THURSDAY, April 11 (HealthDay News) -- Chocolate is a sweet treat for many people, but for dogs it can be a killer.

The message, from the U.S. Food and Drug Administration, is especially important now because chocolates from Easter may still be in many homes.

Chocolate contains a substance called theobromine that is similar to caffeine and is toxic to dogs at certain levels. The minimum amount of theobromine dangerous to dogs ranges from 46 to 68 milligrams per pound (mg/lb), according to the FDA's Center for Veterinary Medicine.

Half the dogs that consume 114 to 228 mg/lb or more of theobromine will die. A number of factors determine whether a dog will have a toxic reaction, including its size, the amount of chocolate the dog ate, and whether it is extra sensitive to theobromine, the agency said in a news release.

The type of chocolate is also important. The amounts of theobromine present are: 704 mg/lb in milk chocolate, 2,400 mg/lb in semisweet chocolate, and 6,240 mg/lb in baking chocolate.

To get 46 mg/lb of theobromine, a dog would have to eat: 1 ounce per 1 pound of its body weight of milk chocolate; 1 ounce per 3 pounds of body weight of semisweet chocolate; and 1 ounce per 9 pounds of body weight of baking chocolate, according to the Center for Veterinary Medicine.

Theobromine toxicity in dogs can cause a number of mild to severe symptoms, including vomiting, diarrhea, rapid heart rate, restlessness, hyperactivity, increased urination, muscle spasms and seizures.

If you think your dog has eaten chocolate, call your veterinarian immediately, the Center for Veterinary Medicine said.

More information

The German Shepherd Rescue of New England has more about chocolate poisoning in dogs.