Regional differences in the in vitro penetration of methylsalicylate through equine skin.
Authors: Mills P C, Cross S E
Journal: Veterinary journal (London, England : 1997)
Summary
# Editorial Summary: Regional Skin Penetration of Methylsalicylate in Horses Topical anti-inflammatory preparations formulated for human use are routinely applied to horses, yet their ability to penetrate equine skin—which differs considerably in thickness and structure across body regions—remained largely uncharacterised. Mills and Cross applied methylsalicylate gel to full-thickness skin samples from the thorax, groin, and dorsal metacarpal region of five Thoroughbreds, measuring both parent compound and salicylate metabolite penetration over 24 hours using in vitro diffusion cells. Leg skin demonstrated significantly superior drug penetration, with total salicylate bioavailability (area under curve) approximately 48% higher than thoracic skin and 54% higher than groin skin, alongside a notably faster initial absorption rate in the first six hours. These findings suggest that whilst commercial methylsalicylate formulations can achieve therapeutic concentrations beneath application sites, clinicians should expect considerably faster onset and greater efficacy when treating distal limb conditions compared to injuries on the trunk—information of particular relevance to farriers and equine therapists managing localised inflammation in different anatomical locations.
Read the full abstract on PubMed
Practical Takeaways
- •Topical NSAID formulations penetrate equine skin more effectively on the lower leg than upper body, suggesting superior efficacy when applied to distal limb conditions
- •Faster initial absorption through leg skin means therapeutic effects may develop more quickly in lower limb applications compared to thoracic or inguinal sites
- •When selecting topical NSAID formulations for horses, consider anatomical location of application as a factor affecting therapeutic outcome
Key Findings
- •Leg skin (dorsal metacarpal) showed significantly higher total salicylate penetration (5491.3 h mg/L) compared to thorax (3710.7 h mg/L) and groin (3571.5 h mg/L), p ≤ 0.02
- •Penetration rate through leg skin in the first 6 hours was significantly faster than upper body regions, p < 0.01
- •Commercial methylsalicylate formulations achieve therapeutic levels of salicylate beneath topical application sites with regional variation in kinetics