is an inhibitor of acetylcholinesterase. Neostigmine binds to the anionic and ester site of acetylcholinesterase, which blocks the enzyme from breaking down the acetylcholine molecules before they reach the postsynaptic membrane receptors. Its action leads to the accumulation of acetylcholine in the neuromuscular junction that compete with the non-depolarizing blocker agent bound to the acetylcholine receptors. By interfering with the breakdown of acetylcholine, neostigmine indirectly stimulates both nicotinic and muscarinic receptors. Unlike physostigmine, neostigmine has a quaternary nitrogen; hence, it is more polar. It does not cross the blood–brain barrier and enter the CNS. However, it does cross the placenta. Neostigmine is administered intravenously. The drug should be administered when a peripheral nerve stimulator shows a second twitch is present or when the first twitch response is considerably above 10% of baseline. Peak effect is at 7 to 10 minutes. Neostigmine has moderate duration of action – usually two to four hours. It is metabolized by enzymes in the liver and excreted in the urine. Chemistry Neostigmine, which can be viewed as a simplified analog of physostigmine, is made by reacting 3-dimethylaminophenol with N-dimethylcarbamoyl chloride, which forms the dimethylcarbamate, and its subsequent alkylation using dimethyl sulfate forming the desired compound. Spectral data Neostigmine shows notable UV/VIS absorption at 261 nm, 267 nm, and 225 nm. Neostigmine's 1H NMR Spectroscopy reveals shifts at: 7.8, 7.7, 7.4, 7.4, 3.8, and 3.1 parts per million. The higher shifts are due to the aromatic hydrogens. The lower shifts at 3.8 ppm and 3.1 ppm are due to the electronic withdrawing nature of the tertiary and quaternary nitrogen, respectively. History Neostigmine was first synthesized by Aeschlimann and Reinert in 1931 and was patented by Aeschlimann in 1933. Neostigmine is made by first reacting 3-dimethylaminophenol with N-dimethylcarbamoyl chloride, which forms a dimethylcarbamate. Next, that product is alkylated using dimethyl sulfate, which forms neostigmine. References External links Acetylcholinesterase inhibitors Aromatic carbamates Dimethylamino compounds Quaternary ammonium compounds World Health Organization essential medicines Wikipedia medicine articles ready to translate Ophthalmology drugs