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Vanderbilt Pediatric Hematology Anticoagulation Guidance Protocol
4/12/12
Warfarin
Warfarin
Background
Monitoring
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Issues specific to infants and children include the following:
• Infant formula is supplemented with vitamin K.
• Breast milk has low variable concentrations of vitamin K.
• Vitamin K antagonists are available only in tablet form.
Based on a prospective cohort study in children (n=319) the average dose required of Warfarin to
achieve an INR 2-3 was the following:
• Infants average dose warfarin 0.33mg/kg/day.
• Children (age 1-13) average dose warfarin 0.14mg/kg/day.
• Teenagers (age 13-18) average dose warfarin 0.09mg/kg/day.
• Adults average dose warfarin 0.04-0.08mg/kg/day.
Warfarin is a teratogen and a pregnancy category X drug, therefore contraindicated with pregnancy
and birth control consideration should be made in children of reproductive age.
Robert F. Sidonio, Jr. MD, MSc.
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If inpatient, consider monitoring INRs daily until consistently therapeutic for at least 2 days.
If possible consider removal of vitamin K from TPN, however maintaining the same dose/timing is ok to
maintain stable INR.
Review common drug/diet interactions with pharmacy and warfarin nurse educator.
Monitor for signs of bleeding as they are higher in younger children compared to adults.
If new medications are initiated inpatient, pharmacist will evaluate potential for drug interactions and
appropriate dosage adjustments.
Frequency of PT/INR Monitoring
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Initial Dosing Recommendations
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When the patient has been recently discharged from hospitalization, the PT/INR will be checked weekly
x 2 until stable. With every dose adjustment recheck INR in 4-6 days.
When the PT/INR and dose of warfarin remains stable for one week, the PT/INR will be checked weekly.
When the PT/INR and dose of warfarin remains stable for two weeks, the PT/INR will be checked every
two weeks.
When the PT/INR and dose of warfarin remains stable for four weeks, the PT/INR will be checked every
4 weeks.
Reversal
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Dose Adjustments for days 2 – 3 (INR goal 2 – 3)
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Day 2-3
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All Warfarin reversal requires cardiology/pharmacy/hematology involvement
Dose Adjustments for days 2 – 3 (INR goal 2.5 – 3.5)
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Dose Adjustment for Day 4 of therapy and beyond (INR goal 2-3)
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Day 4
The decision to reverse the effect of warfarin depends on the degree of elevation of the INR and the
presence or absence of bleeding.
Generally, a repeat PT should be obtained at once to confirm an extremely high INR before reversal is
given. If bleeding is present, a CBC/platelets/PTT should be obtained as well.
The following recommendations are provided as guidelines to be available when the clinical pharmacist
or pharmacy resident notifies the MD of an extremely high INR.
In general, studies have suggested that most patients with an INR <10 can be managed by holding
warfarin alone!
Dose Adjustment for Day 4 of therapy and beyond (INR goal 2.5-3.5)