DEFINITION of 'Bioequivalence'

Bioequivalence is the similarity of two drugs that share the same desired outcome for patients. Pharmaceutical equivalence means two drugs release the active ingredient into the bloodstream at the same amount and same rate. When assessing how well a generic drug works, scientists evaluate its bioequivalence to the name-brand version.

BREAKING DOWN 'Bioequivalence'

Bioequivalence is determined by pharmacokinetic studies to determine whether a commercially available brand product and a potential to market generic version share core attributes. For a generic drug manufacturer to get the U.S. Food and Drug Administration’s (FDA) stamp of approval, they must prove it is pharmaceutically equal to the name-brand version. A drug maker must also get FDA approval before marketing or selling a different version of an approved drug. For example, it must prove a once-a-week tablet is bioequivalent to a daily tablet. In addition, the FDA has different bioequivalence standards depending on whether the drug is taken as a pill, injection, patch, inhaler or through another method. When a generic drug is not bioequivalent to the name-brand version, it might still be approved for another use, but not be approved as a substitute for the name-brand version.

Unlike their name-brand counterparts, generic drugs usually don’t need to go through the full clinical trial process to get approved because generic drugs only have to be bioequivalent. The company applying for approval to market the generic drug must only test the generic drug against the brand-name drug on two small groups of test subjects, draw timed blood samples from each patient, and show through statistical analysis that any difference in the drug’s bioavailability in participants taking the brand name version versus participants taking the generic version is not clinically significant.

It is easier to make a bioequivalent form of a traditional pill or injectable drug than to make a bioequivalent form of a biologic drug. As a result, the generic versions of biologic drugs, called “biosimilars,” may have to undergo clinical trials to gain approval.

'Bioequivalence' Issues

While bioequivalent drugs offer patients many benefits, some concerns still remain. Bioequivalence problems have been reported by physicians and patients that many approved generic drugs do not have the same desired impact as the branded counterparts. Certain classes are more prone to these discrepancies from specific chemical reactions. Some of these include poorly absorbed drugs, chiral drugs and other complex delivery mechanisms. Physicians are cautious in switching patients from branded to generic products, or between different generic manufacturers when prescribing ant-epileptic drugs and blood thinners.  

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