Apomorphine Hydrochloride

Emetic; Dopamine receptor agonist Opioid derivative (aporphine alkaloid)

Dosage & Administration Guidelines

Species Route Dose Frequency Duration & Clinical Notes
Dog IV 0.02-0.04 mg/kg Single dose Duration: Single administration
Notes: IV administration is rapid; may cause hypotension and CNS depression. Use lower end of dose range.
Dog IM 0.04-0.08 mg/kg Single dose Duration: Single administration
Notes: IM administration is reliable; onset of emesis within 5-10 minutes.
Dog SC 0.04-0.08 mg/kg Single dose Duration: Single administration
Notes: SC administration is commonly used; may cause local irritation.
Dog Conjunctival (ophthalmic) 0.1-0.2 mg/kg (or 1-2 drops of 1% solution) Single dose Duration: Single administration
Notes: Apply to conjunctival sac; onset within 10-15 minutes. May cause conjunctival irritation.
Cat Not recommended Not established Not applicable Duration: Not applicable
Notes: Cats are unreliable responders; use alternative emetics like xylazine or dexmedetomidine.

Clinical Indications & Species Uses

General Indications
  • Induction of emesis in dogs for decontamination after ingestion of toxins or foreign bodies
Dog (Canine)
  • Induction of emesis in cases of toxin ingestion or foreign body ingestion (when appropriate)

Pharmacology & Mechanism of Action

Drug Class: Emetic; Dopamine receptor agonist | Pharmacological Group: Opioid derivative (aporphine alkaloid)

Mechanism of Action: Apomorphine is a non-selective dopamine receptor agonist, primarily acting on D2 receptors in the chemoreceptor trigger zone (CRTZ) of the medulla oblongata. Stimulation of these receptors triggers the vomiting reflex. It also has weak opioid agonist properties, but its emetic effect is primarily due to dopamine receptor activation. In dogs, it is a potent emetic; in cats, it is less effective due to differences in receptor distribution and sensitivity.

Pharmacodynamics: Apomorphine induces vomiting within minutes of administration. It also has sedative and antiemetic effects at lower doses, but at therapeutic doses for emesis, it acts centrally. It may cause central nervous system depression and respiratory depression, especially at higher doses. In dogs, it also has some antitussive effects.

⚡ Pharmacokinetics Summary

Absorption: Apomorphine is well absorbed after subcutaneous or intramuscular injection. Oral administration is less reliable due to first-pass metabolism and variable absorption. Onset of emesis is typically 5-10 minutes after SC/IM injection, and 10-15 minutes after conjunctival administration.
Distribution: Apomorphine is widely distributed, crosses the blood-brain barrier, and has a volume of distribution of approximately 1-2 L/kg in dogs. It is distributed into the CNS, where it acts on the CRTZ.
Metabolism: Apomorphine undergoes extensive hepatic metabolism, primarily via glucuronidation and sulfation. It is metabolized to inactive conjugates. In dogs, the half-life is short, approximately 1-2 hours.
Excretion: Apomorphine and its metabolites are excreted primarily in the urine, with a small amount in feces. Renal excretion is the main route of elimination.
Half-Life: Dog: 1-2 hours; Cat: approximately 1 hour (less predictable)
Bioavailability: Oral bioavailability is low and variable (approximately 20-30%) due to first-pass metabolism. SC/IM administration provides near-complete bioavailability.
Protein Binding: Approximately 90-95% bound to plasma proteins in dogs.

Available Formulations & Strengths

Injectable Solution 10 mg/mL (as hydrochloride) (IV, IM, SC)
Ophthalmic Solution (extemporaneous) 1% solution (10 mg/mL) prepared from injectable (Conjunctival)
Tablet (compounded) Various strengths (e.g., 5 mg, 10 mg) - not commercially available in many countries (PO (not recommended due to poor bioavailability))

