The two novel ion-pairs (PB-TPB and NB-TPB) of quaternary ammonium drugs; propantheline bromide(PB). N,N-Diisopropyl-N-methyl-N-[2-(xanthen-9ylcarbonyloxy)ethyl] ammonium bromide and neostigmine bromide (NB), 3-(dimethylcarbamoyloxy) phenyl]-trimethylazanium have been synthesized, respectively and incorporated in poly (vinyl chloride)-based membrane electrodes for the quantification of propantheline bromide and neostigmine bromide in different pharmaceutical preparations. The influences of membrane compositions on the potentiometric responses of membrane electrodes have been found to substantially improve the performance characteristics. The best performance was reported with membranes having composition (w/w) of PB-TPB or NB-TPB (6%): PVC (34%): o-NPOE (60%). The proposed electrodes exhibit nernstian response in the concentration ranges of 2.1 x 10(-7) M to 1.0 x 10(-2) M and 4.4 x 10(-7) M to 1.0. x 10(-2) M with detection limit of 1.5 x 10(-7) M and 3.3 x 10(-7) M, respectively. Both the membrane electrodes perform satisfactorily over pH ranges of (3.5-7.5 and 4.0-7.0) with fast response times (11s and 13s), respectively. These drugs (PB and NB) were further utilized as different ion-pairs of Prostaglandin E-1 (PGE(1)) and Deoxycholate (DOC) in poly (vinyl chloride)-based membrane electrodes for the determination of bioavailability of Prostaglandin E-1 and Deoxycholate in plasma of different patients. (C) 2009 Elsevier Ltd. All rights reserved.