[dkduncan]

what's the rational for giving warfarin at night?

[sonja77]

I have learned in nursing school that you give warfarin/coumadin at 1700/1800 (depending on the hospital) because it reaches its "peak" in time for the routine am labs.

Ok, I did a little more research and it looks like it it given at night, so the physician can look at the PT/INR in the morning and adjust the next evening dose if necessary.

[pagandeva2000]

Good question...I always wanted to know this myself.

[dan_haifa]

"Warfarin sodium and other coumarin anticoagulants act by inhibiting the synthesis of vitamin K dependent clotting factors..."
"...An anticoagulation effect generally occurs within 24 hours after drug administration. However, peak anticoagulant effect may be delayed 72 to 96 hours. The duration of action of a single dose of racemic Warfarin is 2 to 5 days..." (www.drugs.com)
Now we can see that administration of Warfarin in the evening hours doesn't related with its' pharmacology. I think the evening hours are convenient for a dose correction(a physician receive results of tests from a laboratory).

[Emmanuel Goldstein]

I believe certain factors can be affected within 6-8 hours, but the primary reason for administering it in the evening is to give the docs time to adjust (or hold) dosages as necessary and to reduce the chance of missed doses due to being NPO for procedures and tests. Most of what I've read is that consistency is most important. Taking the med at the same time of day, maintaining a consistent diet (rather than restricting vit k foods), that kind of thing.

[GrumpyRN63]

Also, once the pt is discharged, they will need f/u labs as an outpt for months, drawn during the day also reflects the plasma/distribution level of the pm dose of Coumadin more accurately in a steady state. If the pt took it at 0700 and had labs drawn at 1000 I would think the coags would be inaccurately elevated , the pm dose allows continuity of f/u also

[MichaelFloridaRN]

I am not really sure why this is done this way. Perhaps it falls under "thats how we always did it and how it will always be".

However, if it was given say at 7 AM and the labs were done at 4 AM, then a result requiring a dose adjustment or holding the dose would result in the docs being called ! And we all know they do not like to be called. And in all actuality why call if something can be fixed when they do rounds.