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Veterinarian Technician March 2011 (Vol 32, No 3)

Toxicology Brief: Food-Related Intoxications

by Mindy Bough, MS, CVT

    Several foods that are generally safe for humans can pose a significant danger to animals. This article identifies several of these foods. Recognizing the potential danger of these foods and knowing when there is reason for concern are critical for veterinary technicians who triage calls from clients regarding toxin exposure.


    Alcoholic beverages, drug formulations containing alcohol, rubbing alcohol (which is usually composed of isopropanol), and unbaked yeast dough have all been implicated in toxic exposures to alcohol in small animals.1 Exposure to alcohol-based hand sanitizers is usually associated only with gastrointestinal (GI) signs in small animals, but the human literature has reported associated alcohol intoxication in people. In animals, as in humans, ethanol is quickly absorbed from the GI tract.2–4 Factors that may hasten or enhance absorption include an empty stomach, a dilute concentration of alcohol, and carbonation.4,5 Factors that may slow absorption include food in the stomach, a high alcohol concentration, compromised GI motility, or the presence of GI disease.4,6

    Even the effects of small doses of alcohol can be significant in pets, so all exposures to alcohol should be considered serious. The signs differ depending on the dose and the rate of absorption. Central nervous system depression should be expected, and frequently reported signs include ataxia, lethargy, vomiting, recumbency, hypothermia, disorientation, and vocalization. More serious signs may include tremors, tachycardia, acidosis, diarrhea, dyspnea, coma, seizures, and death.1,2

    Yeast Dough

    It is not uncommon for dogs to ingest yeast dough that has been left to rise before baking. Ingestion of this dough may lead to mechanical obstruction and alcohol intoxication. The warm, moist, acidic environment of the stomach causes the dough to expand and produce carbon dioxide, resulting in bloating and making it difficult for the dough to pass into the small intestine. It has been theorized that expansion of the dough can lead to gastric dilatation–volvulus, potentially resulting in gastric rupture. Vomiting, retching, pain, and recumbency may also occur.7

    Decontamination may be performed with caution and may include induction of emesis or lavage using cold water. Passage of a stomach tube may help expel gas within the stomach. Surgery may be recommended in some situations.7

    Food-Related IntoxicationsYeast fermentation in the stomach produces ethanol and can rapidly result in alcohol intoxication; therefore, treatment of yeast dough ingestion should include immediate treatment of alcohol intoxication. See the previous section on alcohol toxicosis for more information.

    Allium Species

    Allium spp are widely used as food, seasonings, herbal medicinal agents, and livestock feed. Examples include Allium cepa (cultivated onion), Allium validum and Allium canadense (wild onion), Allium porrum (leek), Alliumschoenoprassum (chive), and Allium sativum (garlic). When Allium spp are crushed or chewed, allicin—a toxic sulfur compound—is produced. Allicin is responsible for the odor associated with these species.8 Allicin hydrolyzes into thiosulfinate and then decomposes into a disulfide—an oxidizer that can cause hemolysis. When erythrocyte membranes are oxidized, Heinz bodies form and methemoglobinemia and anemia develop.9 Cats are especially sensitive to these effects because cats have eight free sulfhydryl groups on their hemoglobin, whereas dogs have four groups (humans have two groups). Another contributing factor is that feline hemoglobin dissociates into dimers 10 times more easily than the hemoglobin of dogs or humans.10 Large animals that may be sensitive to Allium spp include cattle, horses, sheep, and goats; however, these species may tolerate Allium spp as a small percentage of the diet.11–14

    Reported signs of Allium spp ingestion in dogs and cats include anorexia, depression, anemia, vomiting, leukocytosis, hemolysis, weakness, salivation, diarrhea, ataxia, hemoglobinuria, Heinz body formation, methemoglobinemia, abnormal breath, and abnormal feces. Signs may begin rapidly after exposure. Hematologic changes generally occur 12 hours to 5 days after exposure.1 One report indicated that the hematocrit normalized 10 to 14 days after exposure without treatment.9


    The avocado originates from Mexico and Central America and is now also cultivated in the southern United States. Of the approximately 150 avocado species (Persea spp), Persea americana is the only one that is considered toxic. There are three varieties of P. americana: Guatemalan, West Indian (Columbian), and Mexican. In addition, there are many hybrids of these varieties. The Guatemalan variety and its hybrids are the ones known to be toxic.15

    Persin is the toxic agent in avocado, but the toxic mechanism is unknown. Mammals that are affected by the toxin include sheep, horses, cattle, rabbits, goats, rats, and mice. In these species, low doses of persin may cause mastitis and agalactia. Reported signs include hard or swollen mammary tissue and changes in maternal milk consistency. High doses of persin may lead to cardiac signs such as edema, cough, weakness, cardiac arrhythmias, respiratory distress, cardiac insufficiency, cardiac failure, and sudden death.15,16

    Nonmammalian species that may be affected include birds and fish. Cardiac effects were present in hens that ate avocado fruit or leaves.17 Sudden death has been reported in caged birds, ostriches, and fish that have been exposed to persin.16–18

    GI signs have been reported when dogs and cats ingest avocado.1 However, mammary gland and cardiac effects are not expected. When dogs are exposed, monitoring for pancreatitis is important because of the high fat content of the fruit. In addition, ingestion of the pit can result in a foreign body obstruction, so monitoring for signs of obstruction may also be warranted.


