Activity of oral antibiotics in middle ear and sinus infections caused by penicillin-resistant Streptococcus pneumoniae: implications for treatment

Bacterial biofilms in the upper airway - evidence for role in pathology and implications for treatment of otitis media

Understanding the nature of the biofilm component in the pathogenesis of otitis media [OM] will likely have a meaningful influence on the development of novel strategies to prevent and/or treat this highly prevalent pediatric disease. The design of vaccine candidates for OM that currently focus on preventing colonization are predicated on the assumption that by reducing the burden of bacteria present in the pediatric nasopharynx, one could reduce or eliminate the likelihood of retrograde ascension of the Eustachian tube by bacteria from the nasopharynx to the middle ear. If effective, this strategy could prevent biofilms from ever forming in the middle ear. Additionally, gaining an improved understanding of the unique properties of bacteria resident within a biofilm and the proteins they express while growing as part of this organized community has the potential to identify novel and perhaps biofilm-specific molecular targets for the design of either therapeutic agents or vaccine candidates for the resolution of existing OM.

Bacteriology and antimicrobial susceptibility of pediatric chronic rhinosinusitis: a 6-year result of maxillary sinus punctures

PURPOSE

Few studies in the past decade have focused on antimicrobial resistance of bacteria in pediatric rhinosinusitis. This study aimed to characterize organisms cultured from pediatric chronic rhinosinusitis, as well as current resistance patterns of pathogens.

MATERIALS AND METHODS

The study was conducted from January 2001 to December 2006. Children with radiograph-proven chronic rhinosinusitis underwent maxillary sinus punctures to obtain pathogens and for analysis of antibiotic resistance.

RESULTS

The total 295 cultures obtained from 165 children yielded 399 isolates. The most common isolates were alpha-hemolytic Streptococcus (20.8%), Haemophilus influenzae (19.5%), Streptococcus pneumoniae (14.0%), coagulase-negative Staphylococcus (13.0%), and Staphylococcus aureus (9.3%). Anaerobes accounted for 8.0% of all isolates. Susceptibility rates of H influenzae for ampicillin and co-trimoxazole were 44.7% and 42.1%, respectively, in the first 3 years of the study and 25% and 40%, respectively, in the next 3 years. Susceptibility rates of S pneumoniae were 83.3% for penicillin, 0% for erythromycin, and 33.3% for clindamycin in the first 3 years and 73.7%, 5.3%, and 28.9%, respectively, in the latter 3 years.

CONCLUSION

This study showed a different pattern of antibiotic resistance in pediatric chronic rhinosinusitis as compared with previous studies in both children and adults. The resistance rate of H influenzae for ampicillin appears to be a growing problem in pediatric rhinosinusitis.

Pathogen shifts and changing cure rates for otitis media and tonsillopharyngitis

Pneumococcal conjugate vaccine use has caused a decrease in the incidence of recurrent and refractory acute otitis media in the United States and a shift in the predominant pathogens. Now Haemophilus influenzae is the most commonly isolated organism (about 60% of the total), and more than half the strains make beta-lactamase, rendering them resistant to amoxicillin. Penicillin nonsusceptible pneumococci, the main target of antibiotic therapy in the 1990s, has become a much less common isolate (10%- 25% of the total). These changes impact antibiotic selection for acute otitis media. Penicillin treatment of group A streptococcal tonsillopharyngitis does not meet the minimum United States Food and Drug Administration standards for first-line treatment, which is 85% or greater eradication at the end of therapy. Recent results with amoxicillin suggest its efficacy is also waning. Cephalosporins have the highest bacteriologic and clinical efficacy. This has implications for optimal antibiotic therapy.

Effect of erythromycin treatment delay on therapeutic outcome of experimental acute otitis media caused by Streptococcus pneumoniae

OBJECTIVE

To evaluate the effect of delayed administration of erythromycin in the course of acute otitis media caused by an erythromycin-susceptible Streptococcus pneumoniae strain in the gerbil model.

METHODS

The bacterium was inoculated by transbullar challenge in the middle ear (ME) and antibiotic treatment at different doses was administered at various times thereafter.

RESULTS

When 2.5 mg/kg of erythromycin was administered as a single dose 2, 5, 18 or 21 h post-inoculation (pi) the bacterial eradication rate was 55, 40, 0 and 0%, respectively. A higher dose (5 mg/kg) administered also as a single dose 2, 5, 18 and 21 h pi achieved bacterial eradication rates of 62.5, 43.8, 0 and 0%, respectively. Using a very high dose (50 mg/kg) repeated three times at 3 h intervals (total dose 150 mg/kg) and starting the treatment 21 h pi only achieved bacterial eradication in 25% of cases. The concentration of erythromycin achieved in the ME 90 min after administration of 5 mg/kg 5 or 21 h pi was very similar (0.74 and 0.79 mg/L) but the ME half-life was longer (98.2 min) with the early administration as compared with the delayed form (47.5 min), which could partially explain the different results. Further experiments showed that the failures observed with the delayed administration were not related to the time elapsed from antibiotic administration to ME sampling or selection of antibiotic-resistant mutants.

CONCLUSION

Bacteriological and clinical efficacies were significantly diminished if antibiotic administration was delayed.

In vitro activities of new ketolide, telithromycin, and eight other macrolide antibiotics against Streptococcus pneumoniae having mefA and ermB genes that mediate macrolide resistance

The comparative in vitro activity of a new ketolide, telithromycin (TEL), and eight other macrolide-lincosamide antibiotics (MLS) against 215 strains, of Streptococcus pneumoniae including penicillin-resistant isolates (PRSP), was determined by the agar dilution method. These strains were isolated from patients with pneumonia, otitis media, and purulent meningitis between 1995 and 1997. Two genes, mefA and ermB, that encode MLS resistance in the strains were identified by polymerase chain reaction (PCR). Of the strains, 30.2% (n = 65) had the mefA gene, 37.7% (n = 81) had the ermB gene, and 1.4% (n = 3) had both resistant genes. The minimum inhibitory concentration (MIC90s) of TEL and 16-membered ring MLS for strains having the mefA gene were 0.063-0.25 microg/ml, which were the same level as those for MLS-susceptible strains. On the other hand, the strains with the mefA gene showed low-level resistance to 14- and 15-membered ring MLS, with MIC90s ranging from 1 to 4 microg/ml. Only the MIC90 of TEL at 0.5 microg/ml, for strains having the ermB gene was superior to that of the 14-, 15-, and 16-membered ring MLS (MIC90, > or =64 microg/ml). TEL also showed excellent activity against PRSP having abnormal pbp1a, pbp2x, and pbp2b genes. Most strains having the mefA and ermB genes were serotyped to 3, 6, 14, 19, and 23. These results suggest that TEL may be a useful chemotherapeutic agent for respiratory tract infections caused by S. pneumoniae.

Bacteriologic and clinical efficacy of high dose amoxicillin for therapy of acute otitis media in children

BACKGROUND

High dose (70 to 90 mg/kg/day) amoxicillin is recommended as first line therapy of acute otitis media (AOM) in geographic areas where drug-resistant Streptococcus pneumoniae is prevalent. Information on the bacteriologic efficacy of high dose amoxicillin treatment for AOM is limited.

OBJECTIVES

To evaluate the bacteriologic and clinical efficacy of high dose amoxicillin as first line therapy in AOM.

METHODS

In a prospective study 50 culture-positive patients ages 3 to 22 months (median, 9 months; 77% <1 year) were treated with high dose amoxicillin (80 mg/kg/day three times a day for 10 days) No antibiotics were administered 72 h before enrollment. Twenty-four (48%) patients presented with their first episode of AOM. Middle ear fluid was cultured by tympanocentesis at enrollment and on Days 4 to 6 of therapy. Additional middle ear fluid cultures were obtained if clinical relapse occurred. Bacteriologic failure was defined by positive cultures on Days 4 to 6 and clinical failure by no change or worsening of AOM signs and symptoms and requirement for additional antibiotics during therapy and/or at end of therapy. Patients were followed until Day 28 +/- 2. Susceptibility to penicillin and amoxicillin was measured by E-test.

