Fluoxetine
Fluoxetine is a selective serotonin reuptake inhibitor used in veterinary behavioral medicine. Its established canine role is separation anxiety alongside behavioral modification. Extra-label applications include selected compulsive or anxiety-associated disorders in dogs and urine marking or other anxiety-related problems in cats. The active metabolite norfluoxetine contributes to prolonged pharmacologic activity.
Group
Selective serotonin reuptake inhibitor
Mechanism of Action
Fluoxetine inhibits the serotonin transporter and reduces presynaptic reuptake of released serotonin. Increased synaptic serotonin availability alters signaling in neuronal circuits regulating anxiety, impulse control and repetitive behavior. Adaptation of receptors and downstream networks during continued treatment contributes to the clinical response. Norfluoxetine also inhibits serotonin reuptake and extends the duration of activity.
Dose Rates
Dogs
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Separation anxiety | 1–2 mg/kg | PO | Every 24 h | Use alongside behavioural modification; clinical benefit can take up to four weeks. |
| Compulsive disorder | 1–2 mg/kg | PO | Every 24 h | Use alongside behavioural modification; clinical benefit can take up to four weeks. |
| Conflict-related aggression | 1–2 mg/kg | PO | Every 24 h | Use alongside behavioural modification; clinical benefit can take up to four weeks. |
| Behavioural disorder – lower-range alternative | 1–1.5 mg/kg | PO | Every 24 h | |
| Behavioural disorder – titrated alternative | 1–3 mg/kg | PO | Every 24 h | Source starts at 1 mg/kg and titrates, if needed, up to 3 mg/kg; the upper value is not the starting dose. |
Cats
| Use / stage | Dose | Route | Schedule | Instructions |
|---|---|---|---|---|
| Aggression adjunct | 0.5–1.5 mg/kg | PO | Every 24 h | |
| Generalised anxiety | 0.5–1.5 mg/kg | PO | Every 24 h | |
| Urine marking or separation anxiety | 0.5–1 mg/kg | PO | Every 24 h | Source also describes a typical fixed amount of 2.5-5 mg per cat; do not independently add that amount. |
| Refractory pruritus adjunct | 1–5 mg/animal | PO | Every 24 h | Obtain baseline laboratory tests, reassess after 1-4 weeks and taper over 6-8 weeks if withdrawing. |
Indications
- Treatment of canine separation anxiety in conjunction with behavioral modification.
- Treatment of selected canine compulsive disorders, including supported repetitive-behavior syndromes.
- Adjunctive management of selected fear- or anxiety-associated aggression after behavioral diagnosis, with variable condition-specific evidence.
- Reduction of anxiety-associated urine marking in cats.
- Treatment of selected other feline anxiety or compulsive disorders within a behavioral treatment plan, with limited disorder-specific evidence.
Contraindications
- Do not use with MAO inhibitors; canine Reconcile labelling excludes epilepsy or a history of seizures.
- Use cautiously in hepatic disease, diabetes, pregnancy and patients with disinhibited aggression.
Interactions
- MAO inhibitors, including selegiline and amitraz, can cause serious serotonin toxicity.
- Trazodone, tramadol, buspirone and TCAs increase serotonergic interaction risk.
- Can increase concentrations/effects of certain beta-blockers, benzodiazepines, phenytoin and warfarin.
Adverse effects
- Reduced appetite, lethargy, vomiting, diarrhoea, agitation or altered elimination.
- Rare seizures, tremors or increased aggression.
Toxicity
Manage CNS/serotonergic toxicity with supportive care, temperature control and seizure treatment; cyproheptadine may be used for serotonin antagonism.
Preparations
| Preparation | Form | Strength | Route |
|---|---|---|---|
| Reconcile 8 mg chewable tablet Fluoxetine equivalent supplied as hydrochloride; veterinary behavioural formulation. | Tablet | 8 mg / tablet | PO |
| Reconcile 16 mg chewable tablet Fluoxetine equivalent supplied as hydrochloride; veterinary behavioural formulation. | Tablet | 16 mg / tablet | PO |
| Reconcile 32 mg chewable tablet Fluoxetine equivalent supplied as hydrochloride; veterinary behavioural formulation. | Tablet | 32 mg / tablet | PO |
| Reconcile 64 mg chewable tablet Fluoxetine equivalent supplied as hydrochloride; veterinary behavioural formulation. | Tablet | 64 mg / tablet | PO |
| Fluoxetine oral solution 20 mg/5 mL Check excipients in the actual human formulation. | Oral Liquid | 20 mg / 5 mL | PO |
Monitoring and Administration
Use a behavioural plan and allow several weeks to assess efficacy. Monitor appetite, weight, behaviour and urinary function.
Withdraw gradually after prolonged therapy. A washout of at least five weeks after fluoxetine before an MAO inhibitor, or two weeks after an MAO inhibitor before fluoxetine, is described in the source.
Avoid transdermal substitution: feline transdermal absorption was low and inconsistent.