Pharmacokinetics and Disposition of Contezolid in Humans: Resolution of a Disproportionate Human Metabolite for Clinical Development.

Contezolid (MRX-I), a novel oxazolidinone antibiotic, was recently approved for the treatment of serious Gram-positive infections. The pharmacokinetics and disposition of [14C]contezolid were investigated in a single-dose human mass balance study. Cross-species comparison of plasma exposure for contezolid and metabolites was performed, and the safety of the disproportionate metabolite in human was evaluated with additional nonclinical studies. After an oral administration of 99.1 µCi/602-mg dose of [14C]contezolid, approximately 91.5% of the radioactivity was recovered in 0 to 168 h postdose, mainly in urine followed by that in feces. The principal metabolic pathway of contezolid in human comprised an oxidative ring opening of the 2,3-dihydropyridin-4-one fragment into polar metabolites MRX445-1 and MRX459, with recovery of approximately 48% and 15% of the dose, respectively, in urine and feces. Contezolid, MRX445-1, and MRX459 accounted for 68.0%, 19.5%, and 4.84% of the plasma exposure of the total radioactivity, respectively. Metabolites MRX445-1 and MRX459 were observed in disproportionately larger amounts in human plasma than in samples from rat or dog, the rodent and nonrodent species, respectively, used for the general nonclinical safety assessment of this molecule. This discrepancy was resolved with additional nonclinical studies, wherein the primary metabolite, MRX445-1, was further characterized. The no-observed-adverse-effect level (NOAEL) of MRX445-1 was determined as 360 mg/kg body weight/day in a 14-day repeat-dose test in pregnant and nonpregnant Sprague Dawley rats. Furthermore, MRX445-1 exhibited no antibacterial activity in vitro. Thus, MRX445-1 is not expected to exert clinically relevant pharmacology and toxicity.

Pharmacokinetics and pharmacodynamics of multiple-dose intravenous nemonoxacin in healthy Chinese volunteers.

This study evaluated the safety and pharmacokinetic/pharmacodynamic profiles of nemonoxacin in healthy Chinese volunteers following multiple-dose intravenous infusion once daily for 10 consecutive days. The study was composed of two stages. In the open-label stage, 500 mg or 750 mg of nemonoxacin (n = 12 each) was administered at an infusion rate of 5.56 mg/min. In the second stage, with a randomized double-blind placebo-controlled design, 500, 650, or 750 mg of nemonoxacin (n = 16 in each cohort; 12 subjects received the drug and the other 4 subjects received the placebo) was given at an infusion rate of 4.17 mg/min. The results showed that, in the first stage, the maximal nemonoxacin concentrations (mean ± SD) at steady state (Cmax_ss) were 9.60 ± 1.84 and 11.04 ± 2.18 µg/ml in the 500-mg and 750-mg cohorts, respectively; the areas under the concentration-time curve at steady state (AUC0-24_ss) were 44.03 ± 8.62 and 65.82 ± 10.78 µg · h/ml in the 500-mg and 750-mg cohorts, respectively. In the second stage, the nemonoxacin Cmax_ss values were 7.13 ± 1.47, 8.17 ± 1.76, and 9.96 ± 2.23 µg/ml in the 500-mg, 650-mg, and 750-mg cohorts, respectively; the AUC0-24_ss values were 40.46 ± 9.52, 54.17 ± 12.10, and 71.34 ± 17.79 µg · h/ml in the 500-mg, 650-mg, and 750-mg cohorts, respectively. No accumulation was found after the 10-day infusion with any regimen. The drug was well tolerated. A Monte Carlo simulation indicated that the cumulative fraction of response of any dosing regimen was nearly 100% against Streptococcus pneumoniae. The probability of target attainment of nemonoxacin therapy was >98% when the MIC of nemonoxacin against S. pneumoniae was ≤1 mg/liter. It is suggested that all of the studied intravenous nemonoxacin dosing regimens should have favorable clinical and microbiological efficacies in future clinical studies. (This study has been registered at ClinicalTrials.gov under registration no. NCT01944774.).

Determination of a novel nonfluorinated quinolone, nemonoxacin, in human feces and its glucuronide conjugate in human urine and feces by high-performance liquid chromatography-triple quadrupole mass spectrometry.

