Emetics in Small Animals

Emesis induction is often the first procedure performed on a poisoned patient, but it is rarely the only one needed. It may also be used to remove foreign bodies that pose an obstruction risk.¹ However, as with other medical procedures, emesis carries risks and therefore should be performed only when the benefits outweigh those risks. This article discusses the indications for and against emesis, as well as agents available for use in achieving it.

Indications for Emesis

Timing

Depending on the time from toxicant ingestion, emesis may be useful in limiting toxic effects.² Rapidly dissolving medications (e.g., chewable, rapid-dissolve, liquid) may be absorbed in as little as 15 to 30 minutes; therefore, after that time period, emesis may be useless. On the other hand, emesis may be warranted for 4 to 6 hours after ingestion of an extended- or sustained-release medication, depending on when the stomach empties. Emesis may be performed up to 4 hours after grain-based rodenticides are ingested, and chocolate, especially if ingested in large quantities, has been recovered up to 12 hours after ingestion. If in doubt, consult an animal poison control center (e.g., ASPCA Animal Poison Control Center, 888-426-4435 [aspca.org/pet-care/animal-poison-control]; the Pet Poison Helpline, 800-213-6680 [petpoisonhelpline.com]).

Dosage

If possible, a dosage should be determined for the ingested toxicant. In this context, dosage is defined as amount of toxicant per unit of body weight.³ Depending on the dosage, signs may not occur, or they may be mild, serious, or life-threatening. Emesis should be reserved for cases in which serious or life-threatening signs would be expected.

Contraindications for Emesis

Species

Certain animals are incapable of vomiting, and emesis should not be attempted in these species. These include rodents, rabbits, and birds.^4,5

Agents

Emesis is contraindicated for ingestion of certain agents, including corrosive agents such as acids, alkalis, and cationic detergents. For these agents, the damage is local to the gastrointestinal (GI) tract, and emesis can reexpose the esophagus and oropharynx to the agent. Emesis should also not be induced in animals that have ingested petroleum distillates owing to increased risk of aspiration pneumonia.²

Preexisting Conditions

Cardiac and respiratory disease may increase the risk of adverse events if emesis is performed. In addition, brachycephalic breeds, especially those with significant pathology such as overlong soft palate, may be at a greater risk for problems (e.g., respiratory difficulties, aspiration). In these cases, if emesis is induced, it is best undertaken by a veterinarian in a clinical setting. Other therapies may be preferable in these patients.

Presence of Clinical Signs

Emesis should not be induced in animals that are already showing signs of intoxication. This includes having already started to vomit, showing central nervous system (CNS) alterations (ataxia, tremors, decreased mentation, seizures, or coma), or experiencing significant bradycardia. In the last instance, stimulation of the vagal nerve to induce emesis may worsen the bradycardia and lead to syncope. Emesis in these animals is unlikely to be helpful and increases the risk of adverse events such as aspiration.²

General Considerations for Inducing Emesis

Feeding

Prior to inducing emesis, if the animal has not eaten recently, a small meal should be fed to increase chances of recovering the toxicant. Torn-up pieces of bread, kibble, or canned food can be used.

Observation

The patient should be monitored throughout the process. Following emesis, the animal should be prevented from ingesting the vomitus and reexposing itself to the toxicant. Similarly, if emesis is performed at home, other animals should be prevented from ingesting the vomitus to avoid exposing them to the poison.

Examination of Vomitus

The vomitus should be examined for signs of the ingested agent. If possible, attempts to quantify how much was recovered should be made and the risk of continued intoxication can then be reevaluated.

Recommended Agents for Emesis

Dogs

Hydrogen Peroxide

Hydrogen peroxide (3%) can be used at home or in the veterinary clinic.⁶

Mechanism of action: Hydrogen peroxide irritates the oropharynx and stomach, leading to emesis.⁷

Form: Hydrogen peroxide is a liquid that is readily available over the counter.

Administration: Hydrogen peroxide is administered at a dose of 2.2 mL/kg (1 mL/lb) PO; the maximum dose is 45 mL (3 tablespoons) per dog. A second dose can be administered 10 to 15 minutes after the first dose only if no emesis is seen.⁶ The hydrogen peroxide can be mixed with a few drops of milk or ice cream to encourage voluntary ingestion, or it may be administered with a dosing syringe. Light exercise may increase the chance of emesis.

Success rate: 90%⁶

Adverse reactions: Overdosage or use of solutions greater than 3% can result in upper GI irritation and hemorrhage. In such cases, sucralfate and acid reducers (histamine H₂ blockers, proton-pump inhibitors) can be given for 5 to 7 days. Even at recommended doses, small hemorrhages can be seen in the stomach but are usually subclinical.⁸ Hydrogen peroxide should not be administered to cats as it can result in severe, even fatal, hemorrhagic gastritis even at recommended doses.⁷ Hydrogen peroxide is best used when time is of the essence and emesis at home is useful. Otherwise, it may be safer to induce emesis in a veterinary setting.

Apomorphine

Mechanism of action: Apomorphine is an opioid derivative that is also a dopamine agonist. In dogs, vomiting is mediated by the chemoreceptor trigger zone (CRTZ) via dopamine receptors.⁹ Apomorphine can also suppress emesis through its stimulation of opioid receptors.⁹ Therefore, administering repeated doses may not be effective.⁹ However, administration of naloxone may block suppression and enhance emesis.¹⁰

Form: Apomorphine comes as a 6.25-mg tablet.² It can also be compounded into a powder or into a sterile solution for intravenous use.

