Spectrofluorimetric Determination of Famotidine in Pharmaceutical Preparations and Biological Fluids through Ternary Complex Formation with Some Lanthanide Ions: Application to Stability Studies

A simple, sensitive and specific method was developed for the determination of famotidine (FMT) in pharmaceutical preparations and biological fluids. The proposed method is based on ternary complex formation of famotidine (FMT) with EDTA and terbium chloride TbCl(3) in acetate buffer of pH 4. Alternatively, the complex is formed via the reaction with hexamine and either lanthanum chloride LaCl(3), or cerous chloride CeCl(3) in borate buffer of pH6.2 and 7.2 respectively. In all cases, the relative fluorescence intensity of the formed complexes was measured at 580 nm after excitation at 290 nm. The fluorescence intensity - concentration plots were rectilinear over the concentration range of 10-100, 5-70, and 5-60 ng/ml, with minimum quantification limits (LOQ) of 2.4, 2.2, and 5.2 ng/ml, and minimum limits of detection (LOD) of 0.79, 0.74, and 1.7 ng/ml upon using TbCl(3), LaCl(3), and CeCl(3) respectively. The proposed method was applied successfully for the analysis of famotidine in dosage forms and in human plasma. The kinetics of both alkaline and oxidative induced degradation of the drug was studied using the proposed method. The apparent first order rate constant and half life time were calculated. A proposal of the reaction pathways is presented.