Behaviour Modifying Drugs - Overview

Although many drugs are used to treat behavioural conditions in animals there are only three psychoactive drugs specifically licensed for use in companion animals to treat behavioural problems. These are:

• Clomipramine (licensed in the dog for treatment of separation anxiety)
• Selegiline (licensed in the dog for treatment of canine cognitive dysfunction syndrome)
• Fluoxetine (licensed in the dog in the USA for treatment of separation anxiety)

Several other drugs are often used to treat behavioural conditions, such as propranolol, phenobarbitone, diazepam and various other common veterinary drugs, however these are not licensed for this purpose. In addition many other drugs are used in behavioural medicine but most are unlicensed for use in any animal species. Examples are listed in the table below, however most uses listed are unapproved, care should therefore be taken with their use:

Class of Drug	Drugs	Uses	Side Effects
Tranquilizers	Acepromazine	Sedation/restraint	Hypotension, CNS stimulation, contradictory responses. Caution in boxers and greyhounds
Benzodiazepines	Alprazolam, Clonazepam, Clorazepate, Diazepam, Lorazepam, Oxazepam	Anxiety, noise phobias, canine submissive urination, feline urine marking	Sedation, ataxia, increased appetite, paradoxical excitation
Tricyclic Antidepressants (TCAs)	Amitriptyline, Clomipramine, Doxepin, Imipramine	Anxiety, separation anxiety, canine and feline fear aggression, feline urine marking, feline compulsive grooming, canine stereotypy	Sedation, gastrointestinal (GI) effects, dry mouth, increased thirst, urinary retention
Selective Serotonin Reuptake Inhibitors (SSRIs)	Fluoxetine, Fluvoxamine, Paroxetine, Sertraline	Aggression, canine separation anxiety, compulsive disorders, feline urine marking	Lethargy, inappetence, anorexia, GI effects
Beta Blockers	Propranolol	Canine fear aggression, noise phobia	Bradycardia, lethargy, hypotension, syncope
Azapirones	Busiprone	Phobia, anxiety, feline urine marking, interact aggression	Uncommon, not sedating
Triazolopyridines	Trazodone
Anticonvulsants	Carbamazepine, Gabapentin, Levetiracetam, Phenobarbital, Potassium bromide	Canine and feline compulsive tail chasing, unprovoked canine rage aggression	Lethargy, ataxia, polyuria, polydipsia, polyphagia
Hormones	Medroxyprogesterone acetate, Megestrol acetate	Last resort for aggression and feline urine marking	Polyphagia, polydipsia, sedation, diabete mellitus, pyometra, mammary hyperplasia, endometrial hyperplasia, carcinoma
Glial Modulators	Propentofylline
Monoamine Oxidase Inhibitors	Selegiline	Canine and feline cognitive dysfunction syndrome, fear related problems, spraying, hyperactivity, compulsive/stereoptypical disorders	GI effects, restlessness or lethargy, anorexia

Benzodiazepines are the only class of drug that consistently succeed in all models, but this may be why they have a dangerous disinhibitory effect on aggression. These drugs eliminate avoidant responses to many kinds of aversive events, increasing confidence in a number of exploratory tests. This is why benzodiazepines can cause dangerous levels of disinhibition in aggressive dogs. Benzodiazepines also inhibit memory formation by affecting NMDA (glutamate) receptors in the hippocampus, which limits their usefulness in behavioural therapy where any kind of learning is required, which is in most situations. They are useful for memory blocking if given at sub-sedative doses prior to or during a predicted traumatic event such as a thunderstorm.

Drugs such as Acepromazine (ACP) and synthetic hormone analogues like megestrol acetate (Ovarid) have little or no rational use in behavioural therapy for reasons of non-specificity, and adverse effects which make their use unjustifiable.

The first port of call when using medication for behavioural problems should be drugs licensed for veterinary use. These drugs have established data about their efficacy, side effects, contraindications and toxicity which makes expected outcomes more reliable. (Merck)