Warfarin (High Risk)

Question 1

How long does it take for the anticoagulant effect of warfarin to develop fully?

Answer 1

48-72 hours.

Question 2

What is the target INR for healthy people?

Answer 2

1.1 or below.

Question 3

What is the target INR for most indications?

Answer 3

2.5.

Question 4

What is the target INR for recurrent DVT or PE?

Answer 4

3.5.

Question 5

How long is warfarin treatment indicated for in isolated calf-vein DVT?

Answer 5

Six weeks.

Question 6

How long is warfarin treatment indicated for in VTE provoked by surgery or other transient risk factors (e.g. COC use, pregnancy, plaster cast)?

Answer 6

Three months.

Question 7

How long is warfarin treatment indicated for in unprovoked proximal DVT or PE?

Answer 7

At least three months, may be required long-term.

Question 8

What are the red flag symptoms associated with warfarin use, which require immediate referral to a doctor?

Answer 8

Haemorrhage (unexplained bleeding or bruising), VTE (pain and swelling in calf, pain in the chest and dyspnoea), haemorrhagic stroke (headaches and confusion), rash, skin necrosis, purple toes, diarrhoea and vomiting.

Question 9

What is used to treat haemorrhage in patients taking warfarin?

Answer 9

Phytomenadione.

Question 10

What monitoring is required with warfarin use?

Answer 10

INR, liver function, renal function, FBC, BP, TFTs.

Question 11

How often is INR monitored in warfarin use?

Answer 11

Every other day in the early days of treatment and then at longer intervals, up to 12 weeks.

Question 12

Can warfarin be used in pregnancy? Why?

Answer 12

No. Teratogenic. Avoid especially in first and third trimesters. Risk of congenital malformations, and placental, foetal, and neonatal haemorrhage.

Question 13

Can warfarin be used in breastfeeding patients? Why?

Answer 13

Yes, with caution. Significant amounts not available in breast milk. Increased risk of haemorrhage, especially in vitamin K deficiency.

Question 14

Which drugs can increase the anticoagulant effect of warfarin when used concomitantly?

Answer 14

Amiodarone, anabolic steroids, azithromycin, cephalosporins, cimetidine, clarithromycin, clopidogrel, high-dose corticosteroids, cranberry juice, dipyridamole, disulfiram, entacapone, erythromycin, esomeprazole, fibrates, fluconazole, fluvastatin, glucosamine, itraconazole, methylphenidate, metronidazole, miconazole (including topical), nalidixic acid, norfloxacin, NSAIDs, ofloxacin, omeprazole, propafenone, rosuvastatin, SSRIs, St. John’s wort, sulphonamides, tamoxifen, testosterone, tetracyclines, thyroid hormones, tramadol, tricyclics, venlafaxine, vitamin E.

Question 15

Which drugs can reduce the anticoagulant effect of warfarin when used concomitantly?

Answer 15

Acitretin, azathioprine, carbamazepine, clopidogrel, griseofulvin, mercaptopurine, phenobarbital, phenytoin, rifamycin, sucralfate, vitamin K.

Question 16

How should warfarin be used in patients with hepatic impairment?

Answer 16

Use in caution with mild to moderate impairment, avoid in severe impairment,

Question 17

How should warfarin be used in patients with renal impairment?

Answer 17

Used with caution in mild to moderate impairment, monitor INR more frequently in severe impairment.

Question 18

What should be issued to all patients upon starting warfarin treatment?

Answer 18

An anticoagulant treatment book and an alert card.

Question 19

If a patient misses their daily dose of warfarin, what should they do?

Answer 19

Wait until the next day’s dose, do not double up on doses.