Determination of silodosin and its active glucuronide metabolite KMD-3213G in human plasma by LC-MS/MS for a bioequivalence study

A novel method to estimate the absorption rate constant for two-compartment model fitted drugs without intravenous pharmacokinetic data

The in vivo performances of most drugs after extravascular administration are fitted well with the two-compartment pharmacokinetic (PK) model, but the estimation of absorption rate constant (k_a) for these drugs becomes difficult during unavailability of intravenous PK data. Herein, we developed a novel method, called the direct method, for estimating the k_a values of drugs without using intravenous PK data, by proposing a new PK parameter, namely, maximum apparent rate constant of disposition (k_max). The accuracy of the direct method in k_a estimation was determined using the setting parameters (k₁₂, k₂₁, and k₁₀ values at high, medium, and low levels, respectively) and clinical data. The results showed that the absolute relative error of k_a estimated using the direct method was significantly lower than that obtained using both the Loo-Riegelman method and the statistical moment method for the setting parameters. Human PK studies of telmisartan, candesartan cilexetil, and tenofovir disoproxil fumarate indicated that the k_a values of these drugs were accurately estimated using the direct method based on good correlations between the k_a values and other PK parameters that reflected the absorption properties of drugs in vivo (T_max, C_max, and C_max/AUC_0-t). This novel method can be applied in situations where intravenous PK data cannot be obtained and is expected to provide valuable support for PK evaluation and in vitro-in vivo correlation establishment.

In silico toxicity assessment and trace level quantification of two genotoxic impurities in silodosin using capillary gas chromatography

A capillary gas chromatographic method using flame ionization detection was developed and validated for the trace quantification of 2-bromoethanol (2-BE) and 2-bromoethylmethanesulfonate (2-BEM) in silodosin, used in the treatment of benign prostatic hyperplasia. Chromatographic separation was performed in spilt mode using nitrogen as carrier gas on a column containing crosslinked polyethylene glycol (30 m × 0.32 mm, 0.25 µm) stationary phase modified with nitroterephthalic acid. A simple matrix precipitation strategy was implemented to eliminate the sample overload and the matrix interference problems. The developed method was linear and accurate in the concentration range of 24–3000 ppm for 2-BE and 24–300 ppm for 2-BEM with r2 ˃ 0.999 and percent recoveries greater than 90% for both the analytes. The developed method was precise for both the analytes with RSD(%) of not more than 4.5%. In silico genotoxicity and carcinogenicity potential of 2-BEM were assessed using ICH M7 principles. The developed method can be applied in the quality control laboratories of pharmaceutical industries for trace level quantification of 2-BE and 2-BEM in silodosin.

A high-throughput LC-MS/MS method for determination of flunarizine in human plasma: Pharmacokinetic study with different doses

A high-throughput and sensitive liquid chromatography-tandem mass spectrometry (LC-MS/MS) method has been developed and validated for the determination of flunarizine in human plasma. Liquid-liquid extraction under acidic conditions was used to extract flunarizine and flunarizine-d8 from 100 μL human plasma. The mean extraction recovery obtained for flunarizine was 98.85% without compromising the sensitivity of the method. The chromatographic separation was performed on Hypersil Gold C₁₈ (50 × 2.1 mm, 3 μm) column using methanol-10 mm ammonium formate, pH 3.0 (90:10, v/v) as the mobile phase. A tandem mass spectrometer (API-5500) equipped with an electrospray ionization source in the positive ion mode was used for detection of flunarizine. Multiple reaction monitoring was selected for quantitation using the transitions, m/z 405.2 → 203.2 for flunarizine and m/z 413.1 → 203.2 for flunarizine-d8. The validated concentration range was established from 0.10 to 100 ng/mL. The accuracy (96.1-103.1%), intra-batch and inter-batch precision (CV ≤ 5.2%) were satisfactory and the drug was stable in human plasma under all tested conditions. The method was used to evaluate the pharmacokinetics of 5 and 10 mg flunarizine tablet formulation in 24 healthy subjects. The pharmacokinetic parameters C_max and AUC were dose-proportional.

Determination of terbinafine in human plasma using UPLC-MS/MS: Application to a bioequivalence study in healthy subjects

A high-throughput and sensitive ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) method has been developed for the determination of terbinafine in human plasma. The method employed liquid-liquid extraction of terbinafine and terbinafine-d7 (used as internal standard) from 100 μL human plasma with ethyl acetate-n-hexane (80:20, v/v) solvent mixture. Chromatography was performed on a BEH C₁₈ (50 × 2.1 mm, 1.7 μm) column using acetonitrile-8.0 mm ammonium formate, pH 3.5 (85:15, v/v) under isocratic elution. For quantitative analysis, MS/MS ion transitions were monitored at m/z 292.2/141.1 and m/z 299.1/148.2 for terbinafine and terbinafine-d7, respectively, using electrospray ionization in the positive mode. The method was validated according to regulatory guidance for selectivity, sensitivity, linearity, recovery, matrix effect, stability, dilution reliability and ruggedness with acceptable accuracy and precision. The method shows good linearity over the tested concentration range from 1.00 to 2000 ng/mL (r²  ≥ 0.9984). The intra-batch and inter-batch precision (CV) was 1.8-3.2 and 2.1-4.5%, respectively. The method was successfully applied to a bioequivalence study with 250 mg terbinafine in 32 healthy subjects. The major advantage of this method includes higher sensitivity, small plasma volume for processing and a short analysis time.