Predictors of unstable anticoagulation in African Americans.
OBJECTIVE
We sought to identify contributors to unstable anticoagulation in African Americans.


METHODS
Sixty African Americans on warfarin were enrolled. Cytochrome P450 2C9 and vitamin K epoxide reductase genotypes and vitamin K intake were assessed, and clinical and dietary data during the 12 months prior to enrollment were collected. Data were compared between stable and unstable patients, classified based on the proportion of international normalized ratio (INR) values outside the therapeutic range.


RESULTS
The median proportion of out-of-range INRs among study participants was 44%; 28 patients had a higher proportion of INRs out-of-range and were included in the unstable group, with the remaining constituting the stable group. The median (IQR) number of clinic visits/year was higher among unstable versus stable patients [18 (15-22) vs. 16 (13-19); P = 0.03]. Higher warfarin doses, lower adherence, vomiting or diarrhea, and use of antiinfective agents were more common among unstable patients. Genotype was not associated with anticoagulation stability. After regression analysis, only poor adherence and gastrointestinal illness remained predictive of unstable anticoagulation. In a control group of Caucasians of similar age and sex distribution, poor adherence, but not gastrointestinal illness, was associated with unstable anticoagulation.


CONCLUSIONS
We conclude that poor warfarin adherence and gastrointestinal illness are major contributors to unstable anticoagulation in African Americans. Our data suggest that, similar to Caucasians, improving warfarin adherence rates may be an important mean to improve anticoagulation control in African Americans. In addition, close monitoring during acute illness may be particularly important in this population.
Cavallari
Larisa H
LH
Department of Pharmacy Practice, University of Illinois at Chicago College of Pharmacy, 833 S. Wood St, Room 164, Chicago, IL 60612-7230, USA. humma@uic.edu
Aston
Jonathan L
JL
Momary
Kathryn M
KM
Shapiro
Nancy L
NL
Patel
Shitalben R
SR
Nutescu
Edith A
EA
D001741:Black or African American; D000368:Aged; D000925:Anticoagulants / Q000008:administration & dosage* / Q000009:adverse effects / Q000097:blood; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D019934:International Normalized Ratio / Q000379:methods; D008297:Male; D008875:Middle Aged; D006899:Mixed Function Oxygenases / Q000097:blood; D010349:Patient Compliance; D011237:Predictive Value of Tests; D012189:Retrospective Studies; D064417:Vitamin K Epoxide Reductases; D014839:Vomiting / Q000097:blood / Q000139:chemically induced; D014859:Warfarin / Q000008:administration & dosage / Q000009:adverse effects / Q000097:blood
D000925:Anticoagulants; D014859:Warfarin; D006899:Mixed Function Oxygenases; D064417:Vitamin K Epoxide Reductases