Key Points
ÎFor many decades, the vitamin K antagonists (VKAs) have been the only oral anticoagulant drugs available for clinical use for the primary and secondary prevention of venous and arterial thromboembolic events. However, VKA treatment has numerous significant drawbacks including multiple drug, food and herbal interactions, hemorrhage and acute thrombotic complications, such as skin necrosis and limb gangrene.
ÎNew oral anticoagulant drugs have the potential to overcome several drawbacks of the VKAs. These drugs can be administered at fixed doses and do not require laboratory monitoring, thus offering a clear advantage over the VKAs.
Treatment Vitamin K Antagonists ÎVKAs are highly susceptible to > 200 drug-drug interactions.
ÎSeveral foods interact with VKAs, among them fish oil, grapefruit, soy milk, seaweed, mangos, avocado in large amounts and high vitamin K content foods/enteral feeds.
ÎNutritional supplements and herbal products are particularly problematic in that warfarin-treated patients often fail to inform physicians that they are using such products, and physicians rarely ask.
ÎAlthough the international normalized ratio (INR) is the standard for following VKA therapy, it has not been validated and should be viewed with some skepticism early in the course of warfarin therapy, particularly when results are obtained from different laboratories.
ÎThe most effective method to avoid adverse outcomes associated with drug interactions is to avoid, when feasible, concurrent use of potentially interacting drugs and to use noninteracting alternatives instead.
ÎWhen noninteracting alternatives are not available, adverse outcomes can be avoided by increasing the frequency of monitoring and adjusting warfarin doses based on INR response.
ÎProspective dosing adjustments are inappropriate because of the unpredictable nature of patient response to drug interactions.
ÎDedicated computer programs may improve dose management and time in therapeutic range.
ÎPatient self testing or patient self management using a point of care instrument represents another model of care with the potential for improved outcomes as well as greater convenience.
ÎThis mode of therapy may not be suitable for all patients and may not be practical or cost-effective in certain settings.
