Antiplatelets and anticoagulants Flashcards
Warfarin: MoA, indications, contraindications, side effects, monitoring
!Anticoagulant!
MoA: Inhibits vitamin K reductase, preventing the regeneration of vitamin K. This is turn inhibits the activation of vitamin K coagulation factors, II, VII, IX and X.
Can be reversed by provision of Vitamin K
NOTE: Due to the half-life of clotting factors there is a period when a bridging therapy is required, to provide anti-coagulation. Heparin is used.
Indications:
- Prophylaxis and treatment of venous thrombosis and pulmonary embolism
- Prophylaxis of embolisation in patients with rheumatic heart disease and AF
- Prophylaxis after prosthetic heart valve insertion
- TIA
Contraindications
- Significant bleeding
- Haemorrhagic stroke
- 48 h post partum
- Should not be given in the first and third trimesters of pregnancy. Use LMWH instead.
- Many drug interactions (metabolised by CytP450)
- CytP450 inhibitors e.g. erythromycin, amiodarone and fibrates, can potentiate the effects of warfarin
- Effects may be reduced by enzyme induces, e.g. barbituates, carbamazepine
Side effects
- Bruising and bleeding excessively
Monitoring
INR monitoring: Measures the time time to clot.
- Normal INR is 1
- INR is increased with warfarin use and also in liver failure (due to decreased production of clotting factors)
Counselling
Patients must stick to their regime. Take at 6 pm. If a dose is missed then 2 doses should not be taken at once and they should inform their doctor at their next blood test.
Female patients should be advised not to become pregnant whilst taking warfarin - warfarin in teratogenic.
Alcohol, green vegetables, beetroot and liver should be consumed in moderation.
Patients should report any blood loss e.g. haemoptysis, blood in the faeces/urine, epistatsis
Heparin: MoA, indications, contraindications, side effects, monitoring
LMWH
MoA: Activates antithrombin III which in turn inhibit the serine proteases which activate coagulation factors IX, X and XI.
Immediate onset of effect.
Indications:
- Thromboembolism and PE prophylaxis
- Treatment of PE
- Treatment of DVT
- Haemodialysis
! Considered safe in pregnancy!
Contraindications:
- After major trauma
- Cerebral haemorrhage
- Acute bacterial endocarditis
- Peptic ulcer
Side effects:
- Longer term use (>5 days) is associated with thrombocytopenia (HIT)
- Haemorrhage
- Skin rashes
Monitoring:
- Monitored via aPTT (intrinsic pathway)
- Check for thrombocytopenia (FBC)
LMWH
- Do NOT require monitoring
Low dose aspirin (75 mg): MoA, indications, contraindications, side effects
MoA: Acts through inhibition of COX, preventing the production of the platelet activating thromboxanes.
(prostaglandins produced by epithelial cells. They are able to regenerate COX, as they have a nucleus)
Indications:
- Prevention of reoccurence of MI and stroke
- Management of ACS
- Following coronary bypass surgery
- Suspected TIA or MI
Contraindications:
- Active peptic ulcer
- Children < 16 (Reye’s syndrome)
Side effects:
Clopidogrel: MoA, indications, contraindications, side effects
MoA: Inhibits ADP induced expression of GP IIb/IIIa
(ADP, released from platelts, induces expression of GP IIb/IIIa. GP IIb/IIIa binds to fibrinogen, allowing for platelet cross linking)
- Abciximab is a monoclonal antibody against IIb/IIIa. It is used for patients undergoing angioplasty. Due to its abilty to induce an immune response it is only given once.
Indications:
- Can be used alongside aspirin to reduce the chance of MI or TIA
Outline the indications of antiplatelets vs anticoagulants
Dipyridamole: MoA, indications, contraindications, side effects
MoA: Inhibits phosphodiesterase, increasing levels of cAMP and thereby inhibiting platelet aggregation.
Prevents adenosine reuptake, adding to its antiplatelet effects.
Indications:
- Prophylaxis of thrombosis
- Often used in conjunction with aspirin
Contraindications:
Side effects:
Fibrinolysis: Mechanism, indication
Mechanism: Acts to cause breakdown of blood clots.
Increased conversion of plasminogen → plasmin, allowing for increased breakdown of clots.
Example: Streptokinase
Indications:
- MI
- DVT, PE, acute arterial aneurysm
Outline the production of thromboxane
