Revisiting Vitamin K
Megan LaBreck, PharmD, BCPS, CACP
Kristian Navickas, PharmD, BCACP, BCPS
Clinical Pharmacists - MHHC Anticoagulation Clinic, Columbus, OH
Most ambulatory care pharmacists encounter anticoagulation patients at some point. Many times, patients have already been counseled by at least one other health care provider before they have made it to you. Sometimes the information that sticks with patients is not entirely optimal. As anticoagulation care providers, we believe it is important to foster the relationships with physician providers in a team setting. We want to ensure we are providing patients with good, up to date information. One of the “myths” we commonly debunk is the idea that patients on warfarin should avoid dietary vitamin K.
What is Vitamin K?
Vitamin K is produced naturally via intestinal flora and is also found in many foods. Vitamin K is best known for its role in normal blood clotting function by way of vitamin K dependent clotting factors.
How does Vitamin K affect the INR?
Warfarin prevents the production of vitamin K dependent clotting factors in the liver, which is the opposite effect of Vitamin K itself.
Once a patient is on a stable dose of warfarin, fluctuations of dietary intake of vitamin K may cause fluctuations in the INR. Dietary intake of foods that contain >/= 200 mcg of vitamin K should be eaten in a consistent, reliable manner. One method of tracking consistency is measured in servings per week.
What should patients know?
Consistency is key. Contrary to many available patient resources, patients should never be told to avoid green leafy vegetables, but rather keep weekly intake of Vitamin K stable. Dosing of warfarin by an anticoagulation provider can be adjusted to account for dietary changes.
Daily multivitamins may contain vitamin K and it is important to have patients consider this as a source of dietary vitamin K. Counsel patients to try to stay with a brand that contains roughly the same amount of vitamin K when purchasing a new bottle.
Patients should be counseled on how to interchange foods that are high in vitamin K to allow alterations to individual dietary habits. For example, if a patient typically eats 200mcg of vitamin K per week, a chart providing vitamin K content of different foods is useful for the patient to determine ways to mix and match foods that would total their desired 200mcg per week.
Are there unusual sources of vitamin K that pharmacists should be aware of?
It is important not to forget about the vitamin K content in nutritional supplements and tube feeds. Boost or Ensure intake can significantly drop the INR due to the vitamin K content that patients would get with daily supplementation.
Caring for a patient with a PEG tube who receives daily tube feeds is also another source of vitamin K that needs to be considered. Typically, patients who provide his or her own tube feeds are cycling over a 10 hour period and unable to separate warfarin doses from tube feedings. Dose adjustments will need to be made around initiation or discontinuation of the tube feeds.
How do you tactfully counsel patients on appropriate vitamin K intake if another practitioner has told them to avoid vitamin K altogether?
In order to truly work in a collaborative fashion, it sometimes may be difficult to broach re-educating a patient regarding vitamin K intake when another provider has given them incorrect, or out-of-date information. Providing written materials is always a good strategy regarding patient education. It is crucial that patients have the opportunity to ask questions regarding the information provided and that a resource for follow up questions or concerns are provided. Anticoagulation care providers can assure a patient that the information they are provided is widely accepted by national associations, such as Anticoagulation (AC) Forum or ASHP.
References:
- National Institutes of Health Clinical Center Drug-Nutrient Interaction Task Force. Sept 2012. <https://www.cc.nih.gov/ccc/patient_education/drug_nutrient/coumadin1.pdf>
- National Institutes of Health Office of Dietary Supplements. Vitamin K fact sheet for health professionals. February 2016. <https://ods.od.nih.gov/factsheets/VitaminK-HealthProfessional/>
- Booth SL. Vitamin K: food composition and dietary intakes. Food Nutr Res 2012;56
- Wofford, James L., Megan D. Wells, and Sonal Singh. "Best strategies for patient education about anticoagulation with warfarin: a systematic review." BMC health services research1 (2008): 40.