INR Elevation Associated with Diarrhea in a Patient Receiving Warfarin

OBJECTIVE: To report a case of international normalized ratio (INR) prolongation in a patient receiving warfarin who experienced several episodes of diarrhea. CASE SUMMARY: A 56-year-old white woman, previously controlled on warfarin therapy (INR 2.5-3.5) after aortic valve replacement, experienced six episodes of INR elevation, each associated with an acute bout of diarrhea lasting from one to four days. The patient had not received additional warfarin or new medications (including nonprescription medications and herbal remedies) prior to the episodes. The patient had no obvious signs of bleeding (except bruising on 1 episode) or signs of infection determined through physician evaluation of the patient and her stools. In addition, she had no diagnosis of liver disease or acute or chronic malabsorption. The patient did report that her dietary intake decreased to 25-50% of normal during these episodes of diarrhea, which may result in decreased vitamin K ingestion. DISCUSSION: This is one of the first case reports documenting a trend of INR elevation specifically with episodes of diarrhea. Since most of the common reasons for acute INR elevation have been eliminated, diarrhea with decreased oral intake are the most probable causes for these observed changes in the INR. Several reports suggest that acute diarrhea results in malabsorption of vitamin K, which can predispose patients taking warfarin to INR elevations, but in many of these reports patients had other risk factors for INR elevation. Although the effect of diarrhea on vitamin K absorption and the INR is difficult to quantify, the INR elevation reported here seemed to be directly associated with the duration of each diarrheal episode. CONCLUSIONS: Diarrhea episodes in patients receiving warfarin can result in prolongation of the INR and possible bleeding. Patients who experience diarrhea or decreased oral intake resulting in elevated INRs should have their INRs evaluated more frequently and their warfarin doses adjusted appropriately.