Inoculum effect and bactericidal activity of cefditoren and other antibiotics against Streptococcus pneumoniae, Haemophilus influenzae, and Neisseria meningitidis

Inoculum effect of β-lactam antibiotics

The phenomenon of attenuated antibacterial activity at inocula above those utilized for susceptibility testing is referred to as the inoculum effect. Although the inoculum effect has been reported for several decades, it is currently debatable whether the inoculum effect is clinically significant. The aim of the present review was to consolidate currently available evidence to summarize which β-lactam drug classes demonstrate an inoculum effect against specific bacterial pathogens. Review of the literature showed that the majority of studies that evaluated the inoculum effect of β-lactams were in vitro investigations of Escherichia coli, Pseudomonas aeruginosa, Klebsiella pneumoniae, Haemophilus influenzae and Staphylococcus aureus. Across all five pathogens, cephalosporins consistently displayed observable inoculum effects in vitro, whereas carbapenems were less susceptible to an inoculum effect. A handful of animal studies were available that validated that the in vitro inoculum effect translates into attenuated pharmacodynamics of β-lactams in vivo. Only a few clinical investigations were available and suggested that an in vitro inoculum effect of cefazolin against MSSA may correspond to an increased likeliness of adverse clinical outcomes in patients receiving cefazolin for bacteraemia. The presence of β-lactamase enzymes was the primary mechanism responsible for an inoculum effect, but the observation of an inoculum effect in multiple pathogens lacking β-lactamase enzymes indicates that there are likely multiple mechanisms that may result in an inoculum effect. Further clinical studies are needed to better define whether interventions made in the clinic in response to organisms displaying an in vitro inoculum effect will optimize clinical outcomes.

In vitro and in vivo activities of piperacillin-tazobactam and meropenem at different inoculum sizes of ESBL-producing Klebsiella pneumoniae

The inoculum effect is a laboratory phenomenon in which the minimal inhibitory concentration (MIC) of an antibiotic is increased when a large number of organisms are exposed. Due to the emergence of extended-spectrum β-lactamase-producing Klebsiella pneumoniae (ESBL-Kpn) infections, the inoculum effect of ESBL-Kpn on β-lactams was studied in vitro and in vivo using an experimental model of pneumonia. The in vitro inoculum effect of 45 clinical ESBL-Kpn isolates on β-lactams was evaluated at standard (10(5) CFU/mL) and high (10(7) CFU/mL) organism concentrations. The MIC50 of piperacillin-tazobactam, cefotaxime and cefepime was increased eight-fold or more and that of meropenem was increased two-fold. The in vivo inoculum effect was evaluated in an ESBL-Kpn pneumonia mouse model treated with bacteriostatic effect-adjusted doses of piperacillin-tazobactam (1000 mg/kg four times daily, %T>MIC; 32.60%) or meropenem (100 mg/kg twice daily, %T>MIC; 28.65%) at low/standard (10(4) CFU/mouse) and high (10(6) CFU/mouse) inocula. In mice administered a low inoculum, no mice died after treatment with piperacillin-tazobactam or meropenem, whereas all the control mice died. In contrast, in the high inoculum model, all mice in the piperacillin-tazobactam-treated group died, whereas all meropenem-treated mice survived and had a decreased bacterial load in the lungs and no invasion into the blood. In conclusion, meropenem was more resistant to the inoculum effect of ESBL-Kpn than piperacillin-tazobactam both in vitro and in vivo. In the management of severe pneumonia caused by ESBL-Kpn, carbapenems may be the drugs of choice to achieve a successful outcome.

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.

Antimicrobial activities of ceragenins against clinical isolates of resistant Staphylococcus aureus

The rise in the rates of glycopeptide resistance among Staphylococcus aureus isolates is concerning and underscores the need for the development of novel potent compounds. Ceragenins CSA-8 and CSA-13, cationic steroid molecules that mimic endogenous antimicrobial peptides, have previously been demonstrated to possess broad-spectrum activities against multidrug-resistant bacteria. We examined the activities of CSA-8 and CSA-13 against clinical isolates of vancomycin-intermediate S. aureus (VISA), heterogeneous vancomycin-intermediate S. aureus (hVISA), as well as vancomycin-resistant S. aureus (VRSA) and compared them to those of daptomycin, linezolid, and vancomycin by susceptibility testing and killing curve analysis. We also examined CSA-13 for its concentration-dependent activity, inoculum effect, postantibiotic effect (PAE), and synergy in combination with various antimicrobials. Overall, the MICs and minimal bactericidal concentrations of CSA-13 were fourfold lower than those of CSA-8. Time-kill curve analysis of the VRSA, VISA, and hVISA clinical isolates demonstrated concentration-dependent bactericidal killing. An inoculum effect was also observed when a higher starting bacterial density was used, with the time required to achieve 99.9% killing reaching 1 h with a 6-log10-CFU/ml starting inoculum, whereas it was>or=24 h with a 8- to 9-log10-CFU/ml starting inoculum with 10x the MIC (P Collapse

