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Table of Contents > Supplements > Vitamin K > Interactions
Possible Interactions with: Vitamin K
Also listed as: Menadione; Menaphthone; Menaquinone; Phylloquinone

If you are currently being treated with any of the following medications, you should not take vitamin K without first talking to your healthcare provider.

Antibiotics, particularly a class known as cephalosporins, reduce the absorption of vitamin K. Extended use of antibiotics may result in vitamin K deficiency because these drugs kill not only harmful bacteria, but also beneficial, vitamin K-activating bacteria. This is particularly a problem for people who already have low levels of vitamin K or are at risk for deficiency (such as those who are malnourished, elderly, or taking warfarin).

Preliminary evidence suggests that vitamin K3 (a synthetic form of vitamin K) may enhance the chemotherapeutic effects of doxorubicin. However, these results have not yet been demonstrated in people. There is also some concern that vitamin K3 causes severe anemia in people. More research is needed to assess if this synthetic form of vitamin K is safe and useful.

Phenytoin interferes with the body's ability to use vitamin K. Taking anticonvulsants (such as phenytoin) during pregnancy or while breastfeeding may deplete vitamin K in newborns.

Vitamin K reduces the effects of the blood-thinning medication warfarin, rendering the medication ineffective. Vitamin K should not be taken while taking warfarin, and foods containing high amounts of vitamin K should be avoided.

Weight Loss Products
Orlistat, a medication used for weight loss and olestra, a substance added to certain food products, are both intended to bind to fat and prevent the absorption of fat and the associated calories. Because of their effects on fat, orlistat and olestra may also prevent the absorption of fat-soluble vitamins such as vitamin K. Given this concern and possibility, the Food and Drug Administration (FDA) now requires that vitamin K and other fat soluble vitamins (namely, A, D, and E) be added to food products containing olestra. How well vitamin K from such food products is absorbed and used by the body is not clear. In addition, physicians who prescribe orlistat add a multivitamin with fat soluble vitamins to the regimen.

The possibility of olestra or orlistat interfering with vitamin K absorption is particularly important to know if you already have a vitamin K deficiency (such as with malnourishment or poor fat absorption from cystic fibrosis) or if you have a tendency to bleed (includign if you take the blood thinner warfarin). On the other hand, the fact that vitamin K is now added to olestra-containing food products is also significant if you should not be taking vitamin K (again, for example, if you are on the blood thinner warfarin or you have a G6PD deficiency).

X-rays and Radiation
X-rays and radiation can deplete vitamin K levels and raise vitamin K requirements.

Each of the following may diminish vitamin K absorption and lead to reduced levels in the body:

  • Aspirin
  • Cholestyramine, one of a class of medications known as bile acid sequestrants used to lower cholesterol
  • Mineral oil laxatives

Drug Interactions
Bile Acid Sequestrants

Copyright © 2004 A.D.A.M., Inc

The publisher does not accept any responsibility for the accuracy of the information or the consequences arising from the application, use, or misuse of any of the information contained herein, including any injury and/or damage to any person or property as a matter of product liability, negligence, or otherwise. No warranty, expressed or implied, is made in regard to the contents of this material. No claims or endorsements are made for any drugs or compounds currently marketed or in investigative use. This material is not intended as a guide to self-medication. The reader is advised to discuss the information provided here with a doctor, pharmacist, nurse, or other authorized healthcare practitioner and to check product information (including package inserts) regarding dosage, precautions, warnings, interactions, and contraindications before administering any drug, herb, or supplement discussed herein.

Vitamin K
  Uses of this Supplement
Bone Cancer
Cystic Fibrosis
Kidney Stones
Myeloproliferative Disorders
  Supplements with Similar Uses
View List by Use
  Drugs that Interact
Bile Acid Sequestrants
  Drugs that Deplete this Substance
View List
  Supplements with Similar Warnings
View List by Warning
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