Three methods were developed and validated for determination of nemonoxacin in human feces and its major metabolite, nemonoxacin acyl-ß- d-glucuronide, in human urine and feces. Nemonoxacin was extracted by liquid-liquid extraction in feces homogenate samples and nemonoxacin acyl-ß- d-glucuronide by a solid-phase extraction procedure for pretreatment of both urine and feces homogenate sample. Separation was performed on a C18 reversed-phase column under isocratic elution with the mobile phase consisting of acetonitrile and 0.1% formic acid. Both analytes were determined by liquid chromatography-tandem mass spectrometry with positive electrospray ionization in selected reaction monitoring mode and gatifloxacin as the internal standard. The lower limit of quantitation (LLOQ) of nemonoxacin in feces was 0.12 µg/g and the calibration curve was linear in the concentration range of 0.12-48.00 µg/g. The LLOQ of the metabolite was 0.0010 µg/mL and 0.03 µg/g in urine and feces matrices, while the linear range was 0.0010-0.2000 µg/mL and 0.03-3.00 µg/g, respectively. Validation included selectivity, accuracy, precision, linearity, recovery, matrix effect, carryover, dilution integrity and stability, indicating that the methods can quantify the corresponding analytes with excellent reliability. The validated methods were successfully applied to an absolute bioavailability clinical study of nemonoxacin malate capsule.

Safety, tolerability, and pharmacokinetics of intravenous nemonoxacin in healthy chinese volunteers.

Nemonoxacin (TG-873870) is a novel nonfluorinated quinolone with potent broad-spectrum activity against Gram-positive, Gram-negative, and atypical pathogens, including vancomycin-nonsusceptible methicillin-resistant Staphylococcus aureus (MRSA), quinolone-resistant MRSA, quinolone-resistant Streptococcus pneumoniae, penicillin-resistant S. pneumoniae, and erythromycin-resistant S. pneumoniae. This first-in-human study was aimed at assessing the safety, tolerability, and pharmacokinetic properties of intravenous nemonoxacin in healthy Chinese volunteers. The study comprised a randomized, double-blind, placebo-controlled, dose escalating safety and tolerability study in 92 subjects and a randomized, single-dose, open-label, 3-period Latin-square crossover pharmacokinetic study in 12 subjects. The study revealed that nemonoxacin infusion was well tolerated up to the maximum dose of 1,250 mg, and the acceptable infusion rates ranged from 0.42 to 5.56 mg/min. Drug-related adverse events (AEs) were mild, transient, and confined to local irritation at the injection site. The pharmacokinetic study revealed that after the administration of 250, 500, and 750 mg of intravenous nemonoxacin, the maximum plasma drug concentration (Cmax) values were 4.826 µg/ml, 7.152 µg/ml, and 11.029 µg/ml, respectively. The corresponding values for the area under the concentration-time curve from 0 to 72 hours (AUC0-72 h) were 17.05 µg · h/ml, 39.30 µg · h/ml, and 61.98 µg · h/ml. The mean elimination half-life (t1/2) was 11 h, and the mean cumulative drug excretion rate within 72 h ranged from 64.93% to 77.17%. Volunteers treated with 250 to 750 mg nemonoxacin exhibited a linear dose-response relationship between the AUC0-72 h and AUC0-∞. These findings provide further support for the safety, tolerability, and pharmacokinetic properties of intravenous nemonoxacin. (This study has been registered at ClinicalTrials.gov under registration no. NCT01944774.).

Integrative population pharmacokinetic/pharmacodynamic analysis of nemonoxacin capsule in Chinese patients with community-acquired pneumonia.

Introduction: Nemonoxacin is an innovative quinolone antibiotic for treatment of community-acquired pneumonia (CAP). As more data are available from clinical studies, it is necessary to perform an integrative pharmacokinetic/pharmacodynamic (PK/PD) analysis to support and justify the optimal dosing regimen of nemonoxacin in clinical practice. Methods and Results: We developed a population PK model using non-linear mixed effect model based on the data of 195 Chinese subjects receiving nemonoxacin in phase I to III clinical trials. The base model was a standard two-compartment PK model defined by clearance (12 L/h) and central volume of distribution (86 L). Covariates included creatinine clearance (CLcr), body weight (BW), sex, disease status and food. Compared to the subject with BW 60 kg, Cmax and A U C 0 - 24 , ss reduced by 24% and 19% in the subject with BW 80 kg, respectively. Compared to the subject with CLcr 150 ml/min, A U C 0 - 24 , ss and T1/2 increased by 28% and 24%, respectively in the subject with CLcr 30 ml/min. Compared to the fasted status, Tmax of nemonoxacin increased by 1.2 h in the subject with fed status. Effects of sex and disease status on PK parameters were small (change of PK parameters ≤19%). AUC0-24/MIC and %T > MIC were identified as the optimal PK/PD indices for predicting clinical efficacy. The AUC0-24/MIC target was 63.3, 97.8, and 115.7 against Streptococcus pneumoniae, Staphylococcus aureus, and Haemophilus influenzae, respectively. The %T > MIC target was 7.96% against Klebsiella pneumoniae. Monte Carlo simulation showed that treatment with nemonoxacin 500 mg q24 h could attain a PK/PD cutoff value higher than the MIC90 against S. pneumoniae and S. aureus. The corresponding cumulative fraction of response (CFR) was greater than 93%, while nemonoxacin 750 mg q24 h would provide higher PK/PD cutoff value against Haemophilus parainfluenzae, and higher CFR (83%) than 500 mg q24 h. Conclusion: Integrative PK/PD analysis justifies the reliable clinical and microbiological efficacy of nemonoxacin 500 mg q24 h in treating CAP caused by S. pneumoniae, S. aureus, and K. pneumoniae, irrespective of patient sex, mild renal impairment, empty stomach or not. However, nemonoxacin 750 mg q24 h would provide better efficacy than 500 mg q24 h for the CAP caused by H. parainfluenzae in terms of CFR.

