Antimicrobial susceptibility of multidrug-resistant Streptococcus pneumoniae strains with penicillin MICs of 8 to 32 mg/L

Cefditoren in upper and lower community-acquired respiratory tract infections

This article reviews and updates published data on cefditoren in the evolving scenario of resistance among the most prevalent isolates from respiratory tract infections in the community (Streptococcus pyogenes, Haemophilus influenzae, and Streptococcus pneumoniae). By relating the in vitro activity of cefditoren (in national and multinational surveillance and against isolates with emerging resistant genotypes/phenotypes) to its pharmacokinetics, the cefditoren pharmacodynamic activity predicting efficacy (in humans, animal models, and in vitro simulations) is analyzed prior to reviewing clinical studies (tonsillopharyngitis, sinusitis, acute exacerbations of chronic bronchitis, and community-acquired pneumonia) and the relationship between bacterial eradication and clinical efficacy. The high in vitro activity of cefditoren against the most prevalent respiratory isolates in the community, together with its pharmacokinetics (enabling a twice daily regimen) leading to adequate pharmacodynamic indexes covering all S. pyogenes, H. influenzae, and at least 95% S. pneumoniae isolates, makes cefditoren an antibiotic that will play a significant role in the treatment of respiratory tract infections in the community. In the clinical setting, studies carried out with cefditoren showed that treatments with the 400 mg twice daily regimen were associated with high rates of bacteriological response, even against penicillin-nonsusceptible S. pneumoniae, with good correlation between bacteriological efficacy/response and clinical outcome.

Enhanced in vivo activity of cefditoren in pre-immunized mice against penicillin-resistant S. pneumoniae (serotypes 6B, 19F and 23F) in a sepsis model

BACKGROUND

Specific antibodies are likely to be present before S. pneumoniae infection. We explored cefditoren (CDN) total and free values of serum concentrations exceeding the MIC (t>MIC) related to efficacy in a mice sepsis model, and the effect of specific gammaglobulins on in-vitro phagocytosis and in-vivo efficacy.

METHODOLOGY/PRINCIPAL FINDINGS

We used three pneumococcal isolates (serotype, MIC OF CDN): Strain 1 (6B, 1 microg/ml), Strain 2 (19F, 2 microg/ml) and Strain 3 (23F, 4 microg/ml). Hyperimmune serum (HS) was obtained from mice immunized with heat-inactivated strains. In-vitro, phagocytosis by HS diluted 1/10 in presence/absence of sub-inhibitory concentrations was measured by flow cytometry including fluorescent bacteria and a neutrophil cell line. In-vivo dose-ranging experiments with HS (dilutions 1/2-1/16) and CDN (6.25 mg/kg-100 mg/kg tid for 48 h) were performed to determine the minimal protective dilution/dose (highest survival) and the non-protective highest dilution/dose (highest mortality: HS-np dilution and CDN-np dose) over 7 days. Efficacy of CDN-np in animals pre-immunized with HS-np (combined strategy) was explored and blood bacterial clearance determined. The CDN measured protein binding was 86.9%. In-vitro, CDN significantly increased phagocytosis (vs. HS 1/10). In non pre-immunized animals, t>MIC values for CDN of approximately 35% (total) and approximately 19% (free) were associated with 100% survival. Significant differences in survival were found between HS-np alone (< or = 20%) or CDN-np alone (< or = 20%) vs. the combined strategy (90%, 60% and 60% for Stains 1, 2 and 3), with t>MIC (total/free) of 22.8%/14.3%, 26.8%/16.0%, and 22.4%/12.7% for Strains 1, 2 and 3, respectively. Prior to the second dose (8 h), median bacterial counts were significantly lower in animals surviving vs. dead at day 7.

CONCLUSIONS/SIGNIFICANCE

In mice (CDN protein binding similar to humans) total t>MIC values of approximately 35% (approximately 19% free) were efficacious, with a decrease in the required values in pre-immunized animals. This reinforces that immunoprotection to overcome resistance may provide lifesaving strategies.