Lewisite

= Lewisite = Lewisite (L) (Chemical formula : C2H2AsCl3), is an organoarsenic compound. It was once manufactured in the U.S., Japan, and Germany for use as a chemical weapon, acting as a vesicant (blister agent) and lung irritant. Although colorless and odorless, impure samples of lewisite are a yellow, brown, violet-black, green, or amber oily liquid with a distinctive odor that has been described as similar to geraniums.

Mode of action as chemical weapon
Lewisite is a suicide inhibitor of the E3 component of pyruvate dehydrogenase. As an efficient method to produce ATP, pyruvate dehydrogenase is involved in the conversion of pyruvate to Acetyl-CoA. The latter subsequently enters the TCA cycle. Peripheral nervous system pathology usually arises from Lewisite exposure as the nervous system essentially relies on glucose as its only catabolic fuel. It can easily penetrate ordinary clothing and even latex rubber gloves; upon skin contact it causes immediate stinging, burning pain and itching that can last for 24 hours. Within minutes, a rash develops and the agent is absorbed through the skin. Large, fluid-filled blisters (similar to those caused by mustard gas exposure) develop after approximately 12 hours and cause pain for 2–3 days. These are severe chemical burns and begin with small blisters in the red areas of the skin within 2–3 hours and grow worse, encompassing the entire red area, for the ensuing 12–18 hours after initial exposure. Liquid lewisite has faster effects than lewisite vapor. Sufficient absorption can cause deadly liver necrosis.

Those exposed to lewisite can develop refractory hypotension (low blood pressure) known as Lewisite shock, as well as some features of arsenic toxicity. Lewisite causes physical damage to capillaries, which then become leaky, meaning that there is not enough blood volume to maintain blood pressure, a condition called hypovolemia. When the blood pressure is low, the kidneys may not receive enough oxygen and can be damaged.

Inhalation, the most common route of exposure, causes a burning pain and irritation throughout the respiratory tract, nosebleed (epistaxis), laryngitis, sneezing, coughing, vomiting, trouble breathing (dyspnea), and in severe cases of exposure, can cause fatal pulmonary edema, pneumonitis, or respiratory failure. Ingestion results in severe pain, nausea, vomiting, and tissue damage. The results of eye exposure can range from stinging, burning pain and strong irritation to blistering and scarring of the cornea, along with blepharospasm, lacrimation, and edema of the eyelids and periorbital area. The eyes can swell shut, which can keep the eyes safe from further exposure. The most severe consequences of eye exposure to lewisite are globe perforation and blindness. Generalised symptoms also include restlessness, weakness, hypothermia and low blood pressure.

It is possible that Lewisite may be a carcinogen since arsenic is categorized as a respiratory carcinogen by the International Agency for Research on Cancer, though it has not been confirmed that lewisite is a carcinogen.[7]

Lewisite causes damage to the respiratory tract at levels lower than the odor detection threshold, but early tissue damage is fairly noticeable due to the pain it causes.

Treatment
British anti-lewisite, also called dimercaprol, is the antidote for lewisite. It can be injected to prevent systemic toxicity, but will not prevent injury to the skin, eyes, or mucous membranes. Chemically, dimercaprol binds to the arsenic in lewisite. It is contraindicated in those with peanut allergies.Other treatment for lewisite exposure is primarily supportive. First aid of lewisite exposure consists of decontamination and irrigation of any areas that have been exposed. Other basic first aid can be used as necessary, such as airway management, assisted ventilation, and monitoring of vital signs. In an advanced care setting, supportive care can include fluid and electrolyte replacement. Because the tube may injure or perforate the esophagus, gastric lavage is contraindicated.

Long-term sequelae
From one acute exposure, someone who has inhaled lewisite can develop chronic respiratory disease; eye exposure to lewisite can cause permanent visual impairment or blindness. Chronic exposure to lewisite can cause arsenic poisoning (due to its arsenic content) and development of a lewisite allergy. It can also cause various long-term illnesses or permanent damage to organs, depending on where the exposure has occurred, including conjunctivitis, aversion to light (photophobia), visual impairment, double vision (diplopia), tearing (lacrimation), dry mucous membranes, garlic breath, burning pain in the nose and mouth, toxic encephalopathy, peripheral neuropathy, seizures, nausea, vomiting, chronic obstructive pulmonary disease (COPD), bronchitis, dermatitis, skin ulcers, basal cell carcinoma, and squamous cell carcinoma.