Antiplatelets Flashcards
(24 cards)
How do arterial and venous thrombosis differ?
Arterial- usually forms at the site of atherosclerosis following plaque rupture. Low fibrin, higher platelet.
Venous- usually due to stasis or damage, high RBC and fibrin content, low platelet.
Arterial thrombi are usually targeted with which drugs?
Antiplatelets and fibrinolytics
Venous thrombi are usually targeted with which drugs?
Anticoagulants
How does aspirin work?
It irreversibly inhibits COX-1, reducing the production of thromboxane A2 and reducing platelet aggregation.
Unable to fully inhibit aggregation due to there being other mediators and mechanisms involved.
In some individuals, polymorphism in cox-1 reduces efficacy
What contraindications are implemented in aspirin use?
Increased bleeding time - haemorrhage stroke or GI bleeding
Reye’s syndrome - avoid in <16yrs
Hypersensitivity
3rd trimester- premature closure of ductus arteriosus
What drug-drug interactions should be considered when prescribing aspirin?
Antiplatelets and anticoag
What dosage of aspirin and in what form should it be taken during an ACS?
300mg loading dose, chewable.
What dose of aspirin and for how long should be given to a patient with an acute ischaemic stroke?
300mg, daily for 2 weeks
What effect do ADP receptor antagonists have?
Inhibit binding of ADP to P2Y12 receptors- inhibiting activation of GPIIb/IIIa receptors. Independent of COX pathway.
What drug class do clopidogrel, prasugrel and ticagrelor belong to?
ADP receptor antagonists
How are clopidogrel and prasugrel different from ticagrelor?
Clopidogrel and prasugrel are irreversible inhibitors, whereas ticagrelor acts reversibly. They are also prodrugs.
Clopidogrel has a slow onset of action, whereas the other two have a more rapid onset.
Ticagrelor also acts at a different site to clopidogrel.
What contraindications are there for ADP receptor antagonists (clopidogrel/ticagrelor)?
Bleeding
GI upset
Thrombocytopenia
Renal and hepatic impairment.
What drug interactions should you be aware of when prescribing clopidogrel?
Omeprazole, ciprofloxacin, erythromycin, some SSRIs - inhibit CYPs
CYP required for activation of clopidogrel.
How long before surgery should ADP receptor antagonists be stopped?
Clopidogrel- 7 days
Ticagrelor - 5 days
Name a glycoprotein IIb/IIIa inhibitor
Abciximab
How do glycoprotein IIa/IIIb inhibitors work?
Blocks binding of fibrinogen and vWF - targets final common pathway.
Leads to >80% reduction in aggregation.
Given IVI with bolus
What contraindications arise with glycoprotein IIb/IIIa inhibitors?
Bleeding
Thrombocytopenia
Hypotension
Bradycardia
What cautions should be taken when prescribing glycoprotein IIb/IIIa inhibitors?
Use of other antiplatelets and anticoagulants.
Phosphodiesterase inhibitors (dipyridamole)work how?
Dipyridamole
Dipyridamole inhibits cellular reuptake of adenosine, increased plasma adenosine and inhibits platelet aggregation via A2 receptors
Also prevents cAMP degradation, inhibiting expression of GPIIb/IIIa
What are the contraindications associated with dipyridamole?
Flushing
Headache
Hypersensitivity
What cautions should you be aware of when prescribing dipyridamole?
Antihypertensives
Antiplatelets
Anticoagulants
Name some fibrinolytic agents
Streptokinase
Alteplase
Dissolve the fibrin within the thrombus
Which fibrinolytic agent has been licensed for use in acute ischaemic stoke <4.5hrs from onset?
Alteplase
Why can streptokinase only be used once?
It develops an antibody response
