Fluvoxamine
**Fluvoxamine** is a selective serotonin-reuptake inhibitor (SSRI) antidepressant used in veterinary medicine to treat a variety of behavior disorders in dogs and cats, including aggression and stereotypic or obsessive-compulsive behaviors. While not as commonly prescribed as fluoxetine, it serves as a viable alternative for behavioral management. **Clinical Pearls:** - Like all SSRIs, fluvoxamine requires a prolonged trial period (typically **6-8 weeks**) to achieve full clinical efficacy due to the time required for neuroreceptor down-regulation. - It should not be abruptly discontinued; tapering over 3-5 weeks is recommended to avoid withdrawal signs. - Anorexia is a common, though usually transient, side effect in dogs that can sometimes be managed by hand-feeding or increasing food palatability.
Mechanism: Fluvoxamine acts by highly selective inhibition of the **serotonin transporter (SERT)** in the central nervous system. **Mechanism:** Blockade of presynaptic reuptake โ increased concentration of **serotonin (5-HT)** in the synaptic cleft โ prolonged receptor stimulation. Over time, this chronic elevation leads to the down-regulation and desensitization of post-synaptic 5-HT receptors, which correlates with the delayed onset of clinical behavioral improvement. It has minimal to no effect on dopamine or norepinephrine reuptake.
Dosing by species
- For treatment of compulsive disorders ยท 0.25-0.5 mg/kg PO once daily ยท PO ยท q24h
- For treatment of behavioral diagnoses ยท 0.25-0.5 mg/kg PO q24h ยท PO ยท q24h ยท Treat for 3-5 weeks minimum to assess effects; then treat until 'well' (minimum another 1-2 months). Continue for another 1-2 months minimum. ยท Treatment should last for a minimum 4-6 months once initiating therapy. If weaning off, do so over 3-5 weeks (or longer).
- For spraying ยท 0.25 mg/kg PO q12h ยท PO ยท q12h ยท Avoid use with benzodiazepines
- For treatment of behavioral diagnoses ยท 0.5-1 mg/kg PO once daily (q24h) ยท PO ยท q24h ยท allow 8 weeks for initial trial
- For treatment of compulsive disorders ยท 0.5-2 mg/kg PO twice daily ยท PO ยท q12h
- For treatment of behavioral diagnoses ยท 1-3 mg/kg PO once daily (q24h) ยท PO ยท q24h ยท allow 8 weeks for initial trial
- For treatment of behavioral diagnoses ยท 1 mg/kg PO q12-24h ยท PO ยท q12-24h ยท Treat for 3-5 weeks minimum to assess effects; then treat until 'well' (minimum another 1-2 months). Continue for another 1-2 months minimum. ยท Treatment should last for a minimum 4-6 months once initiating therapy. If weaning off, do so over 3-5 weeks (or longer).
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Routes of administration
Contraindications
- Patients with known hypersensitivity to fluvoxamine or other SSRIs
- Concurrent use of Monoamine Oxidase Inhibitors (MAOIs) such as selegiline or amitraz
- Concurrent use of cisapride
Adverse effects
- Anorexia/decreased appetite (common)
- Lethargy or sedation
- Gastrointestinal upset (vomiting, diarrhea)
- Anxiety, irritability, or agitation
- Insomnia or hyperactivity
- Panting (dogs)
- Changes in elimination patterns (cats)
- Paradoxical aggressive behavior in previously non-aggressive dogs
Drug interactions
- Buspirone ยท Fluvoxamine may paradoxically decrease the clinical efficacy of buspirone.
- Cisapride ยท Fluvoxamine may increase plasma levels of cisapride, leading to toxicity. Concurrent use is contraindicated.
- Cyproheptadine ยท May decrease or reverse the effects of SSRIs (useful in treating serotonin syndrome).
- Diazepam, Alprazolam, Midazolam ยท Fluvoxamine may increase diazepam (and other benzodiazepine) levels.
- Diltiazem ยท Fluvoxamine may increase the effects of diltiazem; bradycardia has been reported in humans.
- MAO Inhibitors (e.g., amitraz, selegiline) ยท High risk for serotonin syndrome; contraindicated. A 5-week washout is required after stopping fluvoxamine, and a 2-week washout if stopping the MAOI first.
- Methadone ยท Fluvoxamine may increase plasma levels of methadone, leading to toxicity.
- Phenytoin ยท Increased plasma levels of phenytoin possible.
- Propranolol, Metoprolol ยท Fluvoxamine may increase these beta-blockers' plasma levels; atenolol may be safer.
- Theophylline ยท Fluvoxamine may increase plasma levels of theophylline.
- Tramadol ยท SSRIs can inhibit the metabolism of tramadol to active metabolites, decreasing efficacy and increasing toxicity risk (serotonin syndrome, seizures).
Monitoring
- Clinical efficacy (behavioral improvement)
- Adverse effects, particularly appetite and body weight
- Baseline liver function tests (consider re-testing as needed)
- ECG (consider baseline and re-test as needed)
Overdose
Limited data exists for animals. Any dosage over **10 mg/kg** can reportedly cause tremors and lethargy. **Clinical Signs of Overdose:** Vomiting, somnolence/coma, tremors, diarrhea, hypotension, heart rate/rhythm disturbances (bradycardia/tachycardia, ECG changes), and seizures. Fatalities have been reported in human overdoses. **Treatment:** - Standard protocols for GI decontamination (drug adsorption/removal) for potentially dangerous overdoses. - Symptomatic and supportive therapy. - **Serotonin Syndrome Management:** Cyproheptadine (1.1 mg/kg PO or rectally) may be used as an adjunctive treatment to negate serotonin effects. - **Seizure Control:** Diazepam may be used to treat seizures or other severe neurologic signs.
VetSheet drug reference is intended for licensed veterinary professionals as a clinical decision-support aid, not a substitute for professional judgement or the manufacturerโs current label.