An ex-situ pharmacokinetic of Triamterene (Trim) drug has been investigated by electrochemical technique using multiwalled carbon nanotube modified glassy carbon electrode, GCE/MWCNT (GCE/MWCNT@Trim(ads)) as a biomimicking carbon network system. Trim is a phenyl ring containing electro-inactive drug that has been widely used for the treatment of diuretic and antihypertensive related diseases. Upon cyclic volumetric measurement of Trim-drug adsorbed GCE/MWCNT at an optimal potential window, -1 to 0.9 V vs Ag/AgCl showed formation of a well-defined surface-confined redox peak at E-o' = 0.1 V vs Ag/AgCl in pH 7 phosphate buffer solution. Calculated surface-excess value is 0.85 x 10(-9) mol cm(-2) and it is proton-coupled electron-transfer in nature. Collective characterization results of the modified electrode by physicochemical techniques (Raman, IR and Mass spectrophotometer) and electrochemical methods (effect of potential window) reveal hydroxylation of the phenyl ring of the Trim-drug to phenolic derivative (intermediate) in association with involvement of H2O2 intermediate species that have been generated by oxygen reduction reaction at negative potential and subsequent oxidation to trihydroxy benzene-Trim drug (Trim-3HQ). The GCE/MWCNT@Trim-3HQ showed selective mediated oxidation current signals for cysteine in relation with importance of the free thiol molecules and its conversion to disulfide (CyS-SCy) at pathogenic condition in the biological system like human serum albumin. As an independent study, amperometric i-t and flow injection analysis of CySH have been demonstrated with a detection limit value 695 nM.