Behaviour modifying drugs are increasingly used in the treatment of companion animal behaviour problems. The rationale for using psychotropic medication is based on their purported neurochemical actions in the brain mainly on GABA, serotonin, dopamine, acetylcholine and noradrenaline. Thus, a knowledge of the neurotransmitters, their receptors and how drugs influence them will provide the foundation on which to base a decision on which psychotropic medication to prescribe, when and why. Combined with an awareness of the pharmacokinetics and pharmacodynamics of these medications a rational approach to psychopharmacological therapy can be achieved.

Drugs should never be used to treat behaviour problems without a concurrent behaviour modification program as many behaviour problems can be managed by behaviour modification alone. Drugs should always be an adjunct to behaviour modification therapy not a replacement.

Before prescribing any drug to modify an animal's behaviour it is vitally important that a diagnosis is made based on a thorough physical examination and behavioural history. Additionally, the treatment of non-specific signs is not acceptable and will ultimately lead to treatment failures.

Owners and veterinarians should be aware that there are no quick fixes and no magic overnight cures for behavioural disorders. In most cases behaviour problems take time to develop and it will therefore take time to modify the behaviour.

As most medications used in veterinary behavioural therapy are not registered for use in animals the rationale for drug use and potential side effects should be clearly explained and the owner should give informed consent to use of the drug on their pet.

The choice of medication may be affected by personal experience of the veterinarian, reported case studies or trials, extrapolation from human literature as well as cost. An attempt to gradually wean off medication once the desired result is achieved and maintained for a period of 2-3 months should be made. However, there are some patients that will require life long medication and this should be made clear to the owner at the outset of therapy.

Clinical indications and drug classes

Behaviour problems where medication has proved useful include anxiety related problems (including fears and phobias), obsessive compulsive behaviours, some types of aggression, abnormal sexual behaviour, and geriatric behaviour problems.

Many classes of medications are have been used in the treatment of behaviour problems. These include antihistamines, antipsychotics, anxiolytics, antidepressants, anticonvulsants, mood stabilisers, beta blockers, CNS stimulants, hormones, opiate antagonists, monoamine oxidase inhibitors, neuroleptics, ergot alkaloids and phenothiazines. Medications that have anxiolytic action include the benzodiazepines, tricyclic antidepressants (TCAs), antihistamines, azapirones, barbiturates, selective serotonin re-uptake inhibitors (SSRIs) and beta blockers. Only drugs in common usage will be discussed in any detail.

Ach, dopamine, serotonin, noradrenaline and GABA are particularly important in the actions and side effects of behaviour modifying drugs.

Pre-treatment screening

Blood tests prior to prescribing medication are recommended. A minimum data base should include a complete blood count, biochemistry panel and urinalysis. As most of the behaviour modifying drugs are metabolised by the liver and excreted via the kidneys, it is important to assess liver enzyme concentrations and kidney function prior to starting drug treatment. All animals on long term behaviour modifying medication should be reassessed every 6-12 months.

BENZODIAZEPINES

Uses: Common uses in cats include anxiety disorders, spraying and over-grooming. In dogs they have been used to assist in the treatment of anxiety disorders and noise phobias. Some examples include diazepam (dose rate: cats: 0.2-0.4 mg / kg po sid-bid, dogs: 0.5-2.2 mg / kg po bid-tid), alprazolam (dose rate: cats: 0.125-0.25 mg / kg po bid, dogs: 0.125-1.0 mg / kg po. No more than 4 mg / day)

Side Effects: These include increased appetite, transient ataxia, paradoxical hyperactivity in some cats, increased affection and drug tolerance.

Contraindications: They should not be used in animals with liver or kidney failure and used with caution in cases of aggression because of dis-inhibition.

