Principles of Therapy of Toxicosis

Topically applied toxicants 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. Oral emetics include syrup of ipecac (10–20 mL, PO in dogs) and hydrogen peroxide (2 mL/kg, PO). Apomorphine can be used in dogs parenterally at a dosage of 0.05–0.1 mg/kg.

Gastric lavage, using an endotracheal tube and the largest bore stomach tube possible, is done on the unconscious or anesthetized animal. The head is lowered to a 30° angle, and 10 mL of lavage fluid (water or saline) per kg of body weight is gently flushed into the stomach and then removed. This process is repeated until returned fluid is clear. Cathartics and laxatives may be indicated in some instances for more rapid elimination of the toxicant from the GI tract. A gastrotomy or rumenotomy may be necessary when lavage techniques are insufficient (or too slow in ruminants).

When the toxicant cannot be physically removed, certain agents administered orally can adsorb it and prevent its absorption from the alimentary tract. Activated charcoal (1–2 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.

Supportive therapy is often necessary until the toxicant 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 toxicants work by various mechanisms. Some complex with the toxicant (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 toxicant (eg, nitrite and thiosulfate ions release and bind cyanide).