Abstract
Although vitamin K antagonists (VKAs) such as warfarin have been used clinically for
decades, evidence supporting how best to manage their use in clinical practice is
lacking, but continues to emerge. This article summarizes available information regarding
the clinical management of VKAs with focus on dosing strategies. For patients with
previously stable international normalized ratio (INR) control, the single mildly
out-of-range INR does not warrant a change in VKA dose. For out-of-range INRs, prompt
repeat testing is associated with better INR control. After the first or second in-range
INR value a maximum recall interval of 28 days is optimal, but after the third or
greater consecutive in-range INR, longer recall intervals (up to 12 weeks for very
stable patients) can be used. The use of validated VKA dosing nomograms is suggested
as a means of reducing unwanted variability in VKA dosing decisions. Ensuring timely
INR monitoring, and adjusting VKA doses when necessary, is important when interacting
medications are prescribed during VKA therapy. Daily low-dose vitamin K supplementation
is unlikely to improve INR control in patients with stable INR control but may be
of benefit in VKA patients with unexplainable variability in the INR response. Dosing
decisions during VKA therapy should follow a systematic and coordinated process as
used in dedicated anticoagulation management services. Patient self-management of
VKA therapy offers advantages for motivated patients who can demonstrate competency
in self-management including fingerstick INR testing. Most patients with excessive
anticoagulation who are not bleeding can be managed without administering vitamin
K. There is an ongoing need for research evaluating VKA dosing practices that can
consistently improve the outcomes of VKA therapy.
Keywords
vitamin K antagonists - warfarin - anticoagulation - international normalized ratio
