Pharmacokinetics and Bioequivalence Comparison of Two Fixed-Dose Combination of Rosuvastatin/Ezetimibe Formulations: A Randomized, Crossover, Open-Label Study in Healthy Volunteers

Objective: To evaluate the bioequivalence (BE) of two fixed-dose combination (FDC) formulations of Rosuvastatin and Ezetimibe: Cresadex® EZE 20/10 mg (Abbott Laboratories) as the reference formulation (R), and Racor® Duo 20/10 mg (Laboratorios Leti, S.A.V.) as the test formulation (T). Method: A randomized, single-dose, two-period, two-sequence, open-label, crossover design was employed. Subjects received a single oral dose of either the Test or Reference formulation under fasting conditions, with a 12-day washout period between treatments. Male subjects aged 18 - 45 years with normal health and laboratory values were included. Exclusion criteria encompassed any medical conditions, recent surgery, drug or alcohol use, and hypersensitivity to the study drugs. Blood samples were collected at pre-dose and multiple post-dose time points and analyzed using a validated LC-MS/MS method to quantify Rosuvastatin and Ezetimibe concentrations in plasma. Descriptive statistics were used to summarize pharmacokinetic (PK) parameters. ANOVA was conducted to compare the ln-transformed values of Cmax, AUC0−t, and AUC0−∞. Schuirmann’s two one-sided t-tests were applied to assess bioequivalence (BE). Results: The 90% Confidence Intervals for the ln-transformed ratios of Cmax, AUC0−t, and AUC0−∞ fell within the acceptance range of 80% to 125%, demonstrating bioequivalence between the Test and Reference formulations. Both formulations were well-tolerated, with no serious adverse events reported. Conclusions: The results of this study confirm the bioequivalence of the two tested FDC Rosuvastatin/Ezetimibe formulations: Cresadex® EZE (Abbott Laboratories) and Racor® Duo (Laboratorios Leti, S.A.V.). These findings endorse the therapeutic interchangeability of these products, providing clinicians with greater flexibility in the treatment of hyperlipidemia.

Pharmacokinetics and Bioequivalence of Dienogest in Healthy Bangladeshi Female Volunteers: An Open-Label, Single-Dose, Randomized, Two-Way Crossover Study

Background: Dienogest is a potential treatment for pelvic pain associated with endometriosis, a condition of significant concern in gynaecology. The current study was conducted as a crossover-randomized bioequivalence assessment of two oral Dienogest 2 mg formulations, aiming to provide valuable insights for healthcare professionals and researchers in this field. Objective: The primary aim of this research was to evaluate and compare the pharmacokinetic characteristics of Dienogest 2 mg tablets. Dinogest (Dienogest 2 mg) tablets, manufactured by Nuvista Pharma Limited in Bangladesh, and Visanne (Dienogest 2 mg) tablets, manufactured by Bayer Pharma in Germany, were the test and reference formulations, respectively. Materials and Method: The study was an open-label, balanced, randomized, two treatments, two sequences, two periods, two-way crossover, laboratory blind, single oral dose bioequivalence study conducted in healthy adult females under fasting conditions. The study was carried out on 13 healthy, non-pregnant female subjects, and all the subjects completed both study periods with a 15-day washout in between. Randomization was used to assign the test and reference formulations to the subjects. Following each oral administration, a series of blood samples were obtained at different time intervals from pre-dose to 72 hours post-dose and analyzed for Dienogest concentrations using a validated bio-analytical method. A standard non-compartmental model was used to analyze the pharmacokinetic parameters. The primary pharmacokinetic parameters were peak plasma drug concentration (Cmax), the area under the plasma concentration-time curve from time zero to time t (AUC0–t), and AUC from t = 0 to infinity (AUC0–∞). The other PK parameters included time to reach Cmax (Tmax), terminal elimination rate constant (Kel), and half-life (t1/2). Result: The ratios and 90% CI for the geometric mean test/reference were 95.53% (86.70% - 105.26%) for Cmax, 101.75% (95.42% - 108.49%) for AUC0−t, and 101.54% (95.59%% - 107.87%) for AUC0−∞. The formulations were bioequivalent since the 90% CIs for the geometric mean test/reference ratios were 80% to 125%, according to the predetermined range of US Food and Drug Administration (FDA) requirements. Conclusion: This single-dose investigation shows that the Dienogest test and reference formulations exhibited a rate and degree of absorption that met the regulatory requirements for bioequivalence.

