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
- 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?
Vitamin K antagonist.
- Warfarin inhibits epoxide reductase. 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 days beforehand
What commonly prescribed medicines interact with warfarin?
INR Depression
- Rifampicin (inducer)
- Carbamazepine (inducer)
- Phenytoin (inducer)
- St Johns Wort (inducer)
INR elevation
- Metranidazole
- Setraline
- Macrolides
- Ciprofloxacin
What are the two mechanisms of action of DOACs?
Direct thrombin inhibitors prevent thrombin generation, preventing development of a clot
- Dabigatran
Direct Xa inhibitors antagonise factor Xa, which inhibits thrombin generation (from prothrombin) and prevents development of clot
- ApiXaban
- EndoXaban
- RivaroXaban
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
- CYP450 Inducers
- Carbamazepine
- Rifampicin
- CYP450 Depressors
- Amiodarone
- Azole antifungals
- Macrolides
- SSRIs/SNRIs
- Verapamil
What is the mechanism of action of LMWH?
LMWH predominantly enhances the action of antithrombin against activated factor Xa (indirect factor Xa inhibitor)
Heparin greatly enhances natural anticoagulant action of circulating antithrombin
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
