Toxicology Brief: Epidemiology and management of strychnine poisoning

Toxicology Brief: Epidemiology and management of strychnine poisoning

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Jun 01, 2010

Strychnine is a bitter indole alkaloid obtained mainly from the seeds of Strychnos nux-vomica and Strychnos ignatii.1 These vine-like trees are indigenous to some southeast Asian countries and northern Australia. All parts of S. nux-vomica and S. ignatii may contain strychnine and brucine (dimethoxystrychnine), a related but less potent alkaloid.1,2

Dried seeds from S. nux-vomica have been used to make extracts, powders, and tinctures of strychnine alkaloid. These preparations have been used as bitters, cathartics, tonics, stimulants, and ruminatorics in the past, but now their use is considered ineffective and dangerous.1 The strychnine content of the dried seeds usually varies from 1% to 2%.2

In this article, we discuss strychnine poisoning cases in animals, its diagnosis, and its treatment as reported in the literature. This article also discusses the ASPCA Animal Poison Control Center's (APCC) strychnine incident data from January 1992 to December 2008.

STRYCHNINE AS PESTICIDE

Since 1978, Environmental Protection Agency (EPA) guidelines have classified strychnine as a restricted-use pesticide except for baits containing strychnine alkaloid at a concentration of 0.5% or less. These baits are generally labeled for below-ground use and are intended for the control of burrowing rodents.3 Numerous states have enacted stricter laws than the EPA guidelines, either forbidding the sale of strychnine to the general public or requiring those who purchase strychnine to register.2

Strychnine-containing baits are mostly used to poison birds, gophers, mice, moles, rats, rabbits, porcupines, and wild carnivores such as coyotes, foxes, and wolves. Bait pellets or strychnine-laced grains are usually dyed green or red. The manufacturer of the last strychnine alkaloid product intended to control house mice canceled its registration in 1989, thereby eliminating all indoor uses of strychnine pesticides.3

PREVALENCE

Malicious or accidental strychnine poisoning cases have been described in several animal species.4-11 In a nationwide survey conducted through the veterinarian members of the American Animal Hospital Association, 415 (12%) of 3,452 poisoning cases were attributed to strychnine.4 Most of these cases were reported based on clinical assessment and were not confirmed by chemical analysis.4 In Alberta, Canada, from April 1990 to September 1990, 57 stomach content samples were submitted for strychnine analysis, and 31 were positive for strychnine.5 Kansas State University Veterinary Teaching Hospital reported 10 cases (7%) of strychnine poisoning in dogs out of 139 large- and small-animal poisonings from 1975 to 1980.6


Figure 1. Yearly distribution of strychnine poisoning cases in the United States. Source: AnTox Database, Urbana, Ill: ASPCA Animal Poison Control Center, 1992-2008.
A review of the ASPCA APCC database shows that 161 strychnine cases were reported from January 1992 to December 2008 (Figure 1). Out of 161 cases, dogs accounted for 82% of the cases (n=132), horses 7% (n=12), cats 4% (n=7), pigs 3% (n=4), and birds 1% (n=2).

The data are consistent with earlier published reports in which strychnine poisoning had been described mainly in small animals—especially in dogs and occasionally in cats—and rarely in livestock.1,7 Other reports have also shown that dogs are more frequently involved in strychnine poisoning cases than are other species.8 For example, in Oklahoma, 162 cases of suspected strychnine poisoning in dogs during a three-year period were described.8 Of the 162 cases investigated, 38 were confirmed by analytical methods, 19 were considered malicious, six were accidental, and 13 cases were not classified into any category.8 In Saskatoon, Canada, 261 cases of strychnine poisoning were confirmed from 1968 to 1982.9 These cases showed that strychnine poisoning was more common in young and large-breed dogs such as German shepherds, male dogs were more commonly affected, and dogs from rural or urban areas were equally affected.