RESULTS

Sixty-five organisms were recovered at enrollment: Haemophilus influenzae (38), Streptococcus pneumoniae (24), Streptococcus pyogenes (2) and Moraxella catarrhalis (1). Eighteen (75%) S. pneumoniae were nonsusceptible to penicillin (MIC > 0.1 microg/ml). All 24 S. pneumoniae isolates had amoxicillin MIC < or = 2.0 microg/ml. Thirteen (34%) of the 38 H. influenzae were beta-lactamase producers. Eradication was achieved in 41 (82%) patients for 54 of 65 (83%) pathogens: 22 of 24 (92%) S. pneumoniae, 21 of 25 (84%) beta-lactamase-negative H. influenzae, 8 of 13 (62%) beta-lactamase-positive H. influenzae, 2 of 2 S. pyogenes and 1 of 1 M. catarrhalis. Seven organisms not initially present were isolated on Days 4 to 6 in 5 patients: 3 beta-lactamase-positive H. influenzae; 1 beta-lactamase-negative H. influenzae; 2 S. pneumoniae; and 1 M. catarrhalis. In total 14 of 50 (28%) patients failed bacteriologically on Days 4 to 6 (persistence + new infection), of whom 9 (64%) had beta-lactamase-positive H. influenzae. Three (33%) of the 9 patients with bacteriologic failure (2 beta-lactamase-positive H. influenzae, 1 S. pneumoniae) failed also clinically on Days 4 to 6.

CONCLUSIONS

The predominant pathogens isolated from children with AOM failing high dose amoxicillin therapy were beta-lactamase-producing organisms. Because its overall clinical efficacy is good, high dose amoxicillin is still an appropriate choice as first line empiric therapy for AOM, followed by a beta-lactamase-stable drug in the event of failure.

Otitis media

Bacterial pathogens are isolated from middle ear fluid in up to 90% of children with acute otitis media (OM). Streptococcus pneumoniae, Haemophilus influenzae and Moraxella catarrhalis predominate. Acute OM can be classified as uncomplicated, persistent, recurrent or chronic. Patient age, symptom severity, prior treatment history and exposure through day-care attendance in children influences pathogen distribution, antimicrobial susceptibility and anticipated clinical and microbiological responses to empirical and pathogen-directed therapies. The natural history of acute OM without intervention is favourable. However, meta-analysis of clinical trials shows an improvement in symptom and middle ear effusion resolution with antimicrobials. Aminopenicillins, cephalosporins and macrolides are often selected as therapy for acute OM. The various agents have differing activity against acute OM pathogens, particularly organisms with resistance mechanisms and they differ in dosing schedule, side effects and compliance enhancing factors. Consideration should be given to pharmacokinetic and pharmacodynamic principles in antibiotic selection. Selection criteria include antibiotic activity against drug-resistant S. pneumoniae and efficacy against beta-lactamase-producing Gram-negative organisms. The necessary duration of treatment for acute OM varies according to multiple factors, including local preferences, but there is growing, compelling data to support short-course therapy. Tympanocentesis has been endorsed in various guidelines as a diagnostic and therapeutic procedure. Best-practice for management of acute OM continues to advocate antibiotic therapy with careful, accurate diagnosis and consideration of the major pathogens and their mechanisms of resistance.

Antibiotic-resistant bacteria in pediatric chronic sinusitis

BACKGROUND

Limited information exists on emerging bacterial resistance patterns in pediatric chronic sinusitis.

METHODS

A retrospective review (1995 to 1998) of the aerobic microbiology of chronic sinusitis in children at a tertiary care children's hospital was conducted. One hundred nineteen children (mean age, 4.9 years) with maxillary sinusitis of >8 weeks duration and no known immunodeficiency or cystic fibrosis who underwent antral irrigation were included.

RESULTS

One hundred sixty-one of 240 (67%) aerobic cultures were positive, yielding 274 isolates. Eighty-eight positive cultures were polymicrobial. The most frequent isolates were nontypable Haemophilus influenzae (24%), Streptococcus pneumoniae (19%), Moraxella catarrhalis (17%), coagulase-negative Staphylococcus (6%), alpha-streptococci (6%), diphtheroids (5%), Staphylococcus aureus (3%) and Neisseria spp. (3%). Rates of nonsusceptibility of Streptococcus pneumoniae were 64% for penicillin (24% high grade resistance), 40% for cefotaxime, 18% for clindamycin and 0% for vancomycin. Rates of nonsusceptibility of S. pneumoniae did not change significantly during the study period. Thirty-nine percent of H. influenzae isolates were beta-lactamase-positive and 44% were nonsusceptible to ampicillin (41% high grade resistance). Beta-lactamase positivity of H. influenzae decreased during the study period (P = 0.06). All M. catarrhalis isolates tested were beta-lactamase-positive.

CONCLUSION

This study indicates that the aerobic pathogens in pediatric chronic sinusitis include bacteria typical of acute sinusitis as well as organisms more characteristic of chronic disease. Moreover it highlights the significant role of antibiotic-resistant aerobes, including multiply resistant S. pneumoniae, in pediatric chronic sinusitis.

Cefprozil versus high-dose amoxicillin/clavulanate in children with acute otitis media

BACKGROUND

The recommendation of the Drug-Resistant Streptococcus pneumoniae Therapeutic Working Group that high-dose amoxicillin, with or without clavulanate, be used to treat acute otitis media (AOM) addressed concerns about the efficacy of existing therapies against drug-resistant S. pneumoniae. This recommendation relied on pharmacodynamic predictions of concentrations of amoxicillin in middle-ear fluid remaining higher than minimum inhibitory concentrations against intermediately resistant S. pneumoniae for >40% of the dosing interval.

OBJECTIVE

This study compared the tolerability and efficacy of cefprozil and high-dose amoxicillin/clavulanate in patients with AOM.

METHODS

Patients were randomized to receive 10 days of investigator-blinded oral treatment with either cefprozil suspension (30 mg/kg/d in 2 divided doses) or amoxicillin/clavulanate (45/6.4 mg/kg/d) plus amoxicillin (45 mg/kg/d) in 2 divided doses. The primary efficacy end point was the clinical cure rate 4 to 7 days after the end of treatment. Clinical response by age (6 months-<2 years vs > or =2-7 years), disease severity, and unilateral versus bilateral ear infection was also examined. The primary measures of tolerability were the frequency and severity of adverse events and their relation to study drug. Adverse events were either spontaneously reported or elicited during examination and questioning of the patient. Identified adverse events were coded and recorded using the COSTART (Coding Symbols for Thesaurus of Adverse Reaction Terms) system.

RESULTS

Three hundred four children between the ages of 6 months and 7 years with > or =1 sign or symptom of AOM were enrolled in the study, and 303 (150 cefprozil, 153 amoxicillin/clavulanate) were treated. Twenty-three patients in each treatment group were not evaluable; thus, 257 children were included in the analysis of evaluable patients. Clinical cure rates were 87% (110/127) with cefprozil and 89% (116/130) with amoxicillin/clavulanate (95% CI for the difference in cure rate, -10.7% to 4.1%). No between-group differences in efficacy were noted by age, disease severity, or unilateral or bilateral involvement. The overall incidence of drug-related adverse events was significantly lower with cefprozil than with amoxicillin/clavulanate (19% vs 32%, respectively; P = 0.008), as was the incidence of diarrhea (9% vs 19%, respectively; P = 0.021). Adverse events prompted discontinuation of therapy in 4 (3%) cefprozil patients and 8 (5%) amoxicillin/clavulanate patients.

CONCLUSIONS

Based on a search of MEDLINE, this study is the first direct comparison of cefprozil versus high-dose amoxicillin/clavulanate. Cefprozil was as effective as high-dose amoxicillin/clavulanate, with a lower incidence of adverse events.

