Time Required for Topical Difluprednate to Suppress the Intradermal Histamine‐Induced Vascular Reaction in Dogs

BACKGROUND: Topical glucocorticoid (GC) is used to manage inflammatory skin diseases in dogs. However, contact times associated with detectable topical GC effects have not been clarified in dogs. Uncertainty regarding contact time may lead to premature removal or overuse, compromising efficacy and safety. OBJECTIVES: To determine contact times at which detectable GC effects are observed after topical difluprednate lotion application in dogs. ANIMALS: Six male Beagle dogs. METHODS: Suppression of the histamine-induced vascular reaction (HVR), based on the principles of the vasoconstrictor assay, was used as an indicator of detectable GC effects. Difluprednate lotion was applied to a circular area (2 cm in diameter) on the lateral trunk 5, 10 and 30 min before intradermal histamine injection. Fluorescein was administered intravenously 5 min before histamine injection to visualise HVR. HVR images were obtained 15 min after histamine injection under UV illumination, and the fluorescent area was measured using ImageJ. Statistical analysis was performed using Dunnett's multiple comparison test. RESULTS: When difluprednate application was performed 5, 10 and 30 min before histamine injection, HVR areas were smaller than untreated control sites (p < 0.01). No significant differences were detected among sites treated 5, 10 and 30 min before histamine injection. CONCLUSIONS AND CLINICAL RELEVANCE: Difluprednate lotion suppressed the HVR when applied 5, 10 and 30 min before histamine injection, indicating detectable dermal GC activity at the evaluated time points. Information regarding contact times at which topical GC effects can be detected may help clinicians to provide contact-time instructions and improve treatment management.