The Effect of Medication Timing on Anticoagulation Stability in Users of Warfarin: The "INRange" RCT
Status:
Completed
Trial end date:
2018-04-27
Target enrollment:
Participant gender:
Summary
Warfarin is an anticoagulant medication that is highly effective at preventing clotting
disorders but which has a narrow therapeutic window. If warfarin is under effective patients
are at risk of stroke, if it is over effective patients are at risk of bleeding
complications. Physicians routinely and regularly measure a blood test (called the "INR")
that determines the effectiveness of warfarin and have a range of test values (the
"therapeutic range") in which they try to keep the patient. By convention warfarin is taken
at dinnertime, however this is the same time of day that highly variable consumption of
dietary vitamin K occurs (found largely in green leafy vegetables) and vitamin K alters the
effectiveness of warfarin. Given vitamin K has a very short half-life (i.e. it is only active
for a short period of time after it is ingested) it may make more sense to take warfarin in
the morning (when very little vitamin K is ingested) to produce a more consistent drug
effect. The purpose of this study is to determine whether switching current warfarin users
from evening to morning dosing decreases time spent outside the therapeutic INR range.