2. Warfarin Flashcards
(45 cards)
Warfarin
MOA
Warfarin competitively inhibits the vitamin K epoxide reductase complex 1 (VKORC1), which is an essential enzyme for activating the vitamin K available in the body. Through this mechanism, warfarin can deplete functional vitamin K reserves and therefore reduce the synthesis of active clotting factors
Warfarin
0.5mg tablet colour
White
Warfarin
1mg tablet colour
Brown
Warfarin
3mg tablet colour
Blue
Warfarin
5mg tablet colour
Pink
Warfarin
How long to start working in body? (Hrs)
48-72hrs
Warfarin LD
5mg 1-2 days
Then
3-9mg OD
everyday on the same time
How to take warfarin
1 full glass of water
Never double the dose
Always carry yellow book
Warfarin
What to monitor (6)
INR on first day, the alternate days then longer up to 12 weeks
Liver function
Renal function
Full blood count
BP
thyroid function
Warfarin
Target INR
Normal
VTE, AF, MI, cardioversion
Recurrent DVT or PE
- 1 or less
- 5
- 5
Warfarin
Target INR which condition?
- 1 INR
- 5 INR
- 5 INR
Normal
VTE, AF, MI, cardioversion
Recurrent DVT or PE
Warfarin
Duration
Isolated calf-vein DVT
Venous thromboembolism PROVOKED by surgery
Or other risk: combined pill, plaster cast or pregnancy
Unprovoked DVT or PE
6 weeks
3 months
3 months + (may be required long term)
Warfarin
Warning ⚠️
Report ASAP
May need antidote
- Haemorrhage
Nosebleeds Bruising Bleeding wounds Haemorrhage stroke (Headache, confusion)
- DVT or PE
(Pain, swelling, tenderness in calf; SOB, chest pain, red skin) - Rash, skin necrosis, purple toes
- Diarrhoea- Vomiting
Warfarin
Antidote
Phytomenadione
(Vit k)
Slow IV 5mg
Warfarin in
Pregnancy
Baby?
Avoid and caution in first trimester,
Best avoided but if benefit Overweight risk only given in 3rd trimester
Babies of mothers taking warfarin at the time of delivery need to be offered immediate prophylaxis with intramuscular phytomenadione (vitamin K1).
Warfarin
Breastfeeding
Not present in milk in significant amounts and appears safe.
Risk of haemorrhage which is increased by vitamin K deficiency.
Warfarin
Hepatic impairment
In general, manufacturers advise caution in mild to moderate impairment;
avoid in severe impairment.
Warfarin
Renal impairment
Use with caution in mild to moderate impairment.
Monitoring
In severe renal impairment, monitor INR more frequently.
Warfarin
+
Vitamin K
Reduced anticoagulant effect
Warfarin
+
Vitamin E
Increased anticoagulant effect
Warfarin
Interaction
Increased and decreased plasma concentration (2)
Corticosteroids
Cholestyramine
Clopidogrel
Warfarin
Interaction with underlying conditions
Enhanced ⬆️ plasma concentration) (9
Hyperthyroidism
Low vitamin K intake
Poor nutritional state
Diarrhea
Liver disease
Congestive heart failure
Cancer
Connective tissue diseases
High fever
Warfarin
Interaction enhanced plasma concentration (⬆️ bleeding risk)
Drugs
Amiodarone Paracetamol Anabolic steroids Azithromicin Cephalogrel Cimetidine Clarithromicin Clopidogrel High dose corticosteroids Cranberry juice Dipyridamole Erythromycin Esomeprazole Fibrates Fluconazole Fluvastatin Itraconazole Methylphenidate Metronidazole Miconazole (including topical use) NSAIDs Omeprazole Propafenone Rosuvastatin SSRIs St John Wort Tamoxifen Testosterone Thyroid hormones Tetracyclines Tramadol Venlafaxine
Warfarin
Interaction (reduced plasma concentration ⬇️= clot risk)
Acictretin Azathioprine Carbamazepine Clopidogrel Griseofulvin Mercaptopurine Phenobarbital Phenytoin Rifamycin Succalfate Vitamin k