A liquid chromatography-tandem mass spectrometry assay for the determination of nemonoxacin (TG-873870), a novel nonfluorinated quinolone, in human plasma and urine and its application to a single-dose pharmacokinetic study in healthy Chinese volunteers.

Nemonoxacin (TG-873870) is a novel C-8-methoxy nonfluorinated quinolone with higher activity than ciprofloxacin, levofloxacin and moxifloxacin against Gram-positive pathogens including methicillin-susceptible or methicillin-resistant Staphylococcus aureus and Streptococcus pneumoniae with various resistant phenotypes. A rapid, sensitive and selective liquid chromatography-tandem mass spectrometric (LC-MS/MS) method was developed and validated to determine the concentration of nemonoxacin in human plasma and urine. Protein precipitation and liquid-liquid extraction were employed for plasma and urine sample preparations, respectively, and extract was then injected into the system. Separation was performed on a C(18) reversed-phase column using acetonitrile-0.1% formic acid as a mobile phase. Both analyte and internal standard (gatifloxacin) were determined using electrospray ionization and the MS data acquisition via the selected reaction monitoring in positive-ion mode. The lower limit of quantification was 5 ng/mL and the calibration curves were linear in the concentration range of 5-1000 ng/mL. The accuracy, precision, selectivity, linearity, recovery, matrix effect and stability were validated for TG-873870 in human plasma and urine. The method was successfully applied to a pharmacokinetic study enrolling 12 healthy Chinese volunteers administered nemonoxacin malate capsules.

Pharmacokinetics and pharmacodynamics of levofloxacin in bronchial mucosa and lung tissue of patients undergoing pulmonary operation.

Levofloxacin is a major antimicrobial agent that is used for the treatment of community-acquired lower respiratory tract infections (LRTIs). The present study was designed to investigate the pharmacokinetics (PK) and pharmacodynamics (PD) of levofloxacin in bronchial mucosa and lung tissue. A total of 32 patients undergoing pulmonary surgery were randomly assigned to one of four groups (8 subjects/group). All patients received a single dose of 500 mg levofloxacin orally prior to the operation. Blood, lung tissue and bronchial mucosa samples were collected prior to treatment and at 1.5, 4, 8, 12 and 24 h following treatment. The drug concentration was determined and PK and PD profiles were calculated using MATLAB software. The peak concentration of levofloxacin was 7.0±1.2 µg/g in lung tissues and 9.4±2.1 µg/g in bronchial mucosa. The corresponding area under the curve between 0 and 24 h (AUC0-24) was 85.7±8.5 and 137.3±19.4 µg h/g. The mean permeability of levofloxacin (ratio of concentration in tissue to that in plasma) was 2.4 in lung tissue and 4.4 in the bronchial mucosa. The PK profiles of levofloxacin in the plasma, lung and bronchial mucosa were described using an integrated one-compartment model. The probability of fAUC0-24/minimal inhibitory concentration (MIC) target attainment of levofloxacin against Streptococcus pneumoniae in the lung and bronchial mucosa was maintained at 100% when MIC ≤1 mg/l, while the cumulative fraction of fAUC0-24/MIC in the corresponding tissues was 94.4 and 98.1%, respectively. The present study demonstrated the high permeability of levofloxacin in the lung and bronchial mucosa of patients undergoing pulmonary surgery. In conclusion, treatment using 500 mg levofloxacin exhibits good clinical and microbiological efficacy for use in LRTIs that are caused by S. pneumoniae. This trial was registered retrospectively in the Chinese Clinical Trial Registry on January 13, 2020 (registration no. ChiCTR2000029096).

Population pharmacokinetics of oral levofloxacin 500 mg once-daily dosage in community-acquired lower respiratory tract infections: results of a prospective multicenter study in China.

