bioequivalence

Bioequivalence is the proof that two medicines, though made by different companies or formulations, behave the same once inside you. If a generic tablet releases its drug into your blood at the same speed and to the same total amount as the brand-name original, doctors can switch between them without expecting any clinical difference. It is the scientific handshake that lets cheaper generics replace innovator products.

Operationally, bioequivalence is judged by comparing the rate and extent of absorption of the test and reference products in a crossover study, usually in healthy volunteers. The key pharmacokinetic measures are AUC (extent) and Cmax (rate, with Tmax noted). Regulators require that the 90% confidence interval for the test-to-reference ratio of these parameters falls within 80.00–125.00% — a deliberately symmetric range on the log scale. Meeting this means the products are statistically indistinguishable in delivery.

Bioequivalence is narrower than pharmaceutical equivalence (same drug, dose and form) and presupposes it: two products can be pharmaceutically equivalent yet not bioequivalent if a formulation difference alters dissolution or absorption. For some BCS Class I and III drugs the in-vivo study can be waived in favour of dissolution testing (a biowaiver). Narrow-therapeutic-index drugs may face tighter acceptance limits because small exposure differences matter clinically.