Are brand-name and generic warfarin interchangeable? A survey of Ontario patients and physicians.

BACKGROUND The issue of therapeutic equivalence has been a source of controversy in Canada since the approval of generic warfarin products in 2000. OBJECTIVES We surveyed Ontario patients and physicians on perceptions of generic warfarin and brand substitution. METHODS Self-administered questionnaires employed 7.0-point Likert scales of agreement. Patient participants were drawn from a thromboembolism clinic in Hamilton, Ontario. Physician participants were from a random sample of 375 Ontario family physicians, internists, cardiologists and hematologists. RESULTS Eighty-one patients responded: 52% female, mean age 63.4 years and 63% brand-name warfarin users. Overall, 33% of respondents agreed or strongly agreed that they would feel comfortable taking generic warfarin. However, seventeen percent agreed or strongly agreed that generic warfarin was neither as safe nor as effective as brand-name warfarin, with this view more common amongst patients taking brand-name than those taking generic warfarin. One hundred and ten (29.3%) physicians returned the survey--29% females, mean age 45.3 years, 22% family physicians. Forty-four percent agreed or strongly agreed that they would rather prescribe brand-name than generic warfarin for patients starting warfarin therapy, while 40.7% agreed or strongly agreed that they would not feel comfortable switching from brand-name to generic warfarin. However, only 19.4% of physicians who had switched patients from brand-name to generic warfarin actually reported difficulties in managing the switch. CONCLUSION While most patients and physicians appear to have accepted the principle of therapeutic equivalence of generic and brand-name warfarin, a sizable minority has concerns that could influence prescribing and compliance.