Antiplatelets- ADP-receptor antagonists

Question 1

What is the mechanism of action?

Answer 1

Prevent platelet aggregation and reduce the risk of arterial occlusion by binding to ADP receptors on surface of platelets.

Clopidogrel and prasugrel are irreversible inhibitors of ADP receptors

Ticagrelor acts reversibly

Question 2

What are common side effects?

Answer 2

Bleeding, GI upset including dyspepsia, abdominal pain, diarrheoa is common

Rarely can affect platelet numbers causing thrombocytopenia

Question 3

Who should not be prescribed ADP antagonist?

Answer 3

Active bleeding
May need to be stopped 7 days before surgery

Question 4

Who should be prescribed with caution?

Answer 4

renal and hepatic impairment

Question 5

What are important clopidogrel interactions and why?

Answer 5

CYP450 Inhibitors as it clopidogrel is a prodrug activated by CYP 450

Question 6

What are examples CYP inhibitors?

Answer 6

omeprazole, ciprofloxacin, erythromycin,some antifungals, some selective SSRI, grapefruit juice.

Question 7

What PPIs can be prescribed with clopidogrel?

Answer 7

lansoprazole or pantoprazole as they are less likely to inhibit clopidogrel activation than omeprazole.

Question 8

What are common interactions with ticagrelor?

Answer 8

It is NOT a prodrug but interacts with CYP inhibitors (which may increase toxcity) and inducers ( which may reduce efficacy)

Question 9

What are common dosages for all indications?

Answer 9

Only used as oral preparation
Low doses require up to full week to reach full effect

ACS-Loading dose- 300mg single dose

regular maintenance 75mg orally daily is started next day

Question 10

When can each type of ADP-antagonist be stopped before surgery?

Answer 10

Clopidogrel/prasugrel- 7 days before :
as they act irreversibly so their effects persist for the lifespan of platelets (7-10)

Ticagrelor- 5 days before :
act reversibly so effects wears off quicker

Question 11

What are common indications

Answer 11

1. For treatment of acute coronary syndrome (ACS), usually in combination with aspirin, where rapid inhibition of platelet aggregation can prevent or limit arterial thrombosis and reduce subsequent mortality.

➋ To prevent coronary artery stent occlusion, usually in combination with aspirin.

➌ For secondary prevention of major adverse cardiovascular events in people with ischaemic heart disease, cerebrovascular disease or peripheral vascular disease, alone or in combination with aspirin