Nerve agents muscular effects

Liquid nerve agents applied dermally cause local sweating and muscular twitching starting 3 min to 2 h after exposure. Signs last for 3 to 5 days. Following dermal exposure to a large drop clinical effects start within 30 min but with small drops a delay of up to 18 h can be seen (Sidell et al, 1997). 

Atropine is an antidotal treatment. It is used to reverse the muscarinic signs, but it will not reverse the nicotinic effects (muscular weakness, diaphragmatic weakness, etc.). Atropine blocks the effects of accumulated acetylcholine (ACh) at the synapse and should be continued until the nerve agent is metabohzed (Midthng et al, 1985). Over-atropinization can cause hyperthermia, tachycardia, agitation, mydriasis, and ileus, which can be life threatening in the horse (Meerstadt, 1982). 

Toxic effects occur within seconds to 5 min of nerve agent vapor or aerosol inhalation. The muscarinic effects include ocular (miosis, conjunctival congestion, ciliary spasm), nasal discharge, respiratory (bronchoconstriction and increased bronchial secretion), gastrointestinal (anorexia, vomiting, abdominal cramps, and diarrhea), sweating, salivation, and cardiovascular (bradycardia and hypotension) effects. The nicotinic effects include muscular fa-sciculation and paralysis. CNS effects can include ataxia, confusion, loss of reflexes, slurred speech, coma, and paralysis. 

After large exposures, the time to onset of effects may be much shorter than for smaller exposures and decreases as the amount of agent increases. For instance, two individuals were decontaminated within minutes of exposure to a drop of nerve agent. There was a 15- to 20-minute, asymptomatic interval before the precipitant onset of effects collapse, loss of consciousness, convulsive muscular jerks, fasciculations, respiratory embarrassment, and copious secretions. Within several minutes, flaccid paralysis and apnea occurred in both (personal observation). 

Little is known about the nervous systems of cestodes and trematodes except that they probably differ from those of nematodes, since milbemycins and avermectins have no effect on them. However, a highly effective anti schistosomal and antitapeworm agent, praziquantel (see Chapter 54 Clinical Pharmacology of the Anthelmintic Drugs), is known to enhance Ca2+ influx and induce muscular contraction in those parasites, though it exerts no action on nematodes or insects. Some benzodiazepine derivatives have activities similar to those of praziquantel these activities are unrelated to the anxiolytic activities in the mammalian central nervous system. The nerves and muscles in schistosomes and tapeworms are thus interesting subjects for future chemotherapeutic studies. 

Succinylcholine, a depolarizing neuromuscular blocking agent (0.3 to 1.1 mg/kg IV over 10 to 30 seconds), is used to induce skeletal muscle relaxation to facilitate intubation, ventilation, or orthopedic manipulations and to lessen muscular contraction in convulsions induced by physicians. A peripheral nerve stimulator may be used to monitor effects and degree of blockade. 

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