Risk Factors of Hylek et al for Excessive Warfarin Anticoagulation

Risk factors for excessive warfarin anticoagulation:

(1) high dose acetaminophen therapy (especially when >= 1,300 mg per day)

(2) starting a drug that potentiates warfarin's anticoagulant effect

(3) diarrhea

(4) advanced malignancy

(5) taking more warfarin than prescribed

Factors associated with a decreased risk for excessive anticoagulation (but higher risk of insufficient anticoagulation):

(1) increased vitamin K intake

(2) regular, moderate alcohol consumption (up to 2 drinks per day)

If there is a change in any of these factors from normal then it may be necessary to monitor the INR more closely and/or adjust the warfarin dose.

Ways to reduce the risk of excessive or inadequate warfarin anticoagulation:

(1) avoid taking large amounts of acetaminophen except under doctor's instructions

(2) keep vitamin K intake stable

(3) reduce the warfarin dose if significant diarrhea occurs

(4) consider the impact on warfarin  when starting or stopping a drug

(5) carefully adhere to the prescribed dose