Regional differences in the in vitro penetration of hydrocortisone through equine skin.

This research investigates how the drug hydrocortisone penetrates the skin of horses in different body regions. The researchers found that the drug penetrates faster through skin on the leg but is retained less at this site compared to the thorax and groin areas.

Objective and Methodology

• The study set out to address the lack of knowledge about the absorption and retention of the steroid hydrocortisone through different regions of horse skin. Commercial formulations of the drug are available for horses, but their absorption and retention have not been previously assessed. The researchers specifically looked at the thorax, groin, and leg regions.
• To conduct the study, skin was taken from the aforementioned regions from five Thoroughbred geldings. The skin was then frozen until needed for the experiment.
• The experiment used Franz-type diffusion cells to study the absorption and retention of the drug. The skin samples were placed in these cells with a saturated solution of hydrocortisone. The solution also contained radiolabeled hydrocortisone, which allowed the researchers to track and measure it as it moved through and remained within the skin samples over a 24-hour period.

Results

• The study found significant regional differences in the penetration and retention of hydrocortisone in horse skin. When the drug was applied to the leg, the maximum flux (rate of movement) was significantly higher than when applied to the skin from the thorax or groin.
• At the same time, whereas the hydrocortisone penetrated more quickly on the leg, significantly less of it was retained within the leg skin after 24 hours compared with the other regions. This suggests that while the drug might absorb faster through the skin at the leg, it might not be retained long enough at the site to have its full effect.

Implication

• These results provide practical insights for the application of topical hydrocortisone to horses. If the aim is to achieve higher systemic drug concentrations quickly, then the leg may be the best application site. However, in the case of treating local inflamed tissue, applying the drug to the thorax or groin might result in greater efficacy due to the longer retention of the drug within the skin at these sites.