Warfarin Institute of America
DEDICATED TO YOUR HEALTH SINCE 2000
INTERACTION OF DICLOXACILLIN WITH WARFARIN (Coumadin, Jantoven)
Halvorsen et al. report the case of a 76-year-old woman with a aortic valve replacement who experienced a clot on her valve after she was started on dicloxacillin. Her INR had been reduced to 1.4. After the dicloxacillin was stopped, it took three weeks of higher than usual warfarin (Coumadin, Jantoven) doses to maintain her INR in the therapeutic range. Then, when the dicloxacillin was stopped, the need for warfarin (Coumadin, Jantoven) was reduced to her pre-dicloxacillin level.
Taylor et al also report on a patient who had this interaction after being switched from intravenous nafcillin to oral dicloxacillin. The interaction started while on the nafcillin but continued when the switch to dicloxacillin was made. The interaction was not as profound as with nafcillin but was present.
I have seen this happen in several patients. The reaction is dramatic at the onset and lengthy to manage during the offset.
My Conclusion: This is a dangerous, but sometimes unavoidable, combination of medications. If it must be used, there must be careful monitoring of the INR during and for up to one month after the dicloxacillin is discontinued.
References:
Halvorsen S, et al. Prosthetic Heart Valve Thrombosis During Dicloxacillin Therapy. Scand Cardiovasc J 1999;33:366-368.
Taylor AT et al. Continuation of warfarin-nafcillin interaction during dicloxacillin therapy. J Fam Pract 1994;39:182-185
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