Evaluating the impact of study-level factors on warfarin control in U.S.-based primary studies: a meta-analysis.
OBJECTIVE
The effect of study-level factors on the proportion of time spent with International Normalized Ratio (INR) values inside the therapeutic range in patients treated with warfarin in the United States was evaluated.


METHODS
Studies evaluated in a previous meta-analysis were screened for potential inclusion, in addition to a systematic literature search of databases from January 2005 through February 2008. Studies were included if they (1) contained at least one warfarin dosing group that enrolled >25 patients for whom INR control was monitored for at least three weeks, (2) included only patients treated in the United States, (3) used a patient-time approach to report outcomes, and (4) reported proportion of time spent in the therapeutic INR range. Analyses included determining how study-level factors, such as study setting, year of study publication, INR interpolation method, study design, and presence of self-management, affected outcomes.


RESULTS
Twenty-four studies, including a total of 43 unique warfarin groups, were included in the analysis. Overall, patients spent 57% of their time in the therapeutic range (95% confidence interval [CI], 55-59%). Compared with anticoagulation clinics, community management resulted in less time (-13%; 95% CI, -18% to -7.9%) and prospective studies resulted in more time (7.3%; 95% CI, 1.5-13.1%) spent in the therapeutic range than retrospective studies. When studies from both the United States and Canada were included, similar results to those in the base-case analysis were seen; however, study year and interpolation method were also found to be significant modifiers of INR control.


CONCLUSIONS
Patients included in the meta-analysis maintained INR values within the therapeutic range 57% of the time, although the use of anticoagulation clinic services appeared to be superior to standard community care in this regard. However, patients treated in anticoagulation clinics had INR values within the therapeutic range less than two thirds of the time.
Department of Pharmacy, Brigham and Women's Hospital, Boston, MA, USA.
Deborah A
DA
Cios
William L
WL
Baker
Stephen D
SD
Sander
Olivia J
OJ
Phung
Craig I
CI
Coleman
D000554:Ambulatory Care Facilities; D000925:Anticoagulants / Q000008:administration & dosage / Q000009:adverse effects / Q000627:therapeutic use*; D003153:Community Health Services; D006801:Humans; D019934:International Normalized Ratio; D011446:Prospective Studies; D016032:Randomized Controlled Trials as Topic / Q000379:methods*; D012189:Retrospective Studies; D016896:Treatment Outcome; D014481:United States; D014859:Warfarin / Q000008:administration & dosage / Q000009:adverse effects / Q000627:therapeutic use*
D000925:Anticoagulants; D014859:Warfarin