Effects of amoxicillin/clavulanate or azithromycin on nasopharyngeal carriage of Streptococcus pneumoniae and Haemophilus influenzae in children with acute otitis media

The effect of antibiotic therapy on nasopharyngeal colonization by Streptococcus pneumoniae and Haemophilus influenzae was evaluated in children diagnosed with acute otitis media. Children were randomly assigned to receive either amoxicillin/clavulanate or azithromycin therapy, and nasopharyngeal swabs were obtained for culture before and after starting therapy. Amoxicillin/clavulanate therapy eradicated or suppressed all strains of S. pneumoniae susceptible to penicillin, 75% of strains with intermediate resistance, and 40% of strains resistant to penicillin. Azithromycin therapy cleared two-thirds of azithromycin-susceptible strains of S. pneumoniae but none of azithromycin-nonsusceptible strains. Selection for antibiotic-resistant strains in individual children was not observed in children who received amoxicillin/clavulanate therapy but was observed in 2 children who received azithromycin therapy. Carriage of H. influenzae was also reduced by antimicrobial therapy but more so by amoxicillin/clavulanate. Antibiotic therapy does not directly increase the number of resistant strains in the population but, by eradicating susceptible strains, allows greater opportunity for carriage and spread of resistant strains.

Antipneumococcal activity of ABT-773 compared to those of 10 other agents

MICs, time-kills, and postantibiotic effects (PAEs) of ABT-773 (a new ketolide) and 10 other agents were determined against 226 pneumococci. Against 78 ermB- and 44 mefE-containing strains, ABT-773 MICs at which 50% of the isolates tested were inhibited (MIC(50)s) and MIC(90)s were 0.016 to 0.03 and 0.125 microgram/ml, respectively. Clindamycin was active only against macrolide-resistant strains containing mefE (MIC(50), 0.06 microgram/ml; MIC(90), 0.125 microgram/ml). Activities of pristinamycin (MIC(90), 0.5 microgram/ml) and vancomycin (MIC(90), 0.25 microgram/ml) were unaffected by macrolide or penicillin resistance, while beta-lactam MICs rose with those of penicillin G. Against 19 strains with L4 ribosomal protein mutations and two strains with mutations in domain V of 23S rRNA, ABT-773 MICs were 0.03 to 0.25 microgram/ml, while macrolide and azalide MICs were all >/=16.0 microgram/ml. ABT-773 was bactericidal at twice the MIC after 24 h for 8 of 12 strains (including three strains with erythromycin MICs greater than or equal to 64.0 microgram/ml). Kill kinetics of erythromycin, azithromycin, clarithromycin, and roxithromycin against macrolide-susceptible strains were slower than those of ABT-773. ABT-773 had longer PAEs than macrolides, azithromycin, clindamycin, or beta-lactams, including against ermB-containing strains. ABT-773, therefore, shows promising in vitro activity against macrolide-susceptible as well as -resistant pneumococci.

Antibiotic-resistant pneumococci in pediatric disease

The surveillance of pneumococcal resistance in nasopharyngeal isolates is a practical way to determine the prevalence of resistant strains and is a reasonable predictor of resistance in systemic isolates. The increasing prevalence of resistance is shifting the distribution of invasive pneumococcal serotypes toward those included in conjugate vaccines. If these vaccines reduce carriage, they may eliminate or greatly reduce the prevalence of resistant strains. Meningitis is the most important infection caused by PRP for which penicillin or ampicillin therapy is inappropriate. Although the extended spectrum cephalosporins will be effective for most cases of PRP meningitis, it is clear that such therapy is not foolproof. It is important for the laboratory to test CSF isolates not only for penicillin resistance but also for resistance to the cephalosporins. beta-Lactam antibiotics can still be considered appropriate empiric therapy for otitis media, pneumonia, or sepsis. However, occasional treatment failures with these agents may necessitate use of alternative therapeutic strategies.

Epidemiology of resistant pneumococci in Hungary

Data on resistance in Streptococcus pneumoniae was analyzed in cohorts of isolates from nasal carriers without respiratory tract infection, nose-throat swabs, and ear fluid specimens of children, from sputum and bronchoalveolar lavage of adults and central spinal fluid, blood, and pleural fluid of patients without a distinction of age group. Colonizing strains in infant carriers showed a higher resistance rate (47.5%) to penicillin than in other children (24.2%). Isolates of inpatients, predominantly infants with respiratory tract infection, presented a higher prevalence of resistance than outpatients in all age groups. Adults showed the lowest resistance rates. Resistance was rarer among S. pneumoniae isolates from patients with systemic infection. The few cases caused by resistant S. pneumoniae should raise concern. Resistance among strains from ear fluid was more prevalent in all investigated population groups than among isolates from throat-nose swabs. The similarity of resistance rates to erythromycin and penicillin was associated with frequent combined resistance. While the prevalent serotype among the resistant strains was 19A, no predominant serotype was found among the susceptible strains.

New prospects for antibacterial agents against multidrug-resistant pneumococci

Since the first description of penicillin-resistant pneumococci nearly 30 years ago, drug-resistance has become widespread throughout the world. This review focuses upon the in vitro susceptibility of penicillin-susceptible and -resistant pneumococci to new and existing agents.

Pneumococcal acute otitis media in children

OBJECTIVES

To evaluate the clinical and laboratory findings of Streptococcus pneumoniae acute otitis media in children during a 1 year period.

METHODS

From October 1995 to September 1996, 113 children aged 2 months to 14 years (median 18 months), with S. pneumoniae acute otitis media were studied. Susceptibility testing was performed by the Kirby-Bauer method and the E-test, and serotyping by the Quellung reaction.

RESULTS

E-test assays detected five isolates (4.4%) to be highly resistant to penicillin and 13 (11.5%) that had intermediate resistance. All isolates were found to be susceptible to vancomycin, rifampicin and cefotaxime. In total, 25 isolates (22.1%) were resistant to one or more drugs. Fifty per cent of the penicillin-resistant or intermediately resistant S. pneumoniae isolates were resistant to multiple drugs, whereas only 2.1% of the penicillin-susceptible isolates were resistant to multiple drugs. The predominating serogroups of the isolates with reduced susceptibility to penicillin were the 19 (61.1%), 9 (16.7%), 23 (11.1%), 6 (5.5%) and 14 (5.5%) whereas those of the susceptible isolates were the 19 (26.3%), 14 (13.7%), 3 (11.6%), 6 (11.6%), 9 (8.4%), 1 (5.3%) and 12 (5.3%).

CONCLUSIONS

Streptococcus pneumoniae isolates from children with acute otitis media were penicillin-insensitive in 15.9%. The multiresistant S. pneumoniae isolates belonged to serogroups: 19 (45.4%), 9 (27.3%), 6 (18.2%) and 23 (9.1%).

Antimicrobial therapy of acute otitis media: review of treatment recommendations

OBJECTIVE

This paper reviews 3 previously published articles that provided recommendations for antimicrobial therapy of acute otitis media (AOM) and combines them to provide revised recommendations.

BACKGROUND

AOM is one of the most common pediatric infections requiring a prescription for an antimicrobial agent. The optimal approach to treatment of AOM requires early, efficacious, and practical therapy. Several experts and organizations have developed recommendations for the management of AOM, but the number of these may overwhelm the busy primary care practitioner. A MEDLINE search of the pediatric and infectious disease literature on AOM treatment recommendations was used to select 3 representative, previously published articles for this review. When selecting an agent, physicians should consider in vitro activity, particularly against drug-resistant Streptococcus pneumoniae; pharmacokinetics; adverse events; palatability of the suspension; and cost. In addition, physicians' clinical experience is an important determinant.

