US FDA
21 CFR Part 320 - Bioavailability and Bioequivalence Requirements
Plain-language explanation, inspection context and common violation patterns.
What it says
Part 320 establishes requirements for demonstrating a drug product's bioavailability, the rate and extent to which the active ingredient is absorbed and becomes available at the site of action, and for demonstrating bioequivalence between a generic product and its reference listed drug, typically through comparative pharmacokinetic studies.
Paraphrased for plain-language clarity. Always verify against the current published regulation text.
What it means in practice
- Bioequivalence demonstration is the scientific foundation underlying generic drug approval under the 505(j) pathway, establishing that a generic product performs equivalently to its reference product despite not requiring the full clinical development programme the original product underwent.
- Dissolution testing under USP <711> often serves as an in vitro surrogate correlating with in vivo bioavailability, meaning a well-designed, discriminating dissolution method can provide ongoing quality assurance that a product continues to perform as its original bioequivalence study demonstrated.
- Post-approval changes to formulation, manufacturing process or site can raise bioequivalence questions requiring reassessment, connecting this framework directly to the change management principles described in ICH Q12.
What FDA inspectors look for
- Whether post-approval manufacturing or formulation changes were assessed for potential impact on bioequivalence, with additional bioequivalence testing conducted where the change's nature warranted it.
- Whether ongoing dissolution testing continues to demonstrate the product performs consistently with what the original bioequivalence study established.
- This is primarily a product development and approval framework rather than a specific manufacturing practice inspected directly during a facility inspection, though its connection to dissolution testing and change control makes it practically relevant to ongoing quality operations.
Most common violation
A post-approval manufacturing or formulation change implemented without adequately assessing whether the change could affect bioequivalence to the originally approved and studied product.
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