With its narrow therapeutic range, warfarin is a tricky drug to use.
Dosing depends on many factors, including interactions with other medications, certain foods, or over-the-counter supplements. Outside of its therapeutic range, warfarin can increase the risk of bleeding or conversely of developing blood clots. Patients had been advised to avoid vitamin K–rich foods so as not to counteract warfarin’s effects, although clinical guidance now recommends consistent intake instead.
But newer findings have weighed in with another option: increase vitamin K intake to maintain stable anticoagulation, and do it with food. At the American Society for Nutrition’s recent annual meeting, Guylaine Ferland, PhD, a professor of nutrition at the University of Montreal in Canada, reported findings from a small study that showed boosting daily dietary vitamin K consumption appears more effective at maintaining stable anticoagulation for patients with a history of warfarin instability than simply offering general dietary advice.
“These are foods most people eat anyway, it’s just that they have to introduce them into their usual diet in a more systematic manner and in perhaps a more well-informed manner,” Ferland said.
Although warfarin has been losing ground to the newer direct oral anticoagulants (DOACs) including apixaban and dabigatran, Ferland said the drug isn’t about to disappear from the anticoagulation landscape. “There remain a number of conditions that will call for warfarin,” such as mechanical heart valves and renal insufficiency, she said. Warfarin also is the drug of choice for antiphospholipid syndrome, noted Paige Christensen, NP, associate medical director of thrombosis and anticoagulation for Intermountain Healthcare in Salt Lake City.
“This conversation and these dietary interests in vitamin K probably aren’t going to go away for a long time,” Christensen added.
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The part of the picture that was cut off is the summary:
“In a recent RCT of 46 patients on #warfarin with INRs in and out of therapeutic range, boosting daily dietary #vitaminK consumption was more effective than general dietary advice at maintaining INR stability”
MarkS. one of our members recommends taking VitK daily for better balance. The thinking ,( which works for me) is that by increasing Vitk intake, then you need to raise warfarin intake. We know that the amount we take is of no significance so long as the resulting INR is stable. so raising dose from say 4.5 to 6 or 7mg is no problem Some people are already on doses in the teens! This means that any dietary changes have less impact INR as the percentage difference in total Vitk intake is much less. I think Mark flagged this up a good five or more years ago.
BobD, I think the medical literature has a whole thread on the subject. If I remember rightly, some report that stability is increased by regular Vit K supplements, but others report swings. There are probably other factors which account for this difference of findings.
In principle the idea of a steady Vit K supplement is that it increases the steady general level and this higher general level buffers that obtained from food. Vit K comes from two sources: diet and gut bacteria. Estimates of how much is made by gut bacteria are hard to find .. please post them if you find them. I have seen the figure of 50% and it is likely to be highly variable, which is another factor muddling the picture.
BTW my take on the reporting of swings when taking a Vit K supplement is that they are trying to achieve too narrow a range, which is known to increase swings. Also, I think that the stability point for some people is not in the artificially decided desirable range, so, some people would be more stable if they aimed for 3 plus or minus, rather than 2.5 plus or minus.
I remember the talk by the UK INR expert at HRC some years ago who said we should be aiming for 3 rather than 2.5 and that up to 5 was not dangerous and acceptable. I think most of us old hands ignore the local computer generated dose and do our own thing based on our experience hence better than 85% in range. Only when I have heeded the surgery (not very often) or have changed drugs (antibiotics etc ) have I gone out of range.
1/ Passmore P Eastwood MA 1986 Human nutrition and dietetics. Edinburgh: Churchill Livingstom pp 140-142
cited in MJ Hill, Intestinal flora and endogenous vitamin synthesis. European Journal of Cancer prevention 1997, vol 6(suppl 1):S43-S45
I hope I have missed something obvious, so please post any other interesting references
I also found this interesting. It is possible that a long term reduced dietry Vit K stimulates gut bacteria increased production. Conly, J.M., and Stein, K. (1992). The production of menaquinones (vitamin K2) by intestinal bacteria and their role in maintaining coagulation homeostasis. Prog. Food. Nutr. Sci. 16, 307-343.
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