Sensitive determination of ambenonium in plasma using inhibitory activity to acetylcholinesterase

A sensitive analytical method for the determination of ambenonium, a selective acetylcholinesterase inhibitor, in plasma was developed. The procedure involves ultrafiltration to remove endogenous plasma cholinesterase, followed by colorimetric measurement of the inhibitory activity to acetylcholinesterase by the thiocholine method. Coefficient of variation of within-day triplicate analysis is less than 20% at the concentration of 5 nM. Detection limit of this method is 1 nM, which is twice lower than the most sensitive HPLC method reported previously. This assay procedure is applied to the pharmacokinetic study of ambenonium after intravenous administration of low dose (10-20 nmol/kg) to rat. This new method is rapid and simple and makes it possible to determine the ambenonium concentration in plasma with good accuracy.