This study aimed to explore the pharmacokinetic features of levofloxacin (LVFX) in Chinese patients with infections and to confirm oral LVFX 500 mg once daily as an optimal treatment regimen based on pharmacokinetic-pharmacodynamic (PK-PD) analysis. A total of 1052 plasma samples from 164 Chinese adult patients with community acquired lower respiratory tract infections (CALRTIs) and 18 healthy volunteers were used for population PK analysis. LVFX 500-mg tablets were given once daily. A nonlinear mixed effects model (NONMEM) program was used for population PK model-building and a two-compartment model with first-order absorption process was established. Creatinine clearance (CL(cr)) and body weight were identified as intrinsic factors which significantly affected oral clearance (CL(t)/F) and the apparent volume of distribution of the central compartment (V1/F), respectively. The final model is described as follows: CL(t)/F (l/h) = (8.97 + 0.917 x (CL(cr) (ml/min)-100.92) x 60/1000) x exp (eta(CLt/F)). V1/F (l) = (85.3 + 1.22 x (weight (kg)-60.75)) x exp (eta(V1/F)). Q/F (l/h) = 0.351. V2/F (l) = 6.81. k(a) (h(-1)) = 1.44 x exp(eta(ka)). Based on the population PK model, mean C(max) and AUC(0-24h) in CALRTI patients were estimated as 5.13 microg/ml and 58.98 microg.h/ml, respectively. A subgroup analysis showed that patients with mild renal dysfunction (50 ml/min < or = CL(cr) < 80 ml/min) had 34% higher AUC(0-24h) values compared to patients with normal renal function (CL(cr) > or = 80 ml/min). Postmodeling simulation using final population PK estimates also showed that C(max) and AUC(0-24h) increased markedly in patients with severe renal dysfunction. The results indicate that LVFX dosage adjustment should be individualized on the basis of the CL(cr), especially in those with CL(cr) less than 50 ml/min. None of the PK parameters had any correlation with the occurrence of adverse events. PK-PD analysis indicated that, in patients treated with LVFX 500 mg once daily, the AUC(0-24h)/MIC ratio exceeded the target for those major CALRTI pathogens isolated. In addition, the C(max)/MIC ratio reached 5 for Streptococcus pneumoniae, indicating that the emergence of LVFX-resistant S. pneumoniae could be prevented during the therapy with this dosage regimen. These results demonstrate that oral LVFX 500 mg once daily has favorable PK parameters and PK-PD features in patients with CALRTIs, and the results strongly support this dosage regimen for the treatment of CALRTI.

Pharmacokinetics of colistin methanesulfonate (CMS) in healthy Chinese subjects after single and multiple intravenous doses.

The high prevalence of extensively drug-resistant Gram-negative pathogens has forced clinicians to use colistin as a last-line therapy. Knowledge on the pharmacokinetics of colistin methanesulfonate (CMS), an inactive prodrug, and colistin has increased substantially; however, the pharmacokinetics in the Chinese population is still unknown due to lack of a CMS product in China. This study aimed to evaluate the pharmacokinetics of a new CMS product developed in China in order to optimise dosing regimens. A total of 24 healthy subjects (12 female, 12 male) were enrolled in single- and multiple-dose pharmacokinetic (PK) studies. Concentrations of CMS and formed colistin in plasma and urine were measured, and PK analysis was conducted using a non-compartmental approach. Following a single CMS dose [2.36 mg colistin base activity (CBA) per kg, 1 h infusion], peak concentrations (Cmax) of CMS and formed colistin were 18.0 mg/L and 0.661 mg/L, respectively. The estimated half-life (t1/2) of CMS and colistin were 1.38 h and 4.49 h, respectively. Approximately 62.5% of the CMS dose was excreted via urine within 24 h after dosing, whilst only 1.28% was present in the form of colistin. Following multiple CMS doses, colistin reached steady-state within 24 h; there was no accumulation of CMS, but colistin accumulated slightly (RAUC = 1.33). This study provides the first PK data in the Chinese population and is essential for designing CMS dosing regimens for use in Chinese hospitals. The urinary PK data strongly support the use of intravenous CMS for serious urinary tract infections.

Short-term Safety, Tolerability, and Pharmacokinetics of MRX-I, an Oxazolidinone Antibacterial Agent, in Healthy Chinese Subjects.

PURPOSE: This study was designed to evaluate the safety and pharmacokinetic profiles of MRX-I tablet, an oxazolidinone antibacterial agent, in healthy Chinese subjects. METHODS: The study was composed of 3 sequential periods. Period 1 was a randomized, double-blind, placebo-controlled, sequential ascending dose (50 to 1800 mg) study. Period 2 included one arm as a randomized, open-label, 3-period, 3 × 3 Latin square single-dose study of 300, 600, and 900 mg MRX-I administration and another arm as a crossover study to evaluate high-fat diet effect. Period 3 was a randomized, double-blind, placebo-controlled multiple-dose study with 600 or 800 mg, q12h regimens over 15 days. FINDINGS: MRX-I was rapidly absorbed and reached peak plasma concentration at about 2 hours post dose. The Cmax was 8.07, 12.24, and 15.25 mg/L and the corresponding AUC0-∞ 29.21, 48.27, and 59.60 mg/h/L, in 300-, 600-, and 900-mg dosing groups, respectively. High-fat diet increased the exposure of MRX-I. No discernable drug accumulation was observed after 15 days of continuous drug administration. About 2% of MRX-I was excreted via kidneys in unchanged form. No obvious hematologic toxicity by MRX-I was observed during the entire study. Based on Monte Carlo simulation, 600 or 800 mg BID can produce satisfactory efficacy against methicillin-resistant Staphylococcus aureus. IMPLICATIONS: MRX-I was well tolerated in healthy Chinese subjects (50-1800 mg). No serious or severe adverse effects were observed. MRX-I 600 or 800 mg BID up to 15 days can be recommended in future clinical trials. Chinese Clinical Trial Registration (http://www.chinadrugtrials.org.cn) identifier: CTR20131214.

