There is a widespread misconception that for a generic drug to be deemed bioequivalent to a branded drug, it must contain 80%-125% of the active ingredient that is present in the branded version. More correctly, bioequivalence is studied in randomized crossover trials that compare the generic drug with the reference agent, and the relevant outcome measures are pharmacokinetic (PK) parameters such as peak drug concentration and area under the curve, which describe the rate and extent of absorption of the drug. The ratio of each PK characteristic of the generic drug to the reference drug is computed; the ideal value of this ratio is 1:1, or just 1.00 (indicating a perfect match, or perfect bioequivalence). Because this ideal is probably unattainable, the US Food and Drug Administration requires that the 90% confidence interval of the PK ratio should lie between 0.80 and 1.25. For the entire 90% confidence interval to meet this requirement, the mean PK value of the generic product should actually lie quite close to that of the reference standard. Therefore, the variation between the generic and the reference is actually small. These concepts are explained in this article with the help of simple, easy-to-understand examples.
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