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Dexmedetomidine oromucosal gel for dogs (brand name Sileo) is a prescription-only medicine (POM-V) authorised for the alleviation of acute anxiety and fear associated with noise. This module gives you the key infomation about the use of dexmedetomidine in the management of noise phobia in dogs. By doing this module you will:

  • understand the mode of action of dexmedetomidine in reducing fear and anxiety

  • be aware of the clinical evidence in support of this use

  • understand how dexmedetomidine is used for treating noise phobia in dogs

  • know the adverse effects in dogs treated for noise phobia

  • know how to help clients use dexmedetomidine safely and effectively.

Related module: 

Imepitoin for noise aversion in dogs

In the UK, fireworks are the most commonly reported type of noise resulting in fear and anxiety in dogs. However, many other noises are also reported to cause significant problems including thunderstorms, gunshots and traffic noise. The signs of noise phobia have been reported to include restlessness, panting, vocalisation, cowering, trembling, frequent elimination, destructive behaviour, inappetence, owner-seeking behaviour and escape behaviours such as bolting. 

Treatment of noise phobia requires a good understanding of the fear response and, in each case, the predisposing, initiating and maintaining factors. Interventions include behavioural therapies such as environmental changes, owner education, desensitisation and counter-conditioning. Behavioural therapies may be supported by adjunctive therapies including dog-appeasing pheromone, nutritional supplements (e.g. alpha-casozepine), herbal remedies and drugs. The potential drug treatments include oral anxiolytics and antidepressants, such as alprazolam and propranolol (both unlicensed in dogs), and clomipramine, fluoxetine and selegiline (which are licensed for the treatment of behavioural disorders in dogs, but not specifically noise phobia). There are currently two drug treatments specifically authorised for use in dogs with fear and anxiety related to noise: one is dexmedetomidine oromucosal gel (brand name Sileo), and the other is imepitoin (brand name Pexion). This module focuses on dexmedetomidine. A separate module covers imepitoin.

The drug dexmedetomidine is the active ingredient in Sileo. Dexmedetomidine is not a new drug in veterinary practice. It has been used for many years in injectable form as the brands Cepadex, Dexdomitor and Sedadex). Dexmedetomidine is used in the form of an injection as a pre-anaesthetic agent and for sedation and pain relief (usually in combination with an opioid) in dogs and cats. In the product Sileo, dexmedetomidine is in the form of a translucent green gel for applying to the mucous membranes of the dog’s oral cavity.

Dexmedetomidine works by binding to specific receptors in the body: alpha-2 adrenoceptors. When it binds to these receptors in the brain, it causes a decrease in the release of the neurotransmitter noradrenaline. This in turn causes a reduction in the activity of the sympathetic nervous system which is involved in controlling anxiety, arousal and sleep, and blood pressure and heart rate. The drug in the gel is absorbed through the mucosa in the mouth. When dexmedetomidine is given in larger doses by the intravenous route it causes sedation but when given in smaller doses via the mucous membrane of the mouth it causes a reduction in anxiety, usually without causing sedation.  The product will not work if the gel is swallowed because after absorption through the stomach the drug will be broken down in the liver.

The main clinical trial evidence supporting the licensed use of dexmedetomidine in dogs with noise phobia is a single randomised, double-blinded, placebo-controlled trial (Korpivaara et al 2017). The trial was carried out on a New Year’s Eve. It included 187 dogs with a history of anxiety and fear caused by fireworks. The dogs were randomised to receive dexmedetomidine oromucosal gel (at a dose of 125 micrograms/m2) or an equivalent volume of a placebo gel (which contained no active drug). Owners applied gel in the dog’s mouth either pre-emptively 1 hour before the anticipated start of the fireworks, immediately when the fireworks were heard, or when the dog began to show signs of anxiety and fear. They were able to reapply the gel after at least 2 hours if the dog began to show signs of anxiety and fear again. They could use the gel up to five times.

A higher proportion of dogs in the dexmedetomidine group had a good or excellent treatment effect compared to the placebo group (72% vs. 37%). It is interesting to note that quite a large proportion of the dogs that received the placebo gel had a good or excellent response. This is possibly because of an expectation of a beneficial effect (the caregiver placebo effect), which may have affected the owners’ behaviour with consequent positive effects on the dogs’ behaviour. In 17% of dogs, dexmedetomidine was judged to have no effect, or to worsen the dogs’ behaviour compared to the previous year (vs. 44% that received the placebo). 

Owners also assessed the dogs’ responsiveness and ability to stand and walk by calling their dog and scoring their observations. More than 85% of dogs were classed as fully functional with no apparent differences between the groups. A few dogs (seven in the dexmedetomidine group and two in the placebo group) were unable to stand up and walk when called. 

In the main clinical trial, the most common reported adverse effect was vomiting. This was reported in four out of 89 dogs receiving dexmedetomidine (around 4%) compared with one of 93 dogs on placebo (around 1%). After applying the gel, the mucous membrane at the application site might have a pale appearance, which is temporary. Other commonly-reported adverse events in clinical trials were sedation and urinary incontinence (these were reported in more than 1 but fewer than 10 in 100 dogs) . Uncommon adverse reactions were anxiety, periorbital oedema, drowsiness and signs of gastroenteritis (these were reported in more than 1 but fewer than 10 in 1,000 dogs).

