It is used to improve muscle tone in people with myasthenia gravis, and also to reverse the effects of non-depolarizing muscle relaxants such as rocuronium and vecuronium at the end of an operation, usually in a dose of 25 to 50 μg per kilogram. Another indication for use is the conservative management of acute colonic pseudo-obstruction, or Ogilvie's syndrome, in which patients get massive colonic dilatation in the absence of a true mechanical obstruction. Hospitals sometimes administer a solution containing neostigmine intravenously to delay the effects of envenomation through snakebite. Some promising research results have also been reported for administering the drug nasally as a snakebite treatment. Neostigmine was approved in the United States in 2013 to reverse the effects of muscle relaxants. It was initially approved in 1939.
Side effects
Neostigmine can induce generic ocular side effects including: headache, brow pain, blurred vision, phacodonesis, pericorneal injection, congestive iritis, various allergic reactions, and rarely, retinal detachment. Neostigmine will cause slowing of the heart rate ; for this reason it is usually given along with a parasympatholytic drug such as atropine or glycopyrrolate. Gastrointestinal symptoms occur earliest after ingestion and include anorexia, nausea, vomiting, abdominal cramps, and diarrhea.
Pharmacology
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 and does not cross the blood–brain barrier and enter the CNS, but it does cross the placenta. Its effect on skeletal muscle is greater than that of physostigmine. Neostigmine has moderate duration of action – usually two to four hours. Neostigmine binds to the anionic and ester site of cholinesterase. The drug blocks the active site of acetylcholinesterase so the enzyme can no longer break down the acetylcholine molecules before they reach the postsynaptic membrane receptors. This allows for the threshold to be reached so a new impulse can be triggered in the next neuron. In myasthenia gravis there are too few acetylcholine receptors so with the acetylcholinesterase blocked, acetylcholine can bind to the few receptors and trigger a muscular contraction.
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.