    Many pets, especially dogs, are attracted to foods and beverages containing chocolate.11 The toxic components in chocolate are the methylxanthines theobromine and caffeine, which are well absorbed from the GI tract.19 The exact toxic mechanism is not known, but signs in dogs are thought to be related to competitive inhibition of cellular adenosine receptors.11,19 Signs of toxicosis typically develop within 2 hours of ingestion, but the onset of signs may be delayed when product packaging is also ingested.1

    Dark chocolate contains higher levels of methylxanthines than light-colored (milk) chocolate. The amount of chocolate ingested determines whether signs are likely and the severity of signs, including vomiting, restlessness, hyperactivity, weakness, tachycardia, cardiac arrhythmias, tachypnea, polyuria, hyperthermia, tremors, seizures, coma, cyanosis, and hypertension; death has occurred from cardiac arrhythmias and respiratory failure.1,11 The combined dose of the two methylxanthines should be calculated to determine the risk to the patient. Combined doses of caffeine and theobromine greater than 15 mg/kg may require decontamination and/or treatment. Doses of 50 mg/kg or more are highly significant and have been reported to cause serious signs.1

    Grapes and Raisins

    There are approximately a dozen genera and hundreds of species in the grape family.15 People consume grapes as fresh fruit, raisins, currants, grape juice, and wine. The toxic component and mechanism of grapes are unknown.

    In 2005, a retrospective evaluation of cases was published in the Journal of Veterinary Internal Medicine. Cases involved dogs that were exposed to either grapes or raisins. The exposures were reported to the ASPCA Animal Poison Control Center, and a common finding was renal failure. Raisin doses that produced renal effects ranged from 2.8 to 36.4 g/kg. Grape doses that produced renal effects ranged from 19.6 to 148.4 g/kg.20

    The grapes and raisins involved in reported cases have been home grown and from grocery stores, including commercial brands of raisins. Evaluations for pesticides, heavy metals, and mycotoxins have been completed on grapes and raisins that were involved in these cases. To date, no involvement of these substances has been identified. Anecdotal reports from pet owners indicate that grapes and raisins are sometimes fed to dogs with no adverse effects, so more research is needed to determine whether only specific animals are susceptible or only certain grapes and raisins can result in toxicosis.1

    The ASPCA currently recommends that dogs not be fed grapes and raisins and that all accidental exposures be treated and/or monitored. There is currently insufficient evidence to indicate that grapes or raisins are toxic to cats, ferrets, or other species. There are no documented cases of grape juice, wine, or grape extracts causing renal effects in dogs or other species.

    Macadamia Nuts

    Macadamia nuts come from Macadamia integrifolia and Macadamia tetraphylla trees, which have been cultivated in Hawaii since the late 1800s.21 The toxic component and mechanism of macadamia nuts are unknown. Dogs are thought to be the only species affected.

    Signs of macadamia nut toxicosis typically develop 2 to 12 hours after exposure and have been reported with ingestions of 2.4 to 62.4 g/kg.21 Associated signs, including vomiting, weakness, depression, ataxia, tremors, reluctance to stand, difficulty walking, and hyperthermia, have been reported to the ASPCA Animal Poison Control Center. These signs were substantiated in a laboratory study in which four dogs were fed macadamia nuts.21

    Generally, signs are self-limiting, resolving within 48 hours.21 However, symptomatic and supportive care may be necessary. Minimizing sensory stimuli is generally beneficial, and confinement may be necessary to prevent injury.


    Xylitol is a sugar alcohol that is used as a sugar substitute or low-calorie sweetener in candy, chewing gum, and foods. It is naturally occurring in many plants and is extracted for use as a sweetener. It does not produce an insulin response in humans and is therefore commonly used in products intended for diabetics.22 In addition, studies have shown xylitol to have some benefit in preventing dental caries, so xylitol is often included as a sweetener in sugarless gums and dental products. Xylitol is also available in granulated form for cooking.

    Dogs, unlike humans, do exhibit an insulin response to xylitol ingestion. When dogs ingest xylitol at doses of 0.25 g/kg or greater, hypoglycemia occurs, possibly causing vomiting, lethargy, ataxia, recumbency, and seizures.22 In 2006, Dunayer and Gwaltney-Brant23 reported that higher doses (1.4 to 2.0 g/kg) of xylitol were associated with hepatic failure. The mechanism for hepatic effects is unknown.


    Veterinary technicians can be instrumental in educating clients about the dangers of pet exposure to many common foods. Clients should be advised not to give these foods to their pets and to make them inaccessible. Information can be provided on clinic bulletin boards and in newsletters but should also be a part of general nutritional discussions with clients during every regular examination.


