USA Home > Product Directory > Cell Biology > Cell Signaling and Neuroscience > Neuroscience > Neurotransmission > Neurotransmitters > Cholinergics > Antagonists
Neostigmine. By far the most commonly used anticholinesterase in anaesthesia is neostigmine. This is a water-soluble quaternary ammonium compound that combines reversibly with the esteratic site of the acetylcholinesterase enzyme rendering it inactive for about 30 minutes. Neostigmine is given as an intravenous injection at a dose of mg/kg (maximum 5mg), and should be administered with glycopyrronium mg/kg or atropine mg/kg. Neostigmine starts to take effect after approximately 2 minutes but has its maximal effect at 5-7 minutes. It is excreted unchanged by the kidney and has a half-life of about 45 minutes.
Pancuronium remains one of the few muscle relaxants logically and rationally designed from structure-action / effects relationship data. A steroid skeleton was chosen because of its appropriate size and rigidness. Acetylcholine moieties were inserted to increase receptor affinity. Although having many unwanted side-effects, a slow onset of action and recovery rate it was a big success and at the time the most potent neuromuscular drug available. Pancuronium and some other neuromuscular blocking agents block M2-receptors and therefore affect the vagus nerve , leading to hypotension and tachycardia . This muscarinic blocking effect is related to the acetylcholine moiety on the A ring on pancuronium. Making the N atom on the A ring tertiary, the ring loses its acetylcholine moiety, and the resulting compound, vecuronium, has nearly 100 times less affinity to muscarin receptors while maintaining its nicotinic affinity and a similar duration of action. Vecuronium is, therefore, free from cardiovascular effects.  The D ring shows excellent properties validating Beers and Reich's rule with great precision. As a result, vecuronium has the greatest potency and specificity of all mono-quaternary compounds.