Warfarin
The anticoagulant warfarin is a vitamin K antagonist well known for its narrow therapeutic index and the need for close therapeutic monitoring. Organisms that are relevant in patients taking warfarin include Escherichia coli and Shigella species, both of which appear to play a key role in the biosynthesis of menaquinone, or vitamin K2.[16] Research by Wang and colleagues found a positive correlation between the amount of vitamin K in the feces and the amount of Escherichia-Shigella in an individual's gut microbiome.[2] Because having a greater number of these organisms leads to greater production of vitamin K, these patients may experience a reduced response to warfarin therapy. Conversely, an abundance of the gut microbe Enterococcus was associated with low concentrations of vitamin K in the feces and increased response to warfarin therapy.[2] Because warfarin underdosing or overdosing can result in dire patient outcomes, the effects of microbiome variability on vitamin K synthesis should be further investigated as a means of assessing individual patients' response to warfarin therapy.
US Pharmacist. 2023;48(2):18-22. © 2023 Jobson Publishing
