According to the FDA, a generic drug must be identical to the proprietary drug with regard to active ingredients, dosage form, safety, strength, route of administration, quality, performance characteristics, and intended use. These similarities support "bioequivalence," which is determined based on the relative bioavailability of the brand-name medicine versus the generic medicine.
The FDA defines bioequivalence as "the absence of a significant difference in the rate and extent to which the active ingredient or active moiety in pharmaceutical equivalents or pharmaceutical alternatives becomes available at the site of drug action when administered at the same molar dose under similar conditions in an appropriately designed study."
According to the FDA, bioavailability refers to "…the extent and rate to which the active drug ingredient or active moiety from the drug product is absorbed and becomes available at the site of drug action." Bioavailability requirements for generic drugs must statistically demonstrate a 90% confidence interval (ie, a bioavailability range of 80%-125%) compared with the brand name drug. This is measured by comparing the area under the concentration curve and maximum concentration of each drug.
Although the active ingredients in generic drugs are the same as their brand-name counterparts, the inactive ingredients and manufacturing methods vary (eg, use of different salt formulation and excipients).
Learn more about FDA regulations for generic drugs.
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Cite this: Mary L. Windle. Fast Five Quiz: Generic Medications - Medscape - Nov 22, 2019.