CONCLUSIONS

Amoxicillin is recommended as the first-line agent to treat uncomplicated AOM. For clinical treatment failures after 3 days of amoxicillin, recommended antimicrobial agents include oral amoxicillin/clavulanate, cefuroxime axetil, cefprozil, cefpodoxime proxetil, and intramuscular (i.m.) ceftriaxone. I.m. ceftriaxone should be reserved for severe cases or patients in whom noncompliance is expected. Tympanocentesis for identification of pathogens and susceptibility to antimicrobial agents is recommended for selection of third-line agents.

Comparison of agar dilution, microdilution, E-test, and disk diffusion methods for testing activity of cefditoren against Streptococcus pneumoniae

This study evaluated the susceptibility of pneumococci to cefditoren by agar dilution and microdilution methods (both in air) and by E-test (AB Biodisk, Solna, Sweden) and disk diffusion methods (both in CO(2)). By the three MIC tests, the MICs at which 50 and 90% of isolates were inhibited (MIC(50)s and MIC(90)s) were, respectively, as follows (in micrograms per milliliter): for the 65 penicillin-susceptible strains tested, 0.016 and 0.03 (by agar dilution), 0.016 and 0.03 (by microdilution), and 0.016 and 0.03 (by E test); for the 68 penicillin-intermediate strains tested, 0.125 and 0.5 (by agar dilution), 0.125 and 0.5 (by microdilution), and 0. 25 and 0.5 (by E test); and for the 67 penicillin-resistant strains tested, 1.0 and 1.0 (by agar dilution), 0.5 and 1.0 (by microdilution), and 1.0 and 1.0 (by E test). With tentative cefditoren breakpoints (in micrograms per milliliter) of /=8.0 (resistant), all strains were susceptible to cefditoren by agar, microdilution, and E-test results; with breakpoints of /=4.0 microg/ml, 97% of strains were cefditoren susceptible by agar dilution results, 98% were susceptible by microdilution results, and 99% were susceptible by E-test results. When microdilution and E-test results were compared to those from the reference agar dilution method, 191 (95.5%) and 183 (91.5%) of strains gave essential agreement (+/-1 log(2) dilution); 8 (2.7%) minor discrepancies were found for both methods with a breakpoint of /=20 (susceptible), 17 to 19 (intermediate), and /=16 mm (susceptible). All three methods for testing the MIC of cefditoren showed excellent correlation.

Prevalence of mefE, erm and tet(M) genes in Streptococcus pneumoniae strains from Central Italy

One hundred and seventy-three Streptococcus pneumoniae strains isolated from surveillance studies conducted in daycare centres were studied. The mefE, erm and tet(M) genes were detected in 16.2, 45.1 and 47.4% of isolates respectively. Agreement between PCR results and antibiotic susceptibility patterns was 100%. Macrolide resistance was due to the presence of erm in 73.6% of strains and to the presence of mefE in the remaining 26.4%. All tetracycline resistant strains carried the tet(M) gene. erm was associated with tet(M) in 98.7% of strains, whereas no isolate carrying mefE carried tet(M). A significant association was found between mefE and serogroup 6 (P < 0.0005) and between erm and tet(M) and serogroup 19 (P < 0.00001).

Penicillin-nonsusceptible pneumococcus in acute otitis media in New York City

OBJECTIVE

To determine the proportion of children with acute otitis media (AOM) presenting in our catchment area in New York City who were infected with nonsusceptible Streptococcus pneumoniae and to determine the susceptibility of these organisms to penicillins and other antibiotics commonly used to treat AOM.

SETTING

Ambulatory clinics and the emergency department of a tertiary care, inner-city medical center.

PATIENTS

During a 2-year period from 1993 to 1995, 115 children (aged 6 months to 12 years) with AOM underwent tympanocentesis. Patients did not receive antibiotics for at least 1 week before tympanocentesis.

RESULTS

Thirty-one children were infected with S pneumoniae, and 83.9% of isolates were susceptible to penicillin. Of the 16.1% strains that were nonsusceptible, most (4 of 5 strains) were intermediately resistant, and only 1 exhibited high-level resistance to penicillin. Of all the cephalosporins tested, only cefotaxime had consistent activity against the intermediately resistant strains. Notably, all nonsusceptible pneumococci were inhibited by macrolides.

CONCLUSIONS

This study provides unique reference data for nonsusceptible Streptococcus pneumoniae in children with AOM and documents that newer cephalosporin agents are not active against all of these strains.

Documentation of the prevalence of penicillin-resistant Streptococcus pneumoniae isolated from the middle ear and sinus fluid of children undergoing tympanocentesis or sinus lavage

With increasing pneumococcal resistance to penicillin and other antibiotics, use of antibiotic therapy for children with upper respiratory tract infections such as otitis media and sinusitis has become difficult. Selecting an appropriate treatment regimen has become more challenging due to frequent concomitant microbial resistance to multiple antibiotics. In a prospective, nonrandomized study, we obtained middle ear and sinus aspirate specimens from all children undergoing outpatient tympanocentesis or sinus lavage for any indication at our institution over two 4-week periods. One hundred fifty-four specimens were obtained. Of these, 12 grew Streptococcus pneumoniae, 7 of which were resistant to penicillin. A 6-month retrospective review of these patients' medical histories evaluated their antibiotic use prior to surgical intervention. An association between penicillin resistance and recent use of 2 or more antibiotics in children with positive S pneumoniae cultures was confirmed, as has been documented in prior reports. Those with penicillin-resistant S pneumoniae also demonstrated a higher incidence of multidrug-resistant organisms.

Drug-resistant Streptococcus pneumoniae: rational antibiotic choices

Increasingly, Streptococcus pneumoniae with reduced susceptibility to penicillin is becoming a healthcare concern, not only because of the high prevalence of infections caused by this pathogen but also because of the rate at which resistance has progressed. The incidence of penicillin resistance in strains of S. pneumoniae approaches 40% in some areas of the United States, and the incidence of high-level resistance has increased by 60-fold during the past 10 years. With the exception of meningitis and otitis media, there is no conclusive evidence that the acquisition of resistance by S. pneumoniae to beta-lactam antibiotics incurs greater morbidity and mortality in infections caused by this pathogen. However, if the current trends of resistance patterns continue, one can expect the morbidity and mortality to increase. The mechanism of beta-lactam resistance of S. pneumoniae involves genetic mutations which alter penicillin-binding protein structure, resulting in a decreased affinity for all beta-lactam antibiotics. In the treatment of infections caused by S. pneumoniae, it should not be assumed that nonsusceptibility to beta-lactam antibiotics correlates with clinical ineffectiveness of these agents. On the contrary, the recommended therapy for nonmeningeal pneumococcal infections (e.g., pneumonia, sepsis, acute otitis media) includes a beta-lactam antibiotic: penicillin G, amoxicillin, amoxicillin/clavulanate, cefuroxime, cefotaxime, or ceftriaxone. Recommended therapy for meningitis is cefotaxime or ceftriaxone, with the addition of vancomycin until susceptibility is known. These agents are recommended because of their ability to achieve serum/tissue concentrations greater than the minimum inhibitory concentrations (MICs) of these agents against penicillin-susceptible, penicillin-intermediate, and most penicillin-resistant strains (e.g., penicillin G, cefotaxime, ceftriaxone, amoxicillin, amoxicillin/clavulanate, and cefuroxime), or their ability to provide adequate concentrations in cerebrospinal fluid (e.g., cefotaxime, ceftriaxone).

Streptococcus pneumoniae: Activity of Newer Agents Against Penicillin-Resistant Strains

Strains of pneumococci resistant to antimicrobial agents have been reported on all continents. In 1997, more than 50% of strains in the United States were not susceptible to penicillin, and 30% were resistant to macrolides. In addition, many strains are resistant to multiple agents, including beta-lactams, macrolides, clindamycin, chloramphenicol, tetracyclines, and trimethoprim-sulfamethoxazole. Although resistance to beta-lactams in nonmeningeal infections can usually be overcome by parenteral administration, clinically significant resistance is an important limitation in meningitis and with oral administration of beta-lactams. Decisions about treatment of pneumococcal infection are based on the site of infection, the degree of resistance to penicillin G, the presence of resistance to other agents, the severity of disease, the presence of underlying conditions, and the dose and route of administration of antimicrobial agents. The application of pharmacokinetic and pharmacodynamic variables to pneumococci has greatly improved the interpretation of susceptibility data and the development of clinically relevant breakpoints.

