Buspirone Hydrochloride

Anxiolytic Azapirone (5-HT1A receptor partial agonist)

Dosage & Administration Guidelines

Species Route Dose Frequency Duration & Clinical Notes
Dog PO 0.5-2 mg/kg q8-12h Duration: 2-4 weeks for full effect; long-term for chronic anxiety
Notes: Start at low end and titrate up. May take 1-2 weeks to see initial effects.
Cat PO 0.5-1 mg/kg q12h Duration: 2-4 weeks for full effect; long-term for chronic anxiety
Notes: Commonly used for FIC and anxiety-related urination. May take up to 4 weeks for full effect.
Horse PO 0.5-1 mg/kg q12h Duration: Variable; monitor response
Notes: Limited evidence; may be used for anxiety-related behaviors.
Rabbit PO 0.5-1 mg/kg q12h Duration: Variable; monitor response
Notes: Limited evidence; use with caution.

Clinical Indications & Species Uses

General Indications
  • Anxiolytic for behavioral disorders in companion animals
Dog (Canine)
  • Anxiety disorders (generalized anxiety, separation anxiety, noise phobias)
  • Obsessive-compulsive behaviors (as adjunctive therapy)
  • Aggression (as adjunctive therapy)
Cat (Feline)
  • Feline idiopathic cystitis (FIC) - to reduce stress-related exacerbations
  • Anxiety-related inappropriate urination
  • Aggression (especially inter-cat aggression)
  • Fear-related behaviors
Horse (Equine)
  • Anxiety-related behaviors (e.g., stall vices, trailer anxiety) - limited evidence
Rabbit & Small Mammals
  • Anxiety-related behaviors (limited evidence)
Exotic & Other Species
  • Anxiety in some exotic mammals (e.g., ferrets, rodents) - limited evidence

Pharmacology & Mechanism of Action

Drug Class: Anxiolytic | Pharmacological Group: Azapirone (5-HT1A receptor partial agonist)

Mechanism of Action: Buspirone is a partial agonist at serotonin 5-HT1A receptors, primarily in the dorsal raphe nucleus, leading to reduced serotonergic activity in the amygdala and other limbic areas. It also has modest antagonistic effects at dopamine D2 receptors and alpha-2 adrenergic receptors, but its anxiolytic effect is primarily mediated by 5-HT1A agonism. Unlike benzodiazepines, it does not interact with GABA-A receptors, does not cause sedation, and has no anticonvulsant or muscle relaxant properties.

Pharmacodynamics: Buspirone reduces anxiety without significant sedation or cognitive impairment. It has a slow onset of action (1-2 weeks for full therapeutic effect). It does not produce tolerance or dependence and has no abuse potential. In animals, it may also have some antidepressant and anti-aggressive effects, particularly in cats.

⚡ Pharmacokinetics Summary

Absorption: Rapidly absorbed after oral administration, but undergoes extensive first-pass metabolism, reducing systemic bioavailability. Peak plasma concentrations occur within 1-2 hours in most species.
Distribution: Widely distributed throughout the body. Protein binding is approximately 95% in humans, but may vary in animals. Crosses the blood-brain barrier.
Metabolism: Extensively metabolized in the liver, primarily by cytochrome P450 enzymes (CYP3A4 in humans, but species-specific). Active metabolite, 1-pyrimidinylpiperazine (1-PP), has alpha-2 adrenergic antagonistic activity but contributes minimally to anxiolytic effects.
Excretion: Excreted primarily in urine as metabolites, with a small amount in feces. Biliary excretion may occur in some species.
Half-Life: Dog: 1-2 hours; Cat: 2-4 hours; Horse: 1-2 hours; Humans: 2-3 hours.
Bioavailability: Low and variable due to first-pass metabolism; approximately 4-10% in humans, but may be higher in some animals.
Protein Binding: Approximately 95% in humans; may be lower in some animal species.

