On May 21^st, 2018 the FDA released draft guidance for Maximal Usage Trials (MUsT). The draft guidance outlines the methodology required for testing active ingredients in topical products being considered for inclusion in an over-the-counter drug monograph, including antiseptic products. This type of testing is intended to provide data on the dermal penetration of and systemic exposure to topical products and their active ingredients.MUsT studies are expected to replicate real-world use conditions that result in the maximum amount of dermal exposure and absorption. In order to structure these trials per this current draft guidance, study developers should consider:

• Existing or anticipated label use instructions
• Whether targeted safety assessments should be included in the study protocol
• FDA input specific to the formulation or active under evaluation

The FDA draft guidance is relatively detailed and includes information regarding study population composition and size (with an emphasis on representative population enrollment), instructions for product application in partial-body or whole-body coverage cases, and general requirements for blood sample collection. Direction related to pediatric and geriatric MUsT testing is also included.

Due to the nature of these studies, which can vary significantly from formulation to formulation, CRL Austin recommends setting up a call with our scientific staff to ensure that your testing plan is developed appropriately for your active ingredient, project budget, and testing objectives.

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