INR (International Normalized Ratio) (Last Updated - 3/29/2005)
-measures PT efficacy
-INR = (Patient PT / Reference PT) ^ ISI (where ISI = International Sensitivity Index supplied by manufacturers)
-used for pts. on long-term Warfarin (Coumadin) to monitor coag functions
-most indications for chronic oral anti-coagulation have a recommended INR between 2.0-3.0 (higher for mechanical heart valves)
-at initiation of tx monitor INR's QD until within recommended therapeutic range for 2 consecutive days --> then Q week --> then Q month
-INR not useful in pts. with the lupus anti-coagulant b/c they have prolonged PT's @ baseline (use anti-factor Xa assay to monitor instead)
-Therapeutic INR Targets For Pts. Taking Chronic Oral Anti-Coagulation With Warfarin (Coumadin):
1) Chronic Atrial Fibrillation (AFib): --> 2.0 - 3.0 (2)
-INR Ranges, Assoc. Risks & Tx:
2.0-3.0:
-~5%/yr risk of serious bleed
> 4.0:
-increased risk of intracranial bleed
< 5.0 but > therapeutic range:
-d/c Warfarin (Coumadin) until INR drops down to therapeutic range
transiently > 5.0
-usually due to a new med (Ex.) Acetaminophen) or change in meds regimen (esp. cyto P450 CYP2C9 inhibitors --> decreased Warfarin (Coumadin) breakdown
5.0-9.0
-Give 1.0 mg - 2.5 mg Vit. K PO*
9.0-20.0
-Give 3.0 mg - 5.0 mg Vit. K PO*
> 20.0
-Give FFP (10-20 mL/kg) immediately plus 10 mg Vit. K slow IV*
* - Vit. K admin will make pts. unresponsive to Warfarin (Coumadin) for several days
- Vit. K admin will take 24-48 hrs. to decrease INR's to therapeutic ranges b/c takes time to synthesize new coag factors
- May use Heparin instead for continued anit-coagulation
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References:
1) Goodman & Gilman's: The Pharmacologic Basis Of Therapeutics - 10th Edition - 2001. Chapter 55.
2) Journal of the American College of Cardiology - May 7, 2003 - Vol. 41 (#9) - Pages 1646-1647.