Because the effect of dexmedetomidine is related to dose, it is possible that a small dog exposed to a large overdose would become sedated. However, on the basis of study results, this would be expected to be transient and followed by a full recovery in a healthy dog.

Dexmedetomidine is contraindicated in dogs with severe cardiovascular disorders and those with severe systemic disease such as end stage renal or liver failure.

The safety of administering the product to puppies younger than 16 weeks old, dogs over 17 years of age, and during pregnancy and lactation is not known. If other drugs that cause sedation are given at the same time, they might add to the effects of dexmedetomidine.

To our knowledge, dexmedetomidine gel has not been compared in a clinical trial with imepitoin (the other product licensed for use in dogs with noise aversion) or been tested for efficacy in noise related phobias other than to fireworks.

The summary of product characterisitics (SPC) for Sileo recommends giving the first dose as soon as the dog shows the first signs of anxiety, or when the owner detects a typical stimulus (e.g. fireworks or thunder) that usually brings on anxiety or fear in the dog. Typical signs of anxiety and fear include panting, trembling, pacing (frequent change of place, running around, restlessness), seeking people (clinging, hiding behind, pawing, following), hiding, trying to escape, freezing (absence of movements), refusing to eat food or treats, and inappropriate elimination and salivation 

The gel needs to be applied onto the oral mucosa, between the dog’s cheek and gum. Sileo comes in an oral syringe that delivers the gel in 0.25 mL increments for a range of doses for dogs weighing from 2kg to 100kg. Each increment is shown as one dot on the plunger; the dosing table in the package leaflet gives the number of dots to be administered corresponding to the dog’s bodyweight. If the total dose required is more than 6 dots (1.5ml), half should be applied to the oral mucosa on one side of the mouth and half on the other side. If the fear-eliciting event continues and the dog shows signs of anxiety and fear again, another dose may be given 2 hours after the previous dose. The product can be dosed up to five times during each event.  

There are specific instructions on handling the packaging and on dose selection – to ensure safety of children and avoid potential overdosing of the dog. It is very important that the client is able to use the product competently because there is scope for incorrect use of the product. For example if the gel is wrongly placed in the mouth and the dog swallows the gel the product will not be effective; if the syringe locking mechanism has not been engaged properly, an overdose may be given. 

There is a clear and helpful package leaflet and an online video showing how to use the product correctly and so the client should be told about these. In the main clinical trial most owners (85%) found the product easy to administer. However, in dogs that are not accustomed to handling procedures, administration has been reported to be more difficult and so there is an important role for the veterinary team to play in giving advice on how to teach a dog to accept such handling.

The client should be informed that the medicine is intended to be absorbed from the inside of the mouth and that if the gel is swallowed it will be ineffective. To prevent the gel from being swallowed, the dog should not be fed or be given treats within 15 minutes after administration of the gel. If the gel is swallowed the dog can be given another dose, if necessary, a minimum of 2 hours after the previous dose. Clients should be told that sedation may occur if the dose is exceeded. If sedation occurs, the dog should be kept warm and the client should contact the vet.

Dexmedetomidine can be absorbed through damaged skin, mucous membranes (mouth/gums), and eyes, so handlers should avoid skin, eye or mucosal contact. The SPC advises that the person administering the gel should wear impermeable disposable gloves (these are not provided with the product). Dexmedetomidine is not considered to be a skin irritant. Pregnant women should avoid contact with the product because systemic exposure to dexmedetomidine can cause uterine contractions and decreased foetal blood pressure. 

The oral syringe must be kept in the carton to protect it from light. The shelf life after first opening the immediate packaging (removal of the cap) is 4 weeks. 

Dexmedetomidine is available in the form of a gel for administering to dogs via the mucosa in the mouth for reducing anxiety and fear associated with noise. In one randomised controlled trial, 72% of owners considered it had a good or excellent effect in reducing fear and anxiety caused by New Year’s Eve fireworks. In the trial, dexmedetomidine appeared to be well tolerated with vomiting being the most commonly reported adverse effect (reported in around 4% of dogs). It is important to ensure that the client knows how to handle and use the product correctly,

Literature search

We searched RCVS Knowledge Discovery Service (including PubMed) and VetMed Resource (CAB Abstracts) on 2 April 2019 using the terms (dexmedetomidine OR Sileo*) AND (fear* OR anxi* OR noise OR phobi* OR fright* OR nervous* OR scared) AND (dog OR dogs OR canine OR canines OR canis)


If you prefer, you can listen to the whole audio presentation of this module using the following podcast. Don't forget that you can also download the podcast to your iPod, music player, tablet or smartphone using the Download link on the right of the audio player.


How we produced this module

Our modules start with a detailed outline and electronic literature search. We commission a collaborating author, who is a specialist in the module topic, to write a draft module. The collaborating author on this module was  Andrea Tarr, Director of Veterinary Prescriber, a specialist in medicines evaluation. The draft was circulated unsigned to topic specialists, practising first-opinion vets and pharmaceutical companies. There is a rigorous editing and checking process and the result is a module that is evidence-based, impartial and relevant to clinical practice. The final module is unsigned because it is the result of collaboration. 


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Committee for Medicinal Products for Veterinary Use (CVMP) (2015). CVMP assessment report for Sileo (EMEA/V/C/003764/0000) International non-proprietary name: dexmedetomidine [online]. [Accessed 30.04.19]

Imepitoin for noise aversion in dogs. Veterinary Prescriber April 2019.

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