Administration: Apomorphine can be administered orally, but owing to the slowness of action and high first-pass effect, this route is not recommended.⁶ It can be given subcutaneously or intramuscularly, but only if a sterile solution is available. The subcutaneous route appears to be more effective than the intramuscular route.¹⁰ The most common methods of administration are conjunctivally or intravenously.

For conjunctival administration, the tablet or powder is instilled in the eye under the lower eyelid. The pill or powder can be dissolved in saline to aid administration, especially in exophthalmic dogs. The author recommends numbing the eye with local anesthetic first. Vomiting will occur within 15 minutes, after which the remaining drug can be flushed out of the eye using sterile saline.⁶

Intravenous administration of 0.03 to 0.1 mg/kg of a sterile solution appears to be the most effective and rapid method of inducing emesis.^6,10 Vomiting is generally rapid following IV administration.

Since vomiting is aided by stimulation of the vestibular system, walking the patient may increase the efficacy of apomorphine.⁹

Success rate: 94% to 100%^2,6,10

Adverse reactions: Since apomorphine is an opioid derivative, it can cause CNS depression. Use with care in animals that have ingested CNS depressants, in which case it may enhance clinical signs. CNS depression can be reversed with naloxone, but this will not reverse the vomiting.² Metoclopramide, a dopamine antagonist⁹; maropitant; or a similar antiemetic can be given to control vomiting.² Installation into the eye may be irritating.

The use of apomorphine in cats is not recommended owing to differences in CRTZ receptors in that species.⁹ Apomorphine has low success rates in cats (<10%) and may cause opioid “mania” in cats.²

Ropinirole

Ropinirole ophthalmic solution (Clevor; Vetoquinol, vetoquinolusa.com) is a U.S. Food and Drug Administration–approved emetic for dogs.

Mechanism of action: Ropinirole is a dopamine agonist with high activity on dopamine D₂-type receptors. In dogs, vomiting is mediated by the CRTZ via these specific receptors.^11,12

Form: Ropinirole is supplied as a 0.3-mL single-dose dropper containing 9 mg of ropinirole.¹²

Administration: Ropinirole is administered as an eye drop at a rate of 3.75 mg/m² (dose range, 2.7 to 5.4 mg/m²; TABLE 1). If the dog does not vomit within 20 minutes of the first dose, a second dose can be administered.¹²

Success rate: In one study, 95% of dogs vomited after administration. Only 1 dose was needed in 86% of the dogs who vomited. Approximately half the dogs vomited within 10 minutes.¹¹

Adverse reactions: Mild ocular irritation was noted but abated within 8 hours. A mild increase in heart rate was also noted, but it resolved within 2 hours.^11,12 For protracted vomiting, metoclopramide (0.5 mg/kg SC/IM), a D₂ antagonist, may be administered.¹³

Ropinirole is not approved for use in cats. Further, as with apomorphine, it is expected that ropinirole, as a D₂ agonist, would not be effective in cats owing to differences in emetic receptors in the CRTZ.

Cats

α₂ Agonists

Xylazine or dexmedetomidine hydrochloride (Dexdomitor; Zoetis, zoetisus.com).

Mechanism of action: In cats, vomiting is mediated via α₂ receptors in the CRTZ.^9,13

Form: Xylazine and dexmedetomidine are injectables.

Administration: Xylazine is administered at 0.44 mg/kg IM. Dexmedetomidine can be administered at 7 µg/kg IM or 3.5 µg/kg IV.¹³ (Anecdotally, some veterinarians have reported increased success by placing the cat in a carrier and slowly spinning the carrier on an office chair immediately after administering the dexmedetomidine.)

Success rate: With xylazine, success rates are approximately 56%, while with dexmedetomidine, they are about 58% to 81%.^13,14

Adverse reactions: CNS depression can be seen.⁹ As with apomorphine, care should be taken when administering these drugs if a CNS depressant was ingested. The effects of α₂ agonists can be reversed with yohimbine 0.11 mg/kg SC/IM/IV (xylazine)¹³ or atipamezole 70 mcg/kg IM¹⁴ (xylazine, dexmedetomidine).

Emetic Agents to Avoid

Salt: Table salt or saltwater should not be used to induce emesis. Retention of sodium can lead to severe hypernatremia, which may cause seizures, coma, and death.²

Syrup of ipecac: Historically, this was given to children to induce emesis. However, production of syrup of ipecac was halted in 2010 after it was found to be of limited use in managing intoxications in children.¹⁵ Additionally, it can cause significant cardiac damage in people who abuse it, such as those with bulimia.¹⁶ Some owners may still have a bottle (likely expired) in their medicine cabinet, but its use is not recommended.^2,10

Dry mustard powder: This product is sometimes recommended to induce emesis by throwing it against the back of the throat. It is not reliable and not recommended.⁹

Liquid dish soap: This product has been recommended to induce emesis by forcing the animal to drink a 50:50 mixture with water. Results are inconsistent. Vomiting may lead to aspiration of the soap with mild to moderate respiratory distress. Liquid dishwasher detergent should not be used as it is extremely alkaline and can cause significant upper GI burns.²

Summary

While inducing emesis remains an important component of managing toxic ingestions in small animal patients, it is important to consider whether emesis is indicated for the specific toxicant and patient in each case. In addition, the emetic agent should be chosen to maximize potential for success.

Acknowledgment

The author would like to thank Tina Wismer, DVM, DABT, DABVT, ASPCA Animal Poison Control Center, for providing information for this article.