A Bioequivalence Study of Empagliflozin/Metformin Fixed-Dose Combination in Healthy Subjects under Fasting Conditions

Background: This study evaluated the bioequivalence of empagliflozin 12.5 mg/metformin 1000 mg tablets compared to Synjardy® (Empagliflozin 12.5 mg/metformin 1000 mg) tablets in healthy male subjects under fasting conditions. Methods: This was a phase I, randomized, single-dose, two-period, two-sequence, crossover study to evaluate the bioequivalence (BE) profiles of two fixed-dose combinations (FDCs) of empagliflozin/metformin. Cmax, AUC0-t and AUC0-∞ from test and reference formulations were evaluated to access BE. The plasma concentrations were measured using a validated liquid chromatography-mass spectrometry (LC-MS/MS) method. Of the 24 subjects enrolled, 23 completed both periods of the study. The two formulations test and reference were considered bioequivalent if 90% confidence interval (CI) fell within 80.00% - 125.00% for Cmax, AUC0-t and AUC0-∞. Tolerability and safety were assessed throughout the study. Results: The pharmacokinetic (PK) parameters were similar between the test product (T) and reference product (R) Synjardy®. The 90% CI of the test/reference ratios of log-transformed PK parameters point estimates was Cmax: 89.87% (85.68% - 94.27%), AUC0-t: 87.91% (83.65% - 92.39%) and AUC0-∞: 87.16% (82.80% - 91.75%) to empagliflozin and Cmax: 92.19% (87.95% - 96.65%), AUC0-t: 91.38% (84.42% - 98.91%) and AUC0-∞: 93.78% (83.82% - 104.93%) to metformin respectively (90% CI for all PK parameters fell within 80.00% - 125.00%). Conclusion: Our results demonstrated BE between the test and reference formulations of oral tablets of empagliflozin 12.5 mg/metformin 1000 mg (FDC) in healthy male subjects under fasting conditions.

Pharmacokinetic Comparison and Bioequivalence Evaluation of Two 20-mg Vonoprazan Fumarate Tablets in Bangladeshi Healthy Male Subjects

Background: Vonoprazan fumarate, a novel potassium-competitive acid blocker, outperforms traditional proton pump inhibitors in acid suppression and can be effectively combined with antibiotics to eradicate Helicobacter pylori. Objective: The study aimed to determine if two Vonoprazan formulations—Vonoprazan Fumarate 20 mg Tablet of Beximco Pharmaceuticals Limited, Bangladesh (test product) and Takecab 20 mg Tablet of Takeda Pharmaceutical Company Limited, Japan (reference product)—met FDA’s bioequivalence requirements by comparing their pharmacokinetic characteristics in healthy Bangladeshi adults. Methods: This was a single-center, randomized, open-label, two-period, two-sequence, laboratory-blind, double-crossover experiment. After 10 hours of fasting, 18 subjects were randomly assigned to receive a single oral dose of either formulation. During each treatment period, blood samples were collected at specific times (pre-dose and up to 48 hours post-dose) to measure plasma Vonoprazan levels using liquid chromatography-tandem mass spectrometry. A non-compartmental model was used to calculate pharmacokinetic parameters using the plasma drug concentration-time profile. A statistical comparison of the pharmacokinetic parameters of the two formulations of the test and reference product was conducted using SAS® statistical software to assess the bioequivalence. Primary pharmacokinetic parameters (Cmax, AUC0-t, and AUC0-∞) and secondary parameters (Tmax, T1/2, Kel, and AUC extrapolation) were calculated for both drug formulations. If the confidence intervals for the natural log-transformed Cmax, AUC0-t, and AUC0-∞ values fell between 80% and 125%, the drug products would be considered bioequivalent. Result: The geometric mean ratio of Vonoprazan between the test and reference groups was found to be 109.04% (99.47% - 119.53%), 101.37% (95.58% - 107.50%), and 101.24% (95.43% - 107.41%), with 90% confidence intervals (CIs) for the Cmax, AUC0–t, and AUC0–∞, and these outcomes met the regulatory requirements for assuming bioequivalence. Conclusion: The results demonstrated that the generic formulation of Vonoprazan 20 mg Tablet of Beximco Pharmaceuticals Limited is bioequivalent to the reference product.

