Patch Adhesion Is Part of Delivery Evidence
FDA's final ANDA guidance measures patch adhesion across the full labeled wear period, under conditions that reflect use.
Contact area changes the delivery question
A transdermal or topical delivery system needs to stay in contact with skin during its labeled wear period. If part of a patch lifts, the area available for drug delivery changes. FDA’s July 2026 final guidance explains why adhesion is measured across the full wear period when evaluating a proposed generic system against its reference product. The guidance concerns studies supporting abbreviated new drug applications (ANDAs); it does not set an adhesion test for every topical format. [1]
Observe the whole wear period
FDA recommends testing the product design intended for market. A change in ingredients, backing, or manufacturing can affect adhesion. The guidance calls for observations at multiple, reasonably spaced times: at least every 12 hours for a 72-hour system, and at least daily for a seven-day system. The study should reflect labeled use conditions, including routine showering when applicable. Investigators should not press a lifted edge back into place or secure it with an overlay. [1]
Adhesion is scored at each time point. Photographs can support a visual estimate, but the final guidance does not use them for automated or photometric measurement. The full series matters because a patch that adheres well at application may not do so later. [1]
For development teams, the broader lesson is to measure a delivery system under the conditions in which it will be used. The FDA’s patch-specific scoring should not be transferred to creams or serums. Those formats need tests suited to their own formulation, target tissue, and use conditions.