Drugs Used for Emesis Induction in Cats

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 cats. To read about drugs used for emesis induction in dogs, click here.

Dexmedetomidine

Dexmedetomidine is an alpha-2–adrenergic agonist that acts on the CRTZ to induce emesis in cats.¹⁶ This drug is generally considered the emetic agent of choice in cats due to high concentration of alpha-2–adrenergic receptors in the CNS; in dogs, however, alpha-2–adrenergic agonists are unlikely to induce emesis. Use of dexmedetomidine as an emetic is extra-label.

Formulation

• Injectable (100 or 500 µg/mL)

Dosage

• 7-10 µg/kg IM (up to 18 µg/kg has been reported)³⁵

• 3.5 µg/kg IV³⁵

Key Points

• Efficacy is reported as 58% to 81%.^4,16

• Evidence in cats supports superior efficacy compared with xylazine.⁴

• Sedative adverse effects can be reversed with atipamezole.³⁵

• Other common adverse effects include peripheral vasoconstriction, hypertension, arrhythmias, and reflex bradycardia.³⁵

• Caution should be used in cats with cardiac disease or hemodynamic instability.

• Administration of butorphanol may reduce the emetic effect.³⁶

• One study evaluating application of oral detomidine transmucosal gel in cats demonstrated that 100% of healthy cats vomited after administration,³⁷ making this route of administration a possible alternative to injectable dexmedetomidine for emesis induction.

  • Avoiding needles may reduce anxiety related to visiting the clinic and promote stress-free handling in cats.

Xylazine

Xylazine is an alpha-2–adrenergic agonist that acts on the CRTZ to induce emesis in cats.³⁸ Although xylazine has historically been the agent of choice in cats, dexmedetomidine is currently more readily available and preferred. Use of xylazine as an emetic is extra-label.

Formulation

• Injectable (20 or 100 mg/mL)

Dosage

• 0.44 mg/kg IM³⁹

• 1.1 mg/kg IM or SC³⁹

Key Points

• Efficacy is reported as 51% to 60%.^4,16,40

• Adverse effects include hypertension, hypotension, bradycardia, CNS depression, and sedation.^39,41

• Alternative drugs should be considered in patients with cardiac disease or hemodynamic instability.

• May be reversed with yohimbine or tolazoline³⁹

Brimonidine

Brimonidine is an ophthalmic alpha-2–adrenergic agonist primarily used in the treatment of elevated intraocular pressure. Use of brimonidine as an emetic is extra-label.

Formulation

• Ophthalmic (0.1%, 0.15%, or 0.2%)

Dosage

• 1 drop in either eye⁴²

Key Points

• Efficacy is reported as 80% to 100% in small populations of cats.^37,43

• Adverse effects include hypotension, hypertension, bradycardia, and CNS depression.⁴²

• Alternative drugs should be considered in patients with cardiac disease or hemodynamic instability.

Hydromorphone

Hydromorphone is a pure mu-opioid agonist that induces emesis through stimulation of the CRTZ. Although the emetic adverse effects of pure mu opioids have been well documented in dogs and cats,^44,45 use as an emetic in dogs is not reported. Use of hydromorphone as an emetic is extra-label.

Formulation

• Injectable (1, 2, or 4 mg/mL)

Dosage

• 0.1 mg/kg SC^46-48

Key Points

• Efficacy is reported as ≈75% in one study.⁴⁸

• Sedation effect may be reduced in cats compared with dexmedetomidine.⁴⁸

• Adverse effects may include sedation and hyperthermia.⁴⁶

• Sedative effects can be reversed with naloxone if needed; it is uncertain whether naloxone has an effect on the emetic actions of hydromorphone.⁴⁶

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.