Strychnine Poisoning

Strychnine is found in the seeds of the Indian tree Strychnos nux-vomica. Strychinine-containing baits are currently labelled for below-ground use and are intended for the control of pocket gophers. Use as an indoor pesticide has been eliminated. In the past, it was used as a pesticide to control rats, moles, gophers, and coyotes. Commercial baits are pelleted and often dyed red or green. Strychnine is highly toxic to most domestic animals. Strychnine poisoning in the US is sometimes seen in dogs and occasionally cats.

The highest concentrations of strychnine are found in the blood, liver, and kidneys. Depending on the amount ingested and the treatment administered, most of the toxic dose can be eliminated within 1 to 2 days. In strychnine poisoning, the muscles contract repeatedly for a long time. Signs begin rapidly, usually within 30 to 60 minutes. Food in the stomach can delay onset. Early signs, which may often be overlooked, consist of nervousness, tenseness, and stiffness. Vomiting usually does not occur. Severe, sustained muscle contractions may begin spontaneously or may be set off by a touch, sound, or sudden bright light. Extreme and overpowering muscle rigidity causes the legs to extend, giving the animal a “sawhorse” stance. Fever and seizures often develop in dogs. The muscle contractions may last from a few seconds to about a minute. Breathing may stop momentarily. Intermittent periods of relaxation seen during convulsions become less frequent as the disease progresses. The mucous membranes become a bluish color, and the pupils enlarge. Seizures become more frequent, and death eventually results from exhaustion and a lack of oxygen reaching body tissues. If untreated, the entire syndrome may last only 1 to 2 hours.

Tentative diagnosis of strychnine poisoning is usually based on history of exposure and signs. Diagnosis can be confirmed by finding strychnine on analysis of the stomach contents, vomit, liver, kidneys, or urine.

Strychnine poisoning is an emergency, and treatment should be started quickly. Treatment should be aimed at removing any strychnine that has not been absorbed, controlling seizures, and providing supportive care. Stomach contents can be removed by inducing vomiting or flushing the stomach, and by administering activated charcoal. However, because signs begin so rapidly, vomiting is often of limited value, and the stomach may need to be flushed. Fluids are given to increase urine output and maintain normal kidney function. Fever and metabolic abnormalities are treated. Artificial respiration may be needed.