Objective: Simple, sensitive, precise, reproducible and validated visible spectrophotometric methods have been developed for the determination of an antimuscarinic drug, namely oxybutynin hydrochloride (OXB) in pure form and in pharmaceutical preparations.Methods: Two spectrophotometric methods are based on the formation of yellow colored ion-pair complexes between the studied drug, and two sulphonphthalein acid dyes, bromocresol purple (BCP) and bromophenol blue (BPB) with absorption maxima at 410 and 416 nm, respectively.Results: The stoichiometric ratio of the formed ion-pair complexes was found to be 1:1 (drug: reagent) for both methods as deduced by Job's method of continuous variation. Several parameters such as pH, buffer type, and reagent volume, sequence of addition and effect of extracting solvent were optimized to achieve high sensitivity, stability, low blank reading and reproducible results. Under the optimum reaction conditions, linear relationships with good correlation coefficients (0.9996-0.9999) were found between the absorbance's and the concentrations of oxybutynin over the concentration ranges of 1.0–8.0 μg ml-1 and 1.0–12 μg ml-1 with LOD of 0.21 and 0.19 μg ml-1, using BCP and BPB methods, respectively. Various analytical parameters have been evaluated and the results have been validated by statistical data.Conclusion: The proposed methods were validated in accordance with ICH guidelines and successfully applied to the analysis of pharmaceutical formulation. Statistical comparison of the results obtained by applying the proposed methods with those of the reference method revealed good agreement and proved that there was no significant difference in the accuracy and precision between the results.Â
