Lindmik Research I FDA Update General Transdermal and Local Drug Delivery System Guidelines
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The US Food and Drug Administration (FDA) on Wednesday (April 13, 2023 Beijing time) submitted two revised draft guidelines for generic drugs using transdermal and topical drug delivery systems (TDS). The revised guidelines explain multiple technical clarifications that initiators of Simplified New Drug Applications (ANDA) should consider when submitting pre market applications.
Women who use transdermal patches for hormone replacement therapy. (Source: iStock)

The revised document updates the previous draft version released in 2018 and clarifies the organization's evolutionary thinking on how to evaluate generic TDS products. (Related: The latest batch of FDA product specific guidelines focus on topical and transdermal drugs, regulatory focus, October 9, 2018)

First guide

In the first guideline, which involves evaluating the adhesion of TDS products, the FDA stated that it is updating the document to clarify the appropriate methods that reporting companies should consider when measuring the surface area of TDS products expected to adhere to patient skin, and how to statistically analyze this data.

The FDA stated that "the amount of drug delivered to and through the patient's skin by TDS depends partly on the surface area of the drug administered." "Under the usage conditions included in the RLD label of the reference drug, the entire contact surface area of TDS should adhere consistently to the patient's skin throughout the entire wearing period. When TDS loses adhesion during the wearing process, the amount of drug delivered to the patient may decrease

Usually, the FDA habitually uses visual assessment and/or dot matrix templates and a five point adhesion scale to estimate the adhesion of TDS to the skin. However, in the updated draft guidelines, the agency encourages applicants to explore alternative scales and discuss them with reviewers during the pre ANDA meeting. The FDA states: "If applicants use levels different from the five point adhesion levels described below to record TDS adhesion measurements, they should report each TDS adhesion measurement value as a score based on the selected level and the corresponding score point adhesion scale based on the five points

The guide also states that although photo evidence is not currently used for automated or photometric analysis, reporting companies can use it to support visual observation of TDS adhesion over time.

Second guide

The second draft guideline proposes recommendations for skin irritation and sensitization (I/S) of TDS products for the design and conduct of in vivo evaluation studies. Compared to the 2018 draft guidelines, the new guidelines clarify recommendations for designing and conducting studies that evaluate the in vivo skin I/S potential of the proposed TDS product.

The FDA points out that the ingredients and composition of TDS formulations, including the properties of the drug substance and/or the degree to which TDS materials prevent the transfer of water vapor from the skin, as well as other factors such as environmental humidity or conditions, may irritate the skin or cause allergic reactions. This reaction may make patients feel unhappy and may affect patient compliance, skin permeability, and/or TDS adhesion to the skin

Attached are two revised draft guide covers:
Therefore, the institution stated that the declaring enterprise should conduct comparative evaluation and research on TDS products and their reference products. This includes skin I/S studies on human subjects to demonstrate that it is not inferior to the reference product.

The skin I/S study aims to compare the similarity between [test] and [reference] TDS products in terms of the likelihood of causing irritation and/or sensitization reactions, "the FDA pointed out." TDS may only cause these reactions in some patients who use this product, but even if the frequency of this occurrence is low, adverse reactions may affect thousands of people

In order to evaluate the potential of I/S, the FDA stated that applicants should compare test products and reference products among at least 200 subjects, and should perform under "stimulus conditions" where the product is repeatedly removed and reapplied to the same part of the skin to maximize the likelihood of I/S response.

This guide also clarifies when in vivo studies may not be necessary to evaluate the sensitization potential of TDS products, and provides detailed instructions on how reporting companies can use alternative scoring scales or methods to compare the I/S between tested and reference TDS products.

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