Management of infections due to antibiotic-resistant Streptococcus pneumoniae

Antibiotic-resistant strains of Streptococcus pneumoniae are becoming more prevalent throughout the world; this has resulted in modifications of treatment approaches. Management of bacterial meningitis has the greatest consensus. Strategies for treating other systemic infections such as pneumonia, bacteremia, and musculoskeletal infections are evolving, in part related to the availability of new antibiotics which are active in vitro against isolates resistant to penicillin and the extended-spectrum cephalosporins. However, there are currently very limited data related to the clinical efficacy of these new agents. The studies upon which current recommendations are based are reviewed. Otitis media represents the single most common infection due to S. pneumoniae. Recommendations for treatment of acute otitis media due to drug-resistant strains and the rationale for these recommendations are discussed.

What role for antibiotics in otitis media and sinusitis?

In patients with otitis media or sinusitis, antibiotics must be used judiciously. First-line treatment for both uncomplicated acute otitis media and acute sinusitis is amoxicillin. Erythromycin ethylsuccinate and sulfisoxazole or TMP-SMZ may be used in patients who are allergic to penicillin. Beta-lactamase-stable agents should be given when no response occurs within 48 to 72 hours. In cases in which penicillin-resistant pneumococcus is suspected, high-dose amoxicillin, with or without clavulanate, or clindamycin should be considered. Antibiotics are not indicated for initial treatment of otitis media with effusion but may be considered for effusions lasting longer than 3 months. Prophylactic antibiotics should be considered only for recurrent acute infections occurring three or more times within 6 months or four or more times within a year. The common cold should not be treated with antibiotics, and antimicrobial therapy should be initiated only when there is reasonable clinical certainty about the presence of acute sinusitis.

Management of acute otitis media caused by resistant pneumococci in infants

OBJECTIVES

To assess the clinical outcome and risk of failure after oral vs. intravenous treatment in otitis media caused by penicillin-resistant pneumococci. To determine the possible correlations between pneumococcal minimal inhibitory concentration (MIC) to penicillin and clinical outcome.

DESIGN

Retrospective study of 156 cases collected between 1993 and 1995. Mean follow-up: 5 months. Setting. Two tertiary academic medical centers in Paris, France.

PATIENTS AND METHODS

Pneumococcus was isolated from 191 of 570 ear samples obtained from children with otitis media and shown to be penicillin-resistant in 156. Medical history, antibiotic therapy during the previous 3 months and day-care center attendance were reviewed. For the current episode microbiologic characteristics of the isolated strains, type of treatment, therapy efficacy and clinical outcome were analyzed. Patients were predominantly young (76.3% were <1 year old) and bacteriologic samples were taken mainly because of previous treatment failure.

RESULTS

Among 156 children with pneumococcal penicillin-resistant otitis media, 72.2% attended day-care centers, 71.8% had been previously treated with aminopenicillin and 52.5% with cephalosporins. Failure of previous empirical oral therapy was noted in 84% (one-third of these had been receiving amoxicillin-clavulanate). Patients treated intravenously had had a more protracted otitis but no greater number of previous episodes of acute otitis media than those receiving oral therapy. Acute mastoiditis occurred in 4 infants resulting in mastoidectomy. Oral treatment (mainly with high dose amoxicillin,120 to 150 mg/kg/day) and intravenous therapy (cephalosporin or glycopeptide) had been used in 59 and 41%, respectively. Mean duration of therapy was 10.7 days. Three failures (1.9%) and 10 recurrences (6.4%, average 28 days) occurred. No statistical difference was found between intravenous and oral therapy with respect to risk of recurrence. A high penicillin MIC value was correlated with previous antibiotic treatment but not with clinical outcome.

CONCLUSIONS

Oral therapy appears to be as effective as intravenous therapy for the treatment of penicillin-resistant pneumococcal otitis media. Intravenous treatment should not necessarily be dictated by the penicillin susceptibility value but should be considered in cases of failure to thrive, persistent otitis or other complications.

In vivo efficacies of amoxicillin and cefuroxime against penicillin-resistant Streptococcus pneumoniae in a gerbil model of acute otitis media

The comparative efficacies of amoxicillin and cefuroxime against acute otitis media caused by a penicillin-resistant (MIC, 2 micrograms/ml) Streptococcus pneumoniae strain were assessed in a gerbil model by challenging each ear with 10(7) bacteria through transbullar instillation. Each antibiotic was tested at two doses (5 and 20 mg/kg of body weight) administered at 2, 10, and 18 h postinoculation. Samples were obtained from the middle ear (ME) on days 3 and 7 postinoculation for determination of bacterial counts. Only amoxicillin, at both doses, was able to significantly halt the weight loss in animals, reducing both the number of culture-positive animals and the bacterial concentration in ME samples versus the values for untreated animals. Comparison of the efficacies between the antibiotics, determined by their ability to achieve culture-negative ME specimens, showed that amoxicillin at 5 mg/kg was significantly more active than cefuroxime at the same dose. The use of higher doses of either amoxicillin or cefuroxime did not produce significantly better results than those obtained with the lower dose but caused a greater inflammatory response. The more favorable results obtained with amoxicillin compared with those obtained with cefuroxime could be related to the antimicrobial susceptibility of the pneumococcal strain (MICs and minimum bactericidal concentrations of 1 and 1 microgram/ml and 4 and 4 micrograms/ml for amoxicillin and cefuroxime, respectively) as well as to the better pharmacokinetic parameters obtained with amoxicillin.

Susceptibilities of penicillin- and erythromycin-susceptible and -resistant pneumococci to HMR 3647 (RU 66647), a new ketolide, compared with susceptibilities to 17 other agents

Susceptibility of 230 penicillin- and erythromycin-susceptible and -resistant pneumococci to HMR 3647 (RU 66647), a new ketolide, was tested by agar dilution, and results were compared with those of erythromycin, azithromycin, clarithromycin, roxithromycin, rokitamycin, clindamycin, pristinamycin, ciprofloxacin, sparfloxacin, trimethoprim-sulfamethoxazole, doxycycline, chloramphenicol, cefuroxime, ceftriaxone, imipenem, and vancomycin. HMR 3647 was very active against all strains tested, with MICs at which 90% of the strains were inhibited (MIC90s) of 0.03 microg/ml for erythromycin-susceptible strains (MICs, < or =0.25 microg/ml) and 0.25 microg/ml for erythromycin-resistant strains (MICs, > or =1.0 microg/ml). All other macrolides yielded MIC90s of 0.03 to 0.25 and >64.0 microg/ml for erythromycin-susceptible and -resistant strains, respectively. The MICs of clindamycin for 51 of 100 (51%) erythromycin-resistant strains were < or =0.125 microg/ml. The MICs of pristinamycin for all strains were < or =1.0 microg/ml. The MIC90s of ciprofloxacin and sparfloxacin were 4.0 and 0.5 microg/ml, respectively, and were unaffected by penicillin or erythromycin susceptibility. Vancomycin and imipenem inhibited all strains at < or =1.0 microg/ml. The MICs of cefuroxime and cefotaxime rose with those of penicillin G. The MICs of trimethoprim-sulfamethoxazole, doxycycline, and chloramphenicol were variable but were generally higher in penicillin- and erythromycin-resistant strains. HMR 3647 had the best kill kinetics of all macrolides tested against 11 erythromycin-susceptible and -resistant strains, with uniform bactericidal activity (99.9% killing) after 24 h at two times the MIC and 99% killing of all strains at two times the MIC after 12 h for all strains. Pristinamycin showed more rapid killing at 2 to 6 h, with 99.9% killing of 10 of 11 strains after 24 h at two times the MIC. Other macrolides showed significant activity, relative to the MIC, against erythromycin-susceptible strains only.

