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

The research examined how effectively a non-steroidal anti-inflammatory drug (NSAID) called methylsalicylate penetrates equine skin in different body areas. The study found significant regional differences, with greater and faster penetration observed through the skin in the leg region compared to the thorax and groin.

Methodology

• The study used skin harvested from five thoroughbred geldings, with samples taken from the thorax, groin, and leg (dorsal metacarpal) regions.
• These skin samples were then frozen at -20 degrees Celsius until required for testing.
• Methylsalicylate (MeSa) gel was applied to the defrosted full-thickness samples, which were set in diffusion cells.
• The researchers measured the penetration of MeSa and its active metabolic product, salicylate (Sa), through these skin samples over a 24-hour period.

Findings

• The results indicated significant regional differences in the penetration of Methylsalicylate through equine skin.
• The total salicylate (which includes both MeSa and Sa components) that penetrated the skin was significantly higher in the leg region.
• In numerical terms, the total salicylate penetration through leg skin was measured as 5491.3 h mg/L, compared to 3710.7 h mg/L through the thorax skin and 3571.5 h mg/L through the groin skin.
• Besides the total amount of salicylate penetration, the rate of penetration was also significantly higher through the leg skin, especially within the first 6 hours after application of the MeSa gel.

Conclusions

• The results support the conclusion that commercial MeSa formulations can be successfully used to achieve therapeutic salicylate levels under sites of topical application on horses.
• The more pronounced and faster response in the leg region, however, suggests that care should be taken with dosages and application areas, to avoid potential overdosing or under-dosing.