A Multispecies Systematic and Critical Review of Intranasal Administration in Veterinary Anaesthesia and Emergency Care: Promising Evidence and Overlooked Challenges.

Intranasal (IN) drug delivery has increasingly considered as an easy, practical and non-invasive alternative to parenteral administration in veterinary medicine, offering rapid systemic and potential nose-to-brain effects. The first part of this review systematically collected and synthesized published evidence on IN administration across animal species, while the second part critically analysed the anatomical, pharmacological and technical factors that determine its success and limitations. Part I consisted a total of 110 eligible studies published between 1991 and 2025, encompassing dogs, cats, rabbits, pigs, ruminants, birds and reptiles. IN delivery has been investigated for a range of purposes and produced clinically meaningful sedation, analgesia and drug reversal, often comparable to intramuscular administration but generally characterized by slower onset and greater variability among species. Despite encouraging and favourable results, IN delivery was not without limitations. Its effectiveness can be strongly influenced by species-specific nasal anatomy and physiology, formulation characteristics and dosing volume. Defensive reactions, poor tolerability, sneezing, nasopharyngeal irritations, hypersalivation or swallowing of the drug are frequently reported. Future progress requires species-specific case selection guidelines and dosing standards, pharmacokinetic validation and developing safe concentrated formulations. Transparent reporting and balanced assessment of both benefits and drawbacks are essential to ensure the safe, effective and ethically responsible integration of IN administration into veterinary anaesthesia and critical care practice.