Warfarin (Coumadin) Toxicity: Be Careful

[CapeCodMermaid, RN]

We are NOT allowed to break tablets in half, scored or not. We get the half doses from the pharmacy.

[animal1953]

My wife is on Warfarin as treatment for post stroke. I believe that the varying dosages and to try to fine tune the medication. The clinic we go to for testing keeps detailed records on dosage and INR results. We found out that some antibiotics given as part of discharge can change the INR results. My wife has finally stabilized her Warfarin dosage to keep her in range.

[studentdrtobe]

But why not just start out with a straight dose (8mg q HS or something) and if the INR remains therapeutic, leave it where it is. Why do doctors start out with complicated dosing schedules?

I already gave you the answer to your question. If you want more detailed information, feel free to utilize Google or a pharmacology reference book or do a lit search on PubMed.

Trust me, whatever the minimal therapeutic benefit, it isn't worth the potential med error. Heck, coumadin doesn't even come scored. Have you ever tried splitting a coumadin tab in half? All those "1/2 mg" doses kind of defeat the purpose.

Yea, I'm going to go ahead and trust my basic science knowledge and clinical training, as well as that of the clinical pharmacists I work with...

So, I ask again: why would we use alternate dosing with a drug that has the potential to be lethal if the therapeutic benefit of the complicated schedule doesn't outweigh the risk of medication error? Seriously, it doesn't make sense to unnecessarily jeopardize patients' health, which is what you seem to think we're doing.

[juan de la cruz, MSN, RN, NP]

But why not just start out with a straight dose (8mg q HS or something) and if the INR remains therapeutic, leave it where it is. Why do doctors start out with complicated dosing schedules? Trust me, whatever the minimal therapeutic benefit, it isn't worth the potential med error. Heck, coumadin doesn't even come scored. Have you ever tried splitting a coumadin tab in half? All those "1/2 mg" doses kind of defeat the purpose.

It would be ideal to write the dose in consistent daily mg but the way Warfarin doses are determined in the out-patient setting (or LTC where you work), adjustments are made based on weekly dosing.

In your example of the patient with alternating doses, the weekly dose for that patient is 44 mg. As you know, Warfarin is dosed based on the target INR (this is different for every anticoagulation indication). There are multiple studies that have made recommendations on dosing guidelines and the emerging theme is that reducing or increasing the dose should be made in 5-15% decrements/increments on the weekly dose based on the target INR.

If the INR on that same patient requires decreasing the dose 5%, that number corresponds to 41.8 mg. You can round that off to 42 and come up with a daily dose that is consistent - 6 mg/day and that would make all the nurses happy. However, if on next INR check, the dose needs to be increased by 15% that number would be 48.3 or 48 mg. If you divide 48 by 7, you get 6.9 or 7 right?

But you know Warfarin doesn't come in that tablet dose (it's available as 1, 2, 2.5, 3, 4, 5, 6, 7.5, and 10 mg) so now you're left with a dosing that calls for 7.5 mg 4 days/week and 6 mg 3 days/week to come up with a weekly dose of 48 mg and you must alternate those doses to maintain daily therapeutic effect. Does that make sense?

And yes, you shouldn't be scoring Warfarin.

[juan de la cruz, MSN, RN, NP]

I've only ever seen one case of Coumadin necrosis. The poor woman turned beet red from head to toe. The next day her skin turned black and started to peel off in strips. She freaked out but made a full recovery.

Yeah that's a rare complication of Warfarin therapy but it is not really associated with Warfarin toxicity per se. When you think of Warfarin toxicity, you think of supratherapuetic drug levels with elevated INR and risk for bleeding. Warfarin necrosis is not related to excessive bleeding due to high INR, in fact, the theory on its etiology is hypercoagulability due to Protein C deficiency. Protein C is a natural anticoagulant in the body that is Vitamin K dependent. When Warfarin, a Vitamin K antagonist, is initiated, it suppresses Protein C in the first few days which can trigger a hypercoagulable cascacde during this period, hence, the necrotic areas of the skin. One way to prevent this is by starting Unfractionated Heparin as an infusion to establish a stable state of anticoagulation prior to initiating a bridge to Warfarin.

[RainMom]

It would be ideal to write the dose in consistent daily mg but the way Warfarin doses are determined in the out-patient setting (or LTC where you work), adjustments are made based on weekly dosing.

In your example of the patient with alternating doses, the weekly dose for that patient is 44 mg. As you know, Warfarin is dosed based on the target INR (this is different for every anticoagulation indication). There are multiple studies that have made recommendations on dosing guidelines and the emerging theme is that reducing or increasing the dose should be made in 5-15% decrements/increments on the weekly dose based on the target INR.

If the INR on that same patient requires decreasing the dose 5%, that number corresponds to 41.8 mg. You can round that off to 42 and come up with a daily dose that is consistent - 6 mg/day and that would make all the nurses happy. However, if on next INR check, the dose needs to be increased by 15% that number would be 48.3 or 48 mg. If you divide 48 by 7, you get 6.9 or 7 right?

But you know Warfarin doesn't come in that tablet dose (it's available as 1, 2, 2.5, 3, 4, 5, 6, 7.5, and 10 mg) so now you're left with a dosing that calls for 7.5 mg 4 days/week and 6 mg 3 days/week to come up with a weekly dose of 48 mg and you must alternate those doses to maintain daily therapeutic effect. Does that make sense?

And yes, you shouldn't be scoring Warfarin.

Yes! I've been trying to convince my brother that he shouldn't be playing around with our mother's dosing. He has set up her pills for 6 mg daily rather than the alternating 5 & 7.5 ordered. Then my sister & I catch him and change it back & obviously this is causing problems! I always had a hard time explaining the rationale behind this since in school we never dug that deep into the coumadin dosing. This explanation may help me convince him that the MD does indeed know what he is doing & to stop playing around with mom's meds! Thank you!

[karenjoydelay]

If warfarin is teratogenic, what are its side effects to the baby? Your reply will be highly appreciated. Thankyouuu. :)

[hootman]

is that why I cant have children? I have an Artificial heart valve and the doctor told me if I had children it could kill me

[CapeCodMermaid, RN]

We can't give medical advice here. Try drugs.com

[Esme12, ASN, BSN, RN]

is that why I cant have children? I have an Artificial heart valve and the doctor told me if I had children it could kill me

YOu need to ask you MD about this.....women with artificial valves do get pregnant and have babies. Why it would "kill you"? Only your PCP can answer that question.