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Fluoxetine is a SSRI. The originally marketed human drug is called Prozac®. Fluoxetine increases serotonin levels within the central nervous system by preventing the re-uptake of serotonin at the level of the presynaptic neuron. This allows serotonin to accumulate in the synaptic cleft and affect the post-synaptic neuron. Serotonin is the neurotransmitter responsible for facilitation of social interactions, general awareness, coping mechanism and adaptability. SSRI drugs are commonly prescribed for humans as a part of the treatment of depression, anxiety disorders, compulsive disorders and difficulty managing aggression. Fluoxetine must be administered for four to eight weeks before the full effect on serotonin levels is realized.
Fluoxetine is well absorbed orally. Although the bioavailability
of transdermal fluoxetine is only about 10 percent of that of the oral
medication, it may be an alternative when oral administration is not feasible
or safe.
Fluoxetine is FDA approved for use in separation anxiety in dogs. All other uses of fluoxetine in dogs and cats are extra-label but there is considerable literature and experience on the use of SSRI's for small-animal behavior problems. In addition to use of medication, much of the behavior literature stresses the importance of behavior modification training, owner training and addressing environmental issues as cornerstones of successful therapy.
Fluoxetine is useful in the treatment of some but not all forms of aggression in dogs. It is used for inter-dog aggression in conjunction with behavioral training and neutering of the less dominant dog. Fluoxetine is also used for the treatment of obsessive-compulsive disorders in dogs. Specific phobias such as fear of storms are usually treated by benzodiazepines because of their episodic nature and the drug's rapid onset of action. There are instances when combining a SSRI and a benzodiazepine are warranted because of the need for a brief period of increased anxiolytic, such as the first half an hour of separation for a dog with marked separation anxiety.
Indoor cats appear to be susceptible to anxiety disorders
due to their lack of social skills and the importance of territorial organization.
Manifestations of anxiety in cats may include inappropriate elimination,
aggression, obsessive-compulsive behavior, hyperactivity or hypervigilance.
Fluoxetine may be helpful for cohabitation anxiety, closed-surrounding
anxiety and territory-related anxiety. Because of the high rate of recidivism
in cats that urine-spray, fluoxetine therapy may need to be continued
for a month or two after the resolution of the spraying problem.
• Dogs: Sedation and anorexia are the most commonly
reported side effects. Other side effects include GI upset and behavior
changes (anxiety, irritability, hyperactivity and insomnia). Aggression
(very uncommon) and seizures have also been reported.
• Cats: Anorexia and behavior changes (anxiety, irritability, hyperactivity/insomnia
and elimination behavior) are the most commonly reported side effects
in cats. Anorexia is a common enough side effect in the cat that the client
should monitor the cat's appetite and weight. Dermatitis may occur at
the site of transdermal application.
• Serotonin syndrome is a potentially life-threatening,
iatrogenic-drug reaction caused by excessive intra-synaptic serotonin.
It is very rare in animals but may occur when multiple serotonergic drugs
are administered, with an overdose or in instances of individual hyper-sensitivity.
This most commonly occurs with a combination of SSRI and MAOI medications,
although there are some opioid analgesics with serotonergic activity.
Symptoms include neuromuscular hyperactivity, hyperthermia, autonomic
hyperactivity and altered mental status.
• Fluoxetine is usually not prescribed for animals with diabetes
mellitus or seizure disorders. Animals with impaired liver function may
need reduced a dose.
• There are active metabolites of fluoxetine for 4- 5 weeks after
discontinuing the drug.
• Some animals appear to stop responding to an individual SSRI medication.
This also occurs in humans but it has not been widely studied in dogs
and cats.
• There are many potential or hypothetical drug
interactions for fluoxetine in dogs and cats although many of these are
extrapolated from experience in humans.
• The list of potential drug interactions includes; acepromazine,
amitraz (including the flea/tick collars and dips) buspirone, cyproheptadine,
diazepam, alprazolam, diuretics, insulin, isoniazid, MAO inhibitors (selegiline),
pentazocine, phenytoin, propanolol, metoprolol, tramadol, tricyclic antidepressants,
trazodone, warfarin.
• Signs of overdose in dogs and cats resemble those
discussed under side effects: lethargy, hyper salivation, agitation. Seizures
may occur in dogs that have received a massive overdose.
• Fluoxetine is well absorbed orally and signs of overdose may present
in 30 to 60 minutes. If an overdose is recognized promptly emesis and
gastric lavage should be attempted in the conscious animal. Activated
charcoal and cathartics may be use subsequently as warranted by clinical
signs. Diazepam should be used in animals that are seizuring. Although
IV fluids will not enhance drug excretion they may be indicated to support
blood pressure, renal function, and aid in thermoregulation.
Dr.
Barbara Forney is a veterinary practitioner in Chester County, Pennsylvania.
She has a master's degree in animal science from the University of Delaware
and graduated from the University of Pennsylvania School of Veterinary Medicine
in 1982.
She began to develop her interest in client education and medical writing 1997. Recent publications include portions of The Pill Book Guide to Medication for Your Dog and Cat, and most recently Understanding Equine Medications published by the Bloodhorse.
Dr. Forney is an FEI veterinarian and an active member of the AAEP, AVMA, and AMWA.
You can purchase books by Dr. Forney at www.exclusivelyequine.com
The information contained on this site
is general in nature and is intended for use as an informational aid. It does
not cover all possible uses, actions, precautions, side effects, or interactions
of the products shown, nor is the information intended as medical advice or
diagnosis for individual health problems or for making an evaluation as to the
risks and benefits of using a particular product. You should consult your doctor
about diagnosis and treatment of any health problems. Information and statements
have not been evaluated by the Food and Drug Administration ("FDA"),
nor has the FDA approved the products to diagnose, cure or prevent disease.
Wedgewood compounded veterinary medicines are not intended for use in food and food-producing animals.
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