RESUMO
A fast, sensitive, and specific reversed-phase high-performance liquid chromatographic (RP-HPLC) method for the determination of letrozole in Wistar rat serum was developed. In this method, liquid-liquid extraction of letrozole was achieved using diethyl ether as the extracting solvent. The analysis was carried out on a reversed-phase C18 (250 mm × 4.6 mm, 5 µm) column with an isocratic mobile phase of methanol-water (70:30,v/v), at a flow rate of 1.0 mL min(-1). Detection was carried out at 239 nm with a UV-visible spectrophoto-metric detector. The method was shown to be selective and linear over the concentration range of 0.15-100 µg mL(-1). The intra-day and inter-day precision studies showed good reproducibility with coefficients of variation less than 11% for the analyte. The relative errors of intra- and inter-day accuracy were within -11.52 to -2.26%. The limit of quantification was evaluated to be 0.15 µg mL(-1). The method was successfully applied for the pharmacokinetic study of letrozole after oral administration of 10 mg kg(-1) of letrozole in six healthy Wistar rats.
RESUMO
Ultraviolet (UV), first derivative, second derivative, and AUC-spectrophotometric methods for the determination of letrozole in pharmaceutical formulations have been developed. For UV-spectrophotometry, the standard solutions were measured at 240.0 nm. The linearity ranges were found to be 0.25-20.0 µgml(-1) in methanol and the regression equation was A=1.20×10(-1)C+2.22×10(-2)(r(2)=0.9994). For the first derivative spectrophotometry, the response (dA/dλ) of standard solutions was measured at 224.0 nm. The calibration curve was constructed by plotting dA/dλ values against concentrations 0.25-20.0 µgml(-1), of letrozole. The regression equation of the linear calibration graph was calculated as D(1)=3.89×10(-3)C+1.85×10(-4)(r(2)=0.9987). For the second derivative spectrophotometry, the response (d(2)A/dλ(2)) of standard solutions was measured at 241.0 nm. The calibration curve was constructed by plotting d(2)A/dλ(2) values against concentrations 0.5-20.0 µgml(-1) of letrozole standards in methanol. The regression equation of the linear calibration graph was calculated as D(2)=-1.59×10(-3)C-4.66×10(-4)(r(2)=0.9985). The AUC-spectrophotometric method was based on the calculation of Area under Curve (AUC), for analysis of letrozole in the wavelength range of 235.0-245.0 nm. The calibration curve was constructed by plotting AUC values against concentrations 0.25-20.0 µgml(-1), of letrozole. The regression equation of the linear calibration graph was calculated as AUC=1.132C+0.2153 (r(2)=0.9994). The methods were validated by following the analytical performance parameters suggested by the International Conference on Harmonization (ICH). All validation parameters were within the acceptable range. The developed methods were successfully applied to estimate the amount of letrozole in pharmaceutical formulations.
