neostigmine [key], drug used to mimic the effects of stimulation of the parasympathetic nervous system. Along with several other drugs that have a similar mode of action, it inhibits the action of the enzyme cholinesterase, which destroys the substance acetylcholine at nerve endings. Because neostigmine increases the effective concentration of acetylcholine, it causes such body changes as contraction of the pupils, increased activity of intestinal muscles, and increased secretion by the salivary and sweat glands. It will cause menstrual bleeding in a nonpregnant woman whose menstrual period is delayed, and it is therefore used as a pregnancy test. Neostigmine and related drugs are also used to diagnose and control the neuromuscular disease myasthenia gravis. Because neostigmine causes decreased fluid pressure in the eye it is used to treat certain types of glaucoma. The drug atropine is sometimes given along with neostigmine to prevent the latter's side effects. Ephedrine often enhances the action of neostigmine.
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