Pharmacokinetics and Bioequivalence Evaluation of Two Rosuvastatin Calcium 20 mg Tablets: A Single Oral Dose, Randomized-Sequence, Open-Label, Two-Period Crossover Study in Healthy Volunteers under Fasting Conditions

Objectives: To compare the rate and extent of absorption of Racor® 20 mg (Rosuvastatin calcium 20 mg) tablet of Laboratorios Leti, S.A.V., with Crestor® 20 mg (Rosuvastatin calcium 20 mg) tablet of AstraZeneca, UK Limited in healthy adult human subjects under fasting conditions. Method: This was an open label, analyst blind, balanced, randomized, two-treatment, two-period, two-sequence, single oral dose, crossover, bioequivalence study in healthy, adult, human subjects under fasting condition. Twenty-four (24) subjects were planned as per the protocol and all subjects completed both periods of the study. The concentrations of Rosuvastatin in plasma were quantitated using a validated LC-MS/MS method of analysis and plasma levels were submitted for statistical analysis. Cmax, AUC0-t, AUC0-∞, Tmax, t1/2, Kel (hrs-1), percent AUC extrapolated [100 * (AUC0-∞ - AUC0-t)/AUC0-∞] (AUC_%Extrapobs) were calculated for rosuvastatin in plasma using SAS® version 9.1.3, SAS Institute. Inc. USA.CARY. ANOVA, 90% confidence interval using Schuirmann’s two one-sided test for bioequivalence, power and ratio analysis, for lntransformed pharmacokinetic parameters Cmax, AUC0-t and AUC0-∞ were computed and reported for Rosuvastatin in plasma for BE. Results: Data showed that 90% confidence intervals for the test/reference geometric mean ratios (GMR) of Cmax (95.01 - 112.66), AUC0-t (93.38 - 111.67) and AUC0-∞ (93.65 - 111.29) were within the BE (80% - 125%) acceptance range. Conclusions: Two products formulation, reference (R) Crestor® (rosuvastatin calcium) of AstraZeneca and test (T), Racor® (rosuvastatin calcium) of Laboratorios Leti S.A.V., with a single dose of 20 mg, under fasting conditions were bioequivalent. No severe, serious or unexpected adverse events (AEs) were reported in this study.

Bioequivalence Study of Diclofenac 150 mg XR: A Single-Dose, Randomized, Open Label, 2-Period Crossover Study in Healthy Adult Volunteers

Objectives: Evaluate the bioequivalence (BE) of two oral tablets formulations of diclofenac 150 mg in healthy male subjects under fasting condition. This was a phase I, randomized, open label, balanced, two period, two sequences, single oral dose, crossover, analyst blind study. Methods: Twenty four (24) healthy subjects were randomly assigned to one of two sequences protocol: 150 mg XR of reference formulation (R), diclofenac sodium in the first period or the test formulation (T), diclofenac potassium in the second or vice versa. The plasma concentrations were determined using a validated LC-MS/MS method. Pharmacokinetic (PK) parameters included: maximum plasma concentration (Cmax), area under the plasma concentration—time curve from time 0 to the last measurable concentration (AUC0-t), and area under the plasma concentration—time from time 0 to infinity (AUC0-∞), were evaluated for BE. Results: The results showed that 90% confidence intervals for the test/reference geometric mean ratios (GMR) of Cmax (90.43 - 107.17), AUC0-t (93.08 - 116.46) and AUC0-∞ (92.52 - 117.39) were within the BE (80% - 125%) acceptance range. Conclusions: Two formulations, reference product (R) Voltaren® (diclofenac sodium) of Novartis and test product (T), Diklason Bi (diclofenac potassium) of Laboratorios Leti S.A.V., with a single dose of 150 mg XR, under fasting conditions were bioequivalent. No severe, serious or unexpected adverse events (AEs) were reported in this study.