Key Words Collapse

MESH Headings

• Anti-Bacterial Agents/chemistry
• Anti-Bacterial Agents/pharmacology
• Drug Resistance, Microbial
• Microbial Sensitivity Tests
• Staphylococcus aureus/drug effects
• Staphylococcus aureus/isolation & purification
• Steroids/pharmacology
• Vancomycin Resistance/drug effects

Collapse

Grants Collapse

Affiliation(s)

Judy N Chin Anti-Infective Research Laboratory, Department of Pharmacy Practice-4148, Eugene Applebaum College of Pharmacy and Health Sciences, Wayne State University, 259 Mack Ave., Detroit, MI 48201, USA
Michael J Rybak
Chrissy M Cheung
Paul B Savage

Collapse

Cefditoren pivoxil: a review of its use in the treatment of bacterial infections

Cefditoren pivoxil (Spectracef, Meiact) is a third-generation oral cephalosporin with a broad spectrum of activity against pathogens, including both Gram-positive and -negative bacteria, and is stable to hydrolysis by many common beta-lactamases. Cefditoren pivoxil is approved for use in the treatment of acute exacerbations of chronic bronchitis (AECB), mild-to-moderate community-acquired pneumonia (CAP), acute maxillary sinusitis, acute pharyngitis/tonsillitis and uncomplicated skin and skin structure infections (indications may differ between countries). In clinical trials in adults and adolescents, cefditoren pivoxil demonstrated good clinical and bacteriological efficacy in AECB, CAP, acute maxillary sinusitis, acute pharyngitis/tonsillitis and uncomplicated skin and skin structure infections and was generally well tolerated. Thus, cefditoren pivoxil is a good option for the treatment of adult and adolescent patients with specific respiratory tract or skin infections, particularly if there is concern about Streptococcus pneumoniae with decreased susceptibility to penicillin, or beta-lactamase-mediated resistance among the common community-acquired pathogens.

Physiological Modeling for Indirect Evaluation of Drug Tissular Pharmacokinetics under Non-Steady-State Conditions: An Example of Antimicrobial Prophylaxis During Liver Surgery

Cefazolin, a time-dependent first-generation cephalosporin with non-linear binding to albumin, is widely recommended for antimicrobial prophylaxis during liver surgery to decrease the incidence of postoperative wound infections. The recommended protocol (2 g IV at anesthesia induction followed by 1 g 4 h later) is expected to maintain the free cefazolin concentration in exposed intratissular fluids above its minimal inhibitory concentration (MIC) for potentially encountered microorganisms, from skin incision to skin closure. Since this dosing protocol fails to take into account either of patients status (total body weight and renal function) or of surgical and anesthetic consequences (variations of cardiac output and regional blood flows, progressive decrease of plasma albumin concentration) on cefazolin tissular pharmacokinetics, a physiological modeling study was conducted to investigate protocol suitability for liver surgery in six populations: obese (body mass index >34), renal insufficiency (GFR = 10, 30 or 50 ml min(-1)) and high intraoperative blood loss (three times that usually observed during this surgery) and none of these features referred to as controls. A previously validated physiologically based pharmacokinetic (PB-PK) model for cefazolin in humans was used and then further adapted to simulate obese or renal insufficiency patients as well as the consequences of general anesthesia and liver surgery on cefazolin pharmacokinetics. Clinical data required for simulation (intraoperative kinetics of percent expired isoflurane and plasma albumin concentration, mean intraoperative blood loss) were obtained from 10 patients who underwent right hepatectomy in our institution. Using a fixed MIC of 2 microg ml(-1) against potentially encountered bacteria, it was concluded that the recommended dosing schedule was suitable in all tested populations, including obese patients, although prolongation of the interval between injections appeared advisable for renal insufficiency patients. Furthermore, when a MIC of 3 microg ml(-1) was considered, the recommended cefazolin-dosing regimen failed to maintain sufficient free cefazolin concentrations in the interstitial fluids during surgery in all tested populations except renal insufficiency patients (GFR < 50 ml min(-1)).

