Do peas affect International Normalized Ratio (INR) in patients on warfarin?

From the Guidelines

Peas can affect International Normalized Ratio (INR) in patients on warfarin due to their vitamin K content, and patients should maintain consistent consumption patterns to avoid INR fluctuations. Peas contain vitamin K, which can counteract warfarin's anticoagulant effects, as evidenced by studies on the relationship between dietary vitamin K intake and warfarin-related overanticoagulation 1. A typical serving of green peas (1/2 cup or about 80g) contains approximately 14-16 micrograms of vitamin K, which is enough to potentially influence INR values if consumed inconsistently.

Some key points to consider:

• Patients on warfarin should not avoid peas completely but should maintain consistent consumption patterns to minimize the risk of INR fluctuations 1.
• Sudden increases or decreases in pea intake can cause INR fluctuations, potentially leading to either reduced anticoagulation (increasing clot risk) or excessive anticoagulation (increasing bleeding risk) 1.
• The interaction between warfarin and dietary vitamin K is complex, and current professional guidelines and FDA drug-labeling materials recommend stable intakes of dietary vitamin K to prevent fluctuations in INRs 1.
• Patients should inform their healthcare provider about their typical pea consumption so appropriate warfarin dosing can be established, and they should notify their provider if they plan significant changes to their pea or other vitamin K-containing food intake.

It is essential to note that the evidence on the relationship between dietary vitamin K intake and warfarin-related overanticoagulation is inconsistent, and more research is needed to fully understand this interaction 1. However, based on the available evidence, maintaining consistent pea consumption patterns is crucial for patients on warfarin to minimize the risk of INR fluctuations.

From the Research

Peas and INR

• Peas are a source of vitamin K, which can affect International Normalized Ratio (INR) in patients on warfarin 2, 3, 4, 5.
• High vitamin K intake can decrease the therapeutic effectiveness of warfarin, while poor vitamin K status appears to increase the sensitivity to small changes in vitamin K intake 2.
• Very large amounts of vitamin K from a single meal with vegetables (400 g of vegetables with 700 to 1500 microg of vitamin K1) can measurably change INR, but occasional typical servings (<100 g) would probably have little lasting impact on INR 2.
• The effect of dietary vitamin K intake on warfarin sensitivity is known, and patients consuming regular diets with high vitamin K intake (>250 microg/day) had lower warfarin sensitivity and required higher maintenance warfarin doses 3.

Vitamin K Intake and INR Stability

• Changes in daily vitamin K intake may contribute to marked variations in INR coagulation indices in patients receiving oral warfarin anticoagulant therapy 4.
• A weekly change of 714 mug dietary vitamin K significantly altered weekly INR by 1 unit, and a weekly change of 14.5 mg warfarin significantly altered weekly INR by 1 unit after adjustment for age, sex, weight, height, and concomitant use of medications known to interact with warfarin 4.
• Long-term anticoagulation effect of warfarin is more stable in patients who take greater than a certain amount of dietary vitamin K (>195.7 μg/day) 5.

Other Foods and INR

• Green tea can be a significant source of vitamin K and thus antagonize the effect of warfarin, leading to decreased INR values 6.
• Patients receiving warfarin need to be routinely questioned about their intake of vitamin K-containing foods and beverages to maintain stable INR values 6.