Most insecticides derived from plants (eg, rotenone from Derris and pyrethrins
have traditionally been considered safe for use on animals. Nicotine in
the form of nicotine
sulfate is an exception. Unless it is carefully used, poisoning may result. Pets are
exposed to tobacco by ingesting commercial tobacco products (eg, cigarettes or
chewing tobacco), whereas livestock may consume discarded tobacco stalks or hay
contaminated with tobacco plant drippings in the barn. The minimum lethal dose of
nicotine is 1 g in cattle, 0.2–0.3 g in horses, 0.1–0.2 g in sheep, and 0.02–0.1 g
in dogs and cats. Affected animals show tremors, incoordination, nausea, disturbed
respiration, muscle paralysis, and finally coma and death. Nicotine and related
alkaloids from tobacco can cross the placenta and produce teratogenic effects.
Recovery from sublethal doses is usually complete within 3 hr. Death occurs within a
matter of hours from paralysis of thoracic respiratory muscles and cardiac arrest.
Necropsy may reveal parts of tobacco leaves or stalks in the rumen contents. Lesions
include pale mucous membranes, dark blood, hemorrhages on the heart and in the
lungs, and congestion of the brain. Treatment consists of removing the material by
washing or by gastric lavage with tannic acid, administering activated charcoal,
providing artificial respiration, and treating for cardiac arrest and shock.
Pyrethrins are insecticides obtained from the flowers of
cinerariaefolium and have been used as insecticides for many years.
Pyrethrins and pyrethroids produce toxicity affecting primarily the sodium
channel, but also chloride and calcium channels of nerve cells. These
insecticides also interact with nicotinic acetylcholine receptors. Synergists,
such as piperonyl butoxide, sesamex, piperonyl cyclonene, etc, are added to
increase stability and effectiveness. This is accomplished by inhibiting mixed
function oxidases, enzymes that detoxify pyrethrins and pyrethroids;
unfortunately, this also potentiates mammalian toxicity.
Pyrethroids are synthetic derivatives of natural
pyrethrins. There are two types of pyrethroids. Type I compounds that lack an
α-cyano substituent include pyrethrin I, allethrin, tetramethrin, kadethrin,
resmethrin, phenothrin, and permethrin. Type II compounds that contain a
stabilizing α-cyano-3-phenoxybenzyl component include cyfluthrin, cypermethrin,
fenpropanthrin, deltamethrin, cyphenothrin, fenvalerate, and fluvalinate. Type I
pyrethroids produce a neurologic syndrome through their effects on both the
central and peripheral nervous systems, with signs including tremors,
incoordination, prostration, seizures, and death. Type II pyrethroids work
primarily by CNS mechanisms to exert the choreoathetosis/salivation syndrome,
characterized by hyperactivity, hunched back, salivation, tremors, and
incoordination progressing to sinuous writhing movements.
Diagnosis of pyrethrin/pyrethroid poisoning is based on
clinical signs, history of exposure, and determination of insecticide residue in
body tissues and fluids. These insecticides do not produce characteristic
Generally, symptomatic and supportive treatment is
required after ingestion of a dilute pyrethrin or pyrethroid preparations.
Toxicity may also be due to the solvent. Induction of emesis may be
contraindicated. A slurry of activated charcoal at 2–8 g/kg may be administered,
followed by a saline cathartic (magnesium or sodium sulfate [10% solution] at
0.5 mg/kg). Vegetable oils and fats, which promote the intestinal absorption of
pyrethrum, should be avoided. If dermal exposure occurs, the animal should be
bathed with a mild detergent and cool water. The area should be washed very
gently so as not to stimulate the circulation and enhance skin absorption.
Initial assessment of the animal's respiratory and cardiovascular integrity is
important. Further treatment involves continuing symptomatic and supportive
care. Seizures should be controlled with either diazepam (administered to effect
at 0.2–2 mg/kg, IV) or methocarbamol (55–220 mg/kg, IV, not exceeding 200
mg/min). Phenobarbital or pentobarbital (IV), to effect, can be used if diazepam
or methocarbamol are too short-acting.
d-Limonene is the major component of the oil extracted
from citrus rind. It is used for the control of fleas on cats and for other
insect pests. Adult fleas and eggs appear to be most sensitive to
d-limonene, which is more effective if combined with
the synergist piperonyl butoxide. At recommended dosages, the solution
containing d-limonene appears to be safe, but increasing
the concentration 5–10 fold in sprays or dips increases the severity of toxic
signs, which include hypersalivation, muscle tremors, ataxia, and mild to severe
hypothermia. The inclusion of piperonyl butoxide in the formulation potentiates
the toxicity in cats. Allergies have also been reported in people in contact
with d-limonene, and it appears to increase dermal
absorption of some chemicals. When orally administered to dogs,
d-limonene causes vomiting (median effective dose 1.6
mL/kg). No antidote is available.
Last full review/revision August 2014 by Ramesh C. Gupta, DVM, MVSc, PhD, DABT, FACT, FACN, FATS