Dermal Toxicology Application Area Changes As Compared To A Theoretical Total Surface Area Of Hanford Miniature Swine Over 18 Weeks

By Madsen T., Liu J., Brown L., and Bouchard G. F.

Dermal toxicology studies are often conducted in growing animal models, where the test compound is applied to a designated dermal application area (DAA), typically set as a specific ratio of the total body surface area (TBSA). Given the significant growth that occurs during the juvenile period, the DAA may be affected over the course of a chronic study. The objective of this study was twofold: (1) to determine whether the ratio of DAA to TBSA changes proportionally over time with the growth of miniature swine, and (2) to compare three different TBSA calculation formulas.

To achieve this, the ratio of DAA (cm² surface area) to TBSA was calculated at periodic intervals over an 18-week period in 16 male and 16 female Hanford miniature swine, all approximately four months old and averaging 14 kg at study initiation. Each animal had two mid-back 5 cm × 5 cm (25 cm²) DAAs, positioned on either side of the spine. TBSA (m²) was calculated using the widely recognized Spector formula (9.5 × BW(g)²/³ / 10,000), as well as the Brodie and Wachtel formulas.

Using the Spector formula, the mean DAA-to-TBSA ratio at Weeks 0 and 8 (N=32) for the application area was 0.46% ± 0.04 and 0.51% ± 0.06 (MEAN ± SD), respectively. After Week 8, subsequent periodic measurements of the DAA-to-TBSA ratio remained stable, indicating that the growth of both DAA and TBSA occurred proportionally over time. The correlation between the three TBSA calculation methods was greater than 0.99, demonstrating consistency among them. These findings confirm that the well-established Spector method is a valid and reliable choice for TBSA calculations in juvenile miniature swine.