Can we predict daily adherence to warfarin?: Results from the International Normalized Ratio Adherence and Genetics (IN-RANGE) Study.
BACKGROUND
Warfarin is the primary therapy to prevent stroke and venous thromboembolism. Significant periods of nonadherence frequently go unreported by patients and undetected by providers. Currently, no comprehensive screening tool exists to help providers assess the risk of nonadherence at the time of initiation of warfarin therapy.


METHODS
This article reports on a prospective cohort study of adults initiating warfarin therapy at two anticoagulation clinics (university- and Veterans Affairs-affiliated). Nonadherence, defined by failure to record a correct daily pill bottle opening, was measured daily by electronic pill cap monitoring. A multivariable logistic regression model was used to develop a point system to predict daily nonadherence to warfarin.


RESULTS
We followed 114 subjects for a median of 141 days. Median nonadherence of the participants was 14.4% (interquartile range [IQR], 5.8-33.8). A point system, based on nine demographic, clinical, and psychosocial factors, distinguished those demonstrating low vs high levels of nonadherence: four points or fewer, median nonadherence 5.8% (IQR, 2.3-14.1); five points, 9.1% (IQR, 5.9-28.6); six points, 14.5% (IQR, 7.1-24.1); seven points, 14.7% (IQR, 7.0-34.7); and eight points or more, 29.3% (IQR, 15.5-41.9). The model produces a c-statistic of 0.66 (95% CI, 0.61-0.71), suggesting modest discriminating ability to predict day-level warfarin nonadherence.


CONCLUSIONS
Poor adherence to warfarin is common. A screening tool based on nine demographic, clinical, and psychosocial factors, if further validated in other patient populations, may help to identify groups of patients at lower risk for nonadherence so that intensified efforts at increased monitoring and intervention can be focused on higher-risk patients.
Platt
Alec B
AB
MSCE, University of Pennsylvania School of Medicine, 707 Blockley Hall, 423 Guardian Dr, Philadelphia, PA 19104-6021, USA. stevek@mail.med.upenn.edu
Localio
A Russell
AR
Brensinger
Colleen M
CM
Cruess
Dean G
DG
Christie
Jason D
JD
Gross
Robert
R
Parker
Catherine S
CS
Price
Maureen
M
Metlay
Joshua P
JP
Cohen
Abigail
A
Newcomb
Craig W
CW
Strom
Brian L
BL
Laskin
Mitchell S
MS
Kimmel
Stephen E
SE
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000925:Anticoagulants / Q000627:therapeutic use*; D015331:Cohort Studies; D005260:Female; D006801:Humans; D016015:Logistic Models; D008137:Longitudinal Studies; D008297:Male; D055118:Medication Adherence / Q000523:psychology*; D008875:Middle Aged; D015233:Models, Statistical; D017063:Outcome Assessment, Health Care; D010349:Patient Compliance / Q000523:psychology; D011446:Prospective Studies; D011584:Psychology; D012959:Socioeconomic Factors; D020521:Stroke / Q000517:prevention & control*; D013923:Thromboembolism / Q000517:prevention & control*; D014859:Warfarin / Q000627:therapeutic use*
D000925:Anticoagulants; D014859:Warfarin