Drugs Used for Emesis Induction in Dogs

Emesis is the action or process of vomiting and is commonly indicated for upper GI decontamination in dogs and cats that have ingested toxic agents or for removal of gastric foreign material.¹ Important contraindications include ingestion of caustic or corrosive agents (eg, bleach, chemicals), high risk for aspiration pneumonia (eg, altered mentation, laryngeal paralysis, absent gag reflex), previous protracted vomiting after toxin ingestion, respiratory distress, ingestion of a nontoxic or very low toxicity substance or dose, severe acid−base abnormalities that could become worse after GI fluid loss, and excessive sedation.²

Physiology

Vomiting is coordinated by the emetic center in the medulla oblongata of the brain stem, leading to an efflux of gastric and proximal duodenal content.³ The emetic center receives afferents from both the CNS and the periphery, particularly the GI tract and vestibular apparatus, but can also include viscera (eg, urinary and reproductive tracts).

The chemoreceptor trigger zone (CRTZ) is located in the medulla oblongata and contains dopamine 2 (D2), neurokinin-1 (NK-1), 5-hydroxytryptamine, acetylcholine, and histamine receptors that respond to substances circulating in the blood. Unlike dogs, cats have a significant number of alpha-2–adrenergic receptors in the CRTZ, making alpha-2–adrenergic agonists more likely to cause emesis.⁴ The forebrain can also provide input to the CRTZ in response to noxious stimuli (eg, pain, repulsive smells or sights).³

Peripheral input from the GI tract acts via NK-1 and serotonin receptors and transmits signals into the emetic center through vagal and other afferents.⁵ The vestibular system can also induce vomiting through histamine and acetylcholine receptors. Knowledge of these receptors is helpful when considering drugs that induce emesis in dogs and cats.

Complications

Complications associated with emesis induction can include aspiration pneumonia, ineffective recovery of ingested substances, sedation, and gastroesophageal intussusception (rare).⁶

Administration of an antiemetic (maropitant, 1 mg/kg IV or SC; metoclopramide, 0.4-0.6 mg/kg SC or 2 mg/kg/day IV CRI; ondansetron, 0.5-1 mg/kg IV) should be considered after successful emesis induction to prevent protracted nausea and/or retching.^7-9

Emetic drugs can act via peripheral or central mechanisms.

Keep scrolling for details on drugs used for emesis induction in dogs. To read about drugs used for emesis induction in cats, click here.

Ropinirole

Ropinirole is an FDA-approved selective D2 agonist that acts on the CRTZ to induce vomiting in dogs.

Formulation

• Ophthalmic solution (30 mg/mL) in single-use droppers

Dosage

• 3.75 mg/m² ophthalmic (see Table for number of drops)¹⁰

Table: Ropinirole Ophthalmic Solution Manufacturer Recommendations¹⁰

*Table adapted from package insert.⁵²

Key Points

• 95% efficacy in healthy dogs in one study¹¹ 

• A second dose can be administered if vomiting does not occur within 20 minutes.¹⁰ 

• Should not be given to patients with pre-existing ocular irritation, ulceration, or injury¹⁰  

• Most commonly reported adverse effects include tachycardia, lethargy, and hypotension. Mildly to moderately injected gums, elevated third eyelid(s), and conjunctival discharge were transiently noted.^11,12  

• Can be specifically antagonized by metoclopramide in cases of protracted emesis¹¹  

• Not expected to work in cats due to the low number of dopamine receptors in the CRTZ¹³ 

• Not labeled for use in cats 

Apomorphine

Apomorphine induces emesis via nonselective dopamine receptor agonism in the CRTZ. Cross-reactivity with opioids, 5-hydroxytryptamine, and alpha-adrenergic receptors can contribute to adverse effects (eg, sedation).¹⁴ Apomorphine is generally the emetic of choice in dogs because of its rapid onset and ability to reverse action; however, this drug is not recommended in cats due to lack of efficacy and dopamine-mediated hyperexcitability.^15,16 Use of apomorphine as an emetic is extra-label in dogs.¹⁷

Formulation

• Injectable and ocular formulations available in various concentrations  

• Tablets available in some areas  

• Usually obtained through compounding pharmacies¹⁷ 

Dosage

• 0.03 mg/kg IV, 0.04 mg/kg IM, or 0.01-0.04 mg/kg SC¹⁷ 

• Subconjunctival: crushed 6.25 mg tablet dissolved in sterile isotonic saline and applied to the conjunctiva 

• Gingival: 6.25 mg tablet dissolved onto the gingival mucosa¹⁸

Key Points

• Appears to be highly effective in dogs, with successful emesis reported in 80% to 97% of cases^12,18,19  

• SC or IV administration may be more effective than IM.²⁰  

  • In a study, SC administration was as effective as IV administration in inducing emesis^12,17,19; however, median time to onset of emesis was 13.5 minutes and 2 minutes for SC and IV administration, respectively. 

