Breakthrough pneumococcal bacteremia in patients being treated with azithromycin and clarithromycin

Guidelines for the management of community-acquired pneumonia. Current recommendations and antibiotic selection issues

Numerous guidelines for CAP have been developed, and although each is different, many principles are common to all recommendations. A guideline should focus on a wide range of issues surrounding the delivery of care, including advice about when to admit patients to the hospital or ICU; which antibiotic regimens to select for specific patient populations; which pathogens to target in empiric therapy; which diagnostic tests to order; how to assess the importance of specific causative pathogens, such as drug-resistant pneumococci, atypical pathogens, and gram-negative pathogens; how to evaluate the response to therapy and when to switch responding patients to oral therapy; and how to prevent CAP effectively through appropriate use of immunization against pneumococcus and influenza. Currently, many new antibiotic choices have emerged in the macrolide, quinolone, beta-lactam, ketolide, and oxazolidinone classes, and specific issues surrounding selection of these agents must be considered. All of the available data can be synthesized into a disease management guideline, and current therapy in the United States generally is consistent with existing recommendations. This consistency not only has led to more uniformity in patient care, but also has led to measurable benefits in patient outcomes, including reduced mortality for hospitalized patients with CAP. Guidelines not only are a useful tool for managing patients with CAP, but also they serve the purpose of defining current issues in patient care and stimulating the search for new tools and management approaches for this important clinical problem.

Bacteriologic and clinical efficacy of high dose amoxicillin/clavulanate in children with acute otitis media

OBJECTIVES

To determine the bacteriologic and clinical efficacy of high dose amoxicillin/clavulanate (90/6.4 mg/kg/day) against common bacterial pathogens causing acute otitis media (AOM), including penicillin-resistant Streptococcus pneumoniae (PRSP).

METHODS

In this open label multicenter study, 521 infants and children with AOM [mean age, 18.6 months; age < 24 months, n = 375 (72%)] were treated with amoxicillin/clavulanate 90/6.4 mg/kg/day in two divided doses for 10 days. Bilateral otitis media, previous episodes of AOM, antibiotic treatment within 3 months and day-care attendance were recorded in 60.1, 35.7, 50.2 and 38.2% of the children, respectively. Tympanocentesis was performed before the first dose and repeated on Days 4 to 6 for all children with S. pneumoniae at 22 centers and for all children with any pathogen at 3 centers. Clinical response was assessed at end of therapy.

RESULTS

Pathogens were isolated from 355 (68%) of 521 enrolled children; 180 children underwent repeat tympanocentesis and were bacteriologically evaluable. Baseline pathogens were S. pneumoniae (n = 122 enrolled/93 bacteriologically evaluable), Haemophilus influenzae (n = 160/51), both (n = 37/32) and others (n = 36/4). Pathogens were eradicated from 172 (96%) of 180 bacteriologically evaluable children. Overall 122 (98%) of 125 isolates of S. pneumoniae were eradicated, including 31 (91%) of 34 PRSP isolates (penicillin MICs 2 to 4 micrograms/ml). Seventy-eight (94%) of 83 isolates of H. influenzae were eradicated. Symptoms and otoscopic signs of acute inflammation were completely resolved or improved on Days 12 to 15 in 263 (89%) of 295 clinically evaluable children with bacteriologically documented AOM.

CONCLUSIONS

On the basis of bacteriologic outcome on Days 4 to 6 and clinical outcome on Days 12 to 15, we found that high dose amoxicillin/clavulanate (90/6.4 mg/kg/day) was highly efficacious in children with AOM, including those most likely to fail treatment, namely children < 24 months of age and those with infectious caused by PRSP.

Macrolide-resistant Streptococcus pneumoniae in Canada during 1998-1999: prevalence of mef(A) and erm(B) and susceptibilities to ketolides

In this study (1998-1999), we collected 215 macrolide-resistant Streptococcus pneumoniae isolates from an ongoing Canadian Respiratory Organism Surveillance Study involving 23 centers representing all regions of Canada. The prevalence of erythromycin-resistant S. pneumoniae was 8% (215 of 2,688). Of the 215 isolates, 48.8% (105 of 215) were PCR positive for mef(A) and 46.5% (100 of 215) were PCR positive for erm(B). The ketolides telithromycin and ABT-773 demonstrated excellent activity against both mef(A) (MIC for 90% of strains [MIC(90)], 0.06 and 0.03 microg/ml, respectively) and erm(B) (MIC(90), 0.06 and 0.03 microg/ml, respectively) strains of S. pneumoniae.

The hidden impact of antibacterial resistance in respiratory tract infection. Clinical failures: the tip of the iceberg?

In pneumococcal meningitis, it is well accepted that resistance in Streptococcus pneumoniae compromises clinical outcome. However, the clinical impact of increasing resistance on community-acquired respiratory tract infections (RTIs) is less clear. Bacteriological eradication should be the aim of antimicrobial therapy. The pharmacodynamics (potency and pharmacokinetics) of an antimicrobial agent against the infecting pathogen can be used to predict the potential for bacterial eradication. Surveillance of clinical isolates from community-acquired RTIs shows that, in many countries, there is a trend towards an increasing prevalence of drug-resistant S. pneumoniae. Results from a number of published clinical trials suggest that resistance has not compromised the clinical efficacy of aminopenicillins when used at the correct dose. However, emerging data indicate that resistance is compromising the efficacy of some other routinely used antimicrobials. There are reports of clinical and bacteriological failure with macrolides and fluoroquinolones in patients with community-acquired pneumonia. Recent retrospective analyses and increasing sporadic reports of clinical failure with these agents may be more representative of the true situation. These reports suggest a need to reassess current empirical therapeutic recommendations for the treatment of community-acquired RTIs.

Comparative serum bactericidal activity of clarithromycin and azithromycin against macrolide-sensitive and resistant strains of Streptococcus pneumoniae

The serum pharmacodynamics of clarithromycin and azithromycin were studied against isolates of S. pneumoniae, including efflux resistant (M. phenotype) strains, by analyzing their serum bactericidal activity (SBA) over time. Normal healthy subjects were given a single 500 mg oral dose of these macrolides and serum samples were collected over 12 hrs. Paired isolates with MICs ranging from 0.25 ug/ml to 8.0 ug/ml were analyzed. Prolonged (at least 6 hrs) SBA was observed with clarithromycin for strains with MICs < or = 2.0 ug/ml. No SBA was observed in strains with MICs >or = 4.0 ug/ml. Azithromycin exhibited SBA for at least 6 hrs for strains up to a MIC = 0.5 ug/ml. No SBA was observed for isolates with MICs > or = 1.0 ug/ml. In contrast to azithromycin, clarithromycin exhibited SBA for at least one-half of its normal dosing interval against S. pneumoniae strains well above its current susceptibility breakpoint concentration of 0.25 microg/ml. These findings may have relevance to the ongoing debate as to the appropriate susceptibility breakpoints for the newer macrolides.