Cefditoren, a new aminothiazolyl cephalosporin

Cefditoren pivoxil, an oral third-generation cephalosporin, was approved by the Food and Drug Administration in September 2001. It has been used in Japan for several years. The greatest therapeutic potential of cefditoren appears to be its activity against gram-positive and gram-negative organisms causing respiratory tract infections and skin and skin-structure infections, such as Haemophilus influenzae, Streptococcus pneumoniae, and Moraxella catarrhalis. Cefditoren is also effective against methicillin-susceptible strains of Staphylococcus aureus. Nevertheless, cefditoren has no activity against atypical pathogens, including Chlamydia pneumoniae, Mycoplasma pneumoniae, and Legionella sp. Moreover, cefditoren does not inhibit Pseudomonas aeruginosa or Bacteroides fragilis. In virtually all studies, cefditoren has compared favorably against other orally administered antibiotics used against the most commonly isolated respiratory tract pathogens. Its side effect profile includes diarrhea, nausea, vomiting, headache, and dyspepsia. Cefditoren is indicated for treatment of mild-to-moderate acute exacerbations of chronic bronchitis, pharyngitis-tonsillitis, and uncomplicated skin and skin-structure infections caused by susceptible strains of organisms in adults and adolescents (> or = 12 yrs of age). Based on its reported antimicrobial activity, cefditoren has potential for empiric management of most commonly encountered respiratory tract infections. Additional studies will further define its role in clinical practice.

In vitro bactericidal activity of piperacillin, gentamicin, and metronidazole in a mixed model containing Escherichia coli, Enterococcus faecalis, and Bacteroides fragilis

An anaerobic, mixed model assay was used to study the bactericidal activities of piperacillin, gentamicin, and metronidazole, alone and in double- and triple-antibiotic combinations against a polymicrobial suspension of E. coli, E. faecalis, and B. fragilis. Only slight differences were noted with the agents when tested against single (10(5) cfu/mL inoculum) versus polymicrobic suspensions (10(6) cfu/mL final inoculum) of susceptible and resistant organisms. Contrary to previous reports in the literature, metronidazole was not active against E. coli in an anaerobic environment (even in the presence of B. fragilis) nor was the activity of metronidazole reduced against B. fragilis in the presence of E. faecalis. Gentamicin demonstrated excellent activity against E. coli when tested in a Bactron anaerobic chamber (5% hydrogen, 5% CO(2,) 90% nitrogen). The pH of the media was only reduced to 6.3-6.7, considerably higher than the pH range of 5-6 needed to significantly reduce the activity of aminoglycosides.

Cefditoren pivoxil

Cefditoren pivoxil is an orally absorbed prodrug that is rapidly hydrolysed by intestinal esterases to the microbiologically active cephalosporin cefditoren. Cefditoren has a broad spectrum of activity against Gram-positive and Gram-negative bacteria, including common respiratory and skin pathogens. Cefditoren has shown excellent in vitro activity against the Gram-positive pathogens penicillin-susceptible and -intermediate Streptococcus pneumoniae, S. pyogenes and methicillin-susceptible Staphylococcus aureus. Cefditoren was inactive against methicillin-resistant S. aureus. Of the important Gram-negative pathogens, cefditoren had potent antibacterial effects against beta-lactamase-positive and -negative Haemophilus influenzae, H. parainfluenzae and beta-lactamase-positive and -negative Moraxella catarrhalis. Cefditoren does not have antibacterial activity against Pseudomonas aeruginosa or atypical respiratory pathogens and has only variable activity against anaerobes. In healthy volunteers, single doses of cefditoren pivoxil 200 and 400mg achieved maximal plasma concentrations of 2.6 to 3.1 mg/L and 3.8 to 4.6 mg/L, respectively. Cefditoren penetrates rapidly into bronchopulmonary and tonsillar tissue as well as inflammatory and noninflammatory blister fluid. In two, randomised, double-blind trials involving patients with acute exacerbations of chronic bronchitis (AECB), cefditoren 200 and 400mg twice daily for 10 days produced clinical cure rates of 88 to 89% within 48 hours of treatment completion. Clinical cure rates in patients with AECB were similar to those of either clarithromycin 500mg twice daily or cefuroxime axetil 250mg twice daily. In patients with streptococcal pharyngitis, a 10-day course of cefditoren pivoxil 200mg twice daily produced clinical cure rates of 94% at 4 to 7 days after treatment, which were similar to those observed for phenoxymethylpenicillin potassium 250 mg four times daily. In uncomplicated skin and skin structure infections, a 10-day course of cefditoren pivoxil 200 or 400mg twice daily produced the same clinical cure rate of 89% within 48 hours of treatment completion. These cefditoren pivoxil dosage regimens were as effective as a 10-day course of either cefadroxil 500 mg twice daily or cefuroxime axetil 250mg twice daily in treating uncomplicated skin and skin structure infections, including those caused by S. aureus and S. pyogenes. The most common adverse events associated with therapeutic doses of cefditoren pivoxil are diarrhoea, nausea, headache, abdominal pain and vaginal candidiasis.

