Peri-op care - Anticoagulants Flashcards
What are the 2 main reasons we use anti-coagulants?
Prophylaxis:
- Primary or secondary prevention of arterial thromboembolism (AF/prosthetic valves)
- Prevention of venous thromboembolism in high risk patients (post hip/knee replacement surgery)
Treatment of acute venous thrombus
-Treatment of PE or DVT
Other indications:
- Non ST elevation MI
- Unstable angina
- as part of PCI: treatment for STEMI
For how long do you have to anticoagulate the following conditions:
- Mechanical and biological heart valves
- VTE
- AF
- Mechanical heart valves: long term
- Biological: may require short term warfarin or aspirin (anti-platelet) can also be sufficient
- VTE: usually 3/12 and determined by patient risk factors and location/severity of thrombosis
- AF: based on CHA2DS2VASc score
What is the MoA of warfarin? What is the normal target INR range?
- Inhibitor of vitamin K epoxied reductive in liver. This enzyme recycles vitamin K, which is required to activate coagulation proteins (fact II, VII, IX, X, protein C and S).
- Aim between 2.0-3.0
Name several conditions in which vitamin K antagonists should never be given:
- Hypersensitivity
- Haemorrhage stroke
- Clinically significant bleeding
- Pregnancy: esp 1st and 3rd trimester
- Severe liver disease or renal impairment
- Within 72h of major surgery
- With concomitant drugs where interactions may lead to significantly increased risk of bleeding.
- Within 48h post partum
What is Warfarin’s half life? Which conditions require fast vs slow loading? What is used as cover during loading?
- 40h
- Loading regimens are required for acute thrombosis (DVT/PE) and for patients who have had a cardiac valve replacement
- Patients with AF do not normally require fast loading
- Loading cover is provided by LWMH, which should be used until INR is within therapeutic range for 2 consecutive days
Warfarin: peri-op management
- Can be continued in patients undergoing minor procedures (cataract surgery)
- Must be stopped or reversed before any invasive procedure at least 4-5 beforehand
What commonly prescribed medicines interact with warfarin?
- Antibacterials: rifampicin (inducer)
- Antiepileptics: carbamazepine (inducer)
What are the two mechanisms of action of DOACs?
- Direct thrombin inhibitors (dabigatran): inhibit thrombin generation, preventing development of a clot
- Direct Xa inhibitors (apiXaban, endoXaban, rivaroXaban): inhibit factor Xa, which inhibits thrombin generation (from prothrombin) and prevents development of clot
What are licensed indications for DOACs?
- Preventing a clot following total hip replacement and total knee replacements in adults
- treatment of DVT and PE and prevention of recurrent DVT and PE
- Prevention of stroke and systemic embolism in non-valvular AF with one or more risk factors
List some C/Is for DOACs
- Hypersensitivity
- Active bleeding or significant risk of bleeding (recent GI ulcer, brain surgery)
- Pregnancy/breast feeding mothers
- Severe liver or renal disease
- Concomitant use with parenteral anticoagulants (LMWH)
- Vitamin K Antagonists (warfarin): except when switching from DOAC to VKA for a few days until INR >= 2
- Antiplatelets and NSAIDS: increased risk of bleeding (except for in ACS, where rivaroxaban + aspirin OR aspirin + clopidrogrel is indicated)
List some medications that tend to interact with DOACs
- Amiodarone
- Azole antifungals
- Carbamazepine
- Macrolides
- Rifampicin
- SSRIs/SNRIs
- Verapamil
What is the mechanism of action of LMWH?
- Heparin greatly enhanced natural anticoagulant action of circulating antithrombin
- LMWH: predominantly enhances the action of antithrombin against activated factor Xa (indirect factor Xa inhibitor)
What are the indications for using LMWH?
- Until patient reaches therapeutic INR with warfarin (INR must be in range for at least 2 consecutive days before stopping heparin)
- Prior to initiating some DOACs: Tx of PE and DVT, if plan is to commence oral anticoagulant with Digabatran/Edoxaban, will need LMWH for 5 days at least (two treatments can’t overlap)
- Cancer patients: more effective than warfarin
- Pregnancy: can get embryopathie between 6-12 weeks but usually treatment of choice
Describe some patient-related risk factors for VTE
- Active cancer or cancer treatment
- Age >60
- Dehydration
- Known thrombophilia
- Obesity
- HRT/OCP
- Pregnancy or < 6 weeks post partum
What important drug interactions should you consider when prescribing LMWH?
- Do not administer with another anticoagulant (except when loading for warfarin)
- NSAIDs
- ACEi: LMWH increases K+ t/f should be careful not to put pt at risk of hyperkalaemia
