Pharmacokinetics, toxicokinetics, distribution, metabolism and excretion of linezolid in mouse, rat and dog

The efficacy of linezolid, alone or in combination with rifampin, against methicillin-susceptible Staphylococcus aureus in rabbits with experimental endocarditis was investigated. Linezolid (50 or 75 mg/kg of body weight), rifampin, and linezolid (25, 50, or 75 mg/kg) plus rifampin produced statistically significant reductions in bacterial counts compared with those in untreated controls. Plasma or valvular vegetation levels of linezolid in the groups treated with the linezolid-rifampin combination were similar to those in the respective linezolid-only treatment groups. At therapeutic levels of linezolid, rifampin resistance was not observed. The results from this experimental model of endocarditis suggest that while rifampin did not provide synergy to the linezolid dosing, it did not antagonize the efficacy of linezolid.

contrasting

confidence: 49%

Efficacy of Linezolid plus Rifampin in an Experimental Model of Methicillin-Susceptible Staphylococcus aureus Endocarditis

Dailey¹,

Pagano²,

Buchanan³

et al. 2003

“…These dosages corresponded to fAUC/MIC ratio values for TR-700 values of 43.1 and 56.9, respectively. In contrast, a dose of 120 mg/kg/day of linezolid did not achieve stasis (fAUC/MIC ratio of 35.7 based on a protein binding rate of 30% in mouse plasma) (12). Indeed, the bacterial burden in the linezolid-treated arm was more than 2 log CFU/g higher than the stasis value (Fig.…”

Section: Resultsmentioning

confidence: 91%

In Vivo Pharmacodynamics of Torezolid Phosphate (TR-701), a New Oxazolidinone Antibiotic, against Methicillin-Susceptible and Methicillin-Resistant Staphylococcus aureus Strains in a Mouse Thigh Infection Model

Louie

Liu

Kulawy

et al. 2011

Torezolid phosphate (TR-701) is the phosphate monoester prodrug of the oxazolidinone TR-700 which demonstrates potent in vitro activity against Gram-positive bacteria, including methicillin-susceptible Staphylococcus aureus (MSSA) and methicillin-resistant S. aureus (MRSA). The pharmacodynamics of TR-701 or TR-700 (TR-701/700) against S. aureus is incompletely defined. Single-dose pharmacokinetic studies were conducted in mice for TR-701/700. Forty-eight-hour dose range and 24-hour dose fractionation studies were conducted in a neutropenic mouse thigh model of S. aureus infection using MRSA ATCC 33591 to identify the dose and schedule of administration of TR-701/700 that was linked with optimized antimicrobial effect. Additional dose range studies compared the efficacies of TR-701/700 and linezolid for one MSSA strain and one community-associated MRSA strain. In dose range studies, TR-701/700 was equally bactericidal against MSSA and MRSA. Mean doses of 37.6 and 66.9 mg/kg of body weight/day of TR-701/700 resulted in stasis and 1 log CFU/g decreases in bacterial densities, respectively, at 24 h, and mean doses of 35.3, 46.6, and 71.1 mg/kg/day resulted in stasis and 1 and 2 log CFU/g reductions, respectively, at 48 h. Linezolid administered at doses as high as 150 mg/kg/day did not achieve stasis at either time point. Dose fractionation studies demonstrated that the area under the concentration-time curve over 24 h in the steady state divided by the MIC (AUC/MIC ratio) was the pharmacodynamic index for TR-701/700 that was linked with efficacy. TR-701/700 was highly active against MSSA and MRSA, in vivo, and was substantially more efficacious than linezolid, although linezolid's top exposure has half the human exposure. Dose fractionation studies showed that AUC/MIC was the pharmacodynamic index linked with efficacy, indicating that once-daily dosing in humans is feasible.

“…The elimination half-life of TR-700 ranged from 3.3 to 4.3 h. The C max increased from 0.2 to 20.1 mg/liter over the dose range, and the AUC ranged from 1.4 to 131 mg · h/liter. Protein binding values were previously reported for linezolid at 30% (51). The binding value for TR-700 was based upon prior studies performed by the sponsor (85%).…”

Section: Resultsmentioning

confidence: 99%

Comparative Pharmacodynamics of the New Oxazolidinone Tedizolid Phosphate and Linezolid in a Neutropenic Murine Staphylococcus aureus Pneumonia Model

Lepak

Marchillo

Pichereau

et al. 2012

Staphylococcus aureus has become a leading cause of community-and hospital-acquired pneumonia. Furthermore, infection with community-and health care-acquired strains of methicillinresistant S. aureus (MRSA) is increasingly common and limits antimicrobial options (13,25,29,31). Tedizolid phosphate (TR-701) is a novel oxazolidinone prodrug. The active moiety, tedizolid (TR-700), exhibits potent activity against Gram-positive bacteria, including MRSA (48). The goals of our studies were to identify the pharmacodynamic (PD) target (AUC/MIC ratio) for TR-700 against methicillin-susceptible S. aureus (MSSA) and MRSA strains in a neutropenic murine pneumonia model and compare the PD targets of TR-700 to that of the only FDA-approved oxazolidinone antibiotic, linezolid. MATERIALS AND METHODSBacteria, media, and antibiotics. Eleven isolates of S. aureus were utilized for these experiments. The strains included four MSSA strains (ATCC 6538P, ATCC 25923, ATCC 29213, and ATCC Smith), one hospital-acquired MRSA strain (ATCC 33591), and six community-acquired MRSA strains (MW2, R2527, 04-045, 04-154, 05-051, and UW 307109). Organisms were grown, subcultured, and quantified in Mueller-Hinton broth (Difco Laboratories, Detroit, MI) and Mueller-Hinton agar (Difco Laboratories, Detroit, MI). Linezolid was obtained from the University of Wisconsin pharmacy. Tedizolid (TR-700) and tedizolid phosphate (TR-701) were supplied by the manufacturer (Trius Therapeutics, San Diego, CA). Prior to in vivo treatment studies, TR-701 was dissolved in sterile water at the appropriate drug concentrations. TR-700 was dissolved in sterile dimethyl sulfoxide (DMSO) and diluted with medium to the appropriate concentration for in vitro susceptibility testing.In vitro susceptibility studies. The MICs of linezolid and TR-700 were determined three times in duplicate using Clinical and Laboratory Standards Institute (CLSI) microdilution methods M07-A8 (15). The duplicates were identical, and the final results were reported as the median value of the three MIC tests (see Table 1).Murine infection model. All animal studies were approved by the Animal Research Committees of the University of Wisconsin and William S. Middleton Memorial VA Hospital. Six-week-old, specific-pathogenfree, female ICR/Swiss mice weighing between 24 and 27 g (Harlan Sprague-Dawley, Indianapolis, IN) were used for all studies. Three mice were utilized for each treatment and control group. Mice were rendered neutropenic (absolute neutrophil count of Ͻ100/mm 3 ) by injecting cyclophosphamide (Mead Johnson Pharmaceuticals, Evansville, IN) intraperitoneally 4 days (150 mg/kg of body weight) and 1 day (100 mg/kg) prior to experimental infection. Previous studies have shown that this regimen produces persistent neutropenia in this animal model for 5 days (3). Broth cultures of freshly plated bacteria were grown to logarithmic phase. The inoculum for each organism was diluted to a 0.3 absorbance at 580 nm. Viable plate count confirmation of the inoculum ranged from 10 6 to 10 7 CFU/ml. Anima...