Generic Warfarin: Implications for Clinical Practice and Perceptions of Anticoagulation Providers

ABSTRACT

For more than 50 years, Coumadin^® was the dominant warfarin sodium product available in the United States. The approval of generic formulations of warfarin sodium has generated much debate over the therapeutic equivalency and the appropriateness of therapeutic substitution for the innovator product. Despite an AB rating by the Food and Drug Administration (FDA) and recent studies documenting successful switch programs from brand name to generic, much controversy remains concerning the approval process for generic formulations and whether substitution for the innovator product is appropriate. The healthcare professionals affected most by these questions are those working in specialized anticoagulation clinics. We conducted a survey to determine the current practice, experience, and views of healthcare professionals practicing in anticoagulation clinics regarding the substitution of generic products. In addition, the survey sought to identify factors important to healthcare professionals when deciding to use generic or brand name warfarin. Many of these healthcare professionals, primarily pharmacists and nurses, are resistant to generic warfarin substitution and prefer to use the innovator product. These perceptions may change over time as additional data showing comparative therapeutic outcomes between generic and brand name formulations are published.

KEYWORDS

Warfarin - generic brand - bioequivalency - anticoagulation providers

REFERENCES

• 1 Ansell J E. Oral anticoagulant therapy-50 years later.  Arch Intern Med. 1993;  153 586-596
• 2 DeCara J M, Croze S, Falk R H. Generic warfarin. A cost-effective alternative to brand-name drug or a clinical wild card?.  Chest. 1998;  113 261-263
• 3 Wittkowsky A K. Generic warfarin: implications for patient care.  Pharmacotherapy. 1997;  17 640-643
• 4 Meyer M, Chan K, Bolton S. Generic warfarin: implications for patient care-another view.  Pharmacotherapy. 1998;  18 884-886
• 5 Benson S R, Vance-Bryan K. In favor of Coumadin over generic warfarin.  Am J Health Syst Pharm. 1998;  55 727-729
• 6 Haines S T. Reflections on generic warfarin.  Am J Health Syst Pharm. 1998;  55 729-733
• 7 FDA position on product selection for ‘narrow therapeutic index’ drugs.  Am J Health Syst Pharm. 1997;  547 1630-1632
• 8 Benet L Z, Goyan J E. Bioequivalence and narrow therapeutic index drugs.  Pharmacotherapy. 1995;  15 433-440
• 9 Hirsh J, Dalen J E, Deykin D et al.. Oral anticoagulants. Mechanism of action, clinical effectiveness, and optimal therapeutic range.  Chest. 1995;  108(Suppl 4) 231S-246S
• 10 The United States Pharmacopeia .Approved Drug Products and Legal Requirements, 18th ed. Rockville, MD; USP Convention, Inc. 1998
• 11 Ansell J E, Hughes R. Evolving models of warfarin management: anticoagulation clinics, patient self-monitoring, and patient self-management.  Am Heart J. 1996;  132 1095-1100
• 12 Wagner J L, Dent L A. Epistaxis associated with elevation of INR in a patient switched to generic warfarin.  Pharmacotherapy. 2000;  20 240-243
• 13 Pfizer Package Insert: Viagra. New York; Pfizer 2000
• 14 Hope K A, Havrda D E. Subtherapeutic INR values associated with a switch to generic warfarin.  Ann Pharmacother. 2001;  35 183-187
• 15 DeMonaco H J, Irby B T. Warfarin sodium: “curiouser and curiouser!”.  Mass Gen Hosp Drug Ther. 1997;  7 1-3
• 16 Warfarin sodium. Package Insert. Pomona, NY; Barr Laboratories 1999
• 17 Apothecon Package Insert: Warfarin sodium. Princeton, NJ; Apothecon 1999
• 18 Taro Pharmaceuticals Package Insert: Warfarin sodium. Hawthorne, NY; Taro Pharmaceuticals 2001
• 19 Richton-Hewett S, Foster E, Apstein C S. Medical and economic consequences of a blinded oral anticoagulant brand change at a municipal hospital.  Arch Intern Med. 1988;  148 806-808
• 20 Therapeutic equivalence of generic drugs (letter to health care practitioners). Federal Drug and Food Administration. Available at: http://www.fda.gov. Accessed January 28, 2004
• 21 Neutel J M, Smith D HG. A randomized crossover study to compare the efficacy and tolerability of Barr warfarin sodium to the currently available Coumadin^® .  Cardiovasc Rev Rep. 1998;  19 49-59
• 22 Handler J, Nguyen T T, Rush S et al.. A blinded, randomized, crossover study comparing the efficacy and safety of generic warfarin sodium to Coumadin^® .  Prev Cardiol. 1998;  4 13-20
• 23 Swenson C N, Fundak G. Observational cohort study of switching warfarin sodium products in a managed care organization.  Am J Health Syst Pharm. 2000;  57 452-455
• 24 Weibert R T, Yeager B F, Wittkowsky A K et al.. A randomized, crossover comparison of warfarin products in the treatment of chronic atrial fibrillation.  Ann Pharmacother. 2000;  34 981-988
• 25 Milligan P E, Banet G A, Waterman A D et al.. Substitution of generic warfarin for Coumadin in an HMO setting.  Ann Pharmacother. 2002;  36 764-768
• 26 Witt D M, Tillman D J, Evans C M et al.. Evaluation of the clinical and economic impact of a brand name-to-generic warfarin sodium conversion program.  Pharmacotherapy. 2003;  23 360-368