Chocolate Poisoning-Dog

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Chocolate

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Introduction

Toxicity is due to the presence of methylxanthines such as theobromine and caffeine in chocolate . Concentrations ranging from of 100-250mg/kg of theobromine and 110-200mg/kg of caffeine have been reported to cause fatalities . The consumption of more than 20mg/kg of total methylxanthines, the dose at which mild signs such as vomiting, diarrhoea and polyuria are induced , is considered the cut-off point in deciding whether or not to treat . The concentration of methylxanthines differs between products and therefore the number of grammes required to reach this threshold vary according to the product; in a 10kg dog 5000g of white chocolate provides the equivalent 20mg/kg dose of methylxanthines that 12-40g of plain chocolate, 83-117g of milk chocolate or 7-25g of cocoa powder does Methylxanthines are also present in beverages and foods other than chocolates .

Signalment

Dog that live indoors are more likely to have access to chocolate. Also puppies and dogs that scavenge are at a greater risk of eating food that is not intended for their consumption. Small breeds of dogs may reach the toxic level of methylxanthine concentration per body weight more easily .

Diagnosis

Clinical Signs

Chocolate poisoning results in CNS, gastrointestinal, cardiovascular, respiratory and urological signs., which are evident soon after ingestion of a toxic amount of chocolate .

• CNS: hyperactivity, behavioural changes, ataxia, muscle tremors, clonic seizures and hyperthermia , , .

• Gastrointestinal: diarrhoea, emesis, haematemesis , .
• Cardiovascular: arrhythmias,tachycardia, bradycardia sometimes, hypotension , .
• Respiratory: tachypnoea .
• Urological: polydypsia and polyuria may also be present .

Laboratory Tests

Diagnosis is usually on the basis of clinical signs and a known history of chocolate ingestion . The following laboratory tests are possible but not commonly used;

• Assays for detection of methylxanthines in bodily fluids such as plasma, urine and stomach contents .
• Blood Glucose: Hypoglycaemia as a sequela to hyperactivity. not seen consistently with chocolate poisoning .
• Urinalysis: Proteinuria, low specific gravity; not seen consistently with chocolate poisoning .

Other

• ECG: rate and rhythm abnormalities .

Pathology

Following absorption from the gastrointestinal tract caffeine and theobromine are metabolised in the liver . Caffeine has a half life of 4.5 hours in dogs while theobromine has a half life of 17.5 hours . In humans the half life of theobromine ranges from 6 to 10 hours, significantly shorter than that in dogs which may explain the susceptibility of dogs to chocolate poisoning REF. Methylxanthines have the following modes of action.

• Antagonism of Adenosine Receptors: this antagonism results in stimulation of the central nervous system and an increase in heart rate and also diureses
• Inhibition of Cyclic Nucleotide Phosphodiesterase: consequently there is an increase in cyclic AMP, which in turn leads to greater catecholamine release and their effects .
• Modulation of Intracellular Calcium Concentrations: .

Ventricular fibrillation, and other cardiac dysrhythmias are most frequently the ultimate cause of death., .

Treatment

Of dogs presenting with clinical signs

• Inital stabilisation of Cardiorespiratory System:
  • Tachycardia: beta-blockers, eg orally administered metoprolol at a dose of 0.5mg to 1mg per kg every 8 hours .
  • Premature Ventricluar Contractions: lidocaine; iv bolus of 2mg to 6mg per kg administered slowly, after which a constant rate infusion of 20ug to 70ug per kg per minute should be given .
  • Bradycardia: Atropine at a dose of 0.01mg to 0.02mg per kg .

• Treatment of seizures and hyperactivity
  • IV Diazepam at a dose of 0.5 to 2 mg/kg .
  • Alternative to diazepam is barbiturates .
  • Treating the seizures and hyperactivity should help restore normal body temperature. If animal still hyperthermic then this should be treated directly .

• Correction of acid/base and electrolyte inbalances ,

• Insertion of urinary catheter
  • Helps prevent further absorption of theobromine and caffeine across bladder wall .

Of dogs with a known history of recent chocolate ingestion but who have not yet developed clinical signs

• Administration of apomorphine (0.03mg/kg IV) or hydrogen peroxide (1-5 ml/kg PO) ref 5 min vet consult in order to induce emesis and/or of activated charcoal in order to minimise further absorption of methylxanthines re 5 min vet consult

Prognosis

If treated correctly and early enough ref 5min consult the prognosis is good and a complete recovery can be expected . For animals presenting with seizures and arrhythmias the prognosis is more cautious.