Sertraline Hydrochloride

Selective Serotonin Reuptake Inhibitor (SSRI) Antidepressant

Dosage & Administration Guidelines

Species Route Dose Frequency Duration & Clinical Notes
Dog PO 1-3 mg/kg q24h (once daily) Duration: Usually 4-8 weeks; may be long-term for chronic conditions
Notes: Start at lower end (1 mg/kg) and titrate up gradually over 2-4 weeks. Administer with food to reduce GI upset. Therapeutic effects may take 2-4 weeks.
Cat PO 0.5-1 mg/kg q24h (once daily) Duration: Usually 4-8 weeks; may be long-term
Notes: Cats are sensitive to side effects; start at 0.5 mg/kg and increase slowly. Use with caution in cats with hepatic or renal impairment.
Horse PO 0.5-1 mg/kg q24h (once daily) Duration: Variable; not well established
Notes: Limited data; use only under veterinary supervision. Monitor for behavioral changes.
Rabbit PO 0.5-1 mg/kg q24h (once daily) Duration: Variable; not well established
Notes: Limited data; use with caution. Monitor for GI stasis.

Clinical Indications & Species Uses

General Indications
  • Behavioral disorders (anxiety, phobias, compulsive behaviors)
  • Adjunctive therapy for aggression
Dog (Canine)
  • Separation anxiety
  • Generalized anxiety
  • Compulsive behaviors (e.g., flank sucking, tail chasing)
  • Aggression (as part of a behavior modification plan)
  • Noise phobias (adjunctive therapy)
Cat (Feline)
  • Urine spraying/marking
  • Anxiety-related inappropriate elimination
  • Compulsive behaviors (e.g., overgrooming)
  • Aggression (as part of a behavior modification plan)
Horse (Equine)
  • May be used off-label for stereotypic behaviors (e.g., cribbing, weaving) in some cases

Pharmacology & Mechanism of Action

Drug Class: Selective Serotonin Reuptake Inhibitor (SSRI) | Pharmacological Group: Antidepressant

Mechanism of Action: Sertraline is a selective serotonin reuptake inhibitor (SSRI) that potentiates serotonergic activity in the central nervous system by blocking the reuptake of serotonin (5-HT) into presynaptic neurons. This increases the availability of serotonin in the synaptic cleft, enhancing neurotransmission. Sertraline has minimal effects on norepinephrine and dopamine reuptake, and it does not bind to muscarinic, histaminergic, or alpha-adrenergic receptors, which contributes to its relatively favorable side-effect profile compared to tricyclic antidepressants.

Pharmacodynamics: Sertraline produces antidepressant and anxiolytic effects by enhancing serotonergic transmission. It also downregulates 5-HT receptors over time, which may contribute to its therapeutic effects. In veterinary medicine, it is used to manage behavioral disorders such as separation anxiety, compulsive behaviors, and aggression. The onset of therapeutic effect is typically 2-4 weeks, requiring consistent dosing. Sertraline also has mild analgesic effects in some neuropathic pain models, but this is not a primary indication.

⚡ Pharmacokinetics Summary

Absorption: Sertraline is well absorbed after oral administration, with peak plasma concentrations occurring approximately 4-8 hours post-dose in dogs. Food increases the area under the curve (AUC) by about 30% and increases peak concentration, so it is recommended to administer with food to reduce gastrointestinal upset and improve consistency.
Distribution: Sertraline is extensively distributed throughout the body, with a large volume of distribution. It crosses the blood-brain barrier and placenta, and is excreted in milk. In dogs, the volume of distribution is approximately 20 L/kg. It is highly lipophilic, leading to accumulation in tissues.
Metabolism: Sertraline undergoes extensive hepatic metabolism, primarily by cytochrome P450 enzymes (CYP2D6, CYP3A4, and others). The major metabolite, N-desmethylsertraline, is significantly less active (approximately 5-10% of the parent drug's activity). In dogs, the half-life of sertraline is approximately 15-20 hours, but the active metabolite may have a longer half-life.
Excretion: Sertraline and its metabolites are excreted primarily in the urine and feces. In humans, about 40-45% is excreted in urine and 45-50% in feces. In veterinary species, similar pathways are expected, but specific data are limited.
Half-Life: Dog: 15-20 hours; Cat: approximately 24 hours (estimated); Horse: approximately 6-8 hours (limited data); Other species: not well documented.
Bioavailability: Oral bioavailability is approximately 80-90% in dogs, but it is reduced by first-pass metabolism. Food increases bioavailability slightly.
Protein Binding: Sertraline is highly protein-bound (approximately 98%) in humans, primarily to albumin and alpha-1-acid glycoprotein. Similar binding is expected in veterinary species.

