Warfarin

Question 1

WARFARIN

1. What is the MoA of Warfarin?
2. What is the INR target of Warfarin for VTE?
3. What is the INR target of Warfarin for recurrent VTE?
4. What is the INR target for Atrial Fibrillation?
5. How is INR calculated?
6. What are side-effects of Warfarin?
7. How do P450 Inducers change INR?
8. How do P450 Inhibitors change INR?
9. Give examples of P450 Inducers
10. Give examples of P450 Inhibitors
11. When is Warfarin generally stopped for surgery?

Answer 1

1. Vitamin K antagonist, affecting clotting factors 10, 9, 7 2 (1972) and Protein C
2. 2.5
3. 3.5
4. 2.5
5. patient’s PT / normal PT
6. Bleeding, teratogenic (but safe for breast feeding), purple toes, skin necrosis
7. P450 Inducers reduce INR
8. P450 Inhibitors increase INR
9. P450 Induces which reduce INR include Phenytoin, Carbamazepine, Phenobarbitone, Rifampicin, St. John’s Wort, CHRONIC alcohol, smoking
10. P450 Inhibitors which increase INR include Erythromycin, Clarithomycin, Ciprofloxacin, Isoniazid, Omeprazole, SSRIs, Allopurinol, Amiodarone, Sodium Valproate, ACUTE alcohol intake
11. 5 days prior surgery

Question 2

MANAGEMENT OF HIGH INR

1. How do you manage a patient with a major bleed?
2. How do you manage a patient with an INR >8 with a minor bleed?
3. How do you manage a patient with an INR >8 with no bleeding?
4. How do you manage a patient with an INR 5.0-8.0 with minor bleeding?
5. How do you management a patient with an iNR 5.0 with no bleeding?

Answer 2

1. Stop Warfarin, give IV Vitamin K 5mg, and Prothrombin Complex Concentrate or Fresh Frozen Plasma
2. Stop Warfarin, IV Vitamin K 1-3mg, repeat Vitamin K if still high in 24 hours. Restart Warfarin once INR below 5.0
3. Stop Warfarin, Oral Vitamin K 1-5mg, repeat Vitamin K if still high in 24 hours. Restart Warfarin once INR below 5.0
4. Stop Warfarin, IV Vitamin K 1-3mg, Restart Warfarin once INR below 5.0
5. Withhold 1-2 doses of Warfarin and reduce subsequent maintenance dose