Apomorphine

Overview

Apomorphine is a rapid-acting, centrally acting emetic primarily used in dogs for the induction of vomiting following recent ingestion of toxins or foreign material. It works reliably and quickly in canine patients, with emesis occurring in the majority of dogs within minutes of administration.

In dogs, apomorphine is considered the emetic of choice in many emergency situations because of its predictable onset, high efficacy, and short duration of action. Vomiting is typically induced within 1 to 15 minutes depending on the route of administration, and the effects usually resolve within a few hours.

Apomorphine is rarely used in cats because it is often ineffective and may cause undesirable neurologic effects. When emesis is indicated in cats, alternative agents (such as alpha-2 adrenergic agonists) are generally preferred.

Mechanism of Action (MOA): Apomorphine stimulates dopamine receptors in the chemoreceptor trigger zone (CTZ) in the brain, leading to activation of the vomiting center. At higher doses, it may also affect other medullary centers, potentially causing CNS or respiratory depression.

Indications

Apomorphine is indicated primarily for the induction of emesis in dogs following recent oral ingestion of toxins, drugs, or foreign material when vomiting is not contraindicated and the patient is clinically stable.

• Induction of emesis in dogs: Used as an emergency decontamination measure after recent ingestion of potentially toxic substances or foreign bodies. Vomiting is induced in approximately 90–100% of dogs when administered appropriately.
• Foreign body ingestion (dogs): May be used to retrieve ingested objects; successful removal has been reported in a substantial proportion of cases when administered promptly after ingestion.
• Early toxin exposure (dogs): Most effective when administered as soon as possible after ingestion, typically within 2 hours, before significant gastric emptying or absorption has occurred.
• Cats: Apomorphine is rarely indicated in cats due to inconsistent efficacy and a higher likelihood of adverse neurologic effects. When emesis is required in cats, alternative agents are generally preferred.

Dosage (Reference)

Dog

In dogs, apomorphine is used extra-label for the induction of emesis following recent oral ingestion of toxins or foreign material. The onset of vomiting is rapid, especially with IV or SC administration.

Cat

Apomorphine is rarely used in cats because it is often ineffective and may cause neurologic adverse effects. When emesis is required in cats, other agents are generally preferred.

Warnings & Precautions

Apomorphine is a potent centrally acting emetic and should be used judiciously, with careful patient selection and timing to minimize the risk of complications. Induction of emesis is not appropriate in all poisoning or foreign body ingestion cases.

• Timing of emesis: Most effective when administered within 2 hours of ingestion. Delayed administration reduces efficacy due to gastric emptying and absorption.
• Contraindicated situations: Do not use in patients that are hypoxic, in cardiovascular shock, in respiratory distress, actively seizuring, comatose, or lacking normal pharyngeal reflexes due to high aspiration risk.
• Caustic or sharp ingestions: Contraindicated after ingestion of sharp objects, strong acids, alkalis, or other corrosive substances because vomiting may worsen esophageal or gastric injury.
• Petroleum distillates: Generally contraindicated due to aspiration risk; may be considered only if the risk of toxicity outweighs the aspiration risk.
• Neurologic risk: Use with extreme caution in animals with a history of seizures, severe CNS depression, or deteriorating neurologic status; emesis may precipitate seizures, especially after ingestion of CNS stimulants.
• Repeated dosing: If emesis does not occur after the initial dose, repeated doses are unlikely to be effective and increase the risk of toxicity.
• Drug-related contraindications: Avoid use in patients with known hypersensitivity to morphine or those with oral opioid or other CNS depressant toxicity.
• Hepatic disease: Patients with hepatic impairment may experience prolonged effects due to hepatic metabolism.
• MDR1 mutation (dogs): Dogs with MDR1 (ABCB1) mutation may develop exaggerated CNS depression and prolonged effects; use cautiously.
• Cats: Use in cats is controversial and generally discouraged due to poor efficacy and increased risk of adverse neurologic effects.
• IV administration (dogs): Although commonly used for rapid emesis, IV administration should be performed with care; IV crystallization and thrombosis have been reported in humans.
• Occupational safety: Classified as a hazardous drug by NIOSH; appropriate personal protective equipment should be used during handling and administration.

Drug Interactions

Drug interactions with apomorphine in dogs (and rarely cats) are mainly related to drugs that alter CNS function, blood pressure, or interfere with the emetic response. Concurrent use is not always contraindicated, but careful risk assessment and monitoring are required.

• Antidopaminergic drugs (eg, metoclopramide, phenothiazines):
  May antagonize dopamine receptors and reduce or completely block the emetic effect of apomorphine.
• Maropitant:
  Negates the emetic effects of apomorphine and should not be used concurrently if emesis is desired.
• Ondansetron:
  May negate the emetic effect; severe hypotension has been reported in humans receiving both drugs.
• Serotonin antagonists (eg, mirtazapine, trazodone):
  May reduce the effectiveness of apomorphine-induced emesis.
• Meclizine:
  May reduce emetic efficacy; additive sedation may occur.
• Opioids (eg, morphine, hydromorphone):
  Additive CNS and respiratory depression may occur; use together cautiously.
• Barbiturates (eg, phenobarbital):
  Increased risk of CNS and respiratory depression and hypotension.
• Other CNS depressants (eg, alpha-2 agonists, benzodiazepines, gabapentin, propofol):
  Additive CNS and respiratory depression may occur.
• Antihistamines with sedative effects (eg, diphenhydramine):
  May enhance sedation.
• Hypotensive agents (eg, amlodipine, enalapril, furosemide, hydralazine, prazosin):
  May increase the risk of hypotension.
• Vasodilators (eg, nitroglycerin, nitroprusside, sildenafil, pentoxifylline):
  Increased risk of hypotension.
• Naloxone:
  May reverse CNS and respiratory depression but can prolong or intensify the emetic effect of apomorphine.
• QT-prolonging drugs (eg, amiodarone, cisapride, clomipramine, quinidine, sotalol):
  May increase the risk of QT interval prolongation.

Side Effects & Overdose

Adverse effects of apomorphine in dogs (and rarely cats) are usually dose related and primarily involve the gastrointestinal and central nervous systems. Most effects are transient and resolve within a few hours with supportive care.

Side Effects

• Protracted nausea and vomiting:
  The most common adverse effect; vomiting may be severe or prolonged, especially with higher doses or subconjunctival administration.
• Sedation and lethargy:
  Frequently observed, particularly with subconjunctival administration.
• Tachycardia:
  Reported in some dogs following administration.
• CNS effects:
  May include depression or stimulation; dogs with the MDR1 (ABCB1) mutation may experience exaggerated CNS depression.

Keynotes

• Dog-specific emetic:
  Apomorphine is highly effective for inducing emesis in dogs but is unreliable and generally avoided in cats.
• Route matters:
  IV administration produces the fastest emetic response, followed by SC; IM and oral routes have slower and less predictable onset.
• Subconjunctival use:
  Can be effective when injectable forms are unavailable, but ocular irritation and prolonged nausea are more common.
• Do not redose:
  Failure to vomit after the initial dose usually indicates poor response; repeat dosing increases toxicity risk without improving efficacy.
• Supportive care remains essential:
  Successful emesis does not eliminate the need for continued monitoring or additional decontamination and treatment.
• Hazardous drug handling:
  Classified by NIOSH as a hazardous drug; appropriate protective measures should be used during preparation and administration.