Sedation via the intranasal route in dogs

In human and veterinary clinical practice the intranasal (IN) route has long been used for the treatment of local and upper respiratory tract diseases. In the last decades this route attracted more interest for systemic drug administration because it is a non-invasive, safe and suitable method allowing rapid onset of action and avoidance of gastrointestinal tract constraints as well of hepatic first-pass metabolism (1). In humans, especially in children and uncooperative patients, the IN route is increasingly used for sedation, thanks to the intense absorption power of the nasal mucosa and to the fast, direct transport of neurotrophic molecules to the Central Nervous System via the olfactory nerves (1). In animals the IN route is not adequately explored although in most species such as dogs, the olfactory epithelium is lined with hundreds of millions of sensory neurons (2). In dogs, the IN administration of 0,5 mg/kg of diazepam for emergency treatment of seizures has been shown to be an effective, alternative route for easy and quick administration of such anticonvulsant drug (3). In clinical settings we administered via the IN route different anesthetic agents such as dexmedetomidine, butorphanol, midazolam and fentanyl to induce sedation and analgesia in dogs. To improve drug absorption by reducing particles diameter and the risk of its expulsion we used a commercial Mucosal Atomization Device (MAD®) produced for humans. We reported(4) that the intranasal administration is easy to perform, painless and well tolerated in dogs. In our experience the IN administration of 20 μg/kg of dexmedetomidine produced effective sedation comparable to that following conventional administration routes; further to that, the IN route showed a shorter onset time compared to the intramuscular route, devoid of undesirable effects. In the same study we showed that the sedative and analgesic proprieties of dexmedetomidine given by IN route can be enhanced by its combination with 0,1 mg/kg of butorphanol administered as a drug mixture (4). Among opioids, fentanyl is particularly suitable for IN administration due to its high lipophily favouring a rapid action onset highly desirable for acute pain treatment; such quality, in fact, promoted different IN formulation of fentanyl (Instanyl®, PecFent®) available on the market for treatment of breakthrough pain in humans (1). The IN administration of fentanyl favourably affects the molecule pharmacokinetics in dogs. In our experience, 4 μg/kg of fentanyl atomized on the nasal mucosa showed a very short onset time (about 9 min) providing a full analgesic effect lasting about 35 minutes (5), slightly longer compared to the 30 minutes effects reported after IV administration in dogs. In conclusion the IN route constitute a non-invasive and effective route for anesthetic drug administration, favouring prompt CNS effects in dogs, with the potential for enhancing and extending the effects of neurotrophic molecules thanks to their direct transport to forebrain trough the olfactory nerves. So far, to our knowledge, no adverse effects linked to the nature of different molecules and to their contact with and absorption trough the nasal mucosa have been reported in humans and in animals.