Review of cefditoren, an advanced-generation, broad-spectrum oral cephalosporin

BACKGROUND

Cefditoren is an advanced-generation, broad-spectrum cephalosporin antibiotic approved for the treatment of acute bacterial exacerbation of chronic bronchitis (AECB), group A beta-hemolytic streptococcal pharyngotonsillitis, and uncomplicated skin/skin structure infections in adult and adolescent patients.

OBJECTIVE

This article briefly reviews the chemistry, antimicrobial activity, pharmacokinetics, efficacy, and safety of cefditoren.

METHODS

Literature was identified by a MEDLINE search (January 1985 to October 2001) of the medical literature, review of the English-language literature, reference lists within these articles, as well as data presented at the 40th Interscience Conference on Antimicrobial Agents and Chemotherapy.

RESULTS

Cefditoren has a broad spectrum of activity against many gram-negative and gram-positive aerobes, including Streptococcus pneumoniae, Staphylococcus aureus, Streptococcus pyogenes, Haemophilus influenzae, and Moraxella catarrhalis. Cefditoren is stable to hydrolysis by many common beta-lactamases. Cefditoren is rapidly absorbed (time to peak plasma concentration, approximately 2-3 hours) from the gastrointestinal tract and is almost completely eliminated via renal clearance of unchanged drug. The terminal disposition half-life of the compound is approximately 0.8 to 1.3 hours.

CONCLUSIONS

Cefditoren is effective in the management of AECB (in regimens of 400 mg twice daily for 10 days) and acute maxillary sinusitis, pharyngotonsillitis due to S pyogenes, and uncomplicated skin/skin structure infections (in regimens of 200 mg twice daily for 10 days). Cefditoren possesses broad activity against common pathogens of the respiratory tract and skin and is stable in the presence of numerous beta-lactamases. Its pharmacokinetic properties, in conjunction with in vitro susceptibility data, document the feasibility of twice-daily dosing.

Protected environments allow parallel evolution of a bacterial pathogen in a patient subjected to long-term antibiotic therapy

Long-term antibiotic treatment offers a rare opportunity to study the evolution of bacteria within the same individual. The appearance of new variants has been suggested to take place via the selection of enhanced resistance in compartments of the body in which the antibiotic concentration is low. Laboratory models of protected compartments have elegantly demonstrated their potential in selecting novel variants. However, comparable data from patients have been rare. In this study, extended antibiotic therapy in a single patient suffering from multiple infected liver cysts has provided the opportunity to observe and analyse the molecular evolution of antibiotic resistance. Each isolate has the same basic ompC gene sequence that is distinct from other Escherichia coli isolates, which suggests that they derive from the same founder population. However, the isolates differ in their auxotrophic markers, in the pI values of their dominant beta-lactamase activities and in the mutations in the promoter region of the ampC gene leading to increased expression of the AmpC enzyme. The data provide strong evidence for a single focal infection expanding via parallel pathways of evolution to give a range of antibiotic-resistant isolates. These data suggest that the infected cysts provide numerous protected environments that are the foci for the separate development of distinct variants.

