Mexiletine-sensitive membrane electrode for medical application

Response characteristics of mexiletine-sensitive membrane electrodes based on crown ether and ion-exchanger were examined in a physiological saline in order to find an electrode suitable for determining concentrations of this drug under physiological conditions. Among various crown ethers screened, 4',4 "(5 ")-di-tert-butyldicyclohexano-18-crown-6 showed the highest sensit ivity to mexiletine in physiological saline containing 0.15 M NaCl and 5 mM 4-(2-hydroxyethyl)-2-piperazineethanesulfonic acid (Hepes)-NaOH (pH 7.4). However, the detection limit of 30 mu M was 10 times higher than that of 3 mu M observed with the electrode based on an ion-exchanger, sodium tetrakis [3,5-bis(2-methoxy-hexafluoro-2-propyl)phenyl]borate. Having high selectivi ty against inorganic cations such as Na+ or K+, the electrode using the ion -exchanger enabled us to determine the level of mexiletine in saliva, the m onitoring of which is quite effective for controlling the dose of this drug noninvasively. The mexiletine concentrations determined with the mexiletin e electrode compared favourably with those determined by high-performance l iquid chromatography which requires an additional procedure to extract mexi letine from saliva. (C) 1999 Elsevier Science B.V. All rights reserved.