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Coumadin adjustment calculator (5 mg tablets)

by Mark Morgan, MD on January 15, 2011

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The new version of this coumadin calculator is at http://www.soapnote.org/cardiovascular/coumadin-calc/. Please update your links/embeds.

summary, references, & relevant links
Summary: This calculator guides a medical provider through adjustment of coumadin (warfarin) dosing using 5 mg tablets. For the same calculator with recommendations in 2.5 mg tablets, please go here.
Point-of-Care Guide and paper-based encounter form at Ebell (2005) Am Fam Physician 71: 1979-82.
University of Michigan Anticoagulation Management Service warfarin adjustment protocol.
Comprehensive article at Ansell (2001) Chest 119: 22S-38S.

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BEGIN: There are two calculators, one for goal INR of 2 to 3 and one for goal INR of 2.5 to 3.5. Click on the appropriate link below to select which calculator.

CHOOSE: Calculator for INR goal 2 to 3 or Calculator for INR goal 2.5 to 3.5

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INR goal 2 to 3

The new version of this coumadin calculator is at http://www.soapnote.org/cardiovascular/coumadin-calc/. Please update your links/embeds.
Current weekly dose (add up all days' doses)
Current INR
Number of consecutive weekly in-range INRs prior to this INR?
Bleeding?
- No significant bleeding
- Serious bleeding
- Life-threatening bleeding
INR < 1.5. Recommended increase is 10 to 20%
12.5 mg is the minimum weekly dose threshold to make a significant dosage change for this INR zone. You may consider manually adding a dose if necessary (see below).
INR 1.5 to 1.7. Recommended increase is 5 to 10%
25 mg is the minimum weekly dose threshold to make a significant dosage change for this INR zone. You may consider adding a dose if necessary (see below).
INR 1.8 to 1.9. Recommended increase is 5 to 10%
25 mg is the minimum weekly dose threshold to make a significant dosage change for this INR zone. At this zone, it is often appropriate to leave the dose unchanged and simply recheck in 7 to 14 days.
INR 2 to 3. No change is recommended
INR 3.1 to 3.2. Recommended decrease is 5 to 10%
25 mg is the minimum weekly dose threshold to make a significant dosage change for this INR zone. At this zone, it is often appropriate to leave the dose unchanged and simply recheck in 7 to 14 days.
INR 3.3 to 3.9. Recommended decrease is 5 to 10%
25 mg is the minimum weekly dose threshold to make a significant dosage change for this INR zone. You may consider manually subtracting a dose if necessary (see below).
INR 4.0 to 4.9. Recommendation is to hold for 0 - 1 day, then decrease 10%
25 mg is the minimum weekly dose threshold to make a significant dosage change for this INR zone. You may also consider manually subtracting a dose if necessary (see below).
INR 5.0 to 8.9. Recommendation is to hold for 1 - 2 days, decrease 10 to 20%, and consider vitamin K
12.5 mg is the minimum weekly dose threshold to make a significant dosage change for this INR zone. You may consider manually subtracting a dose if necessary (see below).
INR 9.0 or more. Recommendation is to hold warfarin therapy; give vitamin K1 5.0 to 10 mg orally; monitor frequently. Resume at lower dose when INR is therapeutic
Manual override: Add or subtract a 2.5 mg dose to new weekly total?
- No
- Add 2.5 mg dose
- Subtract 2.5 mg dose
At lower weekly doses and/or at zones close to the goal INR, occasionally the new recommended weekly dosage will be unchanged. Often this indicates that a dosage change is not warranted and retesting should be performed at the recommended interval. You can, however, manually change the recommended dose by adding or subtracting a dose. You may do so by making a selection above.

