The carbamates are esters of carbamic acid. Unlike organophosphates, carbamates are not structurally complex. Presently, the volume of carbamates used exceeds that of organophosphates because they are considered to be safer than organophosphates.
The oral LD50 in rats is 0.9 mg/kg and the dermal LD50 in rabbits is 5 mg/kg. Dogs are frequently poisoned with malicious intent.
The oral LD50 in rats is 307 mg/kg and the dermal LD50 in rabbits is 2000 mg/kg. A 2% spray is nontoxic to calves; 4% is nontoxic to mature cattle when applied dermally.
The oral LD50 in rats, dogs, chickens, ducks, pheasants, quails, and wild birds is 8, 19, 6.3, 0.415, 4.2, 5.0, and 0.42 mg/kg, respectively. Dogs are commonly poisoned with malicious intent by tainting food. The minimum toxic dose in cattle and sheep is 4.5 mg/kg, becoming lethal at 18 and 9 mg/kg, respectively. Cattle and other domestic animals are often poisoned by accidental exposure. Pigs have been poisoned after drinking water contaminated by this compound. In Africa, wildlife populations (including deer, lions, and birds) are declining due to malicious use of carbofuran. Dermal LD50 in rabbits is 2550 mg/kg.
The oral LD50 in rats is 17 mg/kg, and dermal LD50 in rabbits is >2,000 mg/kg. Dogs have been commonly poisoned with malicious intent by tainting food. Cattle have been reported to be poisoned after consumption of forage inadvertently sprayed with this compound.
The oral LD50 is 95 mg/kg in rats and >800 mg/kg in goats. The dermal LD50 in rabbits is >1,000 mg/kg.
The carbamate insecticides act similarly to the organophosphates (see Insecticide and Acaricide (Organic) Toxicity: Organophosphates (Toxicity)) in that they inhibit AChE at nerve synapses and neuromuscular junctions. This inhibition is reversible because the inhibiting bond is much less durable; thus, the inhibition of blood AChE frequently is not evident at the laboratory. Signs include hypersalivation, GI hypermotility, abdominal cramping, vomiting, diarrhea, sweating, dyspnea, cyanosis, miosis, muscle fasciculations (in extreme cases, tetany followed by weakness and paralysis), and convulsions. In brief, the acronym SLUD (salivation, lacrimation, urination, and diarrhea) describes the overall clinical features of carbamates poisoning. Death usually results from respiratory failure and hypoxia due to bronchoconstriction leading to tracheobronchial secretion and pulmonary edema.
This usually depends on history of exposure to a particular carbamate and response to atropine therapy. However, when a history of carbamate poisoning is not provided, but cholinergic signs and a clear positive response to atropine suggest carbamate or organophosphate poisoning, AChE activity levels should be determined in RBC or whole blood (live animals), or brain cortex (dead animals). Enzyme activity that is significantly inhibited (>50%) is confirmatory. Signs of hypercholinergic activity are usually seen with AChE inhibition >70%. Screening GI contents for carbamate insecticides by gas chromatography coupled with mass spectrometry is helpful in identification, confirmation, and quantitation of a particular carbamate and aids in differential diagnosis if an organophosphate insecticide is also involved.
Treatment of carbamate poisoning is similar to that of organophosphate poisoning in that atropine sulfate injections readily reverse the effects. Recommended dosages for atropine are as follows: dogs and cats—dosed to effect (repeated as needed), usually 0.2–2 mg/kg, parenterally, one-fourth of the dose given IV and the remainder given SC (cats should be dosed at the lower end of the range); cattle and sheep—0.6–1 mg/kg, one-fourth of the dose IV and the remainder SC, repeated as needed; horses and pigs—0.1–0.2 mg/kg, IV, repeated as needed.
Pralidoxime (2-PAM) has been used to treat carbamate poisoning but its value is controversial. Poisoning may be caused by a mixture of organophosphates and carbamates, and 2-PAM may be beneficial. Signs of excessive cholinergic activity may warrant its use, in case the cause is organophosphate exposure. 2-PAM administration can be fatal if given too rapidly; it must be given slowly (ie, in 5% saline over a 10-min period). Also see Insecticide and Acaricide (Organic) Toxicity: Organophosphates (Toxicity). Also, 2-PAM solution should be prepared freshly, because the old solution is known to produce cyanide. Use of morphine or barbiturates is contraindicated.
Last full review/revision March 2012 by Ramesh C. Gupta, DVM, MVSc, PhD, DABT, FACT, FATS