Pearls of Wisdom: What Medication Caused the Major Destabilization of INR?
Question: Joshua is an 80-year-old man who had been stable on coumadin for 12 months, consistently demonstrating an INR of 2.2 to 3.1. He is on coumadin for atrial fibrillation and has been taking the same 6 mg/d dose for over a year.
Today, Joshua presented with an INR of 21.4, which results in immediate admission to the hospital.
He has not changed his warfarin dose and has not been ill. When asked of other medications, he opens his “pill box” to show you that he is taking atenolol 50 mg/d, isosorbide mononitrate 20 mg/d, and diltiazem 400 mg/d. (Note: It is unusual to have a patient receive both a beta blocker and rate-slowing calcium channel blocker since that combination could lead to problematic bradycardia, but that is how this case was reported.)
Which of the following could have resulted in such a dramatic change in INR?
A. Increased onions in the diet
B. Change from morning to evening coumadin administration
C. Topical miconazole cream
D. A change from trade name atenolol (Tenormin) to generic
What is the correct answer?
(Answer and discussion on next page)
Louis Kuritzky, MD, has been involved in medical education since the 1970s. Drawing upon years of clinical experience, he has crafted each year for almost 3 decades a collection of items that are often underappreciated by clinicians, yet important for patients. His “Pearls of Wisdom” as we like to call them, have been shared with primary care physicians annually in an educational presentation entitled 5TIWIKLY (“5 Things I Wish I Knew Last Year”…. or the grammatically correct, “5 Things I Wish I’d Known Last Year”).
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Answer: Topical miconazole cream
There are some patients who appear to be doing everything right while managing their coumadin, yet still encounter problems. This is not too surprising, since the list of medications and foods that interact with coumadin is extensive and continues to expand after 4 decades of use.
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Pearls of Wisdom: Keeping INR in Range
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While our patient tried to be helpful by bringing in all of his medications, he neglected to mention that he was prescribed miconazole cream for tinea cruris 2 weeks prior since he didn’t consider a topical cream to be a medication. These type of omissions can affect the physician’s opportunity to detect culprit medications; counsel your patients to understand that over-the-counter medications are not free of risk.
Topical Miconazole and Coumadin Interaction
Treatment
Our patient received fresh frozen plasma, which promptly restored his coagulation status to a more appropriate level. He was restarted on the same 6 mg/d daily coumadin dose and was noted to have a therapeutic INR weeks later.
What’s the “Take Home”?
Patients on coumadin may not think of topical agents as a medicine, and hence neglect to report the use of topicals when queried about interacting substances. However, as we see in this case, topical miconazole can have a meaningful impact upon INR.
Reference:
1. Devaraj A, O'Beirne JP, Veasey R, Dunk AA. Interaction between warfarin and topical miconazole cream. BMJ. 2002;325(7355):77.