The upcoming Easter celebrations mean that there may be many chocolate eggs and treats to tempt pets. Chocolate poisoning in dogs is one of the most common enquiries received by the VPIS, with the severity of the poisoning being influenced by the amount of eaten, and the type of chocolate (milk or dark) involved. Milk and dark chocolate differ greatly in the amount of theobromine, a methylxanthine similar to caffeine, they contain, which in turn is reflected in the toxic dose. The initial clinical effects are vomiting and diarrhoea, which may lead to dehydration given that theobromine is also a diuretic. Theobromine also stimulates the myocardium and the CNS, leading to hyperactivity and pyrexia, and developing hypertension and severe tachycardia; in extreme cases muscle rigidity, tremors and convulsions may be seen. Fatal chocolate poisoning is uncommon.

Chocolate is also toxic to cats, rabbits and rodents, but there is insufficient data to determine a toxic dose. Treatment is essentially supportive with the emphasis on rehydration, reducing the stimulant effects with sedatives and monitoring vital signs. The use of repeated doses (4 hourly) activated charcoal to enhance elimination, is particularly useful, as theobromine undergoes enterohepatic recirculation.