  • IV administration has a faster onset than IM or SC; therefore, the IV route should be used following ingestion of toxicants associated with rapid GI absorption.  

• Depending on regional availability, the injectable form may need to be compounded or made by aseptically dissolving a tablet and administering through a filter.^21,22 

  • Apomorphine solutions are not stable and should be freshly made before each administration.   

• Gingival administration (ie, massaging one tablet onto the gingiva for 3-5 seconds until fully dissolved) can be highly effective.¹⁸ 

  • Not effective when administered orally due to heavy first-pass metabolism¹⁸  

• Should be freshly made before applying to the conjunctiva; diluting the pill with sterile saline minimizes ocular irritation, and the eye should be copiously flushed once vomiting occurs.¹⁷  

• Ocular inserts (2 mg/insert) can also be used successfully (83.5%).²³ 

• Administration can be repeated if needed, but adverse effects (eg, sedation) are dose dependent.¹⁹ 

  • Other adverse effects include excessive vomiting, tachycardia, and CNS depression, which may be exacerbated in patients with the multidrug sensitivity gene (MDR1 gene, also known as ABCB1 gene).^24,25  

  • Ocular irritation may occur with conjunctival administration.^12,17,26  

• Naloxone reverses sedation without affecting nausea.¹⁷  

Hydrogen Peroxide

Hydrogen peroxide induces emesis through direct stimulation of peripheral afferents in the esophagus and stomach and is typically administered by the pet owner or when other emetics are unavailable. This drug should not be given to cats due to the high risk for adverse effects (including potentially fatal necroulcerative hemorrhagic gastritis) and inconsistent emetic effects.²⁷ Use of hydrogen peroxide as an emetic is extra-label in dogs.

Formulation

• 3% solution 

• Higher concentrations (eg, 30% solutions) should not be used.

Dosage

• 1-2.2 mL/kg PO (maximum, 45-50 mL/dog)^26,28 

Key Points

• Efficacy of up to 90% was reported in one study.²⁶ 

• An additional dose may be administered if emesis is not successful after 10 to 15 minutes.²⁸ 

• Adverse effects include persistent GI signs and lethargy. Significant esophageal and gastric lesions, including necrosis and air embolization, can occur even in healthy dogs.^26,29 

• Risk for adverse effects should be weighed against the danger of the toxicant prior to recommending at-home emesis induction.

Tranexamic Acid

Tranexamic acid (TXA) is a plasminogen lysine analogue primarily studied for its antifibrinolytic effects. TXA is thought to induce vomiting via NK-1 receptor agonism and has been shown to bind within the emetic center and CRTZ.³⁰ Use of TXA as an emetic is extra-label in dogs and is rarely used for this purpose.

Formulation

• Injectable (100 mg/mL)

Dosage

• 50 mg/kg IV once (repeat administration of 20-50 mg/kg may be given 1-2 times if needed)^31-33 

Key Points

• Efficacy of 94% in one study³³; generally causes 1 to 2 episodes of vomiting within minutes 

• Adverse effects are rare but may include seizures and hemostatic disorders, including decreased fibrinolysis.^33,34 

• Availability may vary significantly by region, and use may be cost prohibitive.

Not Recommended

Salt 

• Risk for hypernatremia and sodium toxicosis⁴⁹ 

Syrup of ipecac  

• Risk for cardiotoxicosis⁴⁹ 

Sodium carbonate or other irritants

• Potential for severe mucosal injury and lower efficacy^50,51 

Conclusion

Many drugs with species-specific indications and adverse effects are available for inducing emesis in dogs and cats. Prompt emesis induction can reduce life-threatening adverse effects of toxicants or bowel obstruction associated with ingestion of foreign material.