Vitamin K antagonists

What can be an antidote to vitamin K antagonists?

Vitamin K

What is the most commonly prescribed VKA?

Warfarin

What are some less commonly prescribed VKAs?

Acenocoumarol and pheninidione

How do Vitamin K antagonists work?

Antagonise Vitamin K effects - vital for forming clotting factors 2, 7, 9 and 10, as well as anticoagulant proteins C and S

What is prescribed when initiating a VKA?

LMWH as anticoagulant cover whilst VKA is building to therapeutic effect

How long do VKAs take to develop their therapeutic effect?

48-72 hours

What is INR?

International normalised ratio - how long the blood takes to clot

What does a high INR value mean?

Blood takes longer to clot, thinner/more anticoagulated blood and greater bleed risk

What does a low INR value mean?

Blood takes less time to clot

What is the aim for warfarin/VKAs in terms of INR?

Increase INR

What are the typical dosing instructions of warfarin?

Take as directed by prescriber

What is determined for INR when the patient is to be initiated on warfarin?

Baseline INR and dosing adjusted to achieve the required target for condition being treated

What is the usual baseline treatment for INR?

Around 1.0 - 0.9-1.2

What is an acceptable range for INR?

0.5 of INR target range

What does the number in INR represent?

Based on prothrombin time from a blood sample, which measures the time taken for blood to clot

What is prothrombin/factor 2?

Plasma protein produced by the liver involved in the bloods clotting process

What is the normal PT time?

11-13 seconds, can be 12-16 seconds

What other conditions, apart from taking anticoagulation, can delay prothrombin time?

Liver disease

What is the initial loading dose of warfarin?

10mg on day one and two

When are loading doses of warfarin used?

DVT or PE

What determines the frequency patients visit a clinic at for initiating warfarin and its dosing?

How long it takes to achieve anticoagulation and how stable patients are once warfarin treatment has been established

How is warfarin dosing initiated in patients with AF to prevent stroke done?

Dosed over 3-4 weeks to reach target of 2.5

What are the common side effects of warfarin?

Bleeding/haemorrhage, alopecia, nausea and vomiting

What are the contraindications of warfarin?

AVOID 48 hours post-partum, haemorrhagic stroke and significant bleeding, 1st trimester of pregnancy

What is the INR target of warfarin for recurrent DVT and PE?

3.5

What is the INR target for warfarin for mechanical heart valves?

Depends on location of valve

What resource should all patients be given when initiated on warfarin?

Anticoagulant yellow book

What does the anticoagulant yellow booklet for warfarin contain?

Counselling advice and provides a record of daily warfarin dose to be taken along with record of INR results

What are the general counselling points for initiation on warfarin?

Explain why pt prescribed warfarin, length of expected treatment e.g., 3 months for DVT, how warfarin works and what the yellow booklet is, what INR is and how it is monitored as well as target level and what a high/low INR means

What explanation of warfarin dosing should be given when counselling patients?

• Tablet identification - colour of each tab strength and how a dose to be taken e.g., 3mg blue, 1mg brown, 5mg pink

• When tk take - usually single dose at tea-time/evening

• How the dose may change depending on INR result

• Take prescribed daily dose as directed

• Don’t double up on a dose in 1 day if there is a missed dose - take normal dose the next day and seek advice from GP about missed dose

• Importance of ordering repeats

What advice about adverse effects/illness should be given for warfarin counselling?

• Unwell - taking Abx, N&V etc can alter INR, clinic advice is required and extra INR checks may be needed

• Explain common side effects

• Explain complications such as bleeding

What bleeding related symptoms should patients with warfarin contact the clinic about?

ANY signs of unusual bleeding e.g., spontaneous nasal bleeds, gum bleeds, pink urine discolouration

What should happen to patients experiencing prolonged bleeding who also take warfarin?

Seek urgent medical advice as an antidote can be given

What advice should patients on warfarin be given about bleeding/bruising?

Will bruise more easily and if cut their finger etc, will bleed for longer than normal

What should patients taking warfarin do if they have any head trauma e.g., banging head or general head injury?

Seek medical attention immediately due to risk of bleed on the brain

What fruit products interact with warfarin?

Cranberry and grapefruit

What advice is given about taking OTC medication for warfarin?

Do not buy OTC meds/herbal meds before consulting a pharmacist when on warfarin

What diet related advice can be given for warfarin?

Binge eating, dieting and changes in weight can affect warfarin, eating lots of green leafy veg containing Vit K can reduce warfarin effects as Vit K antagonises warfarin, alcohol should be taken in moderation (no more than 2 units per day), don’t binge drink

What effect does alcohol typically have when patients take warfarin?

Increases INR and affects anticoagulant control

What contraceptive advice can be given for warfarin?

Counsel on contraceptives and inform anticoagulant clinic urgently if they become pregnant, COC/HRT can increase VTE complications in patients with a diagnosed PE/DVT and should be avoided

Who should patients let know they are taking warfarin?

Healthcare professionals e.g., surgeons, dentists if undergoing procedures or admitted to hospital, inform if having an injection