Brand Name versus Generic Warfarin

A Systematic Review of the Literature

Francesco Dentali, M.D.; Marco P. Donadini, M.D.; Nathan Clark, Pharm.D.; Mark A. Crowther, M.D.; David Garcia, M.D.; Elaine Hylek, M.D.; Dan M. Witt, Pharm.D.; Walter Ageno, M.D.


Pharmacotherapy. 2011;31(4):386-393. 

In This Article

Literature Search Strategy

Study Selection

The literature search was performed using the MEDLINE (1950–August 2010) and EMBASE (1980–August 2010) databases. We used multiple key words and standardized terminology. Relevant abstracts were also searched among those presented at the meetings of three scientific societies and published online: American Society of Hematology (2004–2009), International Society of Thrombosis and Haemostasis (2003–2009), and American College of Clinical Pharmacy (1999–2010). Manual search of the reference lists of the included articles was also performed. Finally, experts in anticoagulation were contacted to obtain information about other potentially relevant publications.

Studies were considered relevant if they were original randomized controlled trials (RCTs) or retrospective or prospective cohort studies, enrolled patients receiving oral anticoagulant treatment, and compared any approved generic warfarin with brand name warfarin using at least one clinical, laboratory, or management outcome. We excluded studies if they enrolled healthy volunteers or did not evaluate any of the required outcomes (see Data Extraction section).

Study Quality Assessment

Study quality was evaluated in RCTs according to a validated scale,[10] taking into account randomization process, allocation concealment, double blinding, and description of withdrawals and dropouts.

Although in observational studies the use of quality scoring systems or quality scales is controversial, study quality was assessed according to the following items for cohort studies: type of study (prospective or retrospective), patient selection (consecutive patients without potential bias of selection), and total number of patients lost to follow-up (≤ 5% or > 5% of patients).[11]

Data Extraction

Data were extracted from each selected study for any of the following outcomes:

  • Clinical: bleeding and thrombotic events, death, hospitalization

  • Laboratory: mean INR, inter- and intra-subject INR variability, proportion of INRs in or out of the therapeutic range, time in therapeutic range, difference in mean INR before and after switching from brand name to generic warfarin or vice versa

  • Management: number of anticoagulation clinic visits, number of INR tests, number of dosage adjustments, daily warfarin dose, medical resource utilization

The selection process, quality assessment, and data extraction were performed independently in duplicate by two authors (F.D. and M.P.D.). Disagreement was resolved by discussion.

Statistical Analysis

In general, a formal combined meta-analysis of all the included studies was not appropriate, due to the heterogeneity of the population considered, the modality of data presentation, and the different outcomes assessed in each trial. Therefore, a narrative synthesis of collected data was undertaken. Data are presented as mean, percentage, and range of variation.


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