Cutaneous Biodistribution: A High-Resolution Methodology to Assess Bioequivalence in Topical Skin Delivery

Abstract

A draft guideline from the European Medicines Agency (EMA) highlights the need for methods to assess the quality/equivalence of topical drug formulations. The "cutaneous biodistribution method", which provides insight into a drug's spatial distribution in the epidermis/dermis, was used to compare cutaneous bioavailability of econazole nitrate (ECZ) from a reference medicinal product (RMP) and two approved bioequivalent generic creams under finite dose conditions. Statistically significant differences between the ECZ biodistributions from the RMP/Generics were determined and used with acceptance criteria based on those from the EMA to evaluate bioequivalence. In porcine skin, ECZ deposition in total skin, epidermis, upper and lower dermis from Generic 1 was within the acceptance interval, contrary to Generic 2, which was marginally below it. For human skin, Generic 1 deposition was marginally above the acceptance interval and not bioequivalent. The results were consistent with those using the EMA's acceptance intervals using the ratio of the mean ECZ depositions of Generic 1 and the RMP. Differences identified using this data-rich technique may not translate to observable differences in clinical efficacy; however, generics with non-statistically different biodistributions to the RMP should have a comparable clinical effect. The cutaneous biodistribution method could benchmark the development of topical generic products.

Keywords: bioequivalence; cutaneous biodistribution profile; econazole nitrate; generics; reference medicinal product; topical skin delivery.

Figure 1

Inter-day reproducibility of the cutaneous biodistribution profile of ECZ in porcine skin lamellae (2 × 20 µm + 19 × 40 µm) to 800 µm (full-depth) for the three formulations: (a) reference medical product (ECZ 1% reference medicinal product (RMP) cream), (b) ECZ 1% Generic cream 1 and (c) ECZ 1% Generic cream 2. Tested groups: Day 1 (●) and Day 2 (○). (Mean ± CI_90%; n = 6). p-values were calculated using a Student’s t test; statistically significant differences are denoted by asterisks (* p < 0.05; ** p < 0.005).

Figure 2

Cutaneous biodistribution profile of ECZ: (a) in porcine skin lamellae (2 × 20 µm + 19 × 40 µm) to 800 µm (full depth) and (b) as a function of position in the anatomical regions of the skin (epidermis, upper and lower dermis) and in total skin. Tested groups: reference medical product (ECZ 1% RMP cream) (●) and non-bioequivalent “negative control” (ECZ 1% ethanolic solution) (○). (Mean ± CI_90%; n = 12 and n = 6, respectively). Intervals of acceptance criteria were calculated based on the mean ECZ deposition from the RMP; () interval of 80.00–125.00% and () interval of 69.84–143.19%. P-values were calculated using a Student’s t test; statistically significant differences are denoted by asterisks (* p < 0.05; ** p < 0.005; *** p < 0.0005; **** p < 0.00005).

Figure 3

Cutaneous biodistribution profile of ECZ: (a) and (c) in porcine skin lamellae (2 × 20 µm + 19 × 40 µm) to 800 µm (full-depth) and (b) and (d) as a function of position in the anatomical regions of the skin (epidermis, upper and lower dermis) and in total skin. Tested groups: reference medical product (ECZ 1% RMP cream) (●) and generic products (ECZ 1% Generic cream 1 and ECZ 1% Generic cream 2) (○). (Mean ± CI_90%; n = 12). Intervals of acceptance criteria were calculated based on the mean ECZ deposition from the RMP; () interval of 69.84–143.19%. P-values were calculated using Student’s t test; statistically significant differences are denoted by asterisks (* p < 0.05).

Figure 4

Cutaneous biodistribution profile of ECZ: (a,c) in human skin lamellae (2 × 20 µm + 19 × 40 µm, to 800 µm (full-depth) and (b,d) as a function of position in the anatomical regions of the skin (epidermis, upper and lower dermis) and in total skin; Tested groups: reference medical product (ECZ 1% RMP cream) (●) and generic product (ECZ 1% Generic cream 1) (○). (Mean ± CI_90%; n = 24 from two donors for (a,b) and n = 12 from one donor for (c,d)). Intervals of acceptance criteria were calculated based on the mean ECZ deposition from the RMP; () interval of 69.84–143.19%. p-values were calculated using Student’s t test analysis; statistically significant differences are denoted by asterisks (* p < 0.05; ** p < 0.005).

Figure 5

Ratio of mean ECZ depositions from the ECZ 1% Generic cream 1 and the RMP (●): (a) in porcine skin lamellae (2 × 20 µm + 19 × 40 µm to 800 µm (full-depth) and (b) as a function of position in the anatomical regions of the skin (epidermis, upper and lower dermis) and in total skin, (c) in human skin lamellae (2 × 20 µm + 19 × 40 µm), from 2 donors, to 800 µm (full-depth), and (d) as a function of position in the anatomical regions of the skin (epidermis, upper and lower dermis) and in total skin. (Ratio ± CI_90%; n = 12 for (a,b) and n = 24 for (c,d)). Intervals of acceptance criteria were chosen according to the EMA guidelines; () interval of 0.6984–1.4319.