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The FNB did not establish ULs for vitamin K because of its low potential for toxicity. In its report, the FNB stated that “no adverse effects associated with vitamin K consumption from food or supplements have been reported in humans or animals.”
Interactions with Medications
Vitamin K interacts with a few medications. In addition, certain medications can have an adverse effect on vitamin K levels. Some examples are provided below. Individuals taking these and other medications on a regular basis should discuss their vitamin K status with their healthcare providers.
Warfarin (Coumadin®) and similar anticoagulants
Vitamin K can have a serious and potentially dangerous interaction with anticoagulants such as warfarin (Coumadin®), as well as phenprocoumon, acenocoumarol, and tioclomarol, which are commonly used in some European countries. These drugs antagonize the activity of vitamin K, leading to the depletion of vitamin K-dependent clotting factors. People taking warfarin and similar anticoagulants need to maintain a consistent intake of vitamin K from food and supplements because sudden changes in vitamin K intakes can increase or decrease the anticoagulant effect.
Antibiotics
Antibiotics can destroy vitamin K-producing bacteria in the gut, potentially decreasing vitamin K status. This effect might be more pronounced with cephalosporin antibiotics, such as cefoperazone (Cefobid®), because these antibiotics might also inhibit the action of vitamin K in the body. Vitamin K supplements are usually not needed unless antibiotic use is prolonged (beyond several weeks) and accompanied by poor vitamin K intake.
Bile acid sequestrants
Bile acid sequestrants, such as cholestyramine (Questran®) and colestipol (Colestid®), are used to reduce cholesterol levels by preventing reabsorption of bile acids. They can also reduce the absorption of vitamin K and other fat-soluble vitamins, although the clinical significance of this effect is not clear. Vitamin K status should be monitored in people taking these medications, especially when the drugs are used for many years.
Orlistat
Orlistat is a weight-loss drug that is available as both an over-the-counter (Alli®) and prescription (Xenical®) medication. It reduces the body’s absorption of dietary fat and in doing so, it can also reduce the absorption of fat-soluble vitamins, such as vitamin K. Combining orlistat with warfarin therapy might cause a significant increase in prothrombin time. Otherwise, orlistat does not usually have a clinically significant effect on vitamin K status, although clinicians usually recommend that patients taking orlistat take a multivitamin supplement containing vitamin K. *