Clinical Pharmacokinetics of Levornidazole in Elderly Subjects and Dosing Regimen Evaluation Using Pharmacokinetic/Pharmacodynamic Analysis.

PURPOSE: Levornidazole, the levo-isomer of ornidazole, is a third-generation nitroimidazole derivative newly developed after metronidazole, tinidazole, and ornidazole. An open-label, parallel-controlled, single-dose study was conducted for the investigation of the pharmacokinetic (PK) profile of levornidazole and its metabolites in healthy elderly Chinese subjects, and for the evaluation of 2 dosing regimens in the elderly. METHODS: Levornidazole was intravenously administered at 500 mg to healthy elderly (aged 60-80 years) or young subjects (aged 19-45 years). The PK profiles of levornidazole and its metabolites in elderly subjects were evaluated and compared with those in the young group. WinNonlin software was used for simulating the PK profile of levornidazole in the elderly population following the dosing regimens of 500 mg BID and 750 mg once daily for 7 days. Monte Carlo simulation was used for estimating the cumulative fraction of response and probability of target attainment of both dosing regimens against Bacteroides spp. RESULTS: The Cmax, AUC0-24, and AUC0-∞ values of levornidazole in the elderly group were 11.98 µg/mL, 131.36 µg·h/mL, and 173.61 µg·h/mL, respectively. The t1/2, CLt, and mean residence time from time 0 to infinity were 12.21 hours, 2.91 L/h, and 16.46 hours. The metabolic ratios of metabolites (M) 1, 2, 4, and 6 were <3.0%, and that of M16 was 17.70%. The urinary excretion values of levornidazole, M1, M2, M4, M6, and M16 over 96 hours were 10.21%, 0.92%, ~0%, 2.69%, 0.54%, and 41.98%. The PK properties of levornidazole and the urinary excretion of all metabolites were not statistically different between the 2 groups. The cumulative fraction of response was >90% against B fragilis and other Bacteroides spp, and the probability of target attainment was >90% when the minimum inhibitory concentration was ≤1 µg/mL, in both groups. IMPLICATIONS: No dosing regimen adjustment is suggested when levornidazole is used in elderly patients with normal hepatic functioning and mild renal dysfunction. The findings from the PK/PD analysis imply that both regimens may achieve satisfactory clinical and microbiological efficacy against anaerobic infections in elderly patients. Chinese Clinical Trial Registry (http://www.chictr.org.cn) identifier: ChiCTR-OPC-16007938.

Selective method for the determination of cefdinir in human plasma using liquid chromatography electrospray ionization tandam mass spectrometry.

A sensitive and selective liquid chromatographic-tandem mass spectrometric (LC-MS/MS) method was developed for the determination of cefdinir in human plasma. After a simple protein precipitation using trichloracetic acid, the post-treatment samples were applied to a prepacked RP18 Waters SymmetryShield column interfaced with a triple quadrupole tandem mass spectrometer. Positive electrospray ionization was employed as the ionization source. The mobile phase consisted of methanol-water-formic acid (25:75:0.075, v/v/v). The analyte and I.S. cefaclor were both detected by the use of selected reaction monitoring mode. The method was linear in the concentration range of 5-2,000 ng/ml. The lower limit of quantification was 5 ng/ml. The intra- and inter-day relative standard deviation across three validation runs over the entire concentration range was less than 4.3%. The accuracy determined at three concentrations (36, 360 and 1,800 ng/ml for cefdinir) ranged from 99.6 to 106.7% in terms of recovery. The chromatographic run time for each plasma sample was less than 3 min. The method herein described was successfully applied for the evaluation of pharmacokinetic profiles of cefdinir capsule in 12 healthy volunteers.

Development of an Liquid Chromatography-Tandem Mass Spectrometry Method for the Determination of Amoxicillin in Broth Medium and its Application to an In Vitro Pharmacokinetic and Pharmacodynamic Model.

A simple, rapid and highly sensitive liquid chromatographic-tandem mass spectrometry (LC-MS-MS) method has been developed and validated for the quantification of amoxicillin in broth-a liquid bacterial culture medium. After appropriate dilution with ultrapure water, broth samples containing amoxicillin and an internal standard (IS) were extracted by acetonitrile and dichloromethane. The extract was injected into the system. The analyte and the IS were separated by a prepacked Atlantis C18 column using acetonitrile-0.1% formic acid as a mobile phase and detected by selected reaction monitoring in electrospray ionization positive ion mode. The calibration curve of amoxicillin was linear over the concentration range of 0.05-20.00 µg/mL. The mean recovery of amoxicillin from broth was 71.7%, and the intra- and interday precision and accuracies of the assay were within 10%. Amoxicillin was stable in broth for 12 h at room temperature (24°C), for 6.5 months at -80°C and for 24 h after preparation in an autosampler at room temperature. It has been successfully applied to an in vitro pharmacokinetic (PK) and pharmacodynamic (PD) model in which the broth is used for bacterial growth. The method provides high-throughput biological analysis to facilitate the in vitro PK and PD model of amoxicillin.

