Anticoagulants, antiplatelets and fibrinolytics

Question 1

What are the 3 main anticoagulants

Answer 1

Heparins
Oral - warfarin
Direct oral anticoagulants (DOACs)

Question 2

Describe the action of warfarin

Answer 2

Warfarin is a vit K antagonist (vit K necessary for coagulant factors)
Anti-coagulant - prevent unwanted thrombosis
Less used now

Question 3

What is INR ?

Answer 3

International normalised ratio
Times how long clotting takes to occur

Question 4

Injectable anticoagulants
Use
Type of drug
Mode of action

Answer 4

Used to treat people at risk of getting a DVT (e.g. due to being bedbound) ; they have immediate action (unlike warfarin)
The drugs are called heparins
They activate anti thrombin III which inactivates some clotting factors and thrombin by inhibiting serine proteases

Question 5

When is aspirin given

Answer 5

Given to people who have had MI
Low dose given daily
Used a secondary prevention of stroke
not used for primary prevention (due to increased chance of stomach bleed)

Question 6

Function of prostacyclin and thromboxane

Answer 6

Prostacyclin (PGI₂) - prevents platelet aggregation by increasing cAMP ; vasodilator released from arachidonic acid in endothelium

thromboxane (TXA₂) - promotes platelet aggregation by decreasing cAMP ; made from arachidonic acid in membrane in platelets specifically

Question 7

Describe the action of aspirin

Answer 7

Irreversibly inhibits COX ; has opposite effects in platelets and endothelial cells

As platelets have no nuclei they cannot make any new COX so no more TXA2 until new platelets made

Endothelial cells have nucleic so make more COX and more PGI2 is produced

Question 8

What is the importance of glycoproteins IIb and IIIa

Answer 8

Drug binding site
ADP released from aggregating platelets leads to expression of GP IIb/IIIa
These glycoproteins bind to fibrinogen which leads to cross linking of platelets and clotting

Question 9

Describe the action of clopidogrel

Answer 9

Inhibits the action of ADP - GP IIb/IIIa are not expressed
Used in combination with aspirin

Question 10

Describe the action, uses and contraindications of thromobolytics

Answer 10

Used in thromboembolic stroke/alternative treatment after MI/pulmonary embolism
Dissolves clot with reperfusion
Contraindicated for patients who have just had recent surgery or a haemorrhaging stroke - as it may result in heavy bleeding

Question 11

What are the two types of stroke

Answer 11

Most caused by a blood clot getting stuck in a vessel in the brain
Some caused by a haemorrhage

Question 12

Uses of warfarin

Answer 12

In patients with replaced heart valves
AF
DVT
Pulmonary embolism

Question 13

DOACs
What are they
Why are they advantageous over warfarin

Answer 13

Direct oral anticoagulants
Advantages - less bleeding, fewer drug interactions, does not require monitoring, just as effective in most patients
However reversal is needed if heavy bleeding occurs

Question 14

Function of NO

Answer 14

Produced by endothelial cells

lowers BP and prevents platelets from unwantedly sticking to the endothelial surface

Question 15

Aspirin shows important interaction with warfarin

true or false

Answer 15

True

Question 16

what is the use of an enzyme inducer in a patient taking warfarin is likely to lead to?

Answer 16

Therapeutic failure as plasma [warfarin] will decrease

Question 17

Following the administration of unfractionated heparin what will occur?

Answer 17

APTT will rise (it is a test for blood clotting time that is specific to heparin)

Question 18

Describe the impact of polymorphism of cytochrome P450 and CYP2D6

Answer 18

Mutations in those two genes can result in a poor or good metabolism

poor metabolism may increase the effect of a drug on a patient (e.g metoprolol) or decrease the effect (tamoxifen)

Question 19

Possible serious complication of LMWH

Answer 19

Heparin‐induced thrombocytopenia (HIT) is a immune mediated adverse drug reaction caused by the emergence of antibodies that activate platelets even in the presence of heparin.

Question 20

Which tests should be ordered when a DVT is diagnosed ?

Answer 20

Measure baseline full blood count, renal and hepatic function, PT and APTT (both these identify i patient has a bleeding disorider)