Description

Avermectin is a new pesticide with a wide margin of safety; however, severe cases of intoxication cause coma, hypotension, acidosis, and even death. Abamectin is highly effective against gastrointestinal nematodes of cattle and ivermectin-resistant strain of Teladorsagia circumcincta in sheep. It is also used in humans to treat Onchocerca volvulus.

Abamectin and ivermectin

Abamectin (avermectin B1) and ivermectin are members of macrocyclic lactone anthelmintics derived from the bacterium Streptomyces avermitilis. Abamectin is an analog of ivermectin. However, they are different. Abamectin is a precursor to ivermectin. It differs from ivermectin in having a double bond at the C22–23 position[1]. Both drugs seem to share a common mode of action, but they differ in their activity against nematode infections, abamectin being more active against nematodes than ivermectin.

Mode of action

Abamectin activates glutamate chloride channels in invertebrate nerve and muscle cells and lowers blood pressure by increasing serum levels of nitric oxide (NO), this effect was not observed in humans. Abamectin stimulates gamma-aminobutyric acid (GABA) receptors in the central nervous system, but due to the blood-brain barrier, humans are less susceptible to the effects of this toxin. Most patients were poisoned in an attempt to commit suicide by abamectin[2].

Toxicity

The toxic dose of 30 mg per kg of body weight of the mice was measured in 50% of cases 2. In one study, abamectin lethal dose was considered to be 10 mg/kg body weight. The toxicity of abamectin is oral, but there are some contact activities. Intoxication manifestations include midriasis, vomiting, tremor, seizure, partial ptosis, confusion, and coma. Mild intoxications manifest symptoms such as nausea, vomiting, diarrhea, and weakness. In severe poisoning, hypotension, coma, and respiratory failure occur. In chronic exposure, fertility failure in men with effect on semen is considered. Based on the unknown antidote for poisoning with this pesticide and the fact that human toxicity of this substance is not fully understood, one abamectin acute poisoning case was reported.

References

[1] Hamed Aminiahidashti, Ali Morad Heidari Gorji, Seyed Reza Jamali. “Conservative care in successful treatment of abamectin poisoning.” Toxicology International 21 3 (2014): 322–4.

[2] Alka. “Efficacy of abamectin against ivermectin-resistant strain of Trichostrongylus colubriformis in sheep.” Veterinary parasitology 121 3 (2004): Pages 277-283.