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What are the indications for aspirin?
Mild to moderate pain: Headaches and transient musculoskeletal pain. Pyrexia and anti-platelet action.
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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.
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What are the contraindications for prescribing aspirin?
- Children <16 years.
- Peptic ulceration (past and active)
- Haemophilia
- NSAID sensitivity
- Avoid in hepatic and renal impairment.
- Avoid towards end of pregnancy or whilst breastfeeding.
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What are the side effects of aspirin?
- GI irritation.
- Increased bleeding time.
- Bronchospasm
- Skin reactions
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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
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How can we reduce side effects of aspirin?
Take after food or enteric coated capsules (slower delivery)
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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
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What is Clopidogrel given for?
Anti-platelet activation:
Preventing atherothrombotic event in arterial disease, post-MI or stroke, or during active ACS event.
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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
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What are the contra-indications to prescribing Clopidogrel?
Active bleeding
Caution in hepatic and renal impairment, or at risk of bleeding
Avoid in Pregnancy/ breastfeeding
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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.
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What dose should be prescribed of Clopidogrel?
- Oral preparations
- Prevention: 75mg OD
ACS: 300mg then 75mg daily (600mg loading dose in STEMI)
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Why is LMWH preferred to unfractionated heparins?
Same efficacy and longer action, but reduced risk of heparin-induced thrombocytopenia
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What is enoxaparin used for?
- Venous Thromboprophylaxis
- DVT and PE treatment
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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)
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How would you treat an enoxaparin overdose?
Protamine (50mg max)
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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
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What is HITTS?
Heparin-induced thrombocytopenia and thrombosis syndrome
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Is it ok to give heparin if there is a previous episode of HITTS?
NEVER!
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What other LMWHs are available?
Tinzaparin, Dalteparin
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What is the mode of action of warfarin?
Inhibits Vitamin K reductase, preventing activation of Factors 10, 9, 7, 2 and therefore blood coagulation
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What is warfarin indicated for?
DVT, PE, AF and prosthetic valves if at risk of embolisation
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What are the contraindications for prescribing Warfarin?
- Pregnancy
- Bleeders
- Active Ulcers
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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.
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What are the side effects of warfarin?
Bleeding, N+V, Diarrhoea, Jaundice, liver dysfunction, pancreatitis, pyrexia, alopecia, 'purple toes'
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How could you assess a patient for risk of VTE and whether warfarin would be needed?
CHADS VASC score
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What target INR would a patient on warfarin have?
2-3
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What baseline tests need to be done for a patient before starting warfarin?
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What should a patient's platelets be above before warfarin could be prescribed?
70
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How can a patient be started on Warfarin?
1) Rapid in-patient
2) Rapid out-patient
3) Slow out-patient
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Does warfarin interact with other drugs?
Many! See BNF
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