Improved pharmacokinetic profile of levornidazole following intravenous infusion of 750mg every 24h compared with 500mg every 12h in healthy Chinese volunteers.

Levornidazole is the levo-isomer of ornidazole with similar anti-anaerobic activity and lower central neurotoxicity compared with ornidazole. This open-label, parallel, randomised, multidose trial was conducted to compare the pharmacokinetics and safety of levornidazole following intravenous (i.v.) infusion 750mg every 24h (q24h) (test group, 12 subjects) versus 500mg every 12h (q12h) (reference group, 12 subjects) for 7 days in healthy Chinese volunteers. Following i.v. infusion for 7 days, the test group showed a 33.8% lower accumulation ratio (AR) and a 45.0% higher volume of distribution of levornidazole than the reference group. The cumulative urinary excretion rate of levornidazole during the 0-72h period (Ae0-72) was 16.6±20.9% in the test group and 24.2±5.7% in the reference group. The metabolite M1/parent and M4/parent ratios were, respectively, 2.18±0.77% and 2.94±0.37% in test group and 3.15±1.09% and 3.18±0.34% in the reference group. The Ae0-72 of M1, M2 and M4 were all <10% in both groups. Both regimens were well tolerated. Drug-related adverse events were generally transient and were mild or moderate in severity. These findings support the recommendation of i.v. infusion of levornidazole 750mg q24h in clinical practice, which shows a lower AR and similar safety compared with the conventional 500mg q12h regimen. [Chinese Clinical Trial Registry identifier: ChiCTR-IPR-14005574.].

[Study of pharmacokinetics/pharmacodynamics of levofloxacin].

OBJECTIVE: To evaluate the dosing regimens of levofloxacin. METHODS: The drug concentrations in serum and urine were assayed by HPLC method and the pharmacokinetic parameters were calculated after intravenous infusion of a single dose of 200 mg, 300 mg and 500 mg levofloxacin to healthy volunteers. The in vitro activity MIC of levofloxacin against 823 clinical isolates were determined and compared with other antimicrobial agents. Based on the above results, the PK/PD parameters C(max)/MIC and AUC/MIC were calculated and the dosing regimens of levofloxacin were proposed for infections caused by different pathogens. RESULTS: The results of clinical pharmacokinetic study showed that the C(max) of levofloxacin was 3.4 mg/L +/- 0.8 mg/L, 4.8 mg/L +/- 1.4 mg/L and 7.6 mg/L +/- 1.1 mg/L respectively, AUC(0-infinity) was 14.4 mg.h/L +/- 2.5 mg.h/L, 21.9 mg.h/L +/- 4.5 mg.h/L and 38.3 mg.h/L +/- 4.9 mg.h/L respectively, T(1)/2 beta was 6.2 h +/- 0.4 h, 6.4 h +/- 0.9 h and 6.5 h +/- 0.6 h respectively, and 69% +/- 5%, 69% +/- 6%, and 65% +/- 4% of the doses were excreted in urine within 24 h after intravenous infusion of a single dose of levofloxacin 200 mg, 300 mg and 500 mg. The in vitro pharmacodynamic study showed that levofloxacin was highly active against Hemolytic streptococcus and Moraxella catarrhalis. It was active against Streptococcus pneumoniae (including penicillin nonsusceptible strains), Hemophilus influenzae, methicillin-sensitive Staphylococcus aureus (MSSA), Klebsiella pneumoniae and Stenotrophomonas maltophilia. Levofloxacin also had good activity against Pseudomonas aeruginosa and K.pneumoniae. However, most of isolates of enterococcal spp. were resistant to levofloxacin. Above 50% of Escherichia coli isolates were resistant to levofloxacin. Based on the results of PK/PD parameters, the adequate dosing regimens of levofloxacin should be once daily 200 mg once daily of levofloxacin was expected to be effective for the treatment of infections caused by M. catarrhalis. The regimen of 300 mg once daily could be effective for the treatment of infections caused by Hemolytic streptococcus. 500 mg once daily of levofloxacin was expected to be effective for the treatment of respiratory tract infections caused by S. pneumoniae or H. influenzae. For treatment of respiratory tract infections and urinary tract infections caused by levofloxacin-susceptible organisms including K. pneumoniae, E. coli, P. aeruginosa, and S.maltophilia, 500 mg once daily of levofloxacin was needed to obtain good clinical efficacy. But PK/PD parameters predicted that 500 mg daily of levofloxacin was not effective for infections caused by methicillin-resistant Staphylococcus aureus (MRSA) and Enterococci. CONCLUSION: The proposed dosing regimens of levofloxacin based on PK/PD concepts are expected to provide good efficacy in clinical practice.