Influence of recent antibiotic therapy on antimicrobial resistance of Streptococcus pneumoniae in children with acute otitis media in Spain

BACKGROUND

Despite the high prevalence of penicillin resistance among Streptococcus pneumoniae strains in Spain (40 to 60% with MIC > or = 0.1 microg/ml), the data on acute otitis media (AOM) isolates are scarce. We conducted a prospective, longitudinal study to determine the rates of antimicrobial resistance of S. pneumoniae isolates from children with AOM in our country and to analyze the effect of previous antibiotic therapy on these rates.

METHODS

Tympanocentesis was performed on 169 children diagnosed with AOM (age range, 1 month to 14 years). Two groups were considered: Group A, 113 patients with non-antibiotic-treated AOM, subdivided into Group A1 (collected from 1989 to 1992) and Group A2 (1992 to 1996); Group B, 56 patients from the period 1992 to 1996, with AOM clinical failure, defined as worsening or persistent symptoms after at least 2 days of appropriate antibiotic therapy. Amoxicillin-clavulanate was the most frequent antibiotic used (68%), followed by azithromycin (21%), cefaclor and cefixime (11%).

RESULTS

A total of 63 S. pneumoniae isolates were recovered, 42 in Group A and 21 in Group B. Resistance to penicillin (MIC > or = 0.1 microg/ml) was found in 38% of strains in Group A (32% in A1 and 50% in A2), but in Group B the rate of resistance reached 90% (P = 0.0002). Erythromycin resistance was also increased from 35% (Group A2) to 62% (Group B), and trimethoprim-sulfamethoxazole resistance rose from 64% to 81%.

CONCLUSIONS

Resistance to penicillin among S. pneumoniae AOM isolates is frequent and is increasing in Spain. After failure of standard antibiotic therapy, the rates of penicillin resistance reached 90% of the isolates.

Postantibiotic effect of sanfetrinem compared with those of six other agents against 12 penicillin-susceptible and -resistant pneumococci

The postantibiotic effect (PAE) and postantibiotic sub-MIC effect (PAE-SME) of sanfetrinem were compared to those of penicillin G, amoxicillin, cefpodoxime, ceftriaxone, imipenem, and clarithromycin against four penicillin-susceptible, four intermediately susceptible, and four resistant pneumococci. The MICs of imipenem were the lowest against all of the strains (0.03 to 0.5 microg/ml), followed by those of sanfetrinem (0.016 to 1.0 microg/ml), amoxicillin and ceftriaxone (0.016 to 2.0 microg/ml), and cefpodoxime (0.03 to 8.0 microg/ml). High-level resistance to clarithromycin (MIC, >64.0 microg/ml) was seen in three selected strains. The PAEs of all of the oral beta-lactams tested were similar for all of the strains, ranging from 1 to 6.5 h. The PAEs of ceftriaxone and imipenem ranged from 1 to 8 h, and those of clarithromycin ranged from 1 to 7 h. The mean PAEs of all of the beta-lactams and clarithromycin were 2.8 to 4.3 and 2.5 h, respectively. PAE-SMEs could not be determined for all of the strains due to complete killing, especially at high subinhibitory concentrations. However, the overall pattern with all of the compounds tested was that PAE-SMEs were longer than PAEs. Measurable PAE-SMEs of sanfetrinem at the three subinhibitory concentrations (0.125, 0.25, and 0.5 times the MIC) were 2 to 7, 2 to 7, and 3 to 6 h, while those of amoxicillin and cefpodoxime were 1 to 7.5, 2 to 4, and 4 to 9 and 2 to 7, 4 to 7, and 4 to 6 h, respectively. Measurable PAE-SMEs of ceftriaxone and imipenem were 1 to 6.5, 2 to 9, and 2 to 9 and 1.5 to 6, 2 to 5.8, and 4 to 7.7 h, respectively. Measurable clarithromycin PAE-SMEs were 1 to 5, 1 to 5, and 1 to 6 h at the three concentrations.

mefE is necessary for the erythromycin-resistant M phenotype in Streptococcus pneumoniae

Recently, it was shown that a significant number of erythromycin-resistant Streptococcus pneumoniae and Streptococcus pyogenes strains contain a determinant that mediates resistance via a putative efflux pump. The gene encoding the erythromycin-resistant determinant was cloned and sequenced from three strains of S. pneumoniae bearing the M phenotype (macrolide resistant but clindamycin and streptogramin B susceptible). The DNA sequences of mefE were nearly identical, with only 2-nucleotide differences between genes from any two strains. When the mefE sequences were compared to the mefA sequence from S. pyogenes, the two genes were found to be closely related (90% identity). Strains of S. pneumoniae were constructed to confirm that mefE is necessary to confer erythromycin resistance and to explore the substrate specificity of the pump; no substrates other than 14- and 15-membered macrolides were identified.

Susceptibility of penicillin-susceptible and -resistant pneumococci to dirithromycin compared with susceptibilities to erythromycin, azithromycin, clarithromycin, roxithromycin, and clindamycin

Agar dilution with incubation in air and CO2 was used to determine the MICs of erythromycin, dirithromycin, azithromycin, clarithromycin, roxithromycin, and clindamycin for 79 penicillin-susceptible, 72 penicillin-intermediate, and 74 penicillin-resistant pneumococci (158 erythromycin-susceptible and 67 erythromycin-resistant pneumococci). MICs obtained in air were usually 1 to 3 dilutions lower than those obtained in CO2. In air, the respective MICs at which 50% (MIC50s) and 90% (MIC90s) of penicillin-susceptible, -intermediate, and -resistant strains are inhibited were as follows: erythromycin, 0.016 and 0.5, 0.03 and > 64, and 2 and > 64 microg/ml; dirithromycin, 0.03 and 0.5, 0.06 and > 64, and 8 and > 64 microg/ml; azithromycin, 0.03 and 0.5, 0.06 and > 64, and 2 and > 64 microg/ml; clarithromycin, 0.016 and 0.06, 0.03 and > 64, and 2 and > 64 microg/ml; roxithromycin, 0.06 and 2, 0.06 and > 64, and 2 and > 64 microg/ml; and clindamycin, 0.03 and 0.06, 0.06 and > 64, and 0.06 and > 64 microg/ml. The MICs of erythromycin, azithromycin, and dirithromycin were very similar; however, clarithromycin MICs were generally 1 to 2 dilutions lower and roxithromycin MICs were 1 to 2 dilutions higher than those of the other compounds tested. Strains resistant to one macrolide were resistant to all macrolides; however, not all macrolide-resistant strains were resistant to clindamycin, and 32 macrolide-resistant (MICs, > or = 28 microg/ml), clindamycin-susceptible (MICs, < or = 0.25 microg/ml) strains were encountered. Time-kill testing of six strains showed similar killing kinetics for all compounds, with 99.9% killing of all strains observed with the compounds only at or above the MIC after 24 h.

Rationale behind high-dose amoxicillin therapy for acute otitis media due to penicillin-nonsusceptible pneumococci: support from in vitro pharmacodynamic studies

To evaluate whether increased doses of amoxicillin should be used to treat acute pneumococcal otitis media, an in vitro pharmacokinetic model was used to evaluate the killing of pneumococci by amoxicillin when middle ear pharmacokinetics were simulated. Logarithmic-phase cultures were exposed to peak concentrations of 3, 6, and 9 microg of amoxicillin per ml every 12 h, and an elimination half-life of 1.6 h was simulated. Changes in viable bacterial counts were measured over 36 h. All three doses rapidly decreased the viable bacterial counts of penicillin-susceptible strains below the 10-CFU/ml limit of detection by 6 to 10 h and maintained counts below this limit through 36 h. The 3-microg/ml peak dose was much less effective against two of three strains with intermediate penicillin resistance and all three penicillin-resistant strains, with bacterial counts approaching those in drug-free control cultures by 12 h. The 6-microg/ml peak dose completely eliminated two of three strains with intermediate penicillin resistance and maintained viable counts of the other nonsusceptible strains at 1.5 to 2 logs below the initial inoculum through 36 h. The 9-microg/ml peak dose was most effective, completely eliminating all three strains with intermediate penicillin resistance and maintaining the viable counts of the resistant strains at 3 to 4 logs below the original inoculum. The pharmacodynamics observed in this study suggest that peak concentrations of amoxicillin of 6 to 9 microg/ml may be sufficient for the elimination of penicillin-nonsusceptible pneumococcal strains causing otitis media, especially those with intermediate resistance to amoxicillin. In vivo pharmacokinetic studies are needed to determine if these levels can be achieved in middle ear fluid with amoxicillin at 70 to 90 mg/kg/day divided into two daily doses. If these levels are reliably achieved, then clinical studies are warranted.

