The FDA has deemed the generic formulations of warfarin bioequivalent to the brand named warfarin: Coumadin®. The process of generic drug approval is quite different than brand named drug processes as illustrated below.

Major differences in drug development between brand and generic drug development include: the clinical safety, efficacy and laboratory studies phase work which, on average, take between 6-7 years and millions of dollars.

Generic drug companies have been described as “ride the coat-tails” of big pharmaceutical companies and arrive to market the day the brand (innovator) drug’s patent and market exclusivity run out.

Obstacles avoided by generic drug companies include: drug molecules that don’t make it to the market but cost millions to their failure, market development costs and education of professionals and consumer. The net result is a cost reduction between 50-75%. Some savings are passed on to consumers.

For patients – generic drugs represent an approximate 30% savings for the same dose of the brand drug. Generic warfarin can be purchased for as little as $4 for a month’s supply for selected strengths at large retail super-stores that offer pharmacy services.

Generic interchangeability has not be studied

A primary concern of using generic warfarin is the lack of studies showing the interchangeability between generic warfarin products. Studies have been conducted to show generic warfarin bio-availability similar to that of brand Coumadin®, however, no studies have been conducted to demonstrate the safe inter-change between one generic and another.

More than one generic warfarin is available. There is heavy competition for shelf space in pharmacies making it possible for generic warfarin “A” to be available one month and generic warfarin “B” another. Patients cannot control which generic warfarin is dispensed by their pharmacist as pharmacies normally carry only one generic line of warfarin in any given month.

Filler agents

A second issue of possible concern includes filler agents used in generic formulations. Some clinics restrict generic warfarin use for their patients because of the non-active ingredients that may influence tolerability or tablet performance. Filler agents include the non-active portion of the tablet including agents (binding) that keep the tablet together.

An unexpected INR test result or series of tests should result in the examination of the tablet being taken. As a general rule, healthcare professionals support patients remaining either on the brand, or on a particular manufacturer’s generic formulation - but not interchanging between generic manufacturer’s generic warfarin.

To reduce INR blood test fluctuations, patients are encouraged to remain consistent in their choices. Checking the shape, color and manufacturer of the warfarin dispensed will help rule out the potential for generic to generic variability.