Cefditoren in vitro activity and spectrum: a review of international studies using reference methods

Cefditoren, a broad-spectrum orally administered cephalosporin ester, has documented in vitro efficacy against many Gram-positive and -negative pathogens and stability against clinically important beta-lactamases. We have reviewed the microbiology and the pharmacokinetic/pharmacodynamic literature regarding the spectrum and potency of this newer agent against the major etiologic agents of community-acquired respiratory infection, (Streptococcus pneumoniae, Hemophilus influenzae and Moraxella catarrhalis), as well as the Enterobacteriaceae and non-enteric Gram-negative bacilli, staphylococci, and other aerobic and anaerobic Gram-positive cocci. The level of cefditoren activity against S. pneumoniae (MIC(90,) 0.5 microg/mL) was superior to all marketed oral cephalosporins and at least equal to amoxicillin +/- clavulanate. H. influenzae (MIC(90,) 0.016-0.03 microg/mL) and M. catarrhalis (MIC(90,) 0.06-0.5 microg/mL) were also very susceptible to cefditoren. In contrast to cefixime and ceftibuten, cefditoren was active against oxacillin-susceptible staphylococci (MIC(90,) < or = 1 microg/mL) at a level comparable to cefuroxime axetil, cefaclor or cefprozil. Enterococci, Pseudomonas aeruginosa and most anaerobes (Gram-negative) were not cefditoren-susceptible, but most Enterobacteriaceae, beta-haemolytic and viridans group streptococci were highly susceptible. Furthermore, an overview of key in vitro susceptibility testing methods and issues including disk diffusion testing and Etest (AB BIODISK, Solna, Sweden) method accuracy, interpretive criteria, and pharmacodynamic considerations for the selection of a breakpoint concentration are provided. The rapid bactericidal nature of the antibacterial activity of cefditoren, its post antibiotic effect, penicillin binding protein targets, and extent of beta-lactamase stability are all favorable qualities. In conclusion, this orally administered (BID) beta-lactam possesses promise for use against commonly isolated problematic respiratory tract pathogens such as penicillin-non-susceptible pneumococci and beta-lactamase-positive M. catarrhalis or H. influenzae. Success in the clinical trials will further define the role of cefditoren in this era of emerging resistant bacterial pathogens.

Susceptibility of Streptococcus pneumoniae and Haemophilus influenzae to cefditoren, and provisional interpretive criteria

In vitro cefditoren antimicrobial activity was tested by broth microdilution and disk diffusion methods against 300 Streptococcus pneumoniae and 299 Haemophilus influenzae isolates. MICs were also determined for three comparison drugs. The MICs of cefditoren were very comparable to those of cefotaxime against both species. If penicillin-resistant pneumococci are to be considered not susceptible to cefditoren, the tentative MIC breakpoints for cefditoren of < or = 0.25 microg/ml for susceptible and > or 1.0 microg/ml for resistant could be selected. With these breakpoints, all penicillin-susceptible pneumococci were cefditoren-susceptible, as were 85% of penicillin-intermediate strains. Provisional zone diameter breakpoints would be > or = 26 mm for susceptible and < or = 20 mm for resistant. If penicillin-resistant pneumococcal infections are shown to clinically respond to cefditoren therapy, then a susceptible MIC breakpoint of < or = 1.0 microg/ml would be appropriate, with a corresponding zone diameter breakpoint of > or = 21 mm. A susceptible MIC breakpoint of < or = 0.5 or < or = 1.0 microg/ml is appropriate for H. influenzae, but lack of correlation between cefditoren MICs and disk diffusion zone diameters when testing H. influenzae leads us to make no recommendations at this time regarding cefditoren disk tests for H. influenzae.

Antimicrobial activity and in vitro susceptibility test development for cefditoren against Haemophilus influenzae, Moraxella catarrhalis, and Streptococcus species

Cefditoren, a third generation orally administered aminothiazolyl cephalosporin, has demonstrated bactericidal activity against many Gram positive and negative bacterial pathogens and stability against clinically important beta-lactamases. Cefditoren was compared to cefaclor, cefixime, and penicillins against 1 435 recently isolated strains of streptococci (312 Streptococcus pneumoniae, 165 viridans group streptococci, 142 beta-haemolytic streptococci), Haemophilus influenzae (521 strains), and Moraxella catarrhalis (295 strains). Streptococcus pneumoniae and viridans group streptococci had penicillin nonsusceptible rates of 37.8 and 35.8%, respectively. Cefditoren (MIC(90) in microg/ml/% susceptible) activity against all tested H. influenzae (0.03/100) and M. catarrhalis (0.06-0.5/100) was comparable to cefixime and significantly greater than cefaclor. Cefditoren (MIC(90), 0.5 microg/ml) was 4- to 128-fold more active than comparison beta-lactams against the pneumoococci and was the most potent beta-lactam (including penicillin) versus beta-haemolytic streptococci. Cefditoren pharmacokinetics demonstrate a T(1/2) of 1.5-2 h and C(max) values of 2.8 and 4.6 microg/ml, respectively with 200 or 400 mg doses of cefditoren pivoxil; plasma concentrations exceed 1 microg/ml for 4 to 6 hours (33-50% of dosing interval). Consequently, a susceptible MIC of </= 1 microg/ml or </= 2 microg/ml was proposed with zone diameter correlates of >/= 18 and >/= 15 mm (5-microg disk) for all cited fastidious species tested. Categorical agreement between MIC and disk tests was 94.6 to 100% with a correlation coefficient (r) range of 0.50 to 0.90 for streptococci. H. influenzae intermethod comparison results using the same interpretive criteria were in complete agreement, but exhibited a low r = 0.39. Cefditoren clearly possesses the most potent activity among currently studied oral cephalosporins or penicillin against commonly isolated bacterial pathogens causing bronchitis, pneumonia, sinusitis, or pharyngitis and was active against nearly all penicillin-resistant streptococci at </= 0.5 microg/ml. Expanded clinical investigations seem warranted.

