answer 19

Haemophilia A (Factor VIII)
- X linked recessive trait
Haemophilia B (factor IX - Christmas disease)
Von Willebrand disease
- defective VWF which binds to factor VIII

Question 20

What is the action of sulphonamides?

Answer 20

They inhibit folic acid production by the bacteria.

Question 21

What are the main contraindications for use of metronidazole?

Answer 21

• alcohol use
• ## warfarin

Question 22

What is the mode of action of apixaban

Answer 22

Inhibition of factor Xa

Question 23

What is the most appropriate pain relief for a patient on dabigatran following an extraction?

Answer 23

Paracetamol - not NSAIDs

Question 24

What type of procedure would require a patient to miss a dose of apixaban?

Answer 24

Extraction of multiple teeth (2molars) in the same visit.