Decontamination
Since strychnine is a rapidly acting convulsant, most animals presented to a veterinarian are already exhibiting clinical
signs. Do not attempt decontamination in animals that are already showing neurologic effects. Control seizures and stabilize
the animal first (discussed below) before decontamination.
Decontamination consists of removing gastric contents either by inducing emesis or by gastric or enterogastric lavage and
binding the remaining bait in the gastrointestinal tract with activated charcoal.
Emesis. If the exposure is recent and no clinical signs are present, induce vomiting with 3% hydrogen peroxide (2.2 ml/kg orally
for a maximum of 45 ml in dogs; repeat once after 10 to 15 minutes if no vomiting occurs), apomorphine in dogs (0.03 mg/kg
intravenously; 0.04 mg/kg intramuscularly; or dissolve a crushed pill in physiologic saline, instill in the conjunctival sac,
and rinse with water after emesis has occurred),12 or xylazine (cats = 0.44 mg/kg intramuscularly; dogs = 1.1 mg/kg subcutaneously or intramuscularly).13 Yohimbine (0.1 mg/kg intravenously in dogs) can be given to reverse the effects of xylazine.13
Induce emesis with great caution since it could trigger seizures in an asymptomatic animal due to stress and due to the fast-acting
nature of strychnine. Do not induce emesis in hyperesthetic, anesthetized, or convulsing animals.
Gastric lavage. Animals receiving gastric lavage should be anesthetized and intubated with a cuffed endotracheal tube to reduce the risk
of aspiration. Tepid water at body temperature can be instilled through a gastric tube at 10 ml/kg.14 Use gravity to instill and to drain the liquid, and repeat until the lavage fluid becomes clear. Use large bore tubes and
multiple flushes for better results.
Enterogastric lavage. Enterogastric lavage, also called a through and through, begins with gastric lavage followed by an enema under low pressure and continues until fluids exit through the gastric tube.
Give a preanesthetic dose of atropine (0.02 to 0.04 mg/kg subcutaneously, intramuscularly, or intravenously)12 before the procedure to relax the patient's intestinal muscles and allow fluids to flow easily. After enterogastric lavage
administer activated charcoal (2 to 3 g/kg mixed with water to make a slurry) with a cathartic such as sorbitol (70% solution
at 1 to 2 ml/kg).14
Seizure control
If convulsions are present or imminent, intravenous pentobarbital sodium is the drug of choice in small animals. It should
be given to effect and repeated as often as necessary. Muscle relaxants such as methocarbamol (100 to 200 mg/kg intravenously;
repeat as needed up to a maximum dose of 330 mg/kg/day) or guaifenesin (5% solution at 110 mg/kg intravenously)14,15 can be tried. Diazepam and xylazine have been used to control strychnine seizures in dogs with variable success.14 Propofol (3 to 6 mg/kg intravenously or 0.1 mg/kg/min as an infusion) can also be tried.12 Isoflurane inhalation anesthesia can be used if seizures are not controlled with the preceding treatment measures.
Supportive care
Intubate severely affected animals, and provide artificial respiration. Urine acidification with ammonium chloride (100 mg/kg
orally b.i.d.) may be useful for ion-trapping and urinary excretion of the alkaloid. Administer intravenous fluids to maintain
normal kidney function and promote diuresis. Monitor and correct the animal's acid-base balance as needed.
Maintain the animal's body temperature within the normal range. In strychnine-poisoned dogs, hyperthermia can occur as result
of severe muscle fasciculation or seizures. Aggressive cooling, by means of ice baths or cold water enemas, may result in
hypothermia and should be avoided. All cooling measures should be stopped when rectal temperature reaches 102 F (38.9 C) to
prevent rebound hypothermia.16
Keep affected animals in a dark quiet room until they have recovered. Most animals may require one to three days of treatment.
CONCLUSION
Sporadic strychnine poisoning still occurs in animals in the United States, even though human poison control data indicate
a decline of 63% in strychnine exposures in people between 1995 and 2004.17 Most strychnine cases in animals are reported in the West, possibly because of the region's proximity to Mexico where strychnine
may be more readily available.
EPA guidelines restrict the use of strychnine to below-ground use. Stricter state and federal guidelines for the use and availability
of strychnine may help reduce these accidental and potentially deadly poisoning cases.
"Toxicology Brief" was contributed by Safdar A. Khan, DVM, MS, PhD, DABVT, and Mary Kay McLean, BS, ASPCA Animal Poison Control
Center, 1717 S. Philo Road, Suite 36, Urbana, IL 61802. The department editor is Petra Volmer, DVM, MS, DABVT, DABT.
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