Most insecticides derived from plants (eg, rotenone from Derris and pyrethrins from Chrysanthemum or Pyrethrum) 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 products (eg, cigarettes, chewing tobacco), whereas livestock may consume discarded tobacco stalks or hay contaminated with tobacco plant drippings in the barn. 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. Death occurs from paralysis of 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. Mildly affected animals recover rapidly and spontaneously.

Pyrethrins

This is a closely related group of naturally occurring compounds that are the active insecticidal ingredients of pyrethrum. Pyrethrins are extracted from the flowers of Chrysanthemum cinerariaefolium and have been effective insecticides for many years. Pyrethrins produce toxicity affecting primarily the sodium channel, but also chloride and calcium channels of nerve cells. 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 destroy pyrethrum; unfortunately, this also potentiates mammalian toxicity.

Pyrethroids

These are synthetic derivatives of natural pyrethrins and include allethrin, cyfluthrin, cyhalothrin, cypermethrin, decamethrin, deltamethrin, fenvalerate, flumethrin, fluvalinate, permethrin, and tetramethrin. Generally, these compounds are more effective and less toxic to mammals than natural pyrethrins; they appear to be not well absorbed from the skin (however, allergic manifestations through skin contact and inhalation are common in humans). Mildly affected animals as well as those in early stages of toxicosis often show hypersalivation, vomiting, diarrhea, mild tremors, hyperexcitability, or depression. This syndrome may be confused with organophosphate or carbamate toxicosis. More severely affected animals can have hyperthermia, hypothermia, dyspnea, severe tremors, disorientation, paralysis of nerves and muscles, and seizures. Death is due to respiratory failure. Clinical signs usually begin within a few hours of exposure, but the onset may be altered by the rate of dermal absorption or the timing of grooming behavior.

Generally, treatment is not required after ingestion of a dilute pyrethrin or pyrethroid preparations. Because the chief hazard may be 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 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

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 March 2012 by Ramesh C. Gupta, DVM, MVSc, PhD, DABT, FACT, FATS