Neostigmine is a parasympathomimetic, specifically, a reversible cholinesterase inhibitor. The drug inhibits acetylcholinesterase which is responsible for the degredation of acetylcholine. So, with acetylcholinesterase inhibited, more acetylcholine is present By interfering with the breakdown of acetylcholine, neostigmine indirectly stimulates both nicotinic and muscarinic receptors which are involved in muscle contraction.. It does not cross the blood-brain barrier.
Neostigmine is a cholinesterase inhibitor used in the treatment of myasthenia gravis and to reverse the effects of muscle relaxants such as gallamine and tubocurarine. Neostigmine, unlike physostigmine, does not cross the blood-brain barrier. By inhibiting acetylcholinesterase, more acetylcholine is available in the synapse, therefore, more of it can bind to the fewer receptors present in myasthenia gravis and can better trigger muscular contraction.
Neostigmine undergoes hydrolysis by cholinesterase and is also metabolized by microsomal enzymes in the liver.
Overdosage of Neostigmine can cause cholinergic crisis, which is characterized by increasing muscle weakness, and through involvement of the muscles of respiration, may result in death. The LD 50 of neostigmine methylsulfate in mice is 0.3 ± 0.02 mg/kg intravenously, 0.54 ± 0.03 mg/kg subcutaneously, and 0.395 ± 0.025 mg/kg intramuscularly; in rats the LD 50 is 0.315 ± 0.019 mg/kg intravenously, 0.445 ± 0.032 mg/kg subcutaneously, and 0.423 ± 0.032 mg/kg intramuscularly.