Interleukin-8 concentration predicts the neutrophil count in middle ear effusion

Interleukin-8 (IL-8), a potent neutrophilic chemoattractant and inflammatory cytokine, is present in middle ear effusions (MEEs) of children with otitis media and is thought to be responsible for the accumulation of neutrophils in MEEs. We hypothesized that IL-8 concentration predicts the total number and proportion of neutrophils in MEEs. IL-8 concentration and total and differential cell counts were measured in MEEs of children undergoing tympanostomy tube placement for otitis media. IL-8 was present in 80 (98%) of 82 effusions. The mean +/- SEM value for IL-8 was 7342 +/- 847 pg/mL. The mean +/- SEM count and percentage of neutrophils were 1.34 x 10(6) +/- 3.44 x 10(5) and 70.6 +/- 3.1%, respectively. IL-8 concentrations correlated positively with the total number (r = +0.30; P = 0.02) and percentage of neutrophils (r = +0.32; P = 0.01) in the effusion. Additionally, purulent effusions had greater IL-8 concentrations (P = 0.003) and greater neutrophil count (P = 0.03) than mucoid or serous effusions. We conclude that IL-8 is consistently present in MEEs of children and IL-8 concentration predicts the total number and proportion of neutrophils. Furthermore, IL-8 concentration and the total number of neutrophils correlate positively with the type of effusion. These results support the hypothesis that IL-8 recruits neutrophils to the middle ear in MEEs.

Antibiotic management of pneumococcal infections in an era of increased resistance

Pneumococci are a leading cause of bacterial meningitis and bacteraemia, as well as pneumonia, otitis media and sinusitis in childhood. These organisms recently have shown a dramatic increase in antibiotic resistance. Penicillin-resistant pneumococci are of special concern as they are often resistant to other unrelated antibiotics. This is of particular significance to Aboriginal children who have among the highest rates of pneumococcal infection in the world. Laboratories should now test all invasive pneumococcal isolates for penicillin and third generation cephalosporin resistance. Local treatment guidelines are required for pneumococcal infections, especially for meningitis, taking into account the prevalence of resistant strains within the community. At present, penicillin and amoxycillin remain the drugs of choice for pneumococcal infections, with the exception of meningitis where initial empirical therapy must be with a third generation cephalosporin. Judicious antibiotic use, which avoids over-prescribing and unnecessary use of broad-spectrum agents, improved living standards in underprivileged communities and introduction of an effective conjugate vaccine, able to reduce the rates of pneumococcal infection and hopefully colonization, may limit the spread of resistant strains.

Susceptibility of twenty penicillin-susceptible and -resistant pneumococci to levofloxacin, ciprofloxacin, ofloxacin, erythromycin, azithromycin, and clarithromycin by MIC and time-kill

This study uses MIC and time-kill methodology to examine the antipneumococcal activity of levofloxacin, ciprofloxacin, ofloxacin, erythromycin, azithromycin, and clarithromycin against 20 pneumococci. Ten strains had levofloxacin MICs of 1.0 microgram/ml, and ten levofloxacin MICs of 2.0 micrograms/ml. Five strains in each group were macrolide susceptible, and five were macrolide resistant. MICs for ciprofloxacin and ofloxacin ranged from 0.5 to 4.0 micrograms/ml and 1.0 to 8.0 micrograms/ml, respectively. MICs of erythromycin, azithromycin, and clarithromycin were similar for macrolide susceptible strains, ranging between 0.004 to 0.06 microgram/ml, and were > or = 128.0 micrograms/ml for macrolide resistant strains. The three quinolones were bactericidal (99.9% killing) for all macrolide-susceptible strains at 2 x MIC at 24 h. The three quinolones yielded 99% killing of all strains after 12 h at 2 x MIC, and 90% killing of all strains after 6 h at the MIC of levofloxacin and ciprofloxacin and 2 x MIC for ofloxacin. Levofloxacin yielded 90% killing of all strains after 4 h at 2 x MIC and ofloxacin at 4 x MIC. For macrolide-susceptible strains, erythromycin and clarithromycin were bactericidal for 9 of 10 strains after 24 h at 4 x and 2 x MIC, respectively, and azithromycin was bactericidal after 24 h at 2 x MIC for 8 of 10 strains. All three macrolides were bactericidal after 12 h only, while 90% killing occurred in 9 of 10 strains at 8 x MIC after 6 h. Quinolone kill kinetics were similar for the 10 macrolide-resistant strains. For macrolide-resistant strains, at 64 to 128.0 micrograms/ml, virtually no decrease in count was seen, with no bactericidal effect.

Susceptibilities of 228 penicillin- and erythromycin-susceptible and -resistant pneumococci to RU 64004, a new ketolide, compared with susceptibilities to 16 other agents

The susceptibilities of 228 penicillin- and erythromycin-susceptible and -resistant pneumococci to RU 64004, a new ketolide, were tested by agar dilution, and the results were compared with those for penicillin G, erythromycin, azithromycin, clarithromycin, rokitamycin, clindamycin, pristinamycin, ciprofloxacin, sparfloxacin, trimethoprim-sulfamethoxazole, doxycycline, chloramphenicol, cefuroxime, ceftriaxone, imipenem, and vancomycin. RU 64004 was very active against all strains tested, with MICs at which 90% of the isolates are inhibited (MIC90s) of 0.016 microg/ml for erythromycin-susceptible strains (MIC, < or = 0.25 microg/ml) and 0.25 microg/ml for erythromycin-resistant strains (MIC, > or = 0.5 microg/ml). All other macrolides had MIC90s of 0.03 to 0.25 and > or = 128 microg/ml for erythromycin-susceptible and -resistant strains, respectively. Among erythromycin-resistant strains, clindamycin MICs for 28 of 91 (30.7%) were < or = 0.125 microg/ml. Pristinamycin MICs for all strains were < or = 1.0 microg/ml. MIC90s of ciprofloxacin and sparfloxacin were 4.0 and 0.25 microg/ml, respectively, and were unaffected by susceptibility to penicillin or erythromycin. Vancomycin and imipenem inhibited all strains at < or = 0.5 and < or = 0.25 microg/ml, respectively. MICs of cefuroxime and cefotaxime rose with those of penicillin G. MICs of trimethoprim-sulfamethoxazole, doxycycline, and chloramphenicol were variable but were generally higher for penicillin- and erythromycin-resistant strains. RU 64004 is the first member of the macrolide group which has low MICs for erythromycin-resistant pneumococci.

Cefprozil treatment of persistent and recurrent acute otitis media

OBJECTIVE

We identified the pathogens causing persistent and recurrent acute otitis media (AOM) and the clinical efficacy of cefprozil as treatment.

STUDY DESIGN

This was a noncomparative, open label multicenter trial. Children ages 6 months to 12 years with signs and symptoms of AOM and evidence of middle ear effusion, as confirmed by pneumatic otoscopy or tympanometry, underwent tympanocentesis and subsequent treatment with cefprozil (15 mg/kg given twice daily) for 10 days. Patients with recurrent otitis media or failure of previous antibiotic therapy or prophylaxis were particularly sought for the study.

