Chemical species with pharmaceutical functions are called medicines, which can be obtained in many different ways, from their production through laboratory syntheses to natural sources, such as plants. In general, these species are produced to provide palliative, healing and preventive actions, as well as clinical diagnoses. However, its excessive use, improper disposal and reduced efficiency can cause deleterious effects for living beings. These effects are attested mainly through environmental analyses and biological samples. Several analytical methodologies can be applied to obtain more information about these species, among them, we can highlight chromatographic methodologies, such as HPLC, capillary electrophoresis analysis and also electrochemical methods. The latter stand out for presenting good sensitivity, selectivity, stability, low cost, in situ analysis, possibility of miniaturization and generation of little waste. In this sense, the present work approached the development of an electrochemical sensor employing a three electrodes system: auxiliary electrode (platinum), reference electrode (Ag|AgCl|Cl-) and a glassy carbon electrode (ECV) (working electrode) with different modifying agents (chitosan + Au nanoparticles, multi-walled carbon nanotubes (MWCNTs) and CdSe, CdSe/CdS, ZnO nanoparticles) in order to quantify drugs. For this, drug standards were applied, such as: captopril, flucloxacillin, amoxicillin, N-Acetyl-L-cysteine and ranitidine (RAN) in electrochemical analysis, through cyclic voltammetry (VC) and differential pulse voltammetry (DPV). The electrochemical responses obtained showed ranitidine as an potential analyte, and this choice was made due to several parameters, such as: user reports regarding its degradation, lack of information in the literature on electrochemical issues and the need for studies focused on its quality. Therefore, modifications were made to the ECV using chitosan, in the absence and presence of nanoparticles (CdSe, CdSe/CdS, ZnO and Au), however, attenuation of the electrochemical response was observed. Thus, MWCNTs were applied with CdSe, CdSe/CdSe and ZnO nanoparticles, highlighting the modification of NTC with CdSe/CdS, which was chosen because it has one of the best sensitivities (44.45 I (µA) mmol-1 L), up to about 10x more sensitive than the other modifications. With the choice of modification, the optimization of chemical parameters was used, and these were: pH=7 for phosphate buffer at a concentration of 200 mM, with the following curve: Ipa (µA) = 44.45(± 0.36) CRAN (mM) - 0.17(± 0.01), linear range (F.L) = 7.0 - 56.6 µM, N = 7, r = 0.999, LD of 0.15 µM, LQ of 7.0 µM and MWCNTs:CdSe/CdS ratio of 1:0.5 (mg). In the electrochemical characterization step, the developed sensor showed an increase of 10% of the electroactive area in relation to the ECV without modification and regarding the ranitidine oxidation process on the sensor surface, a combination of diffusion and adsorption processes was observed. Electrochemical impedance spectroscopy analysis was also used, demonstrating a 66.5% reduction in the resistance of the electrode/solution interface of the modified sensor. Finally, the analysis of possible interferents did not show an RSD value greater than 5% and, in the recovery test with the presence of synthetic urine, the recoveries ranged from 100.3 to 102.8%. When applied in pharmaceutical formulations, such values were from 95.8 to 99.0%.