Principles of Therapy of Toxicosis in Animals

Topically applied toxic agents usually can be removed by thorough washing with soap and water; clipping of the hair or wool may be necessary. Emesis is of value in dogs, cats, and pigs if done within a few hours of ingestion. Emesis is contraindicated when the swallowing reflex is absent; the animal is convulsing; corrosive agents, volatile hydrocarbons, or petroleum distillates are involved; or risk of aspiration pneumonia is imminent. Hydrogen peroxide (3% solution, 1–2 mL/kg, PO) is an oral emetic and can be repeated one additional time. Apomorphine can be used in dogs parenterally at a dosage of 0.05–0.1 mg/kg, 0.04 mg/kg IM, or 0.03 mg/kg IV. Cats can be induced to vomit by treating with xylazine (0.44 mg/kg, IM) or dexmedetomidine (5–10 mcg/kg, IM). The efficacy of emetics in cats is as low as 50%, and there can be excess sedation or cardiovascular collapse.

Inappropriate methods of decontamination include oral administration salt or syrup of ipecac, forced vomiting by means of digital stimulation of the throat. Substances or solutions such as liquid dish soap, raw eggs, hot sauce, mustard, or similar are also contraindicated and owners should be advised against these things.

Gastric lavage, with placement of an endotracheal tube to prevent aspiration via largest bore nasogastric tube possible, is done after appropriate sedation or general anesthesia is administered. The head is lowered to a 30° angle, and 5–10 mL of lavage fluid (tepid water or 0.9% saline solution) per kg of body weight is gently flushed into the stomach and then removed. This process is repeated until returned fluid is clear. Concurrent administration of cathartics and laxatives may be indicated in some patients for more rapid elimination of the toxic agent from the GI tract. In ruminants, a gastrotomy or rumenotomy may be necessary when lavage techniques are insufficient. Gastric lavage are particularly relevant in species such as horses that do not vomit; and if emesis is unsuccessful, if there is a large volume of stomach contents, in symptomatic patients with a history of large volume ingestion, or for potentially life-threatening toxicosis.

When the toxic agent cannot be physically removed via lavage, certain agents administered orally can adsorb it and prevent its absorption from the GI tract. Activated charcoal (1–5 g/kg) effectively adsorbs a wide variety of compounds and usually is the adsorbent and detoxicant of choice when toxicosis is suspected. The maximum amount of a drug adsorbed by activated charcoal is ~100–1,000 mg/g of charcoal. Sorbitol is sometimes added to activated charcoal to increase its palatability (in people) and to increase the GI transit time and flush out charcoal-bound toxins more rapidly.

Activated charcoal should not be used in animals with known hypersensitivity or allergy to the drug. With administration of high doses, vomiting, constipation, or diarrhea may occur, and feces will appear black. Contraindications to using activated charcoal include:

• ingestion of a caustic substance or hydrocarbon

• planned endoscopy or abdominal surgery

• risk for or suspected gastric or intestinal obstruction

• high risk of aspiration pneumonia

• severe dehydration

• hypernatremia

• hypovolemic shock

• ileus

• recent intestinal surgery

• protracted vomiting

Supportive therapy is often necessary until the toxic agent can be metabolized and eliminated. The type of support required depends on the animal’s clinical condition. Supportive efforts may include control of convulsive seizures, maintenance of respiration, treatment for shock, correction of electrolyte imbalance and fluid loss, and control of cardiac dysfunction, as well as alleviation of pain.

Specific antidotes for various toxic agents work by various mechanisms. Some complex with the compound (eg, the oximes bind with organophosphorous insecticides, and EDTA chelates lead). Others block or compete for receptor sites (eg, vitamin K competes with the receptor for coumarin anticoagulants). A few affect metabolism of the toxic agent (eg, nitrite and thiosulfate ions release and bind cyanide). Specific antidotes for use in food animal species have been limited for the past 10 years, but options are being considered by the FDA in the US.

• Also see pet health content regarding general treatment of poisoning.