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What are the indications for aspirin?
Mild to moderate pain: Headaches and transient musculoskeletal pain. Pyrexia and anti-platelet action.
What is the mode of action of aspirin?
Irreversible inactivation of the COX-1 enzyme required for prostaglandin and thromboxane synthesis. Blocking Thromboxane A2 prevent platelet aggregation.
What are the contraindications for prescribing aspirin?
- Children <16 years.
- Peptic ulceration (past and active)
- NSAID sensitivity
- Avoid in hepatic and renal impairment.
- Avoid towards end of pregnancy or whilst breastfeeding.
What are the side effects of aspirin?
- GI irritation.
- Increased bleeding time.
- Skin reactions
What is the dose and potential routes of administration of aspirin?
Oral: 300-900mg every 4-6 hours (max 4g)
Rectal: 450-900mg every 4 hours (max 3.6g)
- For long-term anti-platelet action:
- 75mg OD
How can we reduce side effects of aspirin?
Take after food or enteric coated capsules (slower delivery)
Does Aspirin interact with other drugs?
Use with other NSAIDs can increase side effects.
Increased risk of bleeding if given with anticoagulants, antidepressants, clopidogrel, steroids, iloprost
What is Clopidogrel given for?
Preventing atherothrombotic event in arterial disease, post-MI or stroke, or during active ACS event.
What is the mode of action of Clopidogrel
Irreversibly inhibits binding of ADP to a receptor on platelets, inhibiting activation and up-regulation of GP IIb/IIIa receptors which prevents platelet aggregation
What are the contra-indications to prescribing Clopidogrel?
Caution in hepatic and renal impairment, or at risk of bleeding
Avoid in Pregnancy/ breastfeeding
What are the side effects of Clopidogrel?
GI discomfort, Bleeding and rare neutropenia
Due to MOA it can take several days for anti-platelet effects to wear off.
What dose should be prescribed of Clopidogrel?
- Oral preparations
- Prevention: 75mg OD
ACS: 300mg then 75mg daily (600mg loading dose in STEMI)
Why is LMWH preferred to unfractionated heparins?
Same efficacy and longer action, but reduced risk of heparin-induced thrombocytopenia
What is enoxaparin used for?
- Venous Thromboprophylaxis
- DVT and PE treatment
What is the mode of action of enoxaparin?
Accelerates action of anti-thrombin III, increasing the inactivation of Factor Xa (prevents conversion of prothrombin to thrombin)
How would you treat an enoxaparin overdose?
Protamine (50mg max)
What is the dose of enoxaparin?
In VTE prophylaxis: 1.5mg/kg OD sub-cut for 5/7
For NSTEMI/UA: 1mg/kg BD
For STEMI: none if patient is for PCI
What is HITTS?
Heparin-induced thrombocytopenia and thrombosis syndrome
Is it ok to give heparin if there is a previous episode of HITTS?
What other LMWHs are available?
What is the mode of action of warfarin?
Inhibits Vitamin K reductase, preventing activation of Factors 10, 9, 7, 2 and therefore blood coagulation
What is warfarin indicated for?
DVT, PE, AF and prosthetic valves if at risk of embolisation
What are the contraindications for prescribing Warfarin?
- Active Ulcers
How is it administered?
- Takes >3 days for therapeutic effect.
- LMWH cover should be given until this is reached as it may leave the patient in a pro-thrombotic state.
What are the side effects of warfarin?
Bleeding, N+V, Diarrhoea, Jaundice, liver dysfunction, pancreatitis, pyrexia, alopecia, 'purple toes'
How could you assess a patient for risk of VTE and whether warfarin would be needed?
CHADS VASC score
What target INR would a patient on warfarin have?
What baseline tests need to be done for a patient before starting warfarin?
What should a patient's platelets be above before warfarin could be prescribed?
How can a patient be started on Warfarin?
1) Rapid in-patient
2) Rapid out-patient
3) Slow out-patient
Does warfarin interact with other drugs?
Many! See BNF