Pharmacokinetics and bioequivalence of two pantoprazole sodium enteric-coated tablet products in healthy Chinese volunteers

Aim To evaluate the pharmacokinetics and bioequivalence of domestic pantoprazole sodium enteric-coated tablets as compared with imported pantoprazole enteric-coated tablets. Methods This was an open randomized, two periods cross over study on twenty healthy male volunteers. The pantoprazole concentrations in plasma after an oral dose of 40 mg pantoprzaole preparations were determined by a HPLC-UV method. Non-compartmental method was used for the calculation of pharmacokinetic parameters. Logarithm-transformed Cmax and A UC were analyzed by the analysis of variance （ANOVA） with 90% confidence intervals. Results The main pharmacokinetics parameters of domestic pantoprazole sodium enteric-coated tablets and imported pantoprazole sodium enteric-coated tablets were as following： Cmax （3610 ± 956）, （3466 ± 1209） ng·mL^-1, tmax （3.00 ± 0.40）, （3.00 ± 0.46） h, AUC0-t （8140 ± 5065）, （8390 ± 5474） ng·h·mL^-1, AUC0-∞ （8293 ± 5094）, （8625 ± 5606） ng·h·mL^-1, t1/2 （1.61 ± 0.28）, （1.85 ± 0.27） h, respectively. Conclusion Domestic pantoprazole sodium enteric-coated tablets were bioequivalent with the imported pantoprazole sodium enteric-coated tablets.

Pharmacokinetics and Bioequivalence of Cefprozil Granules and Cefprozil Tablets in Healthy Chinese Volunteers

Aim To develop a rapid, simple, and sensitive high-performance liquid chromatographic (HPLC) method for the determination of cefprozil in human plasma and to study its pharmacokinetics and bioequivalence after 0.5 g oral doses of cefprozil granules and tablets. Methods The blood concentration of cefprozil was analyzed after extracted with 6% trichloroacetic acid, using tinidazole as internal standard (I.S.). A C_ 18 column was used to separate cefprozil with mobile phase of methanol, purified water and glac...

Bioequivalence of bicalutamide capsules and tablets in Chinese healthy volunteers

Aim To establish a HPLC method for the determination of bicalutamide plasma concentration and to evaluate the bioequivalence of bicalutamide capsules （test） and tablets （reference）. Methods A single oral dose of 50 mg bicalutamide capsules or tablets were given to 48 Chinese healthy volunteers in a one period parallel design test. Bicalutamide in plasma was analyzed using a XB-C18 column with a mobile phase of acetonitrile-water （60：40, V/V） and the dectection wavelength of 272 nm and it is pharmacokinetic parameters were calculated and evaluated using DAS2.0. Results The linear range of bicalutamide was 10 - 1200 ng·mL^-1. The main pharmacokinetic parameters of the test and reference were as the followings, t1/2 （138.36 ± 32.03） and （146.12 ± 27.04） h, Tmax （17.17 ± 4.65） and （16.92 ± 4.85） h, Cmax（910.83 ± 130.49） and （868.71 ± 115.35） ng·mL^-1 AUC0-672（172437.08 ± 3986.07） and （176842.34 ± 35733.85） ng·mL^-1·h, and AUC0-∞ （179456.55 ± 43127.65） and （185270.39 ± 39688.63） ng·mL^-1·h, respectively. The two-one side t-test analysis showed that the confidence intervals of Crux, A UC0-672 and A UC0-∞ were （98.9% - 100.7%）, （98.8% - 100.6%） and （99.7% - 101.7%）, respectively. Conclusion The relative bioavailability of bicalutamide capsules was 97.51%. The bioequivalence was demonstrated by the two-one side t-test

Sensitive and rapid determination of amantadine without derivatization in human plasma by LC–MS/MS for a bioequivalence study

