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# Maximal Usage Trial Draft Guidance
- URL: https://www.fdaweb.com/maximal-usage-trial-draft-guidance/
- Published: 2018-05-22T12:00:00.000Z
- Updated: 2026-09-15T00:06:46.000Z
- Author: David McFarland
- Tags: Drugs, #legacy-id-D5141505

FDA has issued a draft guidance, *Maximal Usage Trials for Topical Active Ingredients Being Considered for Inclusion in an Over-the-Counter Monograph: Study Elements and Considerations*, with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 the subject ingredients. The [document](https://www.fda.gov/downloads/Drugs/GuidanceComplianceRegulatoryInformation/Guidances/UCM608356.pdf?ref=fdaweb.com) says a maximal usage trial (MUsT) is a standard approach to assess the *in vivo* bioavailability of topical drug products.

“The methodology described in this guidance adapts MUsT principles for active ingredients being considered for inclusion in an over-the-counter monograph,” the guidance says. “Because information from a MUsT can help identify the potential for systemic exposure to a topically applied active ingredient, such information can help inform an FDA determination of whether additional safety data are needed to support a finding that an OTC drug containing that active ingredient is generally recognize as safe and effective for its intended use.”

The document 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 pediatric and geriatrics. It also is said to encourage study sponsors to seek feedback from FDA on their overall approach and the design of a particular study.