Haematological (Vitamin K Antagonists)

Question 1

Examples of drug (Vitamin K Antagonists)

Answer 1

• Warfarin

Question 2

Mechanism of action (Vitamin K Antagonists)

Answer 2

• Inhibits vitamin K epoxide reductase.
• Prevents recycling of vitamin K to reduced form after carboxylation of coagulation factors II, VII, IX and X.
• Prevents thrombus formation.

Question 3

Indications (Vitamin K Antagonists)

Answer 3

• Treatment of venous thromboembolism

- Thromboprophylaxis in: AF / metallic heart valves / cardiomyopathy

Question 4

Side effects (Vitamin K Antagonists)

Answer 4

• Bleeding (risk increases with increasing INR)
• Warfarin necrosis
• Osteoporosis

Question 5

Important pharmacokinetics/pharmacodynamics (Vitamin K Antagonists)

Answer 5

• Numerous drug interactions / food interactions
• Reversal by giving vitamin K
• Polymorphisms in key metabolising enzymes (VKORC1 and CYP2C9)
• Needs therapeutic drug monitoring and monitored loading regimen
• Monitored with INR and dose adjusted according to indication

Question 6

Patient information (Vitamin K Antagonists)

Answer 6

• Need for compliance / attendance at visits for monitoring
• Care needed with alcohol
• Must inform doctor before starting new drugs – avoid over the counter aspirin preparations