Toxicology Brief: Epidemiology and management of strychnine poisoning - Veterinary Medicine
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Toxicology Brief: Epidemiology and management of strychnine poisoning


VETERINARY MEDICINE


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.

REFERENCES

1. Osweiler GD, Carson TL, Buck WB, et al. Strychnine. In: Clinical and diagnostic veterinary toxicology. 3rd ed. Dubuque, Iowa: Kedall/Hunt Publishing Co, 1985;345-348.

2. MICROMEDEX editorial staff. Strychnine. Anderson M, et al., eds. MICROMEDEX Healthcare Series Integrated Index, Vol. 102. Englewood, Colo: MICROMEDEX, expires 12/04.

3. United States Environmental Protection Agency. Reregistration Eligibility Decision (RED) Facts: Strychnine. Prevention, Pesticides, and Toxic Substances. July 1996.

4. Osweiler GD. Incidence and diagnostic consideration of major small animal toxicoses. J Am Vet Med Assoc 1969;155:2011-2015.

5. Lowes NR, Smith RA, Beck BE. Roquefortine in the stomach contents of dogs suspected of strychnine poisoning in Alberta. Can Vet J 1992;33:535-538.

6. Barton J, Oehme FW. The incidence and characteristics of animal poisonings seen at Kansas State University from 1975 to 1980. Vet Hum Toxicol 1981;23:101-102.

7. Morgan S, Martin T, Edwards WC, et al. Investigating a case of strychnine poisoning. Vet Med 1987;82:1044-1047.

8. Edwards WC, Kerr LA, Whaley MW. Strychnine poisoning in dogs: sources and availability. Vet Med Small Anim Clin 1981;76:823-824.

9. Blakley BR. Epidemiologic and diagnostic considerations of strychnine poisoning in the dog. J Am Vet Med Assoc 1984;184:46-47.

10. Martens PR, Vandevelde K. A near lethal case of combined strychnine and aconitine poisoning. J Toxicol Clin Toxicol 1993;31:133-138.

11. Warnock N, Schwarzbach SE. Incidental kill of dunlin and killdeer by strychnine. J Wildl Dis 1995;31:566-569.

12. Plumb DC. Plumb's veterinary drug handbook. 6th ed. Stockholm, Wis: PharmaVet Inc, 2008.

13. Hall K. Toxicosis treatments. In: Bonagura JD, Twedt DC, eds. Kirk's current veterinary therapy XIV: small animal practice. St. Louis, Mo: WB Saunders, 2009;112-116.

14. Kahn CM, Line S. The Merck veterinary manual. 9th ed. Whitehouse Station, N.J.: Merck & Co Inc, 2005.

15. Bailey EM, Szabuniewicz M. Use of glyceryl guaiacolate ether in treating strychnine poisoning in the dog. Vet Med Small Anim Clin 1975;70:170-174.

16. Podell M. Seizures and sleep disorders. In: Morgan RV, ed. Handbook of small animal practice. 3rd ed. Philadelphia, Pa: WB Saunders Company, 1997;220-229.

17. Blondell JM. Decline in pesticide poisonings in the United States from 1995 to 2004. Clin Toxicol 2007;45:589-592.


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