Strychnine is a toxin obtained from the seeds of the Indian tree Strychnos nux-vomica. It is mainly used as a pesticide to control rats, moles, gophers, and coyotes. Strychnine is highly toxic to most domestic animals including dogs.
Strychnine affects the nervous system by causing uncontrolled firing of the nerves that cause muscle movement. This causes muscle injury, muscle cell breakdown, and hyperthermia. The respiratory muscles are contracted resulting in difficulty breathing, lack of oxygen to the body, and death if not treated. Having a very short duration of action, clinical signs may be present within 10 minutes to 2 hours of ingestion.
Strychnine poisoning in dogs occurs usually from ingestion of baits designed for use against rodents (especially gophers and moles) and coyotes. Toxicity can also occur from the ingestion of poisoned rodents and birds. An approximate lethal dose for a dog is 0.75 mg per kg body weight.
Common symptoms associated with this poisoning include:
Severe spasms leading to arching of the head, neck and back in extreme hyperextension (opisthotonus)
Uncontrolled violent seizures (sometimes in response to bright lights or noise)
Breathing difficulties, inability to breathe
Elevated heart rate
High body temperature