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High risk drugs > warfarin > Flashcards

warfarin Flashcards

1
Q

what is warfarin used for (indications)

A
  • 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)
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2
Q

what are the contraindications for warfarin (+ all vitamin k antagonists)

A
  • use within 48 hours postpartum
  • hemorrhagic stroke
  • significant bleeding
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3
Q

what are the cautions for warfarin

A
  • history of GI bleeding
  • hyper/hypothyroidism
  • uncontrolled hypertension
  • recent ischaemic stroke
  • changes in diet (intake of vitamin K)
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4
Q

can warfarin be used during pregnancy

A

should not be given in the 1st trimester. should also avoid in the 3rd trimester

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5
Q

is warfarin safe for breastfeeding

A

yes. Not present in milk in significant amounts and appears safe.

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6
Q

how often is the monitoring on warfarin

A

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

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7
Q

name 2 types of juice that interact with warfarin

A
  • Cranberry juice
  • Pomegranate juice

both increase the INR of warfarin = increased anticoagulant effect

note increased INR= increased risk of bleeding

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8
Q

how do you know the therapeutic range (dose) of warfarin for a patient

A

the dose of warfarin depends on the patients INR

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9
Q

what are the symptoms of warfarin toxicity

A

Haemorrhage (bleeding)

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10
Q

which conditions have a target INR of 2.5

A
  • 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)

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11
Q

what condition has an INR of 3.5

A
  • RECURRENT deep-vein thrombosis or pulmonary embolism in patients currently receiving anticoagulation and with an INR above 2
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12
Q

what is the INR for Mechanical prosthetic heart valves

A

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

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13
Q

how long does it take for the full anticoagulant effect of vitamin-K antagonists to develop

A

at least 48-72 hours

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14
Q

when would you deem an INR result as satisfactory

A

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

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15
Q

what is the treatment plan if a patient taking warfarin has a MAJOR bleed

A
  • 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
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16
Q

what is the treatment plan for all patients taking warfarin if they have an INR of 5-8 and MINOR bleeding

A
  • stop warfarin sodium + give phytomenadione (vitamin K1) by slow intravenous injection
  • restart warfarin sodium when INR <5.0
17
Q

when should a patient who has stopped warfarin due to high INR/bleeding restart warfarin

A

when the INR is less than 5 (<5.0)

18
Q

when is the only time a patient is given phytomenadione (vitamin K1) by mouth using the intravenous preparation orally [unlicensed use]

A

if the patient has an INR >8.0 but no bleeding

19
Q

what is the treatment if a patient has an INR 5.0-8.0 and NO bleeding

A

withhold 1 or 2 doses of warfarin sodium and reduce subsequent maintenance dose

20
Q

describe how to manage a patient on warfarin before ELECTIVE surgery

A
  • 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
21
Q

what is the treatment plan if a patient on warfarin requires EMERGENCY surgery

A
  • 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
22
Q

what is given to reverse the anticoagulant effect of warfarin

A

I.V phytomenadione (vitamin K1)

note the I.V formulation can be given orally (unlicensed)

23
Q

why might a patient taking warfarin need their warfarin dose reduced if they get an acute infection (including covid)

A

because acute infections (including covid) can exaggerate the effect of warfarin.

monitor the patients INR to reduce risk of bleeding

24
Q

why should your monitor patients taking vitamin-k antagonists INR every time they start a new medicine

A

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

25
Q

name of examples of when patients taking vitamin k antagonists should notify their GP

A
  • 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
26
Q

why should warfarin patients speak to their doctor if they develop a painful rash

A

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*
27
Q

when should a woman postpartum start taking warfarin again

A

delay warfarin until risk of bleeding is low (usually 5-7 days after birth delivery)

28
Q

how can major diet changes affect anticoagulant control in patients taking vitamin k antagonists

name examples of foods high in vitamin k

A

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
29
Q

which juice interacts with warfarin to increase the INR

A

both Cranberry and Pomegranate juice increase the INR of warfarin

increase in INR= blood is taking longer to clot so increased risk of bleeding

30
Q

can alcohol consumption affect the anticoagulant effect of warfarin

A

yes, alcohol consumption (in those who drink heavily) potentially decreases the anticoagulant effect of Warfarin.

31
Q

when is it advised that pregnant women stop taking vitamin k antagonists

A

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

32
Q

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)

A

TRUE

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