Organophosphates
Organophosphates
• Organophosphate nerve agents (ONA) are the most toxic nerve agents known.
• Tabun (known as GA) and sarin (GB) were developed in Germany during 1936-1945 but were not used until the Gulf War, 1981 to 1987, by Iraq against Iran.
• Sarin was released over the city of Matsumoto in Japan on June 27, 1994, resulting in 600 illnesses and 7 deaths. It was also released in a Tokyo subway in March . 1995, resulting in 12 deaths.
• Even a small dose of ONA can be fatal.
• ONA inhibit acetylcholinesterase, leading to excess acetylcholine at the autonomic (muscarinic and nicotinic) receptors.
• The muscarinic receptors stimulate defecation, urination, miosis, bronchospasm, bronchorrhea, bradycardia, emesis, lacrimation, and salivation (DUMBBELS). The
. three “B’s” are life-threatening.
• Nicotinic receptors are present in both the sympathetic and parasympathetic nervous systems; excitation will produce hypertension and tachycardia at low doses . . and hypo-tension and weakness at high doses.
• Central nicotinic stimulation can cause seizures, coma, and respiratory center depression.
• The mnemonic for excess nicotinic stimulation is “MTWHF” for mydriasis, tachycardia, weakness, hypertension, and fasciculation.
• High-dose ONA may cause fasciculations followed by paralysis (similar to succinylcholine administration).
• G-type agents (sarin, soman, tabun) are colorless, clear, tasteless, water-soluble liquids.
• As gases, sarin is odorless, tabun is fruity-smelling, and tabun has a fruity odor. All are heavier than air.
• Nerve agent VX is an oily liquid that can be absorbed through the skin with minimal contact time.
• Healthcare workers must wear personal protective equipment to prevent secondary exposure, which may include respiratory protection.
• ATROPINE controls life threatening muscarinic symptoms such as bronchospasm, bronchorrhea, and bradycardia. Dosing is 1-2 mg, IV or IM, or up to 6 mg for . . . severe exposures followed by 2 mg every 5-10 minutes prn.
• Therapy for nicotinic symptoms is supportive and involves ventilatory support and VASOPRESSORS for hypotension.
• Seizures are usually controlled with DIAZEPAM.
• More definitive therapy consists of the use of an oxime such as PRALIDOXIME chloride (15 mg/kg over 5-10 minutes).
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