Efficacy of ceftriaxone and gentamicin given once a day by using human-like pharmacokinetics in treatment of experimental staphylococcal endocarditis

Community-onset bacteraemia of unknown origin: clinical characteristics, epidemiology and outcome

Bacteraemia of unknown origin is prevalent and has a high mortality rate. However, there are no recent reports focusing on this issue. From 2005 to 2011, all episodes of community onset bacteraemia of unknown origin (CO-BSI), diagnosed at a 700-bed university hospital were prospectively included. Risk factors for Enterobactericeae resistant to third-generation cephalosporins (3GCR-E), Pseudomonas aeruginosa, Staphylococcus aureus and Enterococcus spp, and predictors of mortality were assessed by logistic regression. Out of 4,598 consecutive episodes of CO-BSI, 745 (16.2 %) were of unknown origin. Risk factors for S. aureus were male gender (OR 2.26; 1.33-3.83), diabetes mellitus (OR 1.71; 1.01-2.91) and intravenous drug addiction (OR 17.24; 1.47-202); for P. aeruginosa were male gender (OR 2.19; 1.10-4.37) and health-care associated origin (OR 9.13; 3.23-25.83); for 3GCR-E was recent antibiotic exposure (OR 2.53; 1.47-4.35), while for enterococci, it was recent hospital admission (OR 3.02; 1.64-5.55). Seven and 30-day mortality were 8.1 % and 13.4 %, respectively. Age over 65 years (OR 2.13; 1.28-3.55), an ultimately or rapidly fatal underlying disease (OR 4.15; 2.23-7.60), bone marrow transplantation (OR 4.07; 1.24-13.31), absence of fever (OR 4.45; 2.25-8.81), shock on presentation (OR 10.48; 6.05-18.15) and isolation of S. aureus (OR 2.01; 1.00-4.04) were independently associated with mortality. In patients with bacteraemia of unknown origin, a limited number of clinical characteristics may be useful to predict its aetiology and to choose the appropriate empirical treatment. Although no modifiable prognostic factors have been found, management optimization of S. aureus should be considered a priority in this setting.

Once-daily gentamicin administration for community-associated methicillin resistant Staphylococcus aureus in an in vitro pharmacodynamic model: preliminary reports for the advantages for optimizing pharmacodynamic index

PURPOSE

Community-associated methicillin resistant Staphylococcus aureus (CAMRSA) infections are increasing. Although gentamicin (GEN) is usually susceptible against CA-MRSA, GEN is rarely considered for treatment as monotherapy. We employed an in vitro pharmacodynamic model (IVPDM) to compare efficacies of GEN against CA-MRSA with two dosing regimens [thrice-daily (TD), once-daily (OD)].

MATERIALS AND METHODS

Using two strains of CA-MRSA, we adopted IVPDM comprised of two-compartments with a surface-to-volume ratio of 5.34 cm(-1). GEN regimens were simulated with human pharmacokinetic data of TD and OD. Experiments were performed over 48 hours in triplicate for each strain and dosing regimen.

RESULTS

MICs of GEN for YSSA1 and YSSA15 were 1 and 2 mg/L, respectively. In OD, indices of peak/MIC were > 8.6 at least, in contrast to < 6.4 in TD. A > or = 3-log(10) reduction in CFU/mL was demonstrated prior to 4 hours in TD and OD, and continued until 8 hours for both strains. However, reductions in the colony counts at 24 and 48 hours were significantly larger for OD compared to TD in both strains (p < 0.001). During TD, resistance developed in YSSA1 and small colony variants (SCVs) were documented in YSSA15. No resistance or SCVs were observed during OD in both strains.

CONCLUSION

TD and OD showed the same killing slopes until 8 hours. After the 24 hours of experiments, OD of GEN would be advantageous not only in having more reductions in colony counts, but also suppressing the development of resistance or SCVs for 48 hours.

Determination of an inoculum effect with various cephalosporins among clinical isolates of methicillin-susceptible Staphylococcus aureus

Using 98 clinical methicillin-susceptible Staphylococcus aureus isolates of known beta-lactamase (Bla) type, we found a pronounced inoculum effect for cephalexin (mostly Bla type A and C strains), a mild inoculum effect for cephalothin (especially types B and C), and no inoculum effects for ceftriaxone and cefuroxime. Ceftobiprole showed the lowest MICs at a high inoculum but with a slight increase for Bla-positive versus Bla-negative strains. Since a potential therapeutic effect associated with a cephalosporin inoculum effect has been described, further studies are warranted.

Simulation of human gentamicin pharmacokinetics in an experimental Enterococcus faecalis endocarditis model

Significant differences between animal and human pharmacokinetics may be responsible for the conflicting results of experimental studies. This study determined the impact of human pharmacokinetic simulation (HPS) on gentamicin activity in an Enterococcus faecalis endocarditis model. The decrease in bacterial counts was greater with HPS than with a dose-equivalent regimen without HPS.