Neostigmine [nee-oh-STIG-meen] is a synthetic compound that is also a carbamic acid ester, and it reversibly inhibits acetylcholinesterase in a manner similar to that of physostigmine. Unlike physostigmine, neostigmine has a quaternary nitrogen; hence, it is more polar and does not enter the CNS. Its effect on skeletal muscle is greater than that of physostigmine, and it can stimulate contractility before it paralyzes. Neostigmine has a moderate duration of action, usually 30 minutes to 2 hours. It is used to stimulate the bladder and GI tract, and it is also used as an antidote for tubocurarine and other competitive neuromuscular blocking agents . Neostigmine has found use in symptomatic treatment of myasthenia gravis, an autoimmune disease caused by antibodies to the nicotinic receptor at neuromuscular junctions. This causes their degradation and, thus, makes fewer receptors available for interaction with the neurotransmitter. Adverse effects of neostigmine include those of generalized cholinergic stimulation, such as salivation, flushing, decreased blood pressure, nausea, abdominal pain, diarrhea, and bronchospasm. Neostigmine does not cause CNS side effects and is not used to overcome toxicity of central-acting antimuscarinic agents such as atropine.

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