Contraindications & Clinical Warnings

Contraindications:
  • Known hypersensitivity to apomorphine or other opioids
  • Ingestion of caustic or corrosive substances (e.g., acids, alkalis) - risk of further esophageal damage
  • Ingestion of sharp objects - risk of perforation
  • Patients with CNS depression, seizures, or respiratory compromise
  • Patients with cardiovascular instability or hypotension
  • Patients with recent abdominal surgery or diaphragmatic hernia
  • Patients with a history of gastric torsion or esophageal disease
Warnings & Clinical Precautions:
  • Use with caution in debilitated or geriatric animals
  • May cause prolonged vomiting; monitor for fluid and electrolyte imbalances
  • May cause CNS depression and respiratory depression; monitor respiratory rate
  • In dogs, may cause hypotension and bradycardia; use with caution in patients with cardiac disease
  • Do not use in animals that cannot vomit (e.g., horses, rabbits, rodents)
  • Protect eyes from contamination when using ophthalmic solution
  • Have emergency equipment and reversal agents (e.g., naloxone) available
  • Use only when emesis is indicated and safe; consider alternative decontamination methods if contraindicated

Adverse Effects & Reactions

Common:

  • Vomiting (prolonged or repeated)
  • Sedation
  • Lethargy
  • Anorexia
  • Hypersalivation
  • Restlessness

Serious / Severe:

  • Respiratory depression
  • Hypotension
  • Bradycardia
  • CNS depression
  • Seizures (rare)
  • Cardiovascular collapse (overdose)

Rare:

  • Allergic reactions (urticaria, angioedema)
  • Hematemesis (due to excessive vomiting)
  • Esophageal irritation or perforation (if contraindicated)

Key Drug Interactions

Interacting Drug / Class Clinical Effect & Mechanism Severity
Opioid antagonists (e.g., naloxone) May reverse the emetic and CNS effects of apomorphine Moderate
Antiemetics (e.g., metoclopramide, maropitant) May antagonize the emetic effect of apomorphine Moderate
Phenothiazines (e.g., acepromazine) May cause additive hypotension and CNS depression; may also reduce emetic efficacy Moderate
Other CNS depressants (e.g., barbiturates, anesthetics) Additive CNS and respiratory depression High
Anticholinergics (e.g., atropine) May reduce the emetic response Mild

Overdose & Toxicity Management

Signs of Toxicity:

  • Severe, prolonged vomiting
  • CNS depression progressing to coma
  • Respiratory depression
  • Hypotension
  • Bradycardia
  • Seizures (rare)
  • Cardiovascular collapse

Emergency Treatment Protocol: Treatment is primarily supportive. Administer naloxone (0.01-0.04 mg/kg IV) to reverse CNS and respiratory effects. Control vomiting with antiemetics (e.g., maropitant 1 mg/kg SC) if necessary. Provide IV fluids for dehydration and electrolyte imbalances. Monitor vital signs closely. In severe cases, provide respiratory support and treat seizures with diazepam or barbiturates.

Food Animal Withdrawal Times

Not approved for use in food animals; no withdrawal times established. Use in food animals is prohibited or extra-label with extended withdrawal periods.

Storage, Handling & Regulatory Information

Storage Temperature: Store at controlled room temperature (20-25°C); protect from light

Light Sensitivity: Light-sensitive — protect from direct exposure.

Handling & Special Conditions: Protect from light; do not freeze. Compounded ophthalmic solutions should be stored refrigerated and used within 30 days.

Dispensing Status: Prescription Required (Rx Only)

Approval Status: FDA-approved for use in dogs (injectable solution).

Extra-Label (Off-Label) Use: In the US, apomorphine is FDA-approved for use in dogs only. Extra-label use in other species is permitted under AMDUCA with appropriate veterinary oversight and withdrawal times.

Clinical Pearls & Practice Notes

💡 Clinical Insights: Apomorphine is the preferred emetic for dogs in many cases due to its rapid onset and high efficacy. It is most effective when administered parenterally (IM or SC) or via the conjunctival route. The conjunctival route is convenient and can be used at home, but it may cause ocular irritation. Always confirm that emesis is safe before administration (e.g., no caustic ingestion, no sharp objects, no CNS depression). After emesis, monitor the patient for signs of aspiration, prolonged vomiting, or CNS depression. In cats, apomorphine is unreliable; consider alternative emetics such as xylazine (0.5-1 mg/kg IV) or dexmedetomidine (0.01-0.02 mg/kg IM). Apomorphine should be used with caution in patients with cardiac disease or respiratory compromise. Have naloxone available for reversal if needed.

References & Literature

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