INR

• Function: Standardized measure of Prothrombin Time (PT), assessing the extrinsic coagulation pathway (Factors II, V, VII, X).
• Primary Use: Monitoring Warfarin (Coumadin) therapy.
  • Warfarin inhibits Vitamin K-dependent factors II, VII, IX, X.
• Key INR Ranges:
  • Normal: ~1.0
  • Therapeutic Goal (most common): 2.0 - 3.0 for A-fib, DVT, PE.
  • Higher Goal: 2.5 - 3.5 for mechanical heart valves.
• Factors that ↑ INR (↑ Bleeding Risk):
  • Drugs (CYP450 Inhibitors): Amiodarone, Metronidazole, Macrolides, Fluoroquinolones.
  • Liver Disease.
• Factors that ↓ INR (↑ Clotting Risk):
  • Drugs (CYP450 Inducers): Rifampin, Phenytoin, Carbamazepine.
  • High Vitamin K Diet (leafy greens).
• Reversal of High INR:
  • Minor Elevation: Hold warfarin.
  • Moderate/High Elevation (no bleed): Oral Vitamin K.
  • Serious Bleed: IV Vitamin K + Prothrombin Complex Concentrate (PCC) or FFP.