Available Formulations & Strengths

Oral Tablet 25 mg, 50 mg, 100 mg (PO)
Oral Capsule 25 mg, 50 mg, 100 mg (PO)
Oral Solution 20 mg/mL (PO)

Contraindications & Clinical Warnings

Contraindications:
  • Hypersensitivity to sertraline or any component of the formulation
  • Concurrent use of MAO inhibitors (e.g., selegiline, amitraz) - risk of serotonin syndrome
  • Concurrent use of other serotonergic drugs (e.g., SSRIs, SNRIs, tramadol, buspirone) - risk of serotonin syndrome
  • Use in animals with severe hepatic impairment
  • Use in animals with a history of seizures (may lower seizure threshold)
Warnings & Clinical Precautions:
  • Use with caution in animals with hepatic or renal disease; dose adjustment may be necessary.
  • Use with caution in animals with cardiovascular disease; may cause bradycardia or hypotension.
  • May cause behavioral changes, including increased anxiety or agitation, especially during initial therapy.
  • Do not discontinue abruptly; taper dose gradually to avoid withdrawal symptoms.
  • Use in pregnant or lactating animals only if clearly needed; safety not established.
  • In cats, monitor for signs of anorexia, vomiting, or lethargy.
  • In horses, use with caution due to limited safety data.
  • May interact with drugs metabolized by CYP450 enzymes; monitor for adverse effects.

Adverse Effects & Reactions

Common:

  • Gastrointestinal upset (vomiting, diarrhea, decreased appetite)
  • Lethargy or sedation
  • Behavioral changes (increased anxiety, agitation)
  • Mydriasis (pupil dilation)

Serious / Severe:

  • Serotonin syndrome (hyperthermia, tremors, seizures, agitation, diarrhea)
  • Hepatotoxicity (elevated liver enzymes)
  • Cardiac arrhythmias (rare)
  • Seizures (especially in animals with a history of epilepsy)

Rare:

  • Hypersensitivity reactions (rash, angioedema)
  • Bleeding disorders (due to platelet dysfunction)
  • Hyponatremia (especially in elderly or dehydrated animals)

Key Drug Interactions

Interacting Drug / Class Clinical Effect & Mechanism Severity
MAO inhibitors (e.g., selegiline, amitraz) Risk of severe serotonin syndrome (hyperthermia, tremors, seizures, death). Avoid concurrent use and allow a washout period of at least 14 days. High
Other SSRIs/SNRIs (e.g., fluoxetine, venlafaxine) Additive serotonergic effects, increased risk of serotonin syndrome. High
Tramadol Additive serotonergic effects, increased risk of serotonin syndrome. High
Buspirone Additive serotonergic effects, increased risk of serotonin syndrome. High
NSAIDs (e.g., carprofen, meloxicam) Increased risk of gastrointestinal bleeding due to platelet inhibition. Moderate
Warfarin and other anticoagulants Increased risk of bleeding due to platelet inhibition. Moderate
CYP2D6 inhibitors (e.g., quinidine, fluoxetine) May increase sertraline levels, leading to toxicity. Moderate
CYP3A4 inducers (e.g., phenobarbital) May decrease sertraline levels, reducing efficacy. Moderate

Overdose & Toxicity Management

Signs of Toxicity:

  • Vomiting
  • Lethargy
  • Tremors
  • Seizures
  • Hyperthermia
  • Agitation
  • Tachycardia or bradycardia
  • Mydriasis
  • Respiratory depression

Emergency Treatment Protocol: Treatment is primarily supportive. Induce vomiting if recent ingestion (within 1-2 hours) and the animal is conscious. Administer activated charcoal to reduce absorption. Provide intravenous fluids for hydration and electrolyte balance. Control seizures with diazepam or barbiturates. Monitor for serotonin syndrome and treat with cyproheptadine (1.1 mg/kg in dogs, 2-4 mg per cat) if severe. Provide symptomatic and supportive care, including temperature regulation and cardiac monitoring.

Food Animal Withdrawal Times

Sertraline is not approved for use in food animals. Withdrawal times are not established. Use in food animals is prohibited or requires a very long withdrawal period; consult regulatory authorities. In the US, extra-label use in food animals is not permitted under AMDUCA for non-approved drugs.

Storage, Handling & Regulatory Information

Storage Temperature: Store at controlled room temperature (20-25°C, excursions permitted to 15-30°C).

Handling & Special Conditions: Protect from moisture. Keep in a tightly closed container. Do not freeze oral solution.

Dispensing Status: Prescription Required (Rx Only)

Approval Status: Not approved for veterinary use; approved for human use.

Extra-Label (Off-Label) Use: Sertraline is not FDA-approved for veterinary use. Use in animals is extra-label. In the US, extra-label use is permitted under AMDUCA for non-food animals only if a valid veterinarian-client-patient relationship exists. Use in food animals is prohibited due to lack of withdrawal times and potential for residues.

Clinical Pearls & Practice Notes

💡 Clinical Insights: Sertraline is used off-label in veterinary medicine primarily for behavioral disorders such as separation anxiety, compulsive behaviors, and aggression. It is a good choice for animals that do not respond to other SSRIs like fluoxetine. Dosing should be individualized, starting low and titrating up. Clinical response may take 2-4 weeks, and owners should be counseled not to expect immediate results. Adverse effects are usually mild and transient, but serious reactions like serotonin syndrome can occur if combined with other serotonergic drugs. Regular monitoring of liver function and behavior is recommended. In cats, use with caution due to sensitivity. Sertraline should be administered with food to reduce GI upset. Abrupt discontinuation should be avoided; taper over 1-2 weeks. Always consider a comprehensive behavior modification plan in conjunction with pharmacotherapy.

References & Literature

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