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# Maximal Usage Trial Monograph Guidance
- URL: https://www.fdaweb.com/maximal-usage-trial-monograph-guidance/
- Published: 2019-05-09T12:00:00.000Z
- Updated: 2026-09-15T01:25:48.000Z
- Author: David McFarland
- Tags: Drugs, #legacy-id-D5144072

FDA has published a guidance, *Maximal Usage Trials for Topically Applied Active Ingredients Being Considered for Inclusion in an Over-the-Counter Monograph: Study Elements and Considerations*, with recommendations for conducting *in vivo* absorption trials for topically applied active ingredients that are under consideration for inclusion in an over-the-counter drug monograph. The [document](https://www.fda.gov/media/124841/download?ref=fdaweb.com) says a maximal usage trial (MUsT) is a standard approach to assess the *in vivo* bioavailability of topical drug products intended for local therapeutic effects.

“Because information from a MUsT can help identify the potential for systemic exposure to a topically applied active ingredient,” FDA says, “such information can help inform an FDA determination of whether additional safety data are needed to support a finding that a topical OTC drug containing that active ingredient is generally recognized as safe and effective for its intended use.”

The guidance outlines agency recommendations for designing and conducting a MUsT for this purpose, including critical study elements, data analysis, and considerations for special topic areas, such as pediatrics and geriatrics. It also encourages sponsors to seek FDA feedback on their overall approach and the design of a particular study.