RESULTS

Two hundred sixty-two (99%) of 265 enrolled children were considered evaluable. The median age of the study group was 1 year. Ninety-eight (37%) of the children had a history (within 30 days) of prior antibiotic use. Ninety-seven (37%) met our definition of recurrent AOM, 48 (18%) met our definition of persistent AOM and 132 (50%) children had 3 or more previous episodes of acute otitis media within 12 months before study. Eighty-two (31%) of the enrollment tympanocentesis had no growth, 150 (57%) had a single bacterial pathogen and 29 (11%) had multiple bacterial pathogens. Of the 93 Streptococcus pneumoniae pretreatment isolates, 50 (54%) were penicillin-susceptible, 12 (13%) were penicillin-intermediate resistant and 31 (33%) were penicillin-resistant. Of the 75 Haemophilus influenzae pretreatment isolates, 42 (56%) produced beta-lactamase as did 4 (27%) of the 15 Moraxella catarrhalis strains. A satisfactory clinical response by pathogen was found in 75% (70 of 93) with S. pneumoniae, 75% (56 of 75) with H. influenzae and 93% (13 of 14) with M. catarrhalis; the response with single pathogen infections was higher than those with multiple pathogens (118 of 150 (78%) and 17 of 29 (59%), respectively; P = 0.03). The response for patients with isolates of S. pneumoniae that were penicillin-susceptible, -intermediate or -resistant were 39 of 50 (78%), 11 of 12 (92%) and 21 of 31 (68%), respectively. Older children had a satisfactory clinical outcome more frequently than younger children (P < 0.001), and the response to therapy varied for persistent, recurrent and recently untreated AOM (P < 0.01).

CONCLUSION

Persistent and recurrent AOM involves the same pathogens as recently untreated AOM but bacteria with reduced antibiotic susceptibility may be more frequently present. This noncomparative study suggests that cefprozil 30 mg/kg/day given in two divided doses for 10 days may be effective in the treatment of children with persistent and recurrent AOM.

Continuous twice daily or once daily amoxicillin prophylaxis compared with placebo for children with recurrent acute otitis media

OBJECTIVE

To determine the effectiveness of amoxicillin administered continuously twice daily vs. once daily vs. placebo to prevent new episodes of acute otitis media (AOM).

DESIGN

Randomized, double blind, placebo-controlled clinical trial at a hospital-based general pediatric clinic and a private pediatric practice, both in Denver, CO.

PARTICIPANTS

One hundred ninety-four children (age 3 months through 6 years) were enrolled with 3 documented AOM episodes within the prior 6 months, without ventilating tubes or associated anatomic defects, immunodeficiency disorders or allergy to penicillin. Thirty-six were noncompliant and were excluded from the study, leaving 158 evaluable subjects.

INTERVENTIONS

The amoxicillin dosage was 20 mg/kg/day either bid or qd. After randomization to placebo twice daily (bid), amoxicillin once daily (qd)/placebo qd or amoxicillin bid, patients were followed monthly and were also seen for upper respiratory infection symptoms during enrollment in the trial. Development of two new AOM episodes terminated the patients from the study.

MEASUREMENTS/MAIN RESULTS

Incidence density (ID) measurements were calculated for all study subjects and were stratified by age and season. Overall study subjects in all 3 arms of the trial had 7243 days at risk during which time they developed 56 new AOM episodes for a annual ID of 2.82. There were no significant differences in the IDs between amoxicillin qd vs. bid or amoxicillin (bid or qd) vs. placebo. After stratifying by age and season of enrollment, there were no significant differences in ID rates among the 3 groups. The proportion of subjects remaining otitis-free was 63% for the placebo group, 64% for once daily amoxicillin and 61% for twice daily amoxicillin.

CONCLUSION

While once-a-day dosing was equivalent to twice-a-day dosing for amoxicillin prophylaxis, there was no benefit of amoxicillin prophylaxis compared with a placebo control in preventing new AOM episodes. Because of the potential of excessive antibiotic use to promote the acquisition of resistant pneumococci and the lack of effectiveness in this trial, routine use of amoxicillin prophylaxis should be discouraged.

Microbiologic activity of the newer macrolide antibiotics

In vitro susceptibility testing has demonstrated good activity of the azalide azithromycin and the macrolide clarithromycin against Gram-positive and -negative pathogens as well as atypical organisms involved in the etiology of upper and lower respiratory tract infections. One difference between these drugs in terms of their antimicrobial spectrum is the activity of azithromycin against Haemophilus influenzae. This organism is 2 to 8 times more susceptible in vitro to azithromycin than to clarithromycin or to erythromycin, the prototypical macrolide antibiotic. A principal concern in the management of respiratory tract infections today is the emergence of penicillin-resistant strains of Streptococcus pneumoniae. Both azithromycin and clarithromycin are active against penicillin-susceptible S. pneumoniae, although the activity of azithromycin is somewhat less than that of erythromycin and clarithromycin. Results of susceptibility testing of resistant organisms have varied among centers; in some areas all of the intermediately and some of the highly penicillin-resistant S. pneumoniae isolates are susceptible to the newer macrolides, whereas in other areas they are not. High tissue antibiotic concentrations achieved with these drugs may contribute to their effectiveness against some of the resistant S. pneumoniae isolates.

Causative pathogens, antibiotic resistance and therapeutic considerations in acute otitis media

Streptococcus pneumoniae, Haemophilus influenzae and Moraxella catarrhalis are the most frequently isolated pathogens in patients with acute otitis media (AOM). Other potential causative pathogens include Streptococcus pyogenes in older children and Chlamydia pneumoniae in younger children. The recent emergence of penicillin-resistant S. pneumoniae and the increasing frequency of beta-lactamase-producing strains of M. catarrhalis and H. influenzae are creating concerns regarding the use of amoxicillin as traditional first line empiric therapy for AOM in younger children. Both the in vitro antibiotic activity against these more resistant causative pathogens and the antibiotic concentrations achieved in middle ear fluid must be considered when selecting antibiotics for treatment of refractory AOM. The newer macrolides, azithromycin and clarithromycin, provide reasonable in vitro coverage against penicillin-resistant S. pneumoniae and beta-lactamase-producing H. influenzae, although azithromycin is more active against the latter. Both drugs also achieve notably higher, sustained concentrations in middle ear fluid than do beta-lactam antibiotics. Thus the newer macrolides represent important new rational alternatives for the management of AOM.

Empiric antibiotic selection criteria for respiratory infections in pediatric practice

BACKGROUND

Respiratory infections in children may occur as a consequence of resistant bacterial pathogens. Streptococcus pneumoniae organisms resistant to penicillin, trimethoprim/sulfamethoxazole and macrolides are increasingly prevalent. Amoxicillin- and macrolide-resistant Haemophilus influenzae and Moraxella (Branhamella) catarrhalis are also more commonly seen. Traditional agents such as amoxicillin and trimethoprim/sulfamethoxazole remain acceptable choices for most children with respiratory infections because currently most patients are not infected by resistant pathogens and there is a high spontaneous cure rate associated with these infections.

OBJECTIVE

To analyze the criteria for the selection of extended spectrum antimicrobials as empiric therapy for respiratory infections.

DISCUSSION

When an extended spectrum antimicrobial is appropriate for empiric therapy, selection should be based on: (1) efficacy; (2) adverse event profile; and (3) compliance-enhancing features (dosing with meals, once or twice daily administration, good palatability in suspension, shortened course of therapy and affordability). A new agent, ceftibuten, has recently joined other extended spectrum cephalosporins and newer macrolides (clarithromycin and azithromycin) as a choice to be considered for empiric therapy for respiratory infections. These antimicrobials are differentiated from each other and traditional agents by differences in activity in vitro against penicillin-resistant pneumococci, relative beta-lactamase stability against Gram-negative bacteria and pharmacodynamic properties. When resistant organisms are isolated or suspected in community-acquired respiratory infections, cautious use of newer antibiotics may have to be considered.