    The author thanks Tina Wismer, DVM, DABVT, DABT—who is affiliated with the ASPCA Animal Poison Control Center in Urbana, Illinois—for her contribution to and review of this article.

    The specially trained staff at the ASPCA Animal Poison Control Center provides treatment recommendations to veterinary staff and pet owners regarding toxic chemicals and dangerous plants, products, or substances. The service operates 24 hours a day, 7 days a week. Hotline: 888-426-4435 (a $65 consultation fee applies); e-mail: vlpp@aspca.org (for nonemergency information only); Web site: www.aspca.org.

    1. American Society for the Prevention of Cruelty to Animals. Unpublished data. Urbana, IL: Animal Poison Control Center; 2010.

    2. Rall TW. Hypnotics and sedatives: ethanol. In: Hardman JG, Limbird LE, eds. Goodman and Gilman’s The Pharmalogical Basis of Therapeutics. New York: Pergamon Press; 1990:345-382.

    3. Ethanol. In: Ellenhorn MJ, Barceloux DG.Medical Toxicology: Diagnosis and Treatment of Human Poisoning. New York: Elsevier; 1988:1857.

    4. Osborn H. Ethanol. In: Goldfrank LR, Flomenbaum NE, Lewin NA, eds. Goldfrank's Toxicologic Emergencies. 5th ed. Norwalk, CT: Appleton & Lange; 1994:813-824.

    5. Rangno RE, Kreeft JH, Sitar DS. Ethanol dose dependent elimination: Michaelis-Menten v. classical kinetic analysis. Br J Clin Pharmacol 1981;12:667-673.

    6. Lin YJ, Weidler DJ, Garg DC. Effects of solid food on blood levels of alcohol in man. Res Commun Chem Pathol Pharmacol 1976;13:713-722.

    7. Means C. Bread dough toxicosis in dogs. J Vet Emerg Crit Care 2003;13(1):39-41.

    8. DerMarderosian A. Garlic. Review of Natural Products. St Louis: Facts and Comparisons; 2000:237-239, 447-449.

    9. Ogawa E, Shinoki T, Akahori F, Masaoka T. Effect of onion ingestion on anti-oxidizing agents in dog erythrocytes. Jpn J Vet Sci 1986;48:685-691.

    10. Robertson JE, Christopher MM, Rogers QR. Heinz body formation in cats fed baby food containing onion powder. JAVMA 1998;212:1260-1266.

    11. Beasley VR. A Systems Affected Approach to Veterinary Toxicology. Urbana, IL: University of Illinois College of Veterinary Medicine; 1999:116-120.

    12. Verhoeff J, Hajer R, van den Ingh TS. Onion poisoning in young cattle. Vet Rec 1985;117:497-498.

    13. Cheeke P. Natural Toxicants in Feeds, Forages, and Poisonous Plants. 2nd ed. Danville, IL: Interstate Publishers; 1998:305-306.

    14. Selim HM, Yamato O, Tajima M, Maede Y. Rumen bacteria are involved in the onset of onion-induced hemolytic anemia in sheep. J Vet Med Sci 1999;61:269-374.

    15. Burrows GE, Tyrl RJ. Toxic Plants of North America. Ames: Iowa State University Press; 2001:744-747.

    16. Pickrell JA, Oehme F, Mannala SA. Avocado. In: Plumlee KH, ed. Clinical Veterinary Toxicology. St. Louis: Mosby; 2004:424-425.

    17. Burger WP, Naude TW, Van Rensburg IB, et al. Cardiomyopathy in ostriches (Struthio camelus) due to avocado (Persea americana varGuatemalensis) intoxication. J South Afr Vet Assoc 1994;65(3):113-118.

    18. Hargis AM, Stauber E, Casteel S. Avocado (Persea americana) intoxication in caged birds. JAVMA 1989;194(1):64-66.

    19. Serafin WE. Methylxanthines. In: Hardman JG, Limbird LE, eds. Goodman and Gilman’s The Pharmacological Basis of Therapeutics. 9th ed. New York: McGraw-Hill; 1995:672-679.

    20. Eubig PA, Brady MS, Gwaltney-Brant SM, et al. Acute renal failure in dogs subsequent to the ingestion of grapes or raisins: a retrospective evaluation of 43 dogs (1992-2002). J Vet Intern Med 2005:19:663-674.

    21. Hansen SR, Buck WB, Meerdink G, Khan SA. Weakness, tremors, and depression associated with macadamia nuts in dogs. Vet Hum Toxicol 2000;42(1):18-21.

    22. Dunayer EK. Hypoglycemia following canine ingestion of xylitol-containing gum. Vet Hum Toxicol 2004;46:87-88.

    23. Dunayer EK, Gwaltney-Brant SM. Acute hepatic failure and coagulopathy associated with xylitol ingestion in eight dogs. JAVMA 2006;229:1113-1117.

    References »

    NEXT: Educating Clients About Fleas (March 2011) [CE]


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