Two Serious Pet No-No's

Chocolate Toxicosis

Chocolate toxicosis is the result of the active chemical ingredient, theobromine. Theobromine is a methylxanthine compound, much like caffeine. Methylxanthines cause changes in intracellular metabolism and increaselevels of circulating neuromuscular stimulant hormones (such as epinephrine - often called adrenaline - and norepinephrine).

Following ingestion and absorption of a toxic dose, a marked increase in irritability and muscular contractility results. Clinical signs can range from standard GI problems (such as vomiting and diarrhea), or nervous stimulation (such as hyperactivity, restlessness, imbalance, and tremors) to a more serious clinical picture, including heart arrhythmias, hyperthermia (excessive fever), seizures, coma, and death. The level of theobromine varies with different chocolate formulations.

While toxicity symptoms develop at a level of 100 mg of theobromine ingested per kilogram of body weight; milk chocolate has only 45 mg per ounce, while unsweetened baking chocolate has 400 mg per ounce. There is no special antidote for the patient with methylxanthine toxicity, but successful treatment requires hospitalization and aggressive therapy.

Evacuation of any remaining ingested chocolate by induced vomiting and/or stomach gavage (washings) is followed by administration of products to bind and eliminate any further toxic material. The main thrust of inpatient care is supportive, and depends on the severity of the toxicity. Rarely but possibly fatal, theobromine toxicity can occasionally require prolonged treatment. Overnight costs, alone, at the emergency clinics can easily top $600-800 US with a serious case.

Onion Poisoning

Onions contain a compound called n-propyl disulfide, and a few other disulfides, that act as oxidant toxins. These compounds cause damage to hemoglobin, the molecule in red blood cells that is responsible for carrying oxygen. Precipitation of the hemoglobin protein produces changes in the RBC shape and reduces its flexibility - a very important feature for these cells as they must traverse the tiny capillary beds throughout the body.

The clumps of altered hemoglobin are known as Heinz bodies. Once they are formed, they do not resolve, the cell is irreversibly damaged. The injured red blood cells are identified as defective by some of the body's white blood cells (macrophages) and are picked out of circulation and destroyed. Or, if enough damage has occured to the red blood cell membranes, these cells may even rupture from inflexibility as they pass through the blood stream.

Occasionally, sufficient oxidant injury occurs to even change the active hemoglobin into methemoglobin, a form that cannot carry any oxygen. Luckily, this reaction can be chemically reversed, as it essentially acts to "asphyxiate" the affected animal. Heinz body formation can result in a number of signs, mostly related to the anemia caused by the red blood cell destruction and breakdown--the patient may be jaundiced, weak, lethargic, have fevers, loss of appetite, vomiting or diarrhea, and enlargement of the spleen.

Methemoglobinemia, however, is more likely to result in respiratory distress, including a chocolate or mud brown colored appearance to the gums and mucus membranes. (Other materials potentially associated with this serious condition include garlic and acetaminophen products).

Severe toxicity can be fatal. Treatment is essentially supportive, and may require oxygen therapy and/or blood transfusion. Again, therapy can be prolonged and definitively, costly.