Quantification of levornidazole and its metabolites in human plasma and urine by ultra-performance liquid chromatography-mass spectrometry.

We developed and validated an ultra-performance liquid chromatographic (UPLC) method coupled with atmospheric pressure chemical ionization (APCI) mass spectrometry for simultaneous determination of levornidazole and its first-pass metabolites, l-chloro-3-(2-hydroxymethyl-5-nitro-l-imidazolyl)-2-propanol (Ml), 2-methyl-5-nitroimidazole (M2) and 3-(2-methyl-5-nitro-1-imidazolyl)-1,2-propanediol (M4), in human plasma and urine. The biological samples were pretreated by protein precipitation and liquid-liquid extraction and analyzed using an ACQUITY UPLC CSH C18 column (2.1×50 mm, 1.7 µm) and a QTRAP mass spectrometer in multiple reaction monitoring mode via APCI. Acetonitrile and 0.1% formic acid in water was used as the mobile phase in gradient elution at a flow rate of 0.6 mL/min. The lower limit of quantification of this method was 0.0100, 0.00500, 0.0200 and 0.00250 µg/mL for levornidazole, M1, M2 and M4, respectively. The linear calibration curves were obtained for levornidazole, M1, M2, and M4 over the range of 0.0100-5.00, 0.00500-2.50, 0.0200-10.0 and 0.00250-1.25 µg/mL, respectively. The intra- and inter-batch precision was less than 12.2% in plasma and less than 10.8% in urine. The intra- and inter-batch accuracy was 87.8-105.7% in plasma and 92.8-109.2% in urine. The mean recovery of levornidazole, M1, M2 and M4 was 91.1-105.1%, 95.8-103.8%, 87.8-96.8%, 96.8-100.6% from plasma and 96.0-100.9%, 96.9-107.9%, 95.1-102.7%, 103.7-105.9% from urine respectively. This method was validated under various conditions, including room temperature, freeze-thaw cycles, long-term storage at -40 ± 5°C, after pretreatment in the autosampler (at 10°C), and 10- and 100-fold dilution. This newly established analytical method was successfully applied in a pharmacokinetic study following single intravenous infusion of levornidazole in 24 healthy Chinese subjects.

Safety and clinical pharmacokinetics of nemonoxacin, a novel non-fluorinated quinolone, in healthy Chinese volunteers following single and multiple oral doses.

BACKGROUND: Nemonoxacin, a novel C-8-methoxy non-fluorinated quinolone, is currently being developed in oral and intravenous formulations. It exhibits potent antibacterial activities against Gram-positive, Gram-negative and atypical pathogens, especially methicillin-resistant Staphylococcus aureus. The first-in-human study of a nemonoxacin capsule was conducted in a Western population. This current study was the first investigation on the clinical pharmacokinetics (PK) of nemonoxacin in a Chinese population, and was designed to determine PK data in a Chinese population and investigate the dose regimen for future clinical use. OBJECTIVE: The objective of this study was to evaluate the PK profile of nemonoxacin as well as its safety and tolerability in healthy Chinese volunteers following single and multiple oral doses. METHODS: The first part of the study was a double-blind, placebo-controlled, sequential ascending single-dose safety and tolerability study. In each cohort, two subjects received a placebo and six received single oral doses of nemonoxacin 125, 250, 500, 750 or 1000 mg. In the second part, the single-dose PK study, three dose levels (250, 500 and 750 mg) of nemonoxacin were administered orally to 12 healthy Chinese volunteers (male : female = 1 : 1) under fasting conditions in a crossover manner. The same volunteers received orally an additional dose of 500 mg under fed conditions after a 7-day washout. In the third part, the multiple-dose PK study, 24 subjects received 500 or 750 mg of nemonoxacin orally once daily for 10 consecutive days. Within each cohort, 12 subjects (male : female = 1 : 1) received the same dose level of nemonoxacin under fasting conditions. The PK profiles, safety and tolerability, and food and sex effects were evaluated. RESULTS: No severe or serious adverse events (AEs) occurred in this study, and no clinically significant abnormalities were noted in the vital signs or on physical examination. Notable AEs, mainly nausea and rash with or without pruritus, were mild and resolved spontaneously. Most laboratory AEs were mild and transient and the subjects recovered without treatment. Nemonoxacin was found to be rapidly absorbed, with peak plasma concentrations (C(max)) attained 1-2 hours after administration. The C(max) and area under the concentration-time curve from time zero to infinity (AUC(∞)) were dose-proportional after single oral doses. The elimination half-life was 10-12 hours. Nemonoxacin was excreted primarily in urine, with a recovery of intact nemonoxacin of 60-70% of the dose over 72 hours. Food had a significant effect on the rate and extent of absorption (p < 0.001), increasing the time to reach C(max) from 1.14 to 3.64 hours and reducing C(max) by 34% and AUC(∞) by 18%, while a sex effect was not found. C(max) and AUC(∞) were similar between the single-dose and multiple-dose PK studies. The multiple-dose PK data suggested no drug accumulation in healthy subjects. CONCLUSION: Nemonoxacin exhibited a linear PK profile in the 250-750 mg dose range with moderate food effects. There was no accumulation following consecutive administration for 10 days. The PK and safety profiles of nemonoxacin in Chinese subjects support evaluation of once-daily dosing in the future development of this agent.

