Warfarin

Answer 1

GPHC loves warfarin Qs

Question 2

Oral Anticoagulants

Answer 2

Used to prevent thrombus formation in veins (less use in arteries)

Coumarins & Phenindione
- Examples: Warfarin, acenocoumarol & Phenindione.
- They antagonise VIT K
Takes at least 48-72 hrs for full effect
warFARin (takes long)
- More immediate effect give UFH or LMWH
Warfarin 4 different strengths- 0.5 = WHITE, 1 = BROWN, 3 = BLUE, 5 = PINK.

2 Important MHRA advice for warfarin
1. Calciphylaxis
- Common in renal disease
- RARE condition that causes painful skin lesions.
REFER, Painful rash

2. Miconazole oral gel
   - Causes bleeding with warfarin
   - STOP and seek medical advice if Unexplained bruising, nose bleeds, blood in urine.

Question 3

Warfarin Antidote

Answer 3

Vitamin K1
- Phytomenadione.
K kills Warfarin.

Question 4

Foods/Drinks with Warfarin

Answer 4

AVOID
Cranberry juice

Pomegranate juice - Increases INR

AVOID BIG diet change (too much green vegs)

Alcohol (Heavy drinking) - Decreases Warfarin effects.

Question 5

Warfarin/Coumarins in Pregnancy

Answer 5

AVOID ALL in pregnancy - They cross the placenta = Foetal abnormalities

AVOID esp. in 1st and 3rd trimester and during last weeks of pregnancy and delivery.

Risk of haemorrhage increase in VIT K deficiency.

Question 6

INRs Warfarin/Bleeding situations

Answer 6

TARGETS
LEARN 3.5 as everything else is 2.5

INR 2.5 (2-3)
Treatment of VTE
AF
Cardioversion
Dilated cardiomyopathy
Mitral stenosis or regurgitation
MI
Acute Arterial embolism

INR 3.5 (3-4)
Recurrent VTE
Mechanical prosthetic heart valves

INR within 0.5 of target values is OK.

INR NOTE: Above target range = Bleeding easy.
Below = Clotting easy.
INR MEASURES HOW LONG IT TAKES FOR UR BLOOD TO CLOT.

What to do in bleeding or HIGH INR (EXAM Q)
CHECK TABLE IN PICs

Summary:
- ANY bleeding/INR >8 = STOP warfarin and use VIT K (Phytomenadione) Restart warfarin when INR <5 EXCEPT in major bleeding DON’T restart.

NOTE: Dry prothrombin and frozen plasma only used in MAJOR bleeds.
Also IV VIT K in bleeding only. NO bleed and VIT K needed then give by oral route
- VIT K can be repeated if INR still high after 24 hrs.

• INR 5-8 no bleed withhold 1 or 2 doses of warfarin. Reduce subsequent maintenance doses.

Question 7

Warfarin DOSES

Answer 7

INTIAL:
5-10mg on day 1.
THEN adjust depending on INR.
Maintenance dose
3-9mg

Question 8

Key Interactions

Answer 8

Miconazole (MHRA warning),
Amiodarone, bezafibrate - Enzyme inhibitor - Increases effect.

St johns wart, Carbamazepine, Alcohol - Enzyme inducers = Decreases effect

Aspirin - Increases bleeding risk.

Warfarin & Miconazole (EXAM Q) - AVOID unless INR cam be monitored closely and keep a eye on symptoms of bleeding/Bruising.

Clotrimazole & Fluconazole:
Clotr - NO EFFECT
FLU - Increases warfarin effect Monitor INR and adjust dose.

Warfarin & Clarithromycin:
Clarithro increases warfarin effect. Monitor INR adjust dose.

Juices:
Cranberry/Pomegranate - AVOID - increases warfarin effect.

Green leafy/Green vegs:
Major diet change and major alcohol change AVOID

Question 9

Combined anticoagulant and antiplatelet therapy (EXAM Q)

Answer 9

Increase risk of bleeding in dual/triple therapy.
- Dual/Triple should be short use.

Higher risk of bleeding with Clopidogrel + Warfarin THAN Aspirin + Warfarin

Withhold antiplatelet if possible until warfarin is done.