The number of cases of accidental poisoning by chocolate in dogs, particularly during the Christmas and Easter holidays, is increasing on both sides of the Atlantic. The same goes for calls reporting that dogs have ingested their owner's medication left lying on a bedside table or other accessible place.

Dogs are sensitive to a class of chemicals of which caffeine and theobromine are two members. Dogs are unable to excrete these chemicals known as methylxanthines as efficiently as humans are. The half-life of these compounds is about 2 hours in a human but in a dog it is more like 18 hours. What happens in dogs is that the compounds travel via the liver and bile duct into the intestine where they are converted back into the original methylxanthines for another circuit through the dog's system. This process keeps on repeating itself so that instead of excreting the substance the dog keeps on repoisoning itself.

It has been calculated that the lethal dose of sweet milk chocolate for a dog is 2 ounces per kilo (2.2lb) of body weight. For an 11lb dog this would be about 10 ozs. The Dark Chocolate is considered to be at least 10 times as lethal. A 22lb dog could die from the methylxanthines contained in just 2 ounces of plain dark chocolate.

The symptoms of methylxanthine poisoning are: vomiting, hyperactivity, restlessness, hypersensitivity to touch, rapid heartbeat and rate of breathing with loss of control of the leg muscles followed by muscle tremors, then seizures, general weakness, coma and ultimately death.

Chocolate can also irritate the gastrointestinal tract causing diarrhoea and possibly gastric bleeding. These symptoms can occur up to two days after the chocolate is eaten.

Treatment is aimed at clearing the chocolate from the dog's stomach, administering activated charcoal and other substances to absorb the poison and keeping the fluid balance of the dog under control. Only your vet can only carry out this treatment. Inducing vomiting within 2 hours of the chocolate being consumed can also help.

Two common sayings should be reconsidered: "Just one won't hurt him" and "let's wait and see what happens". Whereas it is unlikely that one chocolate will poison a dog it will give him a taste for chocolate. Far better to keep a treat jar for these occasions containing chocolate flavoured treats made especially for dogs, as these don't carry the same risks.

Since dogs do not seem to be as sensitive to bitter tastes as humans they may eat the more concentrated, and thus even more toxic, baking chocolate if a chance arises. Alternatively it will consume a toxic amount of milk or dark chocolate if it can get into an improperly stored supply.

Should your dog find and consume a quantity of chocolate it is important to seek advice from your vet immediately. The sooner treatment is started the more hopeful the outcome. Chocolate can kill a dog.

However well trained a dog is it is still a dog and like us is tempted by the smell and tastes of things it finds. Like a small child its curiosity leads it to put things it finds in its mouth.

The only safe answer is to keep medication and chocolate out of reach of your pet, preferably in a secure cupboard. At least that way you will save yourself the heartache and expense incurred by an increasing number of owners.