Drug Class: Vitamin K Inhibitor Flashcards
1
Q
Example of vitamin K inhibitor
A
WARFARIN
2
Q
Mode of action of WARFARIN + conditions used in
A
- Inhibits production of active clotting factors
Used in prevention of DVT, PE, stroke
- In renal failure
- Significantly obese patients
3
Q
Side effects of WARFARIN
A
Bleeding
4
Q
Drug-drug interactions of WARFARIN
A
- Interaction with other drugs via CYP450
↑ warfarin activity - Aspirin, Cotrimoxazole, Trimethoprim = decrease albumin binding= ↑INR
- Cimetidine, erythromycin= inhibit degradation by inhibiting CYP450
- Oral antibiotics= interfere with Vit K synthesis -> decrease synthesis of clotting factors
↓ warfarin activity - Barbiturate, phenytoin, alcohol= induction of CYP450
- Vitamin K= promote clotting factor synthesis
- Cholestyramine= reduce absorption
↑↑ bleeding - NSAIDs/ Aspirin= inhibition of platelets/prostaglandins
- Heparin metabolites= inhibition of clotting factors
5
Q
Contraindications of WARFARIN
A
Narrow therapeutic range - International normalised ratio (INR) - Normal INR 1 - Therapeutic INR 2.5-4 Avoid in pregnancy (esp. 1st-3rd trimesters) - TERATOGNEIC (chondrodysplasia) - Retroplacental and fetal intracerebral BLEEDING - Replace with subcutaneous/IV heparin