QUANTITATIVE GAS-LIQUID-CHROMATOGRAPHIC METHOD FOR DETERMINATION OF NEOSTIGMINE AND PYRIDOSTIGMINE IN HUMAN-PLASMA

A sensitive and selective analytical method was used to measure the concentration of neostigmine and pyridostigmine in human plasma. The procedure involved preliminary ion-pair extraction of the drugs into dichloromethane, followed by concentration and analysis of the ion-pair complex using a GLC system fitted with a N detector. Using the peak area ratio technique, pyridostigmine bromide was used as the internal standard for the quantitation of neostigmine in plasma; neostigmine bromide was the internal marker for the determination of pyridostigmine. The method depends on the thermal dequaternization of the quaternary amines and can be used to detect 5 ng/ml in a 3-ml plasma sample. Accurate measurement can be made at levels of 50-1000 ng/ml. This assay procedure was applied to the separate determination of the plasma concentration of neostigmine and pyridostigmine after single administration of i.v. doses in anesthetized patients.