Chocolate Toxicosis

Filed Under: Dogs, Cats, Poisoning

Think giving your pet chocolate is a suitable treat? Unfortunately, chocolate is toxic in dogs and many other species of animals. Most cases of poisoning involve dogs due to readily available sources of chocolate. In fact, consumption of chocolate is the 7th most common toxicosis in the dog. Dogs are infamous for getting into bags of chocolate morsels, a box of candy left on the coffee table, or the infamous Easter basket. Toxicities and death have also been reported in livestock when cocoa byproducts or mulch from cocoa-bean hulls were fed.

Chocolate is derived from the roasted seeds of Theobroma cacao. The toxic substances in chocolate are the methylxanthines - theobromine and caffeine. The concentration of theobromine is three to ten times more than that of caffeine but both toxins contribute to the development of clinical symptoms. The concentration of theobromine varies with the type and brand of chocolate. One ounce of milk chocolate contains 44 mg/oz of theobromine, while semisweet contains 140 mg/oz and unsweetened baking chocolate contains up to 450 mg/oz. The toxic dose of theobromine is 100 to 150 mg/kg in the dog. This makes 1 oz of milk chocolate per pound a toxic dose in the dog with semisweet or unsweetened chocolate requiring less than half that amount to induce poisoning. White chocolate, which is more of a confection rather than a chocolate, contains an insignificant amount of methylzanthines. The half-life of theobromine in the dog is 17.5 hours. This is the time it takes the body to remove ½ of the toxic substance. The half-life of caffeine in dogs is 4.5 hours.

Methylxanthines cause Central Nervous System stimulation, diuresis, and tachycardia. Methylxanthines also increase intracellular levels of calcium which cause increased strength and contractility of skeletal and cardiac muscles. Methylxanthines also increase levels of AMP, epinephrine, and norepinephrine thereby stimulating the sympathetic nervous system. The sympathic nervous system is the body’s alarm or stress system which ordinarily becomes activated when you are enraged or frightened, resulting in a variety of clinical consequences.

Methylxanthines are eliminated primarily through metabolism by the liver.

Clinical signs of poisoning occur within six to twelve hours of ingestion. Initially clinical signs will include vomiting, diarrhea, restlessness with abdominal pain, and distension. The dog may exhibit polydipsia (increased thirst). Clinically, the signs progress to hyperactivity, hyperthermia (increase in body temperature), polyuria (increase in urine production), ataxia (unbalanced), muscle tremors, seizures and coma. The heart will become affected resulting in cardiac arrhythmias including tachycardia (increase in heart rate), premature ventricular contractions or PVC’s (essentially lost and bizarre heart beats), and hypertension (increase in blood pressure). In the final stages of the poisoning the pet will become hypotensive (low blood pressure), and bradycardiac (slow heart rate). Hypokalemia (low potassium levels) may occur late in the toxicosis and will also contribute to the cardiac dysfunction.

The high fat content of chocolate may also trigger a case of pancreatitis (inflammation of the pancreas) in susceptible animals. Death ensues due to cardiac arrhythmias or respiratory failure usually within 18 to 24 hours after the onset of clinical signs, but may be delayed for several days.

The differential diagnosis should include amphetamine, ephera/caffeine, pseudoephedrine cocaine, antihistamine overdose, or any other Central Nervous System stimulant. Diagnosis of chocolate toxicosis is dependent on a history of exposure and the observation of pertinent clinical signs.

When caught early, less than one hour after consumption, vomiting may be induced to bring up the offending chocolate, followed by activated charcoal to limit adsorption of the toxic factors. When the patient is showing marked excitement or is comatose and has lost the gag reflex, gastric lavage should be used to evacuate the offending substance. Activated charcoal may be repeated at eight hour intervals due to the enterohepatic recycling of the methylxanthines. There is no specific antidote for methylxanthines. Diazepam (Valium) may be used to control muscle tremors or mild seizures with barbiturates often being required to control severe seizure activity. The type of cardiac arrhythmia occurring may be determined through the use of a cardiac monitor or periodic EKGs. Treatment of a cardiac arrhythmia is then tailored to the type of arrhythmia occuring at any particular time. Propranolol has been used for tachycardia whereas atropine is used for bradycardia. Lidocaine may be necessary for PVC’s. Control of cardiac arrhythmias requires close monitoring by your veterinarian.

Fluid therapy may assist in stabilizing the cardiovascular function and hasten the urinary excretion of the offending methylxanthines. Gastric protectants such as ranitidine or famotidine may decrease GI irritation.

Clinical signs may persist over a 72 hour period in severe cases.

References:

Kahn, Cynthia Editor. The Merck Veterinary Manual. 9th Edition. 2005. Pp.2362- 2364.

“Animals Eat the Darndest Things.” Veterinary Forum. April 2007. p. 18.

Macintire, Douglass DVM, and Kenneth Drobatz DVM. Manual of Small Animal Emergency and Critical Care Medicine. Lippincott Williams & Wilkins. P. 389.

Peterson, Michael DVM and Patricia Talcott DVM. Small Animal Toxicology. Saunders Co. Pp. 848-851.

Guyton, Arthur. Textbook of Medical Physiology. W.B. Saunders Co. 5th Edition. 1976. Pp. 773-774.

Topics: chocolate, people food

Symptoms: abdominal pain, diarrhea, vomiting

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