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pharma > Warfarin > Flashcards

Warfarin Flashcards

1
Q

When is warfarin used for INR range 2-3? (incl. time frames)

A

DVT: 3-6 months
PE: 6 months
AF: until risk > benefit

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2
Q

When is warfarin used for INR range 2.5-4.5?

A

Mechanical prosthetic valves (high risk)
patients with recurrent thromboses / warfarin
thrombosis associated with inherited thrombophilia conditions (hypercoagulibility)

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3
Q

What are other uses of warfarim?

A

cardiac thrombus
CVA especially with AF
cardiaomyopathy (walls thick / stenosed)

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4
Q

Adverse effects of warfarin?

A

bleeding / bruising

teratogenic

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5
Q

where are sites of bleeding / bruising from warfarin?

A

intracranial

epistaxis, injection, GI loss

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6
Q

what are the risks of warfarin in a woman of child bearing age?

A

risk of pregnancy due to indications with COCP (CYP450)

as well as being teratogenic

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7
Q

What are reversal therapies for warfarin?

A

parental vitamin K
fresh frozen plasma
prothrombin complex concentration

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8
Q

why is fresh frozen plasma preferred over vitamin K?

A

faster acting, contains active clotting factors

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9
Q

when is fresh frozen plasma given?

A

in severe bleeding

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10
Q

indications for initiation of treatment in PMH?

A

peptic ulcer disease
sub-arachnoid haemorrhage
bleeding disorders
previous stroke

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11
Q

what are reviews required before commencing treatment?

A

age
mobility (blood tests)
falls risk score (bleeding from falls > condition you’re trying to treat) : CHADS2-VASC & HAS-BLED

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12
Q

what are investigations required before commencing treatment?

A

review blood tests:

LFTs, platelet levels, INR (baseline)

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13
Q

what is required in the initiation of warfarin as a treatment regime?

A

consider loading dose to take treatment up to therapeutic window
use heparin to cover for the initial 3 days until warfarin starts working

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14
Q

why does it take warfarin a few days to work?

A

warfarin inhibits vitamin K synthesised proteins (protein C & S, clotting factors 2, 7, 9, 10) so have to wait until those proteins are completely used up / out of the system

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15
Q

what are the interactions of warfarin?

A

alcohol, cranberry / grapefruit juice

they are inhibitors of CYP450, so warfarin NOT metabolised, so warfarin concentration builds up

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16
Q

What should you give patients started on warfarin?

A

anticoagulated card

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17
Q

what is prothrombin complex concentrate (PCC)?

A

factor IX complex

made of clotting factors 2, 7, 9, 10

18
Q

why is fresh frozen plasma good for rapid bleeds?

A

contains active clotting factors

19
Q

when else is warfarin reversal given?

A

elective surgery: don’t want excessive bleeding during surgery
(non-emergency)

20
Q

when is IV vitamin K used?

A

not for serious bleeds

takes a few days to work

21
Q

what is the management of INR <6?

A

reduce warfarin / stop

22
Q

when do you restart warfarin?

A

when INR < 5

23
Q

what is the management of INR 6-8? (with no or minor bleeding)

A

stop warfarin

restart when INR < 5

24
Q

what is the management of INR >8? (with no or minor bleeding)

A

stop warfarin

consider 0.5-2.5mg vitamin K (oral)

25
Q

what is the management of high INR with MAJOR bleeding?

A

give prothrombin complex concentrate (PCC)

give 5mg vitamin K (oral)

26
Q

what is the CHADS-VASC2 score?

A

important in determining if patients are suitable for anticoagulation: if they are in AF / at risk of stroke
useful when considering with HASBLED

27
Q

what is the HASBLED score used for?

A

1 year risk of major bleeding in patients with AF (fibrillation)

28
Q

what is the mechanism of action of warfarin?

A

inhibits production of vitamin K dependent clotting factors
stops conversion of vitamin K to active reduced form
lack of vit. K for factors 2, 7, 9, 10 production (extrinsic pathway)
(all by blocking enzymes: vitamin K reductase & vit. K epoxide reductase)

29
Q

how is warfarin absorbed?

A

GI

so give orally (esp. long term use)

30
Q

how is warfarin metabolised?

A

hepatic

CYP450

31
Q

pharmacokinetics of warfarin?

A

slow onset of action (initially requires heparin)

heavily protein bound (can be displaced by some drugs DDI: toxic levels)

32
Q

how often is warfarin required?

A

once daily dosing

long 1/2 life

33
Q

why is warfarin teratogenic?

A

crosses placenta

do NOT give in 1st trimester of pregnancy or 3rd

34
Q

dangers of giving warfarin in 3rd trimester?

A

brain haemorrhage

35
Q

how to monitor blood plasma warfarin levels?

A

extrinsic pathway factors: prothrombin time (PT)
citrated plasma clotting time
after adding calcium & thromboplastins

36
Q

what is the concentration of warfarin expressed as?

A

INR (ratio)

37
Q

what are the mechanisms of potentiating plasma warfarin?

A
  1. inhibit hepatic metabolism (CYP 450)
  2. inhibit platelet function (can’t clot as well as warfarin blocking clotting cascade earlier on)
  3. reduce vitamin K from gut bacteria (reduced clotting factors produced in active reduced form)
38
Q

what are drugs inhibiting hepatic metabolism therefore potentiating warfarin concentrations?

A 
ingesting alcohol
amiodarone
quinolone
metronidazole
cimetidine
39
Q

what are drugs inhibiting platelet function therefore potentiating warfarin concentrations?

A

aspirin (anti-platelet)

40
Q

what are drugs reducing vit. K absorption from gut therefore potentiating warfarin concentrations?

A

cephalosporin

antibiotics

41
Q

what are drugs inhibiting warfarin? (reducing concentration)

A

antiepileptics
rifampicin
st john’s wort

42
Q

how do drugs reduce warfarin concentrations?

A

CYP450 inducer
induce hepatic enzymes
decreased INR

pharma (3 decks)

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