Establishment of norvancomycin fluorescence polarization immunoassay for therapeutic drug monitoring.

To establish a rapid and simple fluorescence polarization immunoassay method for determination of norvancomycin serum concentration, we collected 300 serum samples from the patients receiving norvancomycin in the hospitals localized in Shanghai, China. The drug concentrations were measured by the established HPLC method and FPIA with vancomycin kit. A FPIA algorithm for the determination of norvancomycin concentration was established according to the correlation between the FPIA and HPLC results. The methods and algorithm were validated in another 70 clinical samples. HPLC determination showed a good linear correlation within the range of 0.5-100 mg l(-1) of norvancomycin concentrations. The method was validated via extraction recovery, intra- and inter-day methodological recovery and stability of norvancomycin in serum. Correlation analysis between the measurements of HPLC and FPIA in 300 serum samples gave the linear regression equation: (concentration by HPLC)=0.760 × (concentration by FPIA)-0.577 (P<0.001, R(2)=0.982). An algorithm was derived from this correlation for measuring the serum norvancomycin concentrations with FPIA. When it was validated in additional 70 serum samples from patients, 'FPIA algorithm' showed good accuracy versus HPLC: 'FPIA algorithm'=0.93 (HPLC)+0.63, R(2)=0.962, and 94.3% of the results from FPIA algorithm fell within the range of -20%/+20% of HPLC. This algorithm developed in this study can be easily used for determination of norvancomycin using TDx analyzer with vancomycin kit indirectly. It may also be useful for norvancomycin therapeutic drug monitoring.

Liquid chromatography/tandem mass spectrometry assay for the simultaneous determination of cefoperazone and sulbactam in plasma and its application to a pharmacokinetic study.

A rapid and highly sensitive liquid chromatography-tandem mass spectrometric (LC-MS/MS) method for simultaneous determination of cefoperazone sodium and sulbactam sodium in human plasma was developed. The analytes and internal standard (IS), cefuroxime sodium, were extracted from human plasma via liquid-liquid extraction with ethyl acetate and separated on a Waters Xterra C18 column within 3.5 min. Quantitation was performed on a triple quadrupole mass spectrometer employing electrospray ionization technique, operating in selected reaction monitoring (SRM) and negative ion mode. The precursor to product ion transitions monitored for cefoperazone, sulbactam and IS were m/z 644.1→528.0, 232.1→140.0, and 423.0→362.0, respectively. The assay was validated in the linear range of 0.1-20 µg/mL for cefoperazone and 0.02-4 µg/mL for sulbactam. The intra- and inter-day precisions (CV%) were within 8.39% for each analyte. The recoveries were greater than 87.3% for cefoperazone and 87.2% for sulbactam. Each analyte was found to be stable during all sample storage, preparation and analytical procedures. The method was successfully applied in a pharmacokinetic study of Sulperazon injection in six hospital-acquired pneumonia (HAP) patients.

Permeability and concentration of levofloxacin in epithelial lining fluid in patients with lower respiratory tract infections.

The purpose of the study was to assess the bactericidal effects of a single oral dose of levofloxacin (LVFX) by examining the concentration of LVFX in alveolar epithelial lining fluid (ELF) from patients with lower respiratory tract infections (LRTI). Forty patients with LRTI took 500 mg of LVFX and then received a fiberoptic bronchoscopic procedure randomly 1, 4, 8, 12, or 24 hours following dosing. Bronchoalveolar lavage fluid and blood were collected at the time of the bronchopulmonary procedure, and the LVFX concentration was determined. The mean peak concentrations of LVFX in plasma and ELF were achieved at 1.5 hours (4.07 mg/L) and 1 hour (3.44 mg/L), respectively. The AUC(24h) samples were 50.12 mg . h/L and 34.51 mg . h/L, respectively. The permeability of LVFX, which was estimated based on the ratio of LVFX concentration in tissue fluids to that in plasma, was 0.78 on average across all time points. After a single dose of LVFX in patients with LRTI, the drug rapidly distributed into bronchopulmonary tissue, thereby suggesting this dose is capable of achieving the concentration in target organs required for bactericidal efficacy.