Available Formulations & Strengths

Oral Tablet 5 mg, 10 mg, 15 mg, 30 mg (PO)

Contraindications & Clinical Warnings

Contraindications:
  • Hypersensitivity to buspirone
  • Severe hepatic or renal impairment (use with caution)
  • Concurrent use with MAO inhibitors (e.g., selegiline) - risk of hypertensive crisis
  • Use in animals with seizure disorders (may lower seizure threshold in some cases)
Warnings & Clinical Precautions:
  • May take 1-2 weeks to achieve therapeutic effect; do not discontinue abruptly.
  • Use with caution in animals with hepatic or renal disease.
  • Safety in pregnant or lactating animals has not been established; use only when clearly needed.
  • May cause paradoxical excitement or aggression in some animals.
  • Do not use in animals with known hypersensitivity.
  • In cats, may cause increased vocalization or affection in some individuals.

Adverse Effects & Reactions

Common:

  • Sedation (less common than benzodiazepines)
  • Gastrointestinal upset (vomiting, diarrhea)
  • Dizziness or incoordination
  • Increased vocalization (especially in cats)

Serious / Severe:

  • Seizures (rare)
  • Hepatotoxicity (rare)
  • Extrapyramidal signs (rare)

Rare:

  • Hypotension
  • Tachycardia
  • Paradoxical aggression

Key Drug Interactions

Interacting Drug / Class Clinical Effect & Mechanism Severity
MAO inhibitors (e.g., selegiline, amitraz) Increased risk of hypertensive crisis and serotonin syndrome High
Trazodone Additive serotonergic effects; increased risk of serotonin syndrome Moderate
Fluoxetine and other SSRIs Additive serotonergic effects; increased risk of serotonin syndrome Moderate
Ketoconazole, itraconazole, erythromycin May increase buspirone plasma concentrations by inhibiting CYP3A4 Moderate
Rifampin, phenobarbital May decrease buspirone plasma concentrations by inducing CYP3A4 Moderate
Diazepam and other benzodiazepines Additive anxiolytic effects; may increase sedation Mild

Overdose & Toxicity Management

Signs of Toxicity:

  • Sedation
  • Dizziness
  • Nausea and vomiting
  • Miosis
  • Tachycardia or bradycardia
  • Respiratory depression (rare)

Emergency Treatment Protocol: Symptomatic and supportive care. Induce vomiting if recent ingestion and animal is conscious. Administer activated charcoal to reduce absorption. Monitor vital signs and provide IV fluids. There is no specific antidote. Seizures may be treated with diazepam or barbiturates.

Food Animal Withdrawal Times

Not approved for food animals; extra-label use in food animals is prohibited in the US. No withdrawal times established.

Storage, Handling & Regulatory Information

Storage Temperature: Store at room temperature (20-25°C, 68-77°F)

Handling & Special Conditions: Protect from moisture. Keep container tightly closed.

Dispensing Status: Prescription Required (Rx Only)

Approval Status: Not FDA-approved for veterinary use; used extra-label in dogs, cats, and other species.

Extra-Label (Off-Label) Use: In the US, extra-label use in food animals is prohibited by AMDUCA. In companion animals, extra-label use is permitted under veterinary supervision.

Clinical Pearls & Practice Notes

💡 Clinical Insights: Buspirone is a non-sedating anxiolytic that is particularly useful for chronic anxiety in dogs and cats. It is often used as an adjunct to behavioral modification. In cats, it is commonly prescribed for idiopathic cystitis and inappropriate urination due to stress. The onset of action is slow, so it is not suitable for acute anxiety or panic situations. It is generally well-tolerated, but may cause gastrointestinal upset. It should be used with caution in animals with hepatic or renal disease. Drug interactions with SSRIs and MAO inhibitors should be avoided. For best results, combine with a comprehensive behavior modification plan.

References & Literature

  • 📚 Plumb's Veterinary Drug Handbook
  • 📚 Papich Veterinary Pharmacology and Therapeutics
  • 📚 Compendium of Veterinary Products (CVP)