My EM Notes

Coagulation

(unfractionated) initiates anticoagulation rapidly but has a short duration of action
can be used in those at high risk of bleeding because its effect can be terminated rapidly by stopping the infusion.

as effective but preferred because have a lower risk of heparin-induced thrombocytopenia.
standard prophylactic regimen does not require anticoagulant monitoring
Compared with UFH, LMWHs have higher anti-Xa/anti-IIa ratios
LMWHs also seem to differ in their effects on platelet function
because of their marked pharmacological differences between LMWHs, there are no agreed equivalent doses

Fondaparinux	synthetic pentasaccharide that inhibits activated factor X. Does not inactivate thrombin (factor IIa), has no effect on platelets and does not X-react with serum of patients with HIT
Tinzaparin	fewest indications 175 IU/kg/day for DVT
Dalteparin	VTE prevention
Enoxaparin	VTE prevention, DVT Rx, ACS

newer oral anticoagulant drugs have the advantage of the ability to administer at fixed doses without the need of laboratory monitoring

Rivaroxaban	- direct inhibitor of activated factor X (Xa). - fixed daily oral dose of 10 mg for VTE
Dabigatran	- selective, reversible, direct thrombin inhibitor - dosing schedules of dabigatran are 150 mg and 220 mg daily - reports of an association of dabigatran with an increased risk of myocardial infarction or acute coronary syndrome
Apixaban	direct factor Xa inhibitor -2.5 mg twice daily

Antiplatelet drugs are classified on mechanism of action. (View cycle) close

Aspirin	• Irreversible dose dependent inhibition of the TXA₂ pathway • Low dose inhibits cycloxygenase-1 (COX-1) in such a way that only TXA₂ production is inhibited and not PGI₂ • Platelet function returns to normal 5-7/7 after cessation
Dipyridamole	• Phosphodiesterase inhibitor - prevents the inactivation of cAMP • second action - inhibition of thromboxane synthase, thus reducing platelet activation • effect is relatively short-lived - repeated dosing or slow-release preparations are required in order to achieve 24-hour inhibition of platelet function, therefore used more if CI to clopidogrel • Side effects relate to its vasodilatory properties • Platelet function returns to normal 24/24 after cessation
Clopidogrel	• Clopidogrel is a prodrug, one of whose metabolites is an inhibitor of ADP-induced platelet aggregation (binds to P2Y₁₂ rec) • PPIs inhibit antiplatelet effects, debate about significance. • Platelet function returns to normal 5-7/7 after cessation
Ticagrelor	• oral antagonist at the P2Y₁₂ adenosine diphosphate receptor • inhibits platelet aggregation and thrombus formation in atherosclerotic disease

Without VTE prophylaxis, the overall VTE incidence in medical and general surgery hospitalized patients: 10%-40%, & major orthopaedic surgery: 40-60%
routine VTE prophylaxis, fatal pulmonary embolism is uncommon in orthopaedic patients and the rates of symptomatic VTE within three months: 1.3-10%.
Hypercoagulability can persist for 3/12 after some orthopaedic surgery

Condition	Strategy
AF
ACS
TIA
Lower limb immobilisation	* Routine use of VTE prophylaxis in ambulatory patients in a short leg cast is controversial * NICE guidance: 'consider' if risk of VTE outweighs risk of bleed
Spinal cord injury	VTE prophylaxis with LMWH once haemostasis restored, if no evidence of spinal haematoma

A synthetic lysine analogue with several mechanisms of action:

inhibits conversion of plasminogen to plasmin by preventing plasminogen from binding to the fibrin molecule
inhibits plasmin activity directly, although only at higher doses
inhibits fibrin cleavage
blocks binding of α2-antiplasmin and inhibits inflammatory reactions

Useful in: