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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 C max was 8.07, 12.24, and 15.25 mg/L and the corresponding AUC 0−∞ 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. [ABSTRACT FROM AUTHOR]

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 C max , AUC 0–24, and AUC 0–∞ 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 t 1/2 , CL t , 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. [ABSTRACT FROM AUTHOR]

Contezolid (MRX-I) is a novel oxazolidinone with potent in vitro activity against gram-positive pathogens. The aim of this study was to establish the dose-pharmacokinetic (PK) exposure-pharmacodynamic (PD)–response relationship and to quantitatively evaluate the variability of MRX-I after continuous oral administration of 600 mg BID and 800 mg BID for 14 days under fed conditions in patients with skin and skin structure infections. Another goal was to evaluate the 2 dosing regimens against methicillin-resistant Staphylococcus aureus infections based on PK/PD analysis. PK data from healthy volunteers and patients were pooled to develop a population PK model using a nonlinear mixed effect modeling method. Monte Carlo simulations were used to predict probability of target attainment (PTA) and cumulative fraction of response after single oral administration of 600 and 800 mg of MRX-I under fed conditions. The PK profile of oral administration of MRX-I was described by using a 2-compartment model with first-order elimination. Absorption of MRX-I may be affected by food intake. Type of volunteers could affect absorption constant rate and volume of distribution in the peripheral compartment, and weight could affect volume of distribution in the central department. No obvious effect on PK parameters was identified for other factors such as age, sex, creatinine clearance, concomitant medicine, and baseline diseases. Based on Monte Carlo simulation, MRX-I 600 or 800 mg BID up to 14 days on ordinary fed status could produce satisfactory efficacy against methicillin-resistant S aureus , with cumulative fraction of response >90% for f AUC 0–24 /MIC targeted at 2.3. At MIC ≤2.0 μg/mL for MRX-I 600 mg BID, or at MIC ≤4.0 μg/mL for MRX-I 800 mg BID, with continuous administration for 14 days at fed status, both regimens could obtain satisfactory clinical and antibacterial efficacy, with PTA >90%. Hence, the MRX-I regimen of 800 mg BID for 7–14 days can be recommended for confirmative clinical trials in patients with skin and skin structure infections. PK profiles of MRX-I were well captured by using a 2-compartment PK model, and disease status, food intake, and weight were found to significantly affect PK profiles. A dosing regimen of 800 mg BID for 7–14 days with ordinary food intake was recommended for pivotal study based on simulated f AUC 0–24 /MIC and PTA values. Results suggest that dose adjustments are not necessary for patient sex in confirmatory studies. Chinese Clinical Trial Registration identifier: CTR20140056. [ABSTRACT FROM AUTHOR]

This study assessed the tolerability and pharmacokinetic (PK) properties of a new-generation oxazolidinone, contezolid (MRX-I), and its major inactive metabolite, M2, after single oral administrations of 800, 1200, and 1600 mg in the fed state, and compared the efficacy of 3 dosing regimens in the treatment of methicillin-resistant Staphylococcus aureus (MRSA) infection based on PK/pharmacodynamic (PD) analysis. A Phase I study at a single study center was conducted with 2 parts. In the first part, 20 healthy subjects received a single oral dose of 1200 or 1600 mg of contezolid or placebo in the fed state in a double-blind, placebo-controlled, dose-escalation tolerance study. In the second part of the study, 52 subjects received a single oral dose of 800 mg of contezolid in the fed state in a single-center, randomized, blinded, 4-period, crossover, thorough QT study. Noncompartmental analyses were used to evaluate the PK properties of contezolid and M2. Steady-state concentrations of contezolid following the 3 dosing regimens (800, 1200, and 1600 mg q12h) were simulated by employing a newly developed 2-compartmental PK model. The minimum inhibitory concentration (MIC) distributions of contezolid were analyzed in 178 Staphylococcus , Enterococcus, and Streptococcus clinical isolates. Monte Carlo simulations were conducted to predict the efficacy of the 3 dosing regimens to obtain probability of target attainment and cumulative fraction of response. Single-dose oral administrations of 800, 1200, and 1600 mg of contezolid were well tolerated in healthy subjects in the fed state, and nonlinear PK was observed. The mean plasma exposures to M2 exceeded 17.3% of contezolid exposure in the 3 groups. Both MIC 50 and MIC 90 (MICs that inhibit the growth of 50% and 90% of microorganisms, respectively) of contezolid against MRSA were 1 mg/L with clinical isolates from China. PK/PD analysis and Monte Carlo simulations predicted that 800 mg q12h of oral contezolid would be efficacious against MRSA infection, with a MIC of ≤4 mg/L (probability of target attainment, >90%; cumulative fraction of response, >90%). Contezolid is a well-tolerated treatment option for MRSA infection, including at supratherapeutic doses up to 1600 mg. The regimen of 800 mg q12h could achieve efficacy in treating bacterial infection with MRSA. To our knowledge, this is the first PK study to predict that a dosing regimen of 800 mg q12h of oral contezolid is sufficient for treating MRSA infection, with a MIC of ≤4 mg/L. A Phase III study of this suggested dosing regimen is being conducted. Chinadrugtrials.org.cn identifier: CTR20161074. [ABSTRACT FROM AUTHOR]