Cefditoren activity against nearly 1000 non-fastidious bacterial isolates and the development of in vitro susceptibility test methods

Cefditoren (formerly ME-1206) is an investigational, orally administered cephalosporin ester with bactericidal activity against many Gram-positive and -negative organisms. Cefditoren potency against nearly 1000 non-fastidious species was determined by National Committee for Clinical Laboratory Standards (NCCLS) reference broth microdilution and standardized disk diffusion methods. Against staphylococci, usable cefditoren activity was completely correlated with oxacillin with respect to potency and susceptibility interpretation (mec A-negative strains). Cefditoren was very active against Klebsiella spp., Proteus mirabilis, Salmonella spp., and Escherichia coli (MIC(90) range, 0.12-1 microg/ml; median zone, 23-26 mm). Cefditoren had more limited activity against Citrobacter spp., Enterobacter spp., Serratia marcescens, and indole-positive Proteae (MIC(50) range, 0.12-1 microg/ml; MIC(90), > 16 microg/ml; median zone, 18-25 mm). Against Pseudomonas aeruginosa, Stenotrophomonas maltophilia, Acinetobacter spp., and other non-fermentors, cefditoren was inactive (MIC(90), > 16 microg/ml; zone, 6 mm). Pharmacokinetic analysis of cefditoren showed that utilized dosages produce a plasma concentration that exceeds 0.5 microg/ml for 5 to 8 h and 1 microg/ml for 4 to 6 hours (T(1/2) ranges from 1.5-2 h). The following interpretive criteria were suggested: </= 2 microg/ml or >/= 15 mm (susceptible) and >/= 8 microg/ml or </= 11 mm (resistance) that yielded an intermethod categorical agreement of 95.8% and very major or major error rates of 0.7% and 0.3%, respectively. Alternatively, </= 1 microg/ml or >/= 18 mm (susceptible) and >/= 4 microg/ml or </= 14 mm (resistant) breakpoints resulted in 96.2% accuracy and combined serious errors of only 1.1%. Cefditoren was observed to be a very active cephalosporin ranking among the most potent available orally active beta-lactams for use against a wide variety of pathogens.

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.

In vitro evaluation of a novel orally administered cephalosporin (Cefditoren) tested against 1249 recent clinical isolates of Haemophilus influenzae, Moraxella catarrhalis, and Streptococcus pneumoniae

Cefditoren (formerly ME-1206), a new orally administered cephalosporin, was evaluated in vitro against 1249 recently isolated strains of Streptococcus pneumoniae (500 strains), Moraxella catarrhalis (250 strains), and Haemophilus influenzae (499 strains). Reference National Committee for Clinical Laboratory Standards methods were used and the strains were representative for the current rates of beta-lactamase production or penicillin resistance. Cefditoren had MIC50/MIC90 results for Moraxella catarrhalis and Haemophilus influenzae of 0.12/0.5 and < or = 0.008/0.015 microgram/mL, respectively. The pneumococci were consistently twofold to eightfold more susceptible to cefditoren than other oral cephalosporins or penicillins. The MIC90 for penicillin-resistant S. pneumoniae was only 2 micrograms cefditoren/mL, and the highest recorded MIC was 4 micrograms/mL. Cefditoren appears to be a very promising beta-lactam possessing the greatest potency and potential spectrum versus contemporary (1997) respiratory tract pathogens.