Linezolid in prophylaxis against experimental aortic valve endocarditis due to Streptococcus oralis or Enterococcus faecalis

Pharmacokinetics of Linezolid and Ertapenem in experimental parapneumonic pleural effusion

Objective

To determine the extent of linezolid and ertapenem penetration into the empyemic fluid using a rabbit model of empyema.

Methods

An empyema was created via the intrapleural injection of Escherichia coli bacteria (ATCC 35218) into the pleural space of New Zealand white rabbits. After an empyema was verified by thoracocentesis, 24 hours post inoculation, linezolid (10 mg/kg) and ertapenem (60 mg/kg) were administered intravenously into 10 and 8 infected empyemic rabbits, respectively. Antibiotic levels were determined in samples of pleural fluid and blood serum, collected serially at 1, 2, 4, 6 and 8 hours, after administration each of the two antibiotics.

Results

Linezolid as well as ertapenem penetrate well into the empyemic pleural fluid, exhibiting a slower onset and decline compared to the corresponding blood serum levels. Equilibration between blood serum and pleural fluid compartments seems to occur at 1.5 hours for both linezolid and ertapenem, with peak pleural fluid levels (Cmax_pf of 2.02 ± 0.73 «mu»g/ml and Cmax_pf of 3.74 ± 1.39 «mu»g/ml, correspondingly) occurring 2 hours post antibiotics administration and decreasing very slowly thereafter. The serum concentrations for both antibiotics were significantly lower from the corresponding pleural fluid ones during the 8 hours collecting data, with the exception of samples collected at the 1^st hour (Cmax_serum of 2.1 ± 1.2 «mu»g/ml for linezolid and Cmax_serum of 6.26 ± 2.98 «mu»g/ml for ertapenem).

Conclusion

Pleural fluid levels of both antibiotics are inhibitory for common specified pathogens causing empyema.

[New anti-Gram+antibiotics: which role in infective endocarditis?]

Though the increased resistance to antibiotics observed worldwide is not a major concern in France, treatment of methicillin-resistant S. aureus has important limitations. New antibiotics have recently been marketed or will soon be (quinupristin-dalfopristin, linelozide, tigecyclin, daptomycin, ceftobiprole, dalbavancin). Their role, which has been documented in several forms of acute infections, remains to be established in infective endocarditis. At present, only treatment of methicillin-resistant S. aureus right-sided endocarditis justifies the use of daptomycin, preferably in association with rifampicin, when the use of vancomycin is not possible or contraindicated.

Single-dose oral amoxicillin or linezolid for prophylaxis of experimental endocarditis due to vancomycin-susceptible and vancomycin-resistant Enterococcus faecalis

Endocarditis prophylaxis following genitourinary or gastrointestinal procedures targets Enterococcus faecalis. Prophylaxis recommendations advocate oral amoxicillin (2 g in the United States and 3 g in the United Kingdom) in moderate-risk patients and intravenous amoxicillin (2 g) or vancomycin (1 g) plus gentamicin in high-risk patients. While ampicillin-resistant (or amoxicillin-resistant) E. faecalis is still rare, there is a concern that these regimens might fail against vancomycin-resistant and/or aminoglycoside-resistant isolates. The present study tested oral linezolid as an alternative. Rats with catheter-induced aortic vegetations were given prophylaxis simulating human pharmacokinetics of oral amoxicillin (2- to 3-g single dose), oral linezolid (600 mg, single or multiple oral doses every 12 h), or intravenous vancomycin (1-g single dose). Rats were then inoculated with the minimum inoculum infecting 90% of the animals (90% infective dose [ID(90)]) or with 10 times the ID(90) of the vancomycin-susceptible E. faecalis strain JH2-2 or the vancomycin-resistant (VanA phenotype) E. faecalis strain UCN41. Amoxicillin was also tested with two additional vancomycin-susceptible E. faecalis strains, 309 and 1209. Animals were sacrificed 3 days later. All the tested bacteria were susceptible to amoxicillin and gentamicin. Single-dose amoxicillin provided 100% protection against all four isolates at both the ID(90) and 10 times the ID(90). In contrast, linezolid required up to four consecutive doses to provide full protection against the vancomycin-resistant isolate. Vancomycin protected only against the vancomycin-susceptible strain. The high efficacy of single-dose oral amoxicillin suggests that this regimen could be used for prophylaxis in both moderate-risk and high-risk patients without additional aminoglycosides. Linezolid appears to be less reliable, at least against the vancomycin-resistant strain.