IC5 Selection of Anticoagulants for SPAF Flashcards
How does AF lead to a stroke?
Atrial fibrillation (AF) leads to an accumulation of clotting factors in the heart, causing a clot to form.
The clot then travels through the heart and into the cerebral circulation.
This leads to insufficient O2 flowing into the brain and death of brain tissue.
Which is more effective for SPAF - Warfarin VS DOACs?
DOACs are more effective than warfarin in stroke prevention.
List out CHA2Ds VA and what it is used for:
C - congestive heart failure - 1pt
H - Hypertension - 1pt
A - Age 75yo & above - 2pt
D - Diabetes mellites - 1pt
S - History of stroke - 2pt
V - Vascular disease - 1pt
A - Age 65-74 - 1pt
CHA2Ds VA is used to determine the need to start an anticoagulant in a patient.
What score, based on CHA2DS VA, do we use anticoagulant?
0 = no anticoagulants
1 = Monitor & consider anticoagulant
2 = Start anticoagulation therapy
What condition do we use warfarin over DOACs in AF?
When patient has mechanical heart valve replacement.
Patients usually have valve replacement due to valvular AF.
DOACs are CI in valvular AF, especially mechanical heart valves.
For bioprosthetic heart valve, we use Aspirin as monotherapy.
List out the HASBLED factors:
H - Hypertension (>160mmHg!!!!!)
A - Abnormal renal & hepatic function
S - History of stroke
B - Bleeding
L - labile INR
E - Elderly (>65yo)
D - Drugs (antiplatelet meds, NSAIDs) & Alcohol
What HASBLED Score indicates high bleeding risk?
A HASBLED score of >3 indicates high bleeding risk.
Having high HASBLED score does not mean we should withhold OACs, but reduce the modifiable risk factors that contribute to the HBR.
What are the dosing and duration of DOACs in SPAF?
(Different from VTE!)
- Rivaroxaban
- 20mg/day
- 15mg/day if CrCl 30-50ml/min
- Contraindicated if CrCl <15ml/min - Apixaban
- 5mg BD
- OR 2mg BD if pt has any 2 of the following: ≥80yo, weight ≤60kg, sCr ≥ 1.5mg/dL - Edoxaban
- 60mg/day
- 30mg/day if pt has any of the following: CrCl 30-50ml/min, ≤60kg, concomitant verapamil, quinidine, dronedarone
- 30mg/day if CrCl <15-30ml/min
- Contraindicated if CrCl <15ml/min
[As long as CrCl < 50ml/min, we must dose adjust all DOACs for SPAF therapy)
What is the Cockroft gault Equation?
[(140-age) x body weight] / [sCr x 72]
(Multiply by 0.85 for female)
sCr in mg/dL
At which Child-Pugh score must you stop DOACs and warfarin?
All DOACs and warfarin must be stopped when the liver deteriorates to Child-Pugh score C.
Note: Warfarin worsens hepatic functions more as compared to DOACs
Which DOACs are substrates of P-gp?
All DOACS are substrates of P-gp.
Which DOACs are substrates of CYP3A4?
Apixaban and Rivaroxaban
What are the 2 kinds of warfarin?
S-warfarin & R-warfarin
Warfarin is a racemic mixture.
S-warfarin is more active than R-warfarin
What is the action of warfarin?
Warfarin inhibits VKORC1. This prevents inactive oxidised Vitamin K from being reduced to form active reduced Vitamin K.
Which enzymes metabolise S & R-warfarin?
S-warfarin - CYP2C9
R-warfarin - CYP3A4
Which clotting factors are affected by Warfarin and how are they affected?
Factor II, VII, IX, X are affected by warfarin.
Factor VII plunges the fastest, and Factor II plunges the slowest.
Our goal is to decrease factor II - prothrombin.
How does antibiotics affect warfarin?
When abx are used, gut bacteria decreases.
Gut bacteria is essential in producing vitamin K , also known as menadione.
A decrease in vitamin K can lead to toxicity of warfarin.
Which abx must we adjust warfarin dose pre-emptively?
- Bactrim
- Ciprofloxacin
How does fluid retention affect warfarin?
In pt with fluid retention, the more oedematous the patient, the less well absorbed warfarin becomes.
Can warfarin be used in pregnant patients?
No, warfarin is teratogenic and should not be used in pregnant patients.
LMWH is the agent to use in pregnant patients.
Can you use DOACs in patients that have tuberculosis and are undergoing RHEZ therapy?
RHEZ - rifampicin, isoniazid, ethambutol, pyrazinamide
No, DOACs are CI with in pt that requires rifampicin.
As TB patients require RHEZ, we cannot use DOACs.
What anticoagulant can we then use for TB patients?
Warfarin.
(We must uptitrate warfarin dose if pt is on rifampicin)
However, as warfarin onset is slow, we can use it to overlap with DOACs first to slowly transition from DOACs to warfarin.
What is the target INR range when using warfarin?
2-3
What condition will warrant an increased INR range of 2.5-3.5 in patients?
Patients with mechanical heart valve have higher INR range of 2.5-3.5.
Which antibiotics will require warfarin to be dose adjusted?
- Bactrim
- Ciprofloxacin
Which antibiotics will not require warfarin to be dose adjusted?
- Macrolides
- Amox-clav
- Doxycycline
Which antibiotic is CI with warfarin?
Metronidazole
- Increases risk of bleeding
For pt w H.pylori infection, which triple therapy can we use together w warfarin?
- Amoxicillin
- Clarithromycin
- PPI
Metronidazole should not be used together with warfarin.
No need to dose adjust warfarin for amoxicillin & clarithromycin.
Which anti-arrhythmic drug cannot be used together with Warfarin?
Amiodarone
- Increases risk of bleeding
What is the reversal agent for warfarin?
Vitamin K
What must you be careful with when using vitamin K as a reversal agent for warfarin?
We cannot dose vitamin K too high as it can resulting clotting.
Too high dose can also delay the time to restart warfarin.
E.g of too high dose - 5 to 10mg
How to manage a bleed if patient is on DOACs?
(Mild, moderate, severe)
If pt has:
a. Mild bleed
- Discontinue next dose
b. Non-life threatening major bleed (use non-pharm measures)
- Mechanical compression
- Surgical haemostasis
- Fluid replacement
- For dabigatran, use idarucizumab
c. Life-threatening bleed
- For dabigatran, use idarucizumab
- For Factor Xa inhibitors, use andexanet-alfa
Can azoles be used with DOACs and warfarin?
Azoles cannot be used with DOACs.
However, azoles can be used with warfarin.
For patients with severe hepatic disease of Child Pugh Score C and worse, can you use warfarin or DOACs?
No, we are not to use warfain or DOACs in pt with severe hepatic disease with Child-Pugh score C and below.
