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 carbamates 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 2,000 mg/kg. A 2% spray
is nontoxic to calves; 4% is nontoxic to mature cattle when applied
The oral LD50 in rats, dogs,
chickens, ducks, pheasants, quails, and wild birds is 8, 19, 6.3, 0.415, 4.2, 5,
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 because of malicious use of
carbofuran. The dermal LD50 in rabbits is 2,550
The oral LD50 in rats is 17 mg/kg,
and the 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
The oral LD50 is 95 mg/kg in rats
and >800 mg/kg in goats. The dermal LD50 in rabbits is
The carbamate insecticides act similarly to the
organophosphates (see Organophosphates (Toxicity)) in that they
inhibit acetylcholinesterase (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 carbamate poisoning.
Death usually results from respiratory failure and hypoxia due to
bronchoconstriction leading to tracheobronchial secretion and pulmonary
Diagnosis of carbamate poisoning 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 RBCs or
whole blood (live animals), or in 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) should not be used to treat carbamate
poisoning. 2-PAM can be beneficial if poisoning is caused by a mixture of
organophosphates and carbamates. Signs of excessive cholinergic activity may
warrant its use, in case the cause is organophosphate exposure. 2-PAM can be
fatal if given too rapidly; it must be administered slowly (ie, in 5% saline
over a 10-min period). Also see Organophosphates (Toxicity). Also,
2-PAM solution should be prepared freshly, because old solutions are known to
produce cyanide. Use of morphine or barbiturates is contraindicated.
Last full review/revision August 2014 by Ramesh C. Gupta, DVM, MVSc, PhD, DABT, FACT, FACN, FATS