Warfarin

Question 1

If INR is >8 with minor bleeding

Answer 1

Stop warfarin
Phytomenadione by slow IV injection (repeat in 24 hours if INR still too high)
Restart warfarin when INR <5

Question 2

If INR >8 with no bleeding

Answer 2

Stop warfarin
Phytomenadione by mouth using IV prep orally (repeat in 24 if INR still too high)
Restart warfarin when INR <5

Question 3

If INR between 5-8 with minor bleeding

Answer 3

Stop warfarin
Phytomenadione by slow IV injection
Restart warfarin when INR <5

Question 4

If INR between 5-8 with no bleeding

Answer 4

Withhold 1 or 2 dose of warfarin
Reduce subsequent maintenance dose

Question 5

If person has major bleeding

Answer 5

Stop warfarin
Refer urgently for IV treatment with phytomenadione and dired prothrombin complex (factors II, VII, IX, X) or fresh frozen plasma if dired prothrombin complex unavailable

Question 6

Typical induction dose of warfarin

Answer 6

10mg for 2 days (tailored to individual requirements)
5mg more suitable for frail/elderly/low BW/liver disease/cardiac failure
Subsequent doses dependent on INR

Question 7

Daily maintenance dose of warfarin

Answer 7

Usually 3-9mg
Exact dose dependent on INR

Question 8

Where immediate effect is required (e.g., DVT/PE)

Answer 8

Give heparin or LMWH concurrently with warfarin (secondary care)

Question 9

Dosing in AF

Answer 9

Slow-loading regimen safe and achieves therapeutic effect in 3-4 weeks
1-2mg starting dose
Maintenance around 5mg (variation)

Question 10

Duration of treatment of warfarin in distal DVT (calf vein thrombosis)

Answer 10

6 weeks

Question 11

Duration of treatment of warfarin in proximal DVT or PE

Answer 11

3 months

Question 12

Duration of treatment of warfarin in idiopathic proximal DVT

Answer 12

6 months

Question 13

Duration of treatment of warfarin in recurrent DVTs or PEs

Answer 13

Long term

Question 14

When should the target INR be achieved for someone with AF undergoing cardioversion?

Answer 14

At least 3 weeks before and 4 weeks after cardioversion (if normal sinus rhythm is maintained).

Question 15

After cardioversion, who needs long-term warfarin treatment?

Answer 15

People at high risk of AF recurrence.

Question 16

Risk factors for recurrent AF

Answer 16

A history of failed attempts at cardioversion.
Structural heart disease (mitral valve disease, left ventricular dysfunction, or an enlarged left atrium).
A prolonged history of AF (greater than 12 months).
Previous recurrences of AF.

Question 17

Duration of treatment of warfarin in mechanical prosthetic heart valves

Answer 17

Long term

Question 18

Type of AF warfarin should be used in

Answer 18

Valvular AF

Question 19

Contraindications for warfarin

Answer 19

Haemorrhagic stroke
Clinically significant bleeding
Severe hepatic impairment
Within 72 hours of major surgery with risk of severe bleeding
Within 48 hours postpartum
Pregnancy (tetratogenic)

Question 20

Cautions for warfarin use

Answer 20

Elderly people
Increased risk of bleeding

Question 21

Risk factors for bleeding

Answer 21

History of gastrointestinal bleeding.
History of peptic ulceration.
Recent ischaemic stroke.
Uncontrolled hypertension.
Concurrent nonsteroidal anti-inflammatory (NSAID) use.
Recent surgery.
The postpartum period — should be delayed until risk of bleeding is low, usually 5–7 days after delivery.

Question 22

Factors that may increase effect of warfarin

Answer 22

Weight loss
Acute illness
Smoking cessation

Question 23

Factors that may decrease effect of warfarin

Answer 23

Weight gain
Diarrhoea
Vomiting

Question 24

When should patients on warfarin seek immediate medical

Answer 24

Spontaneous bleeding that does not stop (gums, nosebleeds, urine/stools, coughing up, eyes, vaginal in postmenopause)
Sudden severe back pain (may indicate spontaneous retroperitoneal bleeding)

Question 25

Rare or very rare side effects of warfarin

Answer 25

Alopecia Nausea Vomiting

Question 26

Skin necrosis in warfarin use

Answer 26

Rare but serious adverse effect Presents as painful, localised skin lesions with subcut fat Most likely in those with HIT or protein C or S deficiency Occurs in fatty tissue such as breasts, abdomen, extremities Stop warfarin

Question 27

Calciphylaxis in warfarin use

Answer 27

Rare but serious adverse effect Vascular calcification with cutaneous necrosis, high mortality rate Mainly occurs in ESRD on dialysis or protein C or S deficiency, hyperphosphataemia, hypercalcaemia, hypoalbuminaemia Seek urgent medical advise if develop painful skin rash Stopping warfarin considered

Question 28

Interactions that may increase effect of warfarin (16)

Answer 28

Alcohol Amiodarone Antibiotics (co-trimoxazole, metronidazole, erythromycin, clarithromycin) Antidepressants (SSRIs, SNRIs, TCAs) Aspirin Azoles (miconazole, fluconazole, variconazole) Cranberry Clopidogrel/dipyridamole Corticosteroids Antivirals (hep C) Fibrates Glucosamine NSAIDs Tamozifen Thyroxine

Question 29

Interactions that may decrease the effect of warfarin (7)

Answer 29

St Johns Wort Griseofulvin Rifampicin Carbamazepine Phenobarbital/primidone Phenytoin Vitamin K