A highly sensitive, rapid and rugged liquid chromatography-tandem mass spectrometw （LC-ESI-MS/MS） method was developed for reliable estimation of amantadine （AMD）, an antiviral drug in human plasma. The analyte and internal standard （IS）, amantadine-d6 （AMD-d6）, were extracted from 200μL plasma by solid phase extraction on Phenomenex Strata-X-C 33 ~t cartridges. Chromatography was performed on Synergi^TM Hydro-RP C18 （150 mm×4.6 mm, 4 μm） analytical column using a mixture of acetonitrile and 10 mM ammonium formate, pH 3.0 （80：20, v/v） as the mobile phase. Detection and quantitation was done by multiple reaction monitoring in the positive ionization mode for AMD （m/z 152.1→ 135.1 ） and IS （m/z 158.0 → 141.1） on a triple quadrupole mass spectrometer. The assay was linear in the concentration range of 0.50-500 ng/mL with correlation coefficient （r^2） 〉 0.9969. The limit of detection of the method was 0.18 ng/mL The intra-batch and inter-batch precisions were 〈 5.42% and the accuracy varied from 98.47% to 105.72%. The extraction recovery of amantadine was precise and quantitative in the range of 97.89%-100.28%. IS-normalized matrix factors for amantadine varied from 0.981 to 1.012. The stability of AMD in whole blood and plasma was evaluated under different conditions. The developed method was successfully applied for a bioequivalence study with 100 mg of AMD in 32 healthy volunteers. The reproducibility of the assay was determined by reanalysis of 134 subject samples.

Quantification of sibutramine and its two metabolites in human plasma by LC-ESI-MS/MS and its application in a bioequivalence study

Obesity can be considered as a chronic illness of epidemic proportion and its incidents have increased exponentially in recent years.The use of anti-obesity drugs such as sibutramine is somewhat helpful.There is a need to quantify such drugs in biological samples,which is generally quite difficult.In this report,we developed and validated a simple,sensitive and specific liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for the quantification of sibutramine (SB) and its two metabolites N-des methyl sibutramine (DSB) and N-di desmethyl sibutramine (DDSB) in human plasma.Zorbax SBC18 (4.6 mm × 75 mm,3.5 μm,80 (A)) analytical column and 5 mM ammonium formate:acetonitrile (10∶90,v/v) mobile phase were used for chromatographic separation of SB,DSB and DDSB.Multiple reaction monitoring (MRM) in the positive mode was used to detect SB,DSB and DDSB at m/z 280.3/124.9,266.3/125.3 and 252.2/124.9,respectively.Liquid liquid extraction was used for the extraction of analytes and internal standard from human plasma.This method was validated over a linear concentration range of 10.0-10,000.0 pg/mL for SB,DSB and DDSB with correlation coefficients (r) of ≥0.9997.The drug and the two metabolites were stable in plasma samples.The validated method was successfully applied in a bioequivalence and pharmacokinetic study with human volunteers under fasting condition.

Virtual population pharmacokinetic using physiologically based pharmacokinetic model for evaluating bioequivalence of oral lacidipine formulations in dogs

The aim of the present study was to investigate virtual population pharmacokinetic using physiologically based pharmacokinetic(PBPK) model for evaluating bioequivalence of oral lacidipine formulations in dogs. The dissolution behaviors of three lacidipine formulations including one commercial product and two self-made amorphous solid dispersions(ASDs)capsules were determined in 0.07% Tween 80 media. A randomized 3-period crossover design in 6 healthy beagle dogs after oral administration of the three formulations at a single dose of 4 mg was conducted. The PBPK modeling was utilized for the virtual bioequivalence study.In vitro dissolution experiment showed that the dissolution behaviors of lacidipine amorphous solid dispersions(ASDs) capsules, which was respectively prepared by HPMC-E5 or Soluplus, as polymer displayed similar curves compared with the reference formulation in 0.07% Tween 80 media. In vivo pharmacokinetics experiments showed that three formulations had comparable maximum plasma drug concentration(Cmax), and the time(Tmax) to reach Cmax of lacidipine tablet, which was prepared by Soluplus, as polymer was slower than other two formulations in consistency with the in vitro dissolution rate. The 90% confidence interval(CI) for the Cmax, AUC0–24 h and AUC0–∞ of the ratio of the test drug to the reference drug exceeded the acceptable bioequivalence(BE) limits(0.80–1.25). However, the 90% CI of the AUC0–24 h, AUC0–∞ and Cmax of the ratio of test to reference drug were within the BE limit,calculated using PBPK modeling when the virtual subjects reached 24 dogs. The results all demonstrated that virtual bioequivalence study can overcome the inequivalence caused by inter-subject variability of the 6 beagle dogs involved in in vivo experiments.