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INR goal 2.5 to 3.5

The new version of this coumadin calculator is at http://www.soapnote.org/cardiovascular/coumadin-calc/. Please update your links/embeds.
Current weekly dose (add up all days' doses)
Current INR
Number of consecutive weekly in-range INRs prior to this INR?
Bleeding?
- No significant bleeding
- Serious bleeding
- Life-threatening bleeding
INR < 1.5. Recommended increase is 10 to 20%
12.5 mg is the minimum weekly dose threshold to make a significant dosage change for this INR zone. You may consider manually adding a dose if necessary (see below).
INR 1.5 to 2.2. Recommended increase is 5 to 10%
25 mg is the minimum weekly dose threshold to make a significant dosage change for this INR zone. You may consider adding a dose if necessary (see below).
INR 2.3 to 2.4. Recommended increase is 5 to 10%
25 mg is the minimum weekly dose threshold to make a significant dosage change for this INR zone. At this zone, it is often appropriate to leave the dose unchanged and simply recheck in 7 to 14 days.
INR 2.5 to 3.5. No change is recommended
INR 3.6 to 3.7. Recommended decrease is 5 to 10%
25 mg is the minimum weekly dose threshold to make a significant dosage change for this INR zone. At this zone, it is often appropriate to leave the dose unchanged and simply recheck in 7 to 14 days.
INR 3.8 to 4.4. Recommended decrease is 5 to 10%
25 mg is the minimum weekly dose threshold to make a significant dosage change for this INR zone. You may consider manually subtracting a dose if necessary (see below).
INR 4.5 to 5.9. Recommendation is to hold for 1 - 2 days, then decrease 10%
25 mg is the minimum weekly dose threshold to make a significant dosage change for this INR zone. You may also consider manually subtracting a dose if necessary (see below).
INR 6.0 to 8.9. Recommendation is to hold for 1 - 2 days, decrease 10 to 20%, and consider vitamin K
12.5 mg is the minimum weekly dose threshold to make a significant dosage change for this INR zone. You may consider manually subtracting a dose if necessary (see below).
INR 9.0 or more. Recommendation is to hold warfarin therapy; give vitamin K1 5.0 to 10 mg orally; monitor frequently. Resume at lower dose when INR is therapeutic
Manual override: Add or subtract a 2.5 mg dose to new weekly total?
- No
- Add 2.5 mg dose
- Subtract 2.5 mg dose
At lower weekly doses and/or at zones close to the goal INR, occasionally the new recommended weekly dosage will be unchanged. Often this indicates that a dosage change is not warranted and retesting should be performed at the recommended interval. You can, however, manually change the recommended dose by adding or subtracting a dose. You may do so by making a selection above.

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Tagged as: anticoagulation, calculator, coumadin, warfarin

{ 8 comments… read them below or add one }

Mark Morgan April 16, 2011 at 8:22 am

I updated the calculators. They now have a recommendation for follow-up INR testing.

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rmerrill November 19, 2011 at 1:26 pm

Thanks for the nice calculator. Is it possible to modify it to actually quote the dose adjustment…such as “reduce/ increase weekly dose to…” I am looking for tools to use on my iPhone/ iPad.

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Mark Morgan November 29, 2011 at 6:13 am: I added the words “NEW DOSE” just after “Recommended adjustment” so that users can compare the “Current weekly dose” to the “NEW DOSE”. If you’ve only selected a small percentage increase or decrease, it’s possible they would be the same. I didn’t want to make any dramatic changes because a lot of people rely on this calculator. Thank you for your suggestion. I hope this helps!

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Marv December 18, 2011 at 1:05 am

Is there an iPhone app for the warfarin calculators?

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Mark Morgan December 18, 2011 at 2:01 pm

Hi. No iPhone app yet, but in the next few days I’ll be releasing changes which should make it easier to use and view on all mobile devices.

Thanks for using soapnote!

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kinjalvora June 2, 2012 at 12:44 pm

Hi Mark,
Thanks for this calculator. Is it possible to see the actual calculator code that uses the logic?

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Mark Morgan June 2, 2012 at 2:26 pm: Hi,
I doubt this is what you were looking for, but the forms can be exported. There is a text file for the calculator for INR goal 2 to 3. You can download it here.

The actual calculation is this: (~|input_1|~*~|input_15|~)+(~|input_1|~*~|input_16|~)+(~|input_1|~*~|input_17|~)+(~|input_1|~*~|input_18|~)+(~|input_1|~*~|input_19|~)+(~|input_1|~*~|input_20|~)+(~|input_1|~*~|input_21|~)+(~|input_1|~*~|input_22|~)+
(~|input_1|~*~|input_23|~)+~|input_5|~+~|input_4|~ . These calculations come up with a number that maps out to a new dose. But this doesn’t really get you very far if you don’t know what input_1, input_2, etc are.

The best way to see those is to go to the form itself and duplicate it. Then you can inspect each of these.

input 1: current dose
input 3: number of consecutive weeks of in-range INRs
input 4: bleeding present?
input 5: add or subtract an extra dose of coumadin?
inputs 15 to 23: these are the different INR zones. These get you a multiplier to use to adjust the current dose.

Once the calculation is performed, it comes up with a raw dose. Based on the raw dose, the calculator puts it into a category with recommended schedule for the coumadin. It does so according to this array:

Life-threatening bleeding, at any INR: Hold warfarin; give prothrombin complex concentrate (or recombinant factor VIIa as an alternative) supplemented with vitamin K1 (10 mg slow IV); repeat as needed|100000|Serious bleeding, at any INR: Hold warfarin; give vitamin K1 10 mg slow IV plus fresh plasma or prothrombin complex concentrate, depending on urgency; repeat vitamin K1 every 12 hours as needed|10000|Very high INR indicates more frequent monitoring|1000|That dosage is out of range!|72.5|NEW DOSE: 70 mg weekly (M 2, Tu 2, W 2, Th 2, F 2, Sa 2, Su 2)|70|NEW DOSE: 67.5 mg weekly (M 1 1/2, Tu 2, W 2, Th 2, F 2, Sa 2, Su 2)|67.5|NEW DOSE: 65 mg weekly (M 1 1/2, Tu 2, W 2, Th 2, F 1 1/2, Sa 2, Su 2)|65|NEW DOSE: 62.5 mg weekly (M 1 1/2, Tu 2, W 1 1/2, Th 2, F 1 1/2, Sa 2, Su 2)|62.5|NEW DOSE: 60 mg weekly (M 2, Tu 1 1/2, W 2, Th 1 1/2, F 2, Sa 1 1/2, Su 1 1/2)|60|NEW DOSE: 57.5 mg weekly (M 2, Tu 1 1/2, W 1 1/2, Th 1 1/2, F 2, Sa 1 1/2, Su 1 1/2)|57.5|NEW DOSE: 55 mg weekly (M 2, Tu 1 1/2, W 1 1/2, Th 1 1/2, F 1 1/2, Sa 1 1/2, Su 1 1/2)|55|NEW DOSE: 52.5 mg weekly (M 1 1/2, Tu 1 1/2, W 1 1/2, Th 1 1/2, F 1 1/2, Sa 1 1/2, Su 1 1/2)|52.5|NEW DOSE: 50 mg weekly (M 1, Tu 1 1/2, W 1 1/2, Th 1 1/2, F 1 1/2, Sa 1 1/2, Su 1 1/2)|50|NEW DOSE: 47.5 mg weekly (M 1, Tu 1 1/2, W 1 1/2, Th 1 1/2, F 1, Sa 1 1/2, Su 1 1/2)|47.5|NEW DOSE: 45 mg weekly (M 1, Tu 1 1/2, W 1, Th 1 1/2, F 1, Sa 1 1/2, Su 1 1/2)|45|NEW DOSE: 42.5 mg weekly (M 1 1/2, Tu 1, W 1 1/2, Th 1, F 1 1/2, Sa 1, Su 1)|42.5|NEW DOSE: 40 mg weekly (M 1 1/2, Tu 1, W 1, Th 1, F 1 1/2, Sa 1, Su 1)|40|NEW DOSE: 37.5 mg weekly (M 1 1/2, Tu 1, W 1, Th 1, F 1, Sa 1, Su 1)|37.5|NEW DOSE: 35 mg weekly (M 1, Tu 1, W 1, Th 1, F 1, Sa 1, Su 1)|35|NEW DOSE: 32.5 mg weekly (M 1/2, Tu 1, W 1, Th 1, F 1, Sa 1, Su 1)|32.5|NEW DOSE: 30 mg weekly (M 1/2, Tu 1, W 1, Th 1, F 1/2, Sa 1, Su 1)|30|NEW DOSE: 27.5 mg weekly (M 1/2, Tu 1, W 1/2, Th 1, F 1/2, Sa 1, Su 1)|27.5|NEW DOSE: 25 mg weekly (M 1, Tu 1/2, W 1, Th 1/2, F 1, Sa 1/2, Su 1/2)|25|NEW DOSE: 22.5 mg weekly (M 1, Tu 1/2, W 1/2, Th 1/2, F 1, Sa 1/2, Su 1/2)|22.5|NEW DOSE: 20 mg weekly (M 1, Tu 1/2, W 1/2, Th 1/2, F 1/2, Sa 1/2, Su 1/2)|20|NEW DOSE: 17.5 mg weekly (M 1/2, Tu 1/2, W 1/2, Th 1/2, F 1/2, Sa 1/2, Su 1/2)|17.5|NEW DOSE: 15 mg weekly (M 1/2, Tu 0, W 1/2, Th 1/2, F 1/2, Sa 1/2, Su 1/2)|15|NEW DOSE: 12.5 mg weekly (M 1/2, Tu 0, W 1/2, Th 0, F 1/2, Sa 1/2, Su 1/2)|12.5|NEW DOSE: 10 mg weekly (M 1/2, Tu 0, W 1/2, Th 0, F 1/2, Sa 0, Su 1/2)|10|NEW DOSE: 7.5 mg weekly (M 1/2, Tu 0, W 1/2, Th 0, F 1/2, Sa 0, Su 0)|7.5|NEW DOSE: 5 mg weekly (M 1/2, Tu 0, W 0, Th 0, F 1/2, Sa 0, Su 0)|5|NEW DOSE: 2.5 mg weekly (M 1/2, Tu 0, W 0, Th 0, F 0, Sa 0, Su 0)|2.5|That dosage is out of range!

The sequence is [recommendation]|[raw dose]. You may be wondering how it came up with 100,000 for a dose. This was the bleeding factor from input_4. If there’s any bleeding I wanted to make sure it doesn’t give a recommendation to adjust coumadin without taking appropriate steps.

So that’s how it was put together. The other calculator for 2.5 to 3 is pretty much the same.

Probably as clear as mud, huh? Let me know if there’s anything else I can do to elaborate.

Sincerely,
Mark

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Mark Morgan, MD June 19, 2013 at 1:58 am

The new version of this coumadin calculator is at http://www.soapnote.org/cardiovascular/coumadin-calc/. Please update your links/embeds.

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Coumadin adjustment calculator (5 mg tablets)

INR goal 2 to 3

INR goal 2.5 to 3.5

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