Micelle and inclusion complex enhanced spectrofluorimetric methods for determination of Retigabine: Application in...

Two new, simple, selective, and highly sensitive spectrofluorimetric methods were developed and validated for the determination of the antiepileptic drug; retigabine (RTG). The first method (Method-I) depends on enhancement of the weak native fluorescence of RTG via the use of an organized medium; sodium dodecyl sulphate (SDS) in acetate buffer (pH 3.74). The second method (Method-II) depends on the enhancement of RTG weak native fluorescence through complexation with a macromolecule; beta cyclodextrin (β-CD) in phosphate buffer (pH 3.20). A full study of different experimental parameters influencing the fluorescence intensity was carried out. In addition, a thorough investigation of the fluorescence quantum yield, fluorophore brightness and mechanism of fluorescence enhancement was performed. A seven-fold improvement in the fluorescence intensity was brought by the first method, whereas a six and half-fold enhancement of the fluorescence intensity was obtained by the second one. Linearity was achieved over wide ranges (0.05-12.5 μg mL^-1) and (0.05-15 μg mL^-1) with low limits of detection (LOD) of 10.6 and 14.3 ng mL^-1, and limits of quantification (LOQ) of 32.0 and 43.2 ng mL^-1 for (Method-I) and (Method-II), respectively. The proposed methods were validated according to ICH and US-FDA guidelines. The applicability of the proposed methods was tested for determination of RTG in its pharmaceutical dosage forms, and to study the stability of RTG under different stress conditions according to ICH guidelines including alkaline, acidic, oxidative, thermal, and photolytic stress conditions. Moreover, the high sensitivity achieved by the proposed methods permitted the determination and detection of RTG in both spiked and real rabbit plasma samples utilizing a simple protein precipitation step followed by liquid-liquid extraction method. Percentage recoveries from rabbit plasma samples were within the acceptable limits; (93.47-104.74%) and (91.33-105.70%) for (Method-I) and (Method-II), respectively.