Quantitation of tadalafil in human plasma using a sensitive and rapid LC-MS/MS method for a bioequivalence study

A highly sensitive liquid chromatography-tandem mass spectrometry（LC-MS/MS） method was developed for the determination of tadalafil（TAD） in human plasma. TAD and its deuterated internal standard（IS）, tadalafil-d3, were extracted from 200 mL plasma using Phenomenex Strata-X-C 33 m extraction cartridges. Chromatographic analysis was carried out on Synergi Hydro-RP C18（100 mm × 4.6 mm, 4 mm）column with a mobile phase consisting of methanol and 10 m M ammonium formate, p H 4.0（90：10, v/v）,delivered at a flow rate of 0.9 m L/min. Quantitation of the protonated analyte was done on a triple quadrupole mass spectrometer using multiple reaction monitoring via electrospray ionization. The precursor to product ions transitions monitored for TAD and TAD-d3 were m/z 390.3-268.2 and m/z393.1-271.2, respectively. The calibration curve was linear over the concentration range of 0.50–500 ng/m L with correlation coefficient, r2 Z 0.9994. Acceptable intra-batch and inter-batch precision（r3.7%） and accuracy（97.8% to 104.1%） were obtained at five concentration levels. The recovery of TAD from spiked plasma was highly precise and quantitative（98.95% to 100.61%）. Further, the effect of endogenous matrix components was minimal. TAD was found to be stable under different storage conditions in human plasma and also in whole blood samples. The validated method was successfully used to determine TAD plasma concentration in a bioequivalence study with 20 mg TAD tablets in 24 healthy volunteers. Method performance was evaluated by reanalyzing 115 study samples.

Improved simultaneous quantitation of candesartan and hydrochlorthiazide in human plasma by UPLC–MS/MS and its application in bioequivalence studies

A validated ultra-performance liquid chromatography mass spectrometric method （UPLC-MS/MS） was used for the simultaneous quantitation of candesartan （CN） and hydrochlorothiazide （HCT） in human plasma. The analysis was performed on UPLC-MS/MS system using turbo ion spray interface. Negative ions were measured in multiple reaction monitoring （MRM） mode. The analytes were extracted using a liquid-liquid extraction （LLE） method by using 0.1 mL of plasma volume. The lower limit of quantitation for CN and HCT was 1.00 ng/mL whereas the upper limit of quantitation was 499.15 ng/mL and 601.61 ng/mL for CN and HCT respectively. CN d4 and HCT-13Cd2 were used as the internal standards for CN and HCT respectively. The chromatography was achieved within 2.0 min run time using a C18 Pheno-menex, Gemini NX （100 mm ~ 4.6 mm, 5 mm） column with organic mixture：buffer solution （80：20, v/v） at a flow rate of 0.800 mL/min. The method has been successfully applied to establish the bioequivalence of candesartan cilexetil （CNC） and HCT immediate release tablets with reference product in human subjects.

Advance in bioequivalence assessment of topica dermatological products

Bioequivalence(BE) assessment of topical dermatological products is a long standing challenge. The development of generic topical dermatological products has often been hampered due to the limited number of acceptable approaches, which are capable of determining the BE between generic products and reference list products. The aim of this manuscript is to review different BE assessment approaches of topical dermatological products. Besides, the advances in BE evaluation and biowaivers are also provided. Currently, except in the case of dermatological corticosteroids, the golden rule to establish the BE of most topical dermatological products still heavily relied on clinical endpoint trials,which are often unreliable, time-consuming and expensive. The regulatory agencies and pharmaceutical industries are forging ahead to the development of new surrogate BE assessment approaches for other topical dermatological products. These promising approaches include dermatopharmacokinetic study(DPK), dermal microdialysis(DMD), in vitro studies, pharmacokinetic study(PK), near-infrared spectrometry(NIR), and confocal Raman spectroscopy(CRS). In addition, the expansion of biowaivers for topical dermatological products has been explored by pharmaceutical scientists. In conclusion, to accelerate the development and approval of topical dermatological products, emphasis should be put on the following areas, i.e., optimizing and standardizing the existing BE assessment methods, exploring novel alternatives of BE assessment approaches, and expanding biowaivers for topical dermatological products.

