The use of liquid cation exchange in the extraction and separation of ( 14 C)neostigmine iodide and its metabolite ( 14 C)3-hydroxyphenyltrimethylammonium iodide from body fluids

Synthesis and preliminary pharmacology of an internal standard for assay of neostigmine

The synthesis of the diethyl analog of neostigmine, its preliminary pharmacology, and its use as an internal standard for the GLC assay of neostigmine are described. Both the diethyl analog and neostigmine undergo thermal demethylation in the injection port. The column selected produced satisfactory resolution and short retention times for neostigmine and the diethyl analog. The diethyl analog apparently possesses acetylcholinesterase-inhibiting properties, as evidenced by potentiation of the contractile response to acetylcholine in the ileum. In addition, acetylcholine levels in the brain were elevated slightly. Water solutions of the diethyl analog appeared to lose biological activity with time. the diethyl analog appears to be suitable for use as an internal standard for the GLC assay of neostigmine.

Reversed-phase, ion-pair liquid chromatography of quaternary ammonium compounds: determination of pyridostigmine, neostigmine and edrophionium in biological fluids

A reversed-phase, ion-pair liquid chromatographic method for the quantitative determination of quaternary acetylcholinesterase inhibitors is described. The method uses an ion-pair extraction to isolate the drugs from biological material prior to liquid chromatographic separation and online UV detection at 214 nm. Quantiation down to 5 ng/ml and within-day precison with coefficient of variation (C.V.) of 1.5% (n = 10, x = 100 ng/ml) for neostigmine, C.V., 1.7% (n = 10, x = 80 ng/ml) for pyridostigmine and C.V., 1.5% (n = 10, x = 100 ng/ml) for edrophonium have been achieved. The assay was designed for pharmacokinetic studies of these drugs in anesthetized patients.

The relationship between the pharmacokinetics, cholinesterase inhibition and facilitation of twitch tension of the quaternary ammonium anticholinesterase drugs, neostigmine, pyridostigmine, edrophonium and 3-hydroxyphenyltrimethylammonium

1 The relationship between the concentration of drug in plasma, the inhibition of erythrocyte acetylcholinesterase and the facilitation of neuromuscular transmission has been studied in the rat after the administration of neostigmine, pyridostigmine, edrophonium and 3-hydroxyphenyltrimethyl-ammonium (3-OH PTMA). 2 After the administration of neostigmine or pyridostigmine, acetylcholinesterase activity recovered only slowly due to the covalent nature of the inhibition. In contrast, recovery from the reversible inhibition caused by edrophonium or 3-OH PTMA was rapid and showed a direct relationship to the plasma concentration of these drugs. 3 There was a statistically significant linear correlation between the logarithm of the plasma concentration of the drugs and the increase in the tibialis twitch tension. 4 The relationship between the inhibition of acetylcholinesterase and the facilitation of neuromuscular transmission was complex. When the enzyme was less than 85% inhibited no facilitation occurred. Between 85% and 98% inhibition, facilitation was linearly related to enzyme inhibition. Above 98% inhibition, facilitation was unrelated to inhibition of the enzyme.

The pharmacokinetics of neostigmine and 3-hydroxyphenyltrimethyl- ammonium in the rat: dose-dependent effects after portal vein administration

1 The elimination kinetics of [(14)C]-neostigmine iodide and [(14)C]-3-hydroxyphenyltrimethyl-ammonium iodide (3-OH PTMA) have been studied in the rat.2 The presence of a renal secretory pathway for neostigmine and 3-OH PTMA has been confirmed.3 For neostigmine and 3-OH PTMA, at a given dose level, the fraction of the dose eliminated unchanged was reduced and the metabolite fraction was increased after portal vein administration when compared to jugular vein administration. This indicates that both compounds are subject to extensive metabolism during the first passage through the liver.4 Neostigmine was eliminated by dose-independent kinetics after jugular vein administration but dose-dependent after portal vein administration. In the latter case the fraction eliminated as neostigmine increased with increasing dose. This increase was not accompanied by any change in the fraction of the metabolites eliminated.5 After portal vein administration of 3-OH PTMA, the fraction of the dose eliminated as 3-OH PTMA also increased with increasing dose. This change was accompanied by a decrease in the fraction of the metabolites eliminated which were excreted at a constant rate.