Session 6.2 - Antiplatelets & Fibrinolytics

Question 1

Aspirin

Answer 1

Drug Class: COX-1 inhibitor

Mechanism of Action: inhibits COX-1, preventing formation of thromboxane A2 (TXA2) from arachidonic acid (AA), reducing platelet aggregation

Common Indicators: ACS, Stroke
low dose = 75mg
loading dose = 300mg

ADRs: GI irritation, GI bleeding (peptic ulcer), haemorrhage (stroke)

Contraindications: Reye’s syndrome, Aspirin hypersensitivity, prevent closure of ductus arteriosus

Important drug-drug rxns: anti-platelets and anticoagulants

Question 2

Clopidogrel
Prasugrel
Ticagrelor

Answer 2

Drug Class: ADP receptor antagonist

Mechanism of Action: inhibit binding of ADP to P2Y12 receptor, inhibiting the activation of GPllb/llla receptors, preventing platelet aggregation

Common Indicators: N/STEMI, Stroke, Dual anti-platelet therapy with Aspirin

ADRs: Bleeding, GI upset - dyspepsia & diarrhoea, thrombocytopenia

Contraindications: High risk of bleeding in patients with renal & hepatic impairment

Important drug-drug rxns: Clopidogrel needs CYP for activation: some PPIs and SSRIs (antidepressants) are CYP inhibitors

Question 3

Dipyridamole

Answer 3

Drug Class: Phosphodiesterase inhibitor

Mechanism of Action:

• inhibits cell re-uptake of adenosine –> increased [adenosine] –> inhibit platelet aggregation
• prevent cAMP degradation –> inhibit expression of GPllb/llla receptors

Common Indicators: Secondary prevention of stroke and TIAs, prophylaxis for valve replacement

ADRs: V + D, dizziness

Important drug-drug rxns: anti-platelets and anticoagulants, adenosine (temporarily stops heart - impending sense of doom)

Question 4

Abciximab

Answer 4

Drug Class: Monoclonal antibody

Mechanism of Action: Directly blocks GPllb/llla receptors, blocking binding of vWF and Fibrinogen –> reducing platelet aggregation

Common Indicators: IV, Only used by specialists in PCI

ADRs: Bleeding

Important drug-drug rxns: anti-platelets and anticoagulants

Question 5

Streptokinase

Alteplase

Answer 5

Drug Class: Fibrinolytic “clot busters”

Mechanism of Action: inhibit formation of plasmin from its precursor plasminogen

Common Indicators: Alteplase used in acute ischaemic stroke, STEMI

ADRs: Bleeding

Important drug-drug rxns: anti-platelets and anticoagulants