Current Pharmaceutical Analysis - Volume 14, Issue 3, 2018

Background: Letrozole (LTZ) is a potent aromatase inhibitor which blocks estrogen synthesis in post-menopausal women. Suitable analytical methods are required to quantify letrozole in bulk and its nanoformulations. Hence a sensitive and robust reverse-phase high performance liquid chromatographic method (RP-HPLC) was developed for the estimation of LTZ. Methods: The method was developed using Kinetex C18 column (250 mm.6 mm; 5μ) and mobile phase comprising acetonitrile (ACN): acetate buffer (pH 4.5) mixture (50:50% v/v) was used to affect the chromatographic separation at 0.8 mL/min flow rate. The responses were measured at 240 nm. Force degradation studies were done by exposing LTZ to acid- and alkali-induced hydrolysis, oxidation (H2O2), thermal and photolysis. Two-level factorial design was used to validate the method as per ICH Q2 (R1) using Design-Expert® software. The effects of independent variables on flow rate, pH, acetonitrile content and column temperature were recorded as responses. Results: Method was linear over the concentration range of 5-2500 ng/mL with a correlation coefficient (R2) of 1.000. Force degradation studies revealed that LTZ was stable to all stress agents except the basic conditions. The inter-day precision results were reproducible with relative standard deviation (% RSD) of 0.078. The peak area RSD and mean recovery of LTZ was found to be <1.0% and 99-102% in drug solution and <1.0% and 98-106% in nanoformulations respectively. Deliberate changes in independent chromatographic parameters analyzed using analysis of variance (ANOVA) indicated that the model was significant (p<0.0001). Conclusion: The developed analytical method was successfully utilized to quantify LTZ in bulk and its nanoformulations.

Background: It is still uncertain whether the accumulation of the bile acids (BAs) in hepatocytes beyond the normal stand after taking medicine which can cause hepatic injury or under the pathological state. Because it is lack of valid and simple analytical methods for the quantification of individual BAs and their taurine and glycine conjugates in the hepatocytes. It is necessary to develop methods for BAs quantification in hepatocytes to study their function in detail. Methods: A simple and sensitive liquid chromatography-tandem mass spectrometry (LC-MS/MS) method has been developed and validated for the simultaneous determination of 6 major BAs, their glycine, and taurine conjugates in rat hepatocytes, liver, bile, urine, and plasma. Results: This method is valid and sensitive with a limit of quantification 5 ng/mL, a large dynamic range (from 4.30 ng/mL to 200000 ng/mL for various analytes). The total run time was 21 min. Detailed BA profiles were obtained from rat hepatocytes, liver, plasma, bile, and urine using this method. The result indicated that total BA concentration in rat hepatocytes was 10892.9 ng/mg. The taurine conjugates BAs constitute 56.2% of the total BAs, unconjugated BAs possess 34.3%, and less than7.5% are glycine conjugated. Conclusion: A sensitive and a simple LC-MS/MS method was described for the simultaneous quantification of the major BAs, as well as their glycine and taurine conjugates in rat hepatocytes, liver, bile, plasma, and urine.