Spectrofluorimetric study of finasteride and bovine serum albumin interaction and its application for quantitative determination of finasteride in tablet dosage form

A new spectrofluorimetric method for measuring finasteride (FIN) in tablet dosage form was developed. The method was based on FIN quenching the intrinsic fluorescence of bovine serum albumin (BSA). BSA was monitored at 337 nm after excitation at 280 nm and the quenching effect of FIN on BSA was monitored at its maximum (332-344 nm). Negative values of Delta S-theta, Delta H-theta and Delta G(theta) were calculated for the interaction, and showed that spontaneous binding occurred with the main contribution from van der Waals forces without eliminating the role of hydrogen bonding. The UV absorption spectra of the FIN-BSA system confirmed the interaction; the absorption intensity of BSA increased gradually with the FIN concentration because of the extended peptide strands of BSA after FIN addition. Three-dimensional and synchronous fluorescence spectra were used to detect conformational changes of BSA in the FIN-BSA complex. Stern-Volmer and Lineweaver-Burk equations were used to determine the quenching mechanism. The linear Lineweaver-Burk plot was used as a calibration curve to apply the method analytically in the range of 0.5-15 mu g mL(-1). FIN was quantified by measuring the fluorescence intensity at 334 nm after excitation at 280 nm. The analytical method is accurate, precise and sensitive, with a limit of detection of 0.16 mu g mL(-1) and a limit of quantification of 0.49 mu g mL(-1). Recovery of FIN with the method was 97.70 +/- 4.65% for tablet dosage form.