TRICYCLIC ANTIDEPRESSANTS (TCA'S)

Uses: In cats they have been used to treat spraying, overgrooming and other anxiety related disorders. In dogs their use has included some forms of aggression (e.g., status-related (Dominance) and fear), separation anxiety and obsessive compulsive disorders. Some examples include amitriptyline (dose rate: cats: 5-10 mg po sid, dogs: 1-2 mg / kg po sidbid, clomipramine (dose rate: cats: 0.25-0.5 mg / kg sid, dogs: 2 mg / kg po bid 2 weeks, then 3 mg / kg po bid-may need up to 4 mg / kg every 12 hours to be effective).

Side Effects: These include anticholinergic effects such as dry mouth, constipation, urinary retention. Also tachycardia, cardiac arrhythmias, syncope and ataxia have been reported.

Contraindications: They should not be used in animals with cardiac dysrhythmia or a history of urinary retention.

SELECTIVE SEROTONIN REUPTAKE INHIBITORS (SSRI'S)

Uses: These have been used in cats to treat urine spraying, obsessive compulsive disorders as well as some types of aggression. In dogs they have been used in the treatment of obsessive compulsive disorders, separation anxiety as well as some types of aggression. Some commonly used examples include fluoxetine (dose rate: cats: 0.5 mg / kg po sid, dogs: 1 mg / kg po sid) paroxetine (dose rate: cats: 1 mg / kg po sid)

Side Effects: Reported side effects include liver changes, GI disturbances and rash.

Contraindications: Concomitant MAO therapy and known allergy to SSRIs precludes their use.

MONOAMINE OXIDASE INHIBITORS

Uses: These have been used in dogs mainly for the treatment of Canine Cognitive Dysfunction Syndrome but also for anxiety disorders. For CDS the dose rate of Selegiline is 0.5 mg/kg po sid, if no response after 4 weeks 1.0 m /kg po sid. It is generally recommended to be given in the morning.

Side effects: Stereotypic behaviours with overdosage has been reported. Other side effects include gastrointestinal effects (vomiting and/or diarrhoea), and hyperactivity or restlessness, pruritis, salivation, anorexia, diminished hearing and listlessness.

Contraindications: Concomitant use of phenylpropanolamine, amitraz, ephedrine, or meperidine or other opioids is not recommended nor concomitant use of antihistamines. Generally a two week washout is required to avoid adverse drug interactions. Concomitant TCA therapy should be avoided with a two week wash out required. Concomitant SSRI therapy should be avoided with a five week washout required especially with fluoxetine.

AZAPARONES

Uses: Buspirone has been used in cats to treat spraying and overgrooming. In dogs it has been used in the treatment of anxiety. Dose rate: cats: 2.5-5 mg po sid-tid, dogs: 2.5 10 mg po bid - tid

Side Effects: Include bradycardia, GI disturbances and stereotypic behaviours.

Contraindications: Allergic reactions

PHEROMONES

Uses: In cats they have been used to treat urine spraying, anxiety disorders, to help cats tolerate clinical examinations and travel, stimulate appetite in hospitalised cats, to help control undesirable scratching behaviour as well as treat some forms of aggression. In dogs they have been used in the treatment of separation anxiety and noise phobias. For cats Feliway, Felifriend both are available as sprays while Feliway is also available as a diffuser. For dogs DAP is currently only available as a diffuser.

Side effects: None have been reported although some clients claim that the alcohol base is irritant.

Contraindications: None known

References

1.  Landsberg, G., Hunthausen, W. & Ackerman, L. (1997). Handbook of behaviour problems of the dog and cat. Oxford: Butterworth-Heinemann.

2.  Overall, K. L. (1997). Clinical behavioral medicine for small animals. St Louis, Missouri: Mosby

3.  Rang, H. P., Dale, M. M., Ritter, J. M. & Gardner, P. (1995). Pharmacology. New York: Churchill Livingstone.

4.  Seksel, K. (2002) Behavior-modifying drugs in J. Maddison, S. Page & D. Curch (Eds) Small Animal Clinical Pharmacology. London, W. B. Saunders