Application of an LC–MS/MS method for the analysis of amlodipine,valsartan and hydrochlorothiazide in polypill for a bioequivalence study

A sensitive and selective method has been proposed for the simultaneous determination of amlodipine(AML),valsartan(VAL) and hydrochlorothiazide(HCTZ) in human plasma by liquid chromatography–tandem mass spectrometry(LC–MS/MS). The analytes and their deuterated analogs were quantitatively extracted from100 μL human plasma by solid phase extraction on Oasis HLB cartridges. The chromatographic separation of the analytes was achieved on a Chromolith RP18 e(100 mm × 4.6 mm) analytical column within 2.5 min. The resolution factor between AML and VAL, AML and HCTZ, and VAL and HCTZ was 2.9, 1.5 and 1.4, respectively,under isocratic conditions. The method was validated over a dynamic concentration range of 0.02–20.0 ng/m L for AML, 5.00–10,000 ng/m L for VAL and 0.20–200 ng/m L for HCTZ. Ion-suppression/enhancement effects were investigated by post-column infusion technique. The mean IS-normalized matrix factors for AML, VAL and HCTZ were 0.992, 0.994 and 0.998, respectively. The intra-batch and inter-batch precision(% CV) across quality control levels was ≤ 5.56% and the recovery was in the range of 93.4%–99.6% for all the analytes. The method was successfully applied to a bioequivalence study of 5 mg AML + 160 mg VAL + 12.5 mg HCTZ tablet formulation(test and reference) in 18 healthy Indian males under fasting. The mean log-transformed ratios of C max, AUC0–120 h and AUC0-inf and their 90% CIs were within 90.2%–102.1%. The assay reproducibility was demonstrated by reanalysis of 90 incurred samples.

Pharmacokinetics and bioequivalence of ranitidine and bismuth derived from two compound preparations

AIM： To evaluate the bioequivalence of ranitidine and bismuth derived from two compound preparations. METHODS： The bioavailability was measured in 20 healthy male Chinese volunteers following a single oral dose （equivalent to 200 mg of ranitidine and 220 mg of bismuth） of the test or reference products in the fasting state. Then blood samples were collected for 24 h. Plasma concentrations of ranitidine and bismuth were analyzed by high-performance liquid chromatography and inductively coupled plasma-mass spectrometry （ICPMS）, respectively. The non-compartmental method was used for pharmacokinetic analysis. Log-transformed Cmax, AUC（0-t） and AUC（0-∞） were tested for bioequivalence using ANOVA and Schuirmann two-one sided t-test. Tmax was analyzed by Wilcoxon＇s test. RESULTS： Various pharmacokinetic parameters of ranitidine derived from the two compound preparations, including Cmax, AUC（0-t）, AUC（0-∞）, Tmax and T1/2, were nearly consistent with previous observations. These parameters derived from test and reference drug were as follows： Cmax（0.67 ± 0.21 vs 0.68 ± 0.22 mg/L）, AUC（0-t）（3.1 ± 0.6 vs 3.0 ± 0.7 mg/L per hour）, AUC（0-∞）（3.3 ± 0.6 vs 3.2 ± 0.8 mg/L per hour）, Tmax （2.3 ± 0.9 VS 2.1 ± 0.9 h） and T1/2 （2.8 ± 0.3 vs 3.1 ± 0.4 h）. In addition, double-peak absorption profiles of ranitidine were found in some Chinese volunteers. For bismuth, those parameters derived from test and reference drug were as follows： Cmax （11.80 ± 7.36 vs 11.40 ± 6.55 μg/L）, AUC（0-t） （46.65 ± 16.97 vs 47.03 ± 21.49 μg/L per hour）, Tmax （0.50 ± 0.20 vs 0.50 ± 0.20 h） and T1/2 （10.2 ± 2.3 vs 13.0 ± 6.9 h）. Ninety percent of confidence intervals for the test/reference ratio of Cmax, AUC（0-t） and AUC（0-∞） derived from both ranitidine and bismuth were found within the bioequivalence acceptable range of 80%-125%. No significant difference was found in Tmax derived from both ranitidine and bismuth. CONCLUSION： The two compound preparations are bioequivalent and may be prescribed interchangeably.

Determination of torasemide in human plasma and its bioequivalence study by high-performance liquid chromatography with electrospray ionization tandem mass spectrometry

A sensitive and selective method using high-performance liquid chromatography coupled with elec- trospray ionization tandem mass spectrometry （HPLC-ESI-MS） to determine the concentration of tor- asemide in human plasma samples was developed and validated. Tolbutamide was chosen as the internal standard （IS）. The chromatography was performed on a GI Sciences Inertsil ODS-3 column （100 mm× 2.1 mm i.d., 5.0 μm） within 5 min, using methanol with 10 mM ammonium formate （60：40, v/ v） as mobile phase at a flow rate of 0.2 mL/min. The targeted compound was detected in negative io- nization at m/z 347.00 for torasemide and 269.00 for IS. The linearity range of this method was found to be within the concentration range of 1-2500 ng/mL （r=0.9984） for torasemide in human plasma. The accuracy of this measurement was between 94.05% and 103.86%. The extracted recovery efficiency was from 84.20% to 86.47% at three concentration levels. This method was also successfully applied in pharmacokinetics and bioequivalence studies in Chinese volunteers.

Simultaneous quantification of prodrug oseltamivir and its metabolite oseltamivir carboxylate in human plasma by LC-MS/MS to support a bioequivalence study

A simple, precise and rapid liquid chromatography-tandem mass spectrometry （LC-MS/MS） method has been developed and validated for the simultaneous determination of oseltamivir and oseltamivir carboxylate, a neuraminidase inhibitor, using their deuterated analogs as internal standards （ISs）. The method involved solid phase extraction of the analytes and ISs from 200 μL human plasma with no reconstitution and drying steps. The chromatographic separation was achieved on a Symmetry C18 （100 mm × 4.6 mm, 5 μm） column using 10 mM ammonium formate and acetonitrile （30：70, v/v） as the mobile phase in a run time of 2.0 min. Quantitation of analytes and ISs were done by multiple reaction monitoring on a triple quadrupole mass spectrometer in the positive ionization mode. The linearity of the method was established in the concentration range of 0.5-200 ng/mL and 2.0-800 ng/mL for oseltamivir and oseltamivir carboxylate respectively. The mean extraction recovery for oseltamivir （94.4%） and oseltamivir carboxylate （92.7%） from spiked plasma samples was consistent and reproducible. The application of this method was demonstratedby a bioequivalence study in 42 healthy Indian subjects with 75 mg oseltamivir phosphate capsules. The assay reproducibility was established by reanalysis of 151 incurred subject samples.

Determination of lercanidipine in human plasma by an improved UPLC–MS/MS method for a bioequivalence study

An improved and reliable ultra-performance liquid chromatography/tandem mass spectrometry （UPLC- MS/MS） method has been developed and validated for the determination of lercanidipine in human plasma. Plasma samples with lercanidipine-d3 as an internal standard （IS） were prepared by solid phase extraction on Phenomenex Strata-X cartridges using 100 μL of human plasma. Chromatographic analysis was performed on UPLC BEH C18 （50 mm × 2.1 mm, 1.7 μm） column under isocratic conditions. Linear calibration curves were obtained over a wide dynamic concentration range of 0.010-20.0 ng/mL. Matrix effect was assessed by post-column infusion, post-extraction spiking and standard-line slope methods. The mean extraction recovery was 〉 94% for the analyte and IS. Inter-batch and intra-hatch precision （% CV） across five quality controls was 〈 5.8%. Bioequivalence study was performed with 36 healthy sub- jects after oral administration of 10 mg of lercanidipine and the assay reproducibility was evaluated by reanalysis of 133 incurred samples.