warfarin Flashcards
what is warfarin used for (indications)
- to prevent embolisation (blood clots) in rheumatic heart disease, atrial fibrillation, after insertion of prosthetic heart valve
- treatment and prevention of venous thrombosis and pulmonary embolism
- treatment of transient ischaemic attacks (mini stroke)
what are the contraindications for warfarin (+ all vitamin k antagonists)
- use within 48 hours postpartum
- hemorrhagic stroke
- significant bleeding
what are the cautions for warfarin
- history of GI bleeding
- hyper/hypothyroidism
- uncontrolled hypertension
- recent ischaemic stroke
- changes in diet (intake of vitamin K)
can warfarin be used during pregnancy
should not be given in the 1st trimester. should also avoid in the 3rd trimester
is warfarin safe for breastfeeding
yes. Not present in milk in significant amounts and appears safe.
how often is the monitoring on warfarin
in the early days of treatment it is daily or on alternate days. After that you can have longer intervals up to every 12 weeks
name 2 types of juice that interact with warfarin
- Cranberry juice
- Pomegranate juice
both increase the INR of warfarin = increased anticoagulant effect
note increased INR= increased risk of bleeding
how do you know the therapeutic range (dose) of warfarin for a patient
the dose of warfarin depends on the patients INR
what are the symptoms of warfarin toxicity
Haemorrhage (bleeding)
which conditions have a target INR of 2.5
- deep vein thrombosis or pulmonary embolism
- atrial fibrillation
- cardioversion (target INR should be achieved 3 weeks before cardioversion + continued for 4 weeks after)
- myocardial infarction
- dilated cardiomyopathy
note: target INR is 2.5 (+/- 0.5 units)
what condition has an INR of 3.5
- RECURRENT deep-vein thrombosis or pulmonary embolism in patients currently receiving anticoagulation and with an INR above 2
what is the INR for Mechanical prosthetic heart valves
There’s no specific INR. Recommended INR depends on:
- type and location of valve
- patient- related risk factors
consider increasing INR or adding antiplatelet drug if embolic events happens during anticoagulation
how long does it take for the full anticoagulant effect of vitamin-K antagonists to develop
at least 48-72 hours
when would you deem an INR result as satisfactory
if it is within 0.5 units of the target value.
note larger deviations from target value than this mean the dose needs to be adjusted
what is the treatment plan if a patient taking warfarin has a MAJOR bleed
- stop warfarin sodium + give phytomenadione (vitamin K1) by slow intravenous injection
- give dried prothrombin complex (factors II, VII, IX, and X); if dried prothrombin complex unavailable, fresh frozen plasma can be given but is less effective
what is the treatment plan for all patients taking warfarin if they have an INR of 5-8 and MINOR bleeding
- stop warfarin sodium + give phytomenadione (vitamin K1) by slow intravenous injection
- restart warfarin sodium when INR <5.0
when should a patient who has stopped warfarin due to high INR/bleeding restart warfarin
when the INR is less than 5 (<5.0)
when is the only time a patient is given phytomenadione (vitamin K1) by mouth using the intravenous preparation orally [unlicensed use]
if the patient has an INR >8.0 but no bleeding
what is the treatment if a patient has an INR 5.0-8.0 and NO bleeding
withhold 1 or 2 doses of warfarin sodium and reduce subsequent maintenance dose
describe how to manage a patient on warfarin before ELECTIVE surgery
- warfarin should be stopped 5 days before surgery. Give I.V phytomenadione (vitamin K1) orally (unlicensed) the day before surgery if INR >1.5
- if patient is considered high risk, still stop warfarin but use interim therapy (bridging) by using low molecular weight heparin but stop this at least 24 hrs before surgery
- if haemostasis ok, restart normal maintenance dose of warfarin the evening of surgery or the next day
what is the treatment plan if a patient on warfarin requires EMERGENCY surgery
- if surgery can be delayed for 6-12 hours, give I.V phytomenadione (vitamin K1) in the meantime to reverse anticoagulant effect
- if surgery can’t be delayed, give I.V phytomenadione (vitamin K1) + dried prothrombin complex. check INR before surgery
what is given to reverse the anticoagulant effect of warfarin
I.V phytomenadione (vitamin K1)
note the I.V formulation can be given orally (unlicensed)
why might a patient taking warfarin need their warfarin dose reduced if they get an acute infection (including covid)
because acute infections (including covid) can exaggerate the effect of warfarin.
monitor the patients INR to reduce risk of bleeding
why should your monitor patients taking vitamin-k antagonists INR every time they start a new medicine
because vitamin k antagonists (e.g warfarin) have a lot of interactions with other medicines (including antibacterials + antivirals) so monitoring at the start of new meds reduces risk of potential interactions
name of examples of when patients taking vitamin k antagonists should notify their GP
- symptoms or confirmed covid infection
- unwell with sickness/ diarrhoea or lost appetite
- have changed their diet, smoking habits or alcohol consumption
- taking any new meds or supplements
- unable to attend next scheduled blood test
why should warfarin patients speak to their doctor if they develop a painful rash
warfarin can lead to calciphylaxis (when calcium accumulates in small blood vessels of skin + fat tissue. leads to infections/ tissue necrosis/ death)
- note it is rare and mostly seen in patients with end-stage renal disease*
when should a woman postpartum start taking warfarin again
delay warfarin until risk of bleeding is low (usually 5-7 days after birth delivery)
how can major diet changes affect anticoagulant control in patients taking vitamin k antagonists
name examples of foods high in vitamin k
food containing vitamin k counteracts the effects of vitamin-k antagonists so reduces anticoagulant effect of vitamin-k antagonists.
examples of food high in vitamin k:
- green leafy vegetables e.g kale, collard greens, broccoli, spinach, cabbage, and lettuce
- salads
- green tea
- kiwi
which juice interacts with warfarin to increase the INR
both Cranberry and Pomegranate juice increase the INR of warfarin
increase in INR= blood is taking longer to clot so increased risk of bleeding
can alcohol consumption affect the anticoagulant effect of warfarin
yes, alcohol consumption (in those who drink heavily) potentially decreases the anticoagulant effect of Warfarin.
when is it advised that pregnant women stop taking vitamin k antagonists
stop vitamin k antagonists before the 6th week of gestation to avoid fetal abnormalities
warfarin should not be taken in the 1st and 3rd trimester - teratogenic
TRUE OR FALSE
if a mother has been taking warfarin at the time of birth, their baby should be given immediate prophylaxis with intramuscular phytomenadione (vitamin K1)
TRUE
