Chocolate is readily available, particularly at certain holiday times, and represents a potential lethal toxin for dogs. Many species are susceptible, but the dog is most commonly affected. Excessive ingestion of chocolate was recently reported as one of the top 20 most common intoxicants in the dog. Cocoa bean hulls or waste used as bedding for large animals, most commonly horses, have been a source of toxicosis as well.

Etiology: Theobromine is found in chocolate, cocoa beans, baker’s chocolate, cola and tea and is believed to be the toxic component of chocolate. Baking chocolate is the most concentrated form of theobromine containing approximately 390 mg/oz versus 44 mg/oz found in milk chocolate. It is readily absorbed orally and widely distributed throughout the body. Theobromine is metabolised by the liver with primarily urinary excretion. In dogs, the LD50 for theobromine is approximately 250-500 mg/kg, however deaths have occurred following ingestion of 115 mg/kg. The half-life of theobromine is very long in dogs (17.5 hours) compared to other species. This may help to account for the susceptibility of canines to theobromine toxicity.

Pathogenesis: Theobromine is a methylxanthine that stimulates the central nervous system, cardiac and skeletal muscle, promotes diuresis and induces smooth muscle relaxation. Mechanisms of action, at the molecular level, include increased intracellular calcium, cAMP accumulation, and release of catecholamines. In aggregate, these cellular events lead to increased skeletal and cardiac muscle activity, and irritability of the sensory cortex resulting in exaggerated responses to normal stimuli. In severe cases, cardiac arrhythmias can lead to death.

Clinical findings: Acutely, dogs may show signs which include restlessness, hyperactivity, vomiting, diarrhea, cardiac arrhythmias, tachycardia, polypnea, ataxia, muscle tremors, hyperthermia, seizures and, if severe enough, coma. If seizures develop, they are typically tonic to tetanic and occur late in the clinical course.

Diagnosis: Generally, historical evidence of chocolate ingestion, clinical signs compatible with chocolate toxicosis and the presence of chocolate in the GI tract are methods of diagnosing theobromine intoxication. Additionally, theobromine levels can be determined by high-performance liquid chromatography (HPLC) in stomach contents, serum or urine.

Gross lesions are non-specific and may include hyperemia of the gastric and duodenal mucosa, and diffuse organ congestion.

Treatment: There is no specific antidote for theobromine; however, a combination of detoxification, supportive and symptomatic treatment can be successful. Detoxification includes emetics within the first 3-4 hours of ingestion, gastric lavage, activated charcoal administration, and oral cathartics. Remember, theobromine has an unusually long half-life in dogs so detoxification should be continued for at least 72 hours. Supportive therapy includes intravenous fluids to prevent dehydration, urinary catheterisation to prevent reabsorption of toxins, appropriate therapy if the animal is in shock and minimizing levels of excitement and stress. Administration of muscle relaxants and control of seizure activity are important symptomatic therapies.

Ultimately, the best solution is prevention. Informing owners of the dangers of feeding chocolate to their pets is crucial to minimizing intoxication by theobromine- containing foods. Limiting pet access to chocolate, particularly during holiday seasons, is one of the most important first steps toward prevention.

By Jennifer Iannaccone, Class 1999
- edited by Brad Njaa, DVM, MVSc and Stephen Hooser, DVM, PhD


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