Anti-Platelets Flashcards
Name two common anti-platelet drugs
Clopidogrel and Aspirin
How does clopidogrel work?
ADP receptor antagonist on the surface of pletelets
Binds to the ADP receptor on platelets preventing them from aggregating
Why is clopidogrel mainly used for arterial thrombi?
Arterial thrombi are mainly made from platelets (white clots) where as venous thrombi are usually made up of primary fibrin
What is Clopidogrel usually prescribed with?
Aspirin
What are the main indications for the use of clopidogrel?
- ACS (with aspirin, used for a further 12 months after an NSTEMI)
- Prevent coronary stent occlusion (given dual therapy for 12 months)
- Secondary prevention of arterial thrombi for individuals with CVD, cerebrovascular disease and PAD
- AF - prevention of intracardiac clot formation where warfarin and NOACs are contraindicated
What are the contra-indications of using clopidogrel?
Active bleeding Bleeding disorders (haemophilia and thrombocytopenia) Peptic Ulcerarion Uncontrolled hypertension Pregnancy (inter uterine bleeding)
When should clopidogrel be used with caution?
Renal/hepatic insufficiency
Stop 7 days before elective surgery
What are the common interactions with clopidogrel?
Clopidogre is a pro drug and requires activation by CYP450 enzymes
- CYP450 inhibitors reduce is antiplartelt effects
- Other antiplateles (aspirin) and anticoagulants (Heparin and NSAIDS) can increase risk of bleeding
What are the common side effects of clopidogrel?
Bleeding
GI upset
Thrombocytopenia
How is clopidogrel excreted?
Hepatic metabolism
Excreted in urine and faeces
How long does clopidogrel take to meet its full anti-platelet effects?
7 days
Do you have to monitor the use of clopidogrel?
No
What do you do when you need fast effects of clopidogrel?
Give a loading dose of 300mg and then a regular mantinaence dose of 75mg
As well as being an anti-platelet drug what other classification does aspirin have?
NSAID
How does aspirin work?
Aspirin irreversibly inhibits COX1 and modifies COX2 activity
COX1 is responsible for thromboxane production from arachidonic acid - thromboxane helps platelet aggregation
COX2 is responsible for an inflammatory environment
Aspirin is also metabolised into salicylic acid which has anti-inflammatory, anti-pyrexial and analgesic effects
What are the main uses for aspirin?
- ACS (with clopidogrel)
- Acute ischaemic stroke (when rapid reduction in platelet aggregation will improve outcome)
- Secondary prevention in arterial thrombi formation in patients with CVD, cerebrovascular disease and PAD
- AF - reduce intracardiac thrombi formation in patients where warfarin and NOACs are contraindicated
- Mild to moderate pain relief and fever control
What are the contra-indications of aspirin?
Aspirin induced hypersensitivity (and other NSAID)
Children under 16 due to Reyes syndrome
Third trimester of pregnancy (premature closure of ductus arterosus)
When should aspirin be used with caution?
Asthma GI ulceration Gout (may trigger attack) Risk of bleeding (peptic ulcer, bleeding disorders, truama/surgery) G6DP deficincency
What is reyes syndrome?
a rare but life-threatening illness that principally affects the liver and brain
What are the common interactions with aspirin?
Other anti-platelets (aspirin) and anti-coagulants (warfarin heparin) can increase risk of bleeding
Can increase warfarin affects
Some other NSAIDS (ibuprofen) decrease anti-platelet effects
What are the common side effects of aspirin?
GI ulceration and irritation Hypersensitivity reactions including bronchospasm High dose can tinnitus Overdose Extra/Intracranial bleeding Thrombocytopenia
How is aspirin eliminated?
Metabolised in liver
Excreted in urine
