Pyrethroid pesticides are one of the most widely used agricultural and household pesticides, accounting for nearly 25% of the global pesticide market [3]. Poisoning incidents caused by pyrethroid pesticides are frequently reported. According to the latest statistic of the Toxicant Exposure Monitoring System of the American Association of Poison Control Centers, pesticide poisoning ranks the ninth among all types of poisoning, which accounts for 3.28% of all intoxication incidents. In China, chenshuyang et Al. [5] analyzed and found 2954 reported cases of pesticide poisoning from 1992 to 2003, accounting for 3.21% of all poisoning cases. Meperfluthrin is also a kind of pyrethroid insecticide, which is often used for mosquito incense, mosquito incense tablets and liquid mosquito incense products, with a concentration of 0.8%, few with concentration of 0.6%, and widely used in Chinese families.
Pyrethroid pesticides are classified into two types based on different chemical structure. Type I does not contain the cyano group (such as pyrethrin) but type II does (such as cypermethrin, deltamethrin) [6], which is alipid-soluble chemical compound that can pass through the blood-brain barrier effectively. It mainly targets and changes the sensitivity of the voltage-gated sodium channels, which keeps the sodium channels open, so the sodium ions flow into the cell and prolong the depolarization,and causes abnormal excitation of the nerve cells. It has been shown that sodium channels in the dorsal root ganglion and peripheral nerves of mammals are more sensitive to type II pyrethroids than type I before sexually mature, and type II can also keep the sodium channel open longer than type I. It has also been suggested that type II pyrethroids can control the voltage-dependent chloride channels in the brain, nerves, muscles and salivary glands, thereby reducing the chloride channel currents [7]. At higher concentrations, pyrethroids can act on the GABA-gated chloride channels, leading to severe type II toxic convulsions. Romero et al [8] found that pyrethroid metabolism produces superoxide anion, hydroxyl radicals and hydrogen peroxide free radicals. Kanbur et al [9] found that cypermethrin exposure increases oxidative stress (malondialdehyde, nitric oxide) in the rat brain, while superoxide dismutase(SOD), antioxidant enzymes such as catalase(CAT) and glutathione peroxidase(GSH-Px) decreased significantly, and this phenomenon became more obvious with prolongation of exposure time.
Because sodium channels are located in type I and type II alveolar epithelium, the permeation gradient may be destroyed by pyrethroids, leading to airway and bronchial mucosal edema [10]. Due to the hypersensitivity caused by pyrethroids, the ongoing inflammatory reaction may also be one of the factors that cause lung damage. In addition, the damages caused by certain organic solvents in pyrethroid drugs, such as chloroform, benzene and ether, may also be the cause of lung lesions.
Pyrethroid drugs are often taken by mistake, mild poisoning can be manifested as upper respiratory tract irritation, cough, sore throat, dizziness, headache, nausea, vomiting, abdominal pain, fatigue, chest tightness, sensory abnormalities. Serious poisoning may cause disturbance of consciousness, seizures, severe pneumonia, dyspnea, cyanosis and coma [6], death is more unlikely to occur [11]. Neurological symptoms are one of the main clinical manifestations [12], type II poisoning can cause muscle clonus and paroxysmal tonic convulsion, similar to epilepsy [13]. The concentration of the drug in this case is 0.8%, and it caused severe convulsion, shortness of breath, dyspnea and progressive lung injury and brain damage. The patient recovered fully after treatment.
When patient is diagnosed with pyrethroid poisoning, 2% - 4% sodium bicarbonate should be used for gastric lavage, and then medicinal carbon should be applied for absorbing the residual solution in the stomach. Because the toxin can cause serious lung injury and nervous system damage, active measures such as controlling static shock, reducing cranial pressure, respiratory support; mechanical ventilation, corticosteroids injection, anti-oxidative stress, infection prevention should be considered in sever case. Atropine in small dosage can also be applied, but atropinization is not recommended. Although pyrethroids belong to the low toxic drugs, they are more likely to cause continuous convulsion, progressive lung injury and even ARDS. Therefore, blood purification should be carried out as early as possible.
Because pyrethroid insecticides are widely used, medical staff needs to pay more attention on health education, reminding parents to prevent children from taking them by mistake. Meanwhile, manufacturers also need tobe alter and have the emergency directions for mistakenly intake, so as to improve the awareness of poisoning and minimize such accidental injuries.