Beagle study finds skin drug penetration factors vary by body site: full analysis

A newly published AJVR study reports that skin structures associated with percutaneous drug penetration vary by body site in Beagles, adding fresh canine data to a question that matters whenever veterinarians rely on topical or transdermal delivery. In the exploratory study, investigators examined skin from the dorsum, lateral trunk, and ventral abdomen of six Beagles and assessed features including epidermal thickness, stratum corneum layering, and dermal vessel density, all of which can influence how a drug moves into and through skin. (sciencedirect.com)

The finding fits with what veterinary pharmacology has suggested for years: transdermal absorption is inherently variable, and that variability doesn't just come from the drug or its vehicle. A 2006 veterinary review emphasized that regional differences within the same animal can alter penetration, while AVMA coverage has similarly noted that skin health, thickness, hydration, and location can all change absorption after topical administration. More broadly, both veterinary and human literature have shown that anatomic site affects percutaneous absorption, making site selection a real pharmacologic variable rather than a minor handling detail. (sciencedirect.com)

There is also biologic plausibility behind the AJVR paper's focus. The stratum corneum is the skin's main barrier to drug movement, and dermal blood flow can shape what happens after a compound crosses that barrier. General veterinary references note that transdermal products in dogs and cats are influenced by fur and skin variation, and comparative canine anatomy sources describe dorsal skin as relatively thicker and ventral trunk skin as thinner. Older canine histology work likewise found site-related differences in stratum corneum thickness, including variation between the back, abdomen, and inguinal region. (pmc.ncbi.nlm.nih.gov)

While detailed numeric results from the new AJVR paper weren't fully available in open search results, the study design itself is notable. The researchers sampled three clinically relevant trunk sites under sedation and local anesthesia from November 2024 through March 2025, focusing on structural measures that are often invoked when clinicians discuss why one application site "works better" than another. That makes the paper more than an anatomy exercise: it starts to build a dog-specific evidence base for choosing and standardizing application sites in research and practice. (sciencedirect.com)

Direct expert reaction to this specific paper was limited in publicly indexed coverage at the time of writing, but broader industry commentary points in the same direction. VIN has reported that transdermal absorption can be erratic and unpredictable, and Merck Veterinary Manual notes that transdermal gels are used in small-animal medicine but require attention to formulation and route-specific behavior. Older veterinary reporting on compounded topical gels also underscored that enthusiasm for easier administration has often outpaced evidence on reliable absorption. Taken together, the reaction from the field has generally been cautious: transdermal delivery is useful, but only when the underlying pharmacology is understood. (news.vin.com)

Why it matters: For veterinary professionals, this study speaks to a familiar tension. Transdermal or topical delivery can improve adherence, reduce stress for the patient and pet parent, and create options when oral dosing is difficult. But if body site materially changes penetration, then inconsistent site selection could contribute to underdosing, overdosing, treatment failure, or misleading impressions of a product's performance. That's especially relevant for compounded preparations, off-label use, clinical trials, and any protocol that depends on reproducible absorption in dogs. (merckvetmanual.com)

The paper may also matter for safety counseling. VIN has documented accidental secondary exposure of pets to human transdermal hormone products, a reminder that canine skin can absorb clinically meaningful amounts of some compounds under real-world conditions. Better understanding of which canine body sites are more permissive or more vascular could eventually inform both therapeutic use and exposure-risk guidance. That is an inference from the broader literature, not a claim made directly by the AJVR study, but it is a practical extension of the same biology. (news.vin.com)

What to watch: The key next development will be translational follow-up, especially studies that pair site-specific histology with actual pharmacokinetic or permeation data for veterinary drugs and compounded formulations. If those studies confirm meaningful differences by site, clinicians may eventually see more explicit guidance on where to apply specific products in dogs, and researchers may need tighter standardization of application sites in study protocols. (sciencedirect.com)