Antipneumococcal activities of a ketolide (HMR 3647), a streptogramin (quinupristin-dalfopristin), a macrolide (erythromycin), and a lincosamide (clindamycin)

A Comparison of the Efficacy of Telithromycin versus Cefuroxime Axetil in the Treatment of Acute Bacterial Maxillary Sinusitis

Background

Telithromycin, a new ketolide, exhibits potent activity against respiratory pathogens, including resistant strains.

Methods

Five days of telithromycin (800 mg once daily) was compared with 10 days of cefuroxime axetil (250 mg twice daily) in subjects (n = 593) with acute bacterial maxillary sinusitis (ABMS). Bacteriologic sampling was accomplished by sinus puncture or nasal endoscopy. The primary efficacy variable was clinical outcome at the posttherapy/test-of-cure evaluation in clinically evaluable patients.

Results

Clinical cure was achieved in 85.2% of telithromycin patients and 82.0% of cefuroxime axetil patients (difference in proportions, 3.2%; 95% confidence interval, 27.1–13.4%). Satisfactory bacteriologic response rates were comparable. Treatment-emergent adverse events for both drugs were mild or moderate. The most frequently reported treatment-emergent adverse events were nausea and diarrhea.

Conclusion

Once-daily telithromycin for 5 days was equivalent in efficacy to twice-daily cefuroxime axetil for 10 days in patients with ABMS. Telithromycin is a suitable option for short-course therapy of ABMS.

Pharmacokinetics and Safety of the Ketolide Telithromycin in Patients with Renal Impairment

The pharmacokinetics and safety of the ketolide telithromycin were evaluated in two separate studies after single and repeat oral dosing in patients with varying degrees of renal impairment and in subjects with normal renal function. The single-dose study was an open-label, nonrandomized, parallel-group design in which all 40 patients received a single oral dose of telithromycin 800 mg. The repeat-dose study was an open-label study with a randomized, balanced, incomplete three-block treatment crossover design. In this study, each of the 36 patients received two of three telithromycin regimens (400, 600, or 800 mg once daily for 5 days), with a washout period of >/= 7 days between treatments. Telithromycin was well tolerated. Adverse events were generally mild in severity, and no serious drug-related adverse events were reported. Plasma exposure to telithromycin (C(max), AUC) showed a tendency to increase with increasing severity of renal impairment in both studies. In patients with severe renal impairment (CL(CR) < 30 mL/min) receiving telithromycin 800 mg in the repeat-dose study, C(max,ss) and AUC((0-24 h)ss) increased 1.5-fold (p < 0.05) to 2.0-fold (p = 0.0005), respectively, compared with healthy subjects. The percentage of dose excreted in urine and renal clearance (CL(R)) of telithromycin was found to decrease significantly with increasing severity of renal impairment in both studies, and CL(R) was found to be independent of telithromycin dose in the repeat-dose study. In conclusion, telithromycin dosage adjustment is not necessary in patients with mild to moderate renal impairment (CL(CR) >/= 30 mL/min). In patients with severe renal impairment (CL(CR) < 30 mL/min), dosage adjustment could be considered.

Review of macrolides (azithromycin, clarithromycin), ketolids (telithromycin) and glycylcyclines (tigecycline)

The advanced macrolides, azithromycin and clarithromycin, and the ketolide, telithromycin, are structural analogs of erythromycin. They have several distinct advantages when compared with erythromycin, including enhanced spectrum of activity, more favorable pharmacokinetics and pharmacodynamics, once-daily administration, and improved tolerability. Clarithromycin and azithromycin are used extensively for the treatment of respiratory tract infections, sexually transmitted diseases, and Helicobacter pylori-associated peptic ulcer disease. Telithromycin is approved for the treatment of community-acquired pneumonia. Severe hepatotoxicity has been reported with the use of telithromycin.

Macrolides, ketolides, and glycylcyclines: azithromycin, clarithromycin, telithromycin, tigecycline

The advanced macrolides, azithromycin and clarithromycin, and the ketolide, telithromycin, are structural analogs of erythromycin. They have several distinct advantages when compared with erythromycin, including enhanced spectrum of activity, more favorable pharmacokinetics and pharmacodynamics, once-daily administration, and improved tolerability. Clarithromycin and azithromycin are used extensively for the treatment of respiratory tract infections, sexually transmitted diseases, and Helicobacter pylori-associated peptic ulcer disease. Telithromycin is approved for the treatment of community-acquired pneumonia. Severe hepatotoxicity has been reported with the use of telithromycin.

Pharmacokinetics of telithromycin using bronchoscopic microsampling after single and multiple oral doses

OBJECTIVES

Bronchoscopic microsampling (BMS) is a new technique for repeated sampling of bronchial epithelial lining fluid (ELF) to obtain the pharmacokinetic profile of drugs. We analyzed the time versus concentration profiles of telithromycin in bronchial ELF obtained by BMS and compared these finding to those in plasma and alveolar ELF obtained by bronchoalveolar lavage (BAL).

METHODS

Bronchial ELF samples were obtained from five healthy subjects using BMS probe at 0, 2, 3, 4, 6, 10 and 24h after single or multiple oral doses of 600 mg of telithromycin. Alveolar ELF was also obtained by BAL 3h after single or multiple oral doses of 600 mg of telithromycin.

RESULTS

The areas under the concentration-time curve from 0 to 24h (AUC0-24) of telithromycin in plasma and bronchial ELF were 2.86+/-0.60 and 19.5+/-10.4 mg h/l after single treatment and 3.60+/-0.49 and 42.2+/-22.7 mg h/l after multiple treatments, respectively. Single and multiple oral doses of telithromycin produced significantly (p<0.05) higher AUC0-24 in bronchial ELF compared to those in plasma. While concentrations in bronchial ELF obtained by BMS were significantly lower than those in alveolar ELF obtained by BAL, they tended to be higher than those in plasma after multiple administration. The telithromycin concentrations obtained by BMS method were very consistent in bronchial ELF at different bronchi at one time point and at the same bronchus at different time points.

CONCLUSIONS

Using the BMS technique, we could describe the pharmacokinetics of telithromycin in bronchial ELF. Furthermore, BMS was reasonably validated and reconfirmed to be a feasible and reliable method for measuring antimicrobial concentrations in bronchial ELF.

Five-Day Telithromycin Once Daily Is as Effective as 10-Day Clarithromycin Twice Daily for the Treatment of Acute Exacerbations of Chronic Bronchitis and Is Associated With Reduced Health-Care Resource Utilization

STUDY OBJECTIVES

To demonstrate equivalence in the clinical efficacy of telithromycin vs clarithromycin treatment of outpatients with acute exacerbations of chronic bronchitis (AECB), and to compare the tolerability and respiratory-related health-care resource utilization associated with these treatment regimens.

DESIGN AND PATIENTS

A randomized, double-blind, multicenter, clinical study was conducted at 105 centers in 14 countries. Adult outpatients (age > or = 30 years) received oral telithromycin, 800 mg qd for 5 days (n = 270), or oral clarithromycin, 500 mg bid for 10 days (n = 282), for the treatment of AECB. Clinical and bacteriologic outcomes were assessed at the posttherapy/test-of-cure (TOC) visit (days 17 to 24; per-protocol population). Health-care resource utilization data were collected for each patient by investigators blinded to study medication up to the late posttherapy visit (days 31 to 36).

RESULTS

Clinical cure rates at the posttherapy/TOC visit were comparable between the groups (telithromycin, 193 of 225 patients [85.8%]; clarithromycin, 206 of 231 patients [89.2%]); bacteriologic outcome was satisfactory for 59 of 72 telithromycin-treated patients (81.9%) vs 63 of 76 clarithromycin-treated patients (82.9%). Health-care resource utilization assessed up to the late posttherapy visit was lower in the telithromycin treatment group than the clarithromycin treatment group, with significantly fewer hospitalizations for respiratory-related causes (one hospitalization vs eight hospitalizations for a total of 4 inpatient days vs 39 inpatient days, respectively), significantly fewer AECB-related emergency department visits (0 vs 8), and fewer unscheduled outpatient visits (11 vs 18). Fewer telithromycin-treated patients reported days lost from work (21 of 91 patients [23.1%]; 133 days) compared with those receiving clarithromycin (30 of 98 patients [30.6%]; 141 days). Telithromycin was well tolerated; adverse events considered possibly related to study medication were reported by 61 of 269 patients (22.7%) and 100 of 280 patients (35.7%) receiving telithromycin and clarithromycin, respectively.

CONCLUSIONS

In this study, 5-day telithromycin treatment was as effective and well tolerated as 10-day clarithromycin treatment for patients with AECB, and was associated with a reduced utilization of health-care resources.

Bacteriological efficacy of 5-day therapy with telithromycin in acute maxillary sinusitis

Increasing resistance among the key pathogens responsible for community-acquired respiratory tract infections, namely Streptococcus pneumoniae, Haemophilus influenzae and Moraxella catarrhalis, has the potential to limit the effectiveness of the antibacterial agents available to treat these infections. Moreover, there are regional differences in the susceptibility patterns observed and, as treatment is usually empirical, choosing an effective treatment can be challenging. Telithromycin, the first ketolide to be approved for clinical use, offers an activity profile that covers the key respiratory pathogens including penicillin- and macrolide-resistant S. pneumoniae as well as beta-lactamase-producing H. influenzae and M. catarrhalis. In a pooled analysis of three large controlled clinical trials involving patients with acute maxillary sinusitis, the bacteriological efficacy of 5- or 10-day treatment with telithromycin and 10-day treatment with comparators was evaluated. Telithromycin administered as a once-daily 800 mg dose for 5 days achieved eradication rates of 91.8, 87.5 and 92.9% for S. pneumoniae, H. influenzae and M. catarrhalis, respectively. Bacteriological eradication of 8/10 and 12/14 isolates of S. pneumoniae resistant to penicillin and erythromycin, respectively, was also reported following 5-day treatment with telithromycin. The clinical efficacy of this regimen was equivalent to that of a 10-day regimen of telithromycin or standard 10-day courses of amoxicillin-clavulanic acid or cefuroxime axetil. Telithromycin 800mg given for 5 days was well tolerated, with the majority of adverse events being of mild or moderate intensity. These data suggest that telithromycin provides effective first-line therapy for use in patients with acute maxillary sinusitis in a short and convenient once-daily dosage regimen.

Telithromycin: The first ketolide antimicrobial

BACKGROUND

Telithromycin is the first of the ketolide antibacterials to receive US Food and Drug Administration (FDA) approval for clinical use. It is approved for the treatment of community-acquired pneumonia (CAP), acute exacerbations of chronic bronchitis (AECB), and acute maxillary sinusitis (AMS) in adults.

OBJECTIVE

This article reviews the mechanism of action, in vitro antimicrobial activity, pharmacokinetics and pharmacodynamics, clinical efficacy, safety, and drug-interaction profile of telithromycin.

METHODS

Relevant studies were identified through a search of the English-language literature indexed on MEDLINE (1990-March 2005) using the terms telithromycin and HMR 3647, a review of the reference lists of identified articles, and a review of the briefing document prepared by the manufacturer of telithromycin for presentation to the FDA Anti-infective Drugs Advisory Committee. A search of abstracts from the Interscience Conference on Antimicrobial Agents and Chemotherapy (2001-2004) also was performed.

RESULTS

The results of in vitro susceptibility studies suggest that telithromycin provides coverage against the key respiratory pathogens, both typical and atypical. In addition, telithromycin may be useful against multidrug-resistant strains of Streptococcus pneumoniae and against Haemophilus influenzae, irrespective of beta-lactamase production. In randomized, double-blind, comparative trials (against amoxicillin, amoxicillin/clavulanate, cefuroxime axetil, clarithromycin, moxifloxacin, or trovafloxacin), telithromycin had comparable efficacy to its comparators in the empiric treatment of CAP (4 studies), AECB (3 studies), and AMS (3 studies). Telithromycin is dosed at 800 mg (two 400-mg tablets) QD in community-acquired respiratory tract infections (RTIs). No dose adjustment is required in the elderly, patients with mild to moderate renal insufficiency, or patients with hepatic insufficiency. The majority of adverse events associated with telithromycin were mild