(T1030-11-73) Industry Understanding for Overcoming Challenges to Demonstrate IVPT Sensitivity by Dose Amount and Dose Duration Modulation as per FDA Draft Guidance for Topical Drug Products

Purpose: In vitro permeation testing (IVPT) examines the penetration profile of active pharmaceutical ingredient across a skin tissue membrane (fresh, flash frozen, or cadaver) using Franz diffusion cell systems containing typically aqueous receiving media. IVPT method development and validation studies for supporting a demonstration of bioequivalence of the reference listed drug and the proposed generic product include various parameters such as equipment, skin and receptor solution qualifications, demonstration of dose depletion, discrimination sensitivity, and so on. Due to the complex nature of skin and the limited permeation of molecules based on various physicochemical properties, the demonstration of discrimination sensitivity using human skin tissue involves many scientific challenges. TER001 is a lipophilic molecule, having a 5.6 log partition coefficient (LogP) and around 800 g/mol molecular weight, which makes its passive delivery across the skin limited and challenging. This abstract focuses on discussing some of the challenges faced during IVPT method development as per FDA draft guidance.

Methods: To conduct studies for the development and validation of an IVPT method for TER001, a sensitive and robust analytical method using LC-MS/MS for quantitation was developed. IVPT feasibility studies using ex vivo dermatomed human skin on static Franz diffusion cells to optimize various parameters such as selection of receiving media to maintain sink conditions, sampling technique, and the duration length of the study were performed. Next, a dose amount modulation study to evaluate the amount of TER001 permeated and the flux profile from 5, 10, 15, 30, 60, and 90 mg dose amount was conducted. A duration modulation study where the product was applied for a duration of 24 hours and then wiped off was then conducted. Based on the findings from this study, a study with dose amount (15 mg, 30 mg, and 60 mg) modulation and dose duration modulation with a washout at 24 hours (Figure 1) to demonstrate discrimination sensitivity was conducted.

Results: 1XPBS + 0.01% gentamicin with a minimum amount of Brij O20 was selected as the receiving media based on data from solubility and adsorption studies. Full receptor sampling as the sampling technique and 120 hours as the duration of the study to see a decline in flux over time was optimized. The results of the dose amount modulations indicated some discrimination between the dose amounts. However, the flux profile did not demonstrate dose depletion or a maximum peak flux and subsequent decline in the flux thereafter as recommended by the FDA draft guidance. The results of dose duration modulation where the product was wiped off after 24 hours showed that the average TER001 permeated across tissues within 96 hours for tissue replicates exposed to a washout event was lesser than for the tissue replicates not exposed to a washout event (positive control). A well-defined flux, demonstrating a J_max and decline in the flux thereafter was seen for cells exposed to washout event compared with positive control (no washout event) as shown in Figure 2. Finally, the results of the study with a modulation of dose amount and the duration with a washout at 24 hours demonstrated a clear discrimination between the three dose groups with a well-defined flux, a J_max and decline in the flux thereafter for all three dose amounts, thereby demonstrating IVPT method sensitivity.

Conclusion: This development work resulted in optimization of various IVPT parameters to obtain a typical IVPT flux profile in parallel with the development of a robust LCMS method for analysis of TER001. IVPT sensitivity by dose amount and dose duration modulation as per FDA draft guidance for topical drug products was successfully demonstrated.

References: In Vitro Permeation Test Studies for Topical Drug Products Submitted in ANDAs. Guidance for Industry, US Food and Drug Administration. (October 2022).

Figure 1: Schematic representation of dose duration modulation IVPT methodology.

Figure 2: Average permeation profile and flux profile for TER001 for tissues exposed to washout event and not exposed to washout event.