Antiplatelets Flashcards
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
