anticoagulant that is highly effective in controlling Norway (Brown) rats
and house mice. It is a chronic rodenticide, odorless, tasteless and effective
in very low dosages. Action is not rapid, usually about a week is required
before a marked reduction in the rodent population is effected. Warfarin
has found very ready acceptance because rodents do not tend to become bait
shy after once testing the material. They continue to consume it until its
anticlotting properties have produced death through internal haemorrhaging.
Though rodents became resistant to warfarin in the late 70's early 80's,
it can now be used again. Warfarin comes in water soluble, ready-to-use
bait, concentrate, powder, liquid concentrate, nylon pouch, coated talc
and dust formulations. The compound also comes in mixed formulations with
pindone, calciferol, and sulphaquinoxaline. It is considered compatible
with other rodenticides
amount of Warfarin that is lethal to one-half (50%) of experimental animals
fed the material is referred to as its acute oral lethal dose fifty, or
LD50. The acute oral toxicity for warfarin in rats is variously reported
to be 3 mg/kg, 1,600 ug/kg, 186 mg/kg (Hartley and Kidd, 1987); 58 mg/kg
in female rats. The acute oral LD50 for rats over 4-5 days is 1 mg/kg/day.
There was no development of ingestion tolerance indicated regardless of
rodent sex or age.
The acute oral LD50 for technical sodium warfarin in rats
was 323 mg/kg for males and 58 mg/kg for females. A single, large dose of
warfarin is about as toxic as a single, small dose. On a multiple-dose basis,
the reported LD100 for rats is 0.2 mg/kg/day for 5 days.
The dermal LD50 for rats was 1,400 mg/kg; 420 mg/kg intraperitoneal
LDlo (Lethal Dose, Low. The lowest dose which causes death in test animals.);
and 320 mg/m3 inhalation LC50. The same source indicated the acute oral
LD50 for mice was 60 mg/kg; 800 mg/kg subcutaneous LDlo; and 165 mg/kg intravenous
Toxicity values for warfarin in other animals are: an oral
LD50 for cats of 2.5-20 mg/kg; an acute oral LD50 of 35 mg/kg for a single
dose or 3 mg/day for 5 days; and 12 mg/kg oral LDlo. The acute oral LD50
for dogs exposed to warfarin was 3 mg/kg/day for 5 days. Technical sodium
warfarin in dogs had an LD50 of 200-300 mg/kg. The acute oral LD50 for warfarin
in cattle was 200 mg/kg/day for 5 days. The LD50 for technical sodium warfarin
in guinea pigs was 182 mg/kg. The oral LDlo for warfarin in pigs was reported
to be 1,200 ug/kg. Death followed 5 daily doses of 1 mg/kg for pigs.
Studies done on rabbits indicated the dermal LD50 of warfarin
to be greater than 8 g/kg. Technical sodium warfarin in rabbits had an LD50
of 800 mg/kg. Rabbits exhibited mild to slight conjunctival irritation in
response to technical warfarin.
Toxicity values for humans exposed to warfarin indicated
an oral-woman TDlo of 15 mg/kg/21 weeks intermittent; 10,200 ug/kg oral-man
TDlo; and 6,667 mg/kg oral-human LDlo. Average or large doses of warfarin
in humans may cause hemorrhage. Warfarin is not known to be an eye irritant.
It has produced hemorrhages in the retina, however, through its systemic
toxicity. The compound is considered highly toxic by inhalation and ingestion
and moderately toxic by dermal absorption. A dose of warfarin at 200 mg/m3
is considered highly toxic and immediately dangerous to life or health.
Warfarin has been established as a human teratogen, because
it causes birth defects in the offspring of women receiving clinical doses
of the compound during any trimester of pregnancy. Therapeutic use by pregnant
women has resulted in fatal hemorrhaging of the fetus and malformations
and mental retardation in infants. However, the amount of warfarin contained
in the rodenticide bait is very low. A single ingestion of warfarin-treated
bait by an adult female would not be likely to cause teratogenic effects.
The acute avian toxicity of warfarin indicates that it is
practically non-toxic to game birds. In subacute studies, warfarin ranged
from moderately toxic to practically non-toxic to upland game birds and
waterfowl. Another source indicated that an acute oral mallard duck study
was performed with a 10% formulation of warfarin. This formulation of warfarin
was considered moderately toxic to mallard ducks (LC50 greater than 120
mg/kg) when administered as a single dose. However, when exposed to 60 mg/kg
for a period of 14 days, 4 out of 5 ducks died.
Effects on Aquatic Organisms:
The toxicity of warfarin to aquatic organisms is felt to be
of low potential due to the fact that warfarin is insoluble in water. A long
field experience shows no potential hazards to aquatic organisms.
A 96-hour rainbow trout study was performed using a 0.54%
formulation of warfarin sodium salt. With a 96-hour LC50 of greater than
10,000 ppm, this formulation is considered non-toxic to rainbow trout.
Effects on Other Animals (Nontarget species):
Warfarin used as a prepared bait (0.13%) is considered non-toxic
to bees when used as prescribed.
The use of warfarin as a hand-placed bait limits the potential
for any secondary exposure of nontarget animals. However, because of its
high degree of mammalian toxicity and its use patterns, warfarin could adversely
affect endangered or threatened species. One study exists on a 50/50 percent
formulation of warfarin-sulfaquinoxaline technical. The warfarin- sulfaquinoxaline
caused secondary poisoning in mammalian carnivores such as mink and dogs
when ingesting prey killed after they were provided with treated bait (carrots
containing 0.025% by weight of the test material). The first death occurred
after 8 days of continuous exposure to treated nutria.
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