Brand Name: Prozac

Available in 10 mg, 15 mg, and 20 mg tablets; 10 mg, 20 mg, 40 mg, and 90 mg capsules; oral liquid

Background

Anxiety, obsessive-compulsive disorder, and depression are common problems for humans. Because the development of drugs that alleviate these conditions is ongoing, there are currently many such medications on the human market. One of the more popular classes of anti-anxiety medications are the selective serotonin reuptake inhibitors, called SSRIs.

Serotonin is a neurotransmitter in the brain associated with, among other things, mood elevation and reduced aggression. Increasing serotonin in the brain means less anxiety and a happier attitude. By inhibiting the brain’s system for removing used serotonin, SSRIs cause serotonin to linger, lasting longer. The more serotonin we have in our brains, the less anxiety, obsession, and depression we get.

Eli Lilly, a prominent pharmaceutical company, tested many related compounds and released fluoxetine as the most specific “selective serotonin reuptake inhibitor” of all of them. Fluoxetine, marketed under the brand name Prozac®, was not quite the first SSRI on the human market but quickly became the most popular.

It was not long after that fluoxetine found its way into veterinary use for animals with anxiety, compulsive behavior, and other behavior issues. When low-cost generic fluoxetine became available, its use increased in the veterinary market and in 2007 Eli Lilly released a version of fluoxetine specifically labeled for animal use and sponsored a behavioral program to go with it. Widespread use of generic human products supplanted the brand name veterinary product for a time, but PRN, another pharmaceutical company, has reintroduced not only the brand name product but also the B.O.N.D. behavior modification program that improves its efficacy (see below).

How this Medication is Used

Fluoxetine has been used in many animal behavior issues: inappropriate urine marking in both dogs and cats, separation anxiety, compulsive chewing, circling, and self-mutilation, even aggression. 

It should be noted that the treatment of behavior disorders requires training in addition to medication. When medication and behavior modification were combined, 42% of dogs with separation anxiety showed improvement by the end of the first week, and 73% improved within eight weeks. These statistics were obtained using the B.O.N.D. training program designed for use with the brand name Reconcile®. For more information, visit Reconcile.com. Obviously, there are a number of training techniques for use in the management of separation anxiety; the point is that the best results are obtained when fluoxetine is combined with training. 

Fluoxetine is usually given once a day, with or without food. If a dose is accidentally skipped, do not double up on the next dose; instead, give the next dose when it is remembered and time the following dose accordingly.

Fluoxetine should not be discontinued abruptly. If you wish to discontinue it, ask your veterinarian for a tapering schedule.

Fluoxetine should be stored at room temperature away from light.

Side Effects

Common Side Effects that Are Generally Not Serious

Vomiting and diarrhea may be seen. These effects are generally eased by giving the medication with food. If appetite loss is a problem, this can generally be solved by reducing the dose and ramping it back up gradually. One dog in three will lose weight but this should not exceed 15% of their original body weight.

Side Effects that Are Less Common but more Serious

Persistent weight loss or appetite loss, tremors, seizures, an increase in aggression, or anxious behavior are not acceptable. Insomnia can result and be problematic. Blood glucose alterations can interfere with the regulation in a diabetic patient

Interactions with Other Drugs

Serotonin syndrome is a potentially dangerous situation that can result when serotonin levels get too high. Elevated heart rate, tremors/shivering, dilated pupils, difficulty breathing, elevated body temperature, hyperactivity, and/or high blood pressure can all be signs of serotonin syndrome. Fortunately, the development of serotonin syndrome generally requires a combination of at least two serotonin-increasing drugs and rarely happens spontaneously with one medication, but it is important to be aware of the symptoms as high blood pressure can be life-threatening if severe enough. Using MAO inhibitors in conjunction with fluoxetine could create serotonin syndrome. MAO inhibitors are rarely used in veterinary patients with the exception of selegiline, a drug used for cognitive dysfunction in dogs; amitraz, an anti-parasite topical used in several tick control products (see our flea and tick product comparison chart); and in Mitaban® dip used against mange. Fluoxetine should not be given in conjunction with an MAO inhibitor such as selegiline or amitraz.

The use of buspirone, tramadol, clomipramine, amitriptyline, or trazodone with fluoxetine can also increase the risk of serotonin syndrome.

Cyproheptadine, an appetite stimulant, may decrease or even reverse the effect of fluoxetine.

Diazepam and alprazolam may have stronger effects if used in conjunction with fluoxetine, as can beta blockers and the blood thinner clopidogrel.

Fluoxetine should not be used in combination with drugs that could increase the likelihood of seizures.

Insulin requirements may change when taking fluoxetine.

Concerns and Cautions

This medication is best not used in patients with diabetes mellitus or with seizure disorders.

Fluoxetine lasts a long time in the body. If planning to discontinue fluoxetine, a tapering course is not necessary unless the patient has been taking fluoxetine for > 8 weeks. In that case, tapering the dose over three to five weeks is a good idea.

Fluoxetine and MAO inhibitors should not be given together, and a "washout" period is needed between them. If you wish to begin an MAO inhibitor (selegiline for cognitive dysfunction or amitraz for parasite control) in a patient presently on fluoxetine, a six-week period is recommended between the last dose of fluoxetine and the first dose of the MAO inhibitor. Similarly, if a patient is on an MAO inhibitor and will be beginning fluoxetine, a two-week period is needed between medications. The period is longer in the former incidence because of the long half-life of fluoxetine in the body..