Theobromine is a methylxanthine occurring as the major alkaloid in chocolate and cocoa powder. Chocolate is made from the fermented, dried and then roasted beans of Theobroma cacao. Chocolate also contains a small amount of caffeine, which is also a methylxanthine. The type of chocolate is defined by the quantity (percentage) of cocoa solids that it contains. Cocoa mulch used in gardening and some laxatives (usually senna-based) are also a potential source of theobromine. 

Clinical signs

Affected dogs present with polydipsia, vomiting, diarrhoea, neurological signs, nervousness (such aspanting and shaking), and often have a chocolatey odour to their breath. On examination, clinical signs may include tachycardia, abdominal pain, occasionally bloat, pyrexia, muscle tremors, hyperactivity, seizures, and cardiac arrhythmias (typically ventricular premature contractions).

Diagnosis

Diagnosis is based on clinical signs, client history and diagnostic investigation. Dogs are most often presented with clinical signs after occasions, such as Christmas and birthday parties, where they have greater access to foods containing theobromine. 

Diagnostic investigation includes an analysis of plasma or urine for theobromine (levels >20 µg/ml in humans). Additionally, ECG to assess tachycardia or ventricular arrhythmia that are associated with symptoms of toxicity. 

Treatment

An emetic can be given but is best avoided in animals with hyperactivity or excitability. A repeated dose of activated charcoal (1-3 g/kg orally every 4 hours) is useful as theobromine appears to undergo enterohepatic re-circulation. IV fluids will support the cardiovascular system and enhance excretion. Diazepam or phenobarbital can be used for seizure control, and lidocaine/propranolol if ventricular arrhythmias are present. Regular bladder emptying with or without catheterization may help reduce reabsorption through urinary tract mucosa.

Prognosis

Prognosis is generally good, with fatal cases being rare. Prognosis is more guarded in dogs with seizures or arrhythmia. Failure of treatment is most likely caused by the owner’s delay in seeking help or if the dog has consumed >200 mg/kg of available theobromine. Other factors include concurrent theophylline medication, or pre-existing conditions such as epilepsy or cardiac disease, and possibly genetic factors.

References

• Theobromine / chocolate poisoning from Vetlexicon Canis, Vetstream Ltd.

Content provided from Vetstream's Vetlexicon Canis - https://www.vetlexicon.com/canis

Vetlexicon is the world’s largest peer-reviewed online clinical reference source. All our content is written and peer-reviewed by over 1,600 of the world’s leading veterinarians, ensuring relevance, accuracy and quality.