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, bakers 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 metabolized 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 nonspecific 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 catheterization 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
-by Jennifer Iannaccone, Class 1999
-edited by Brad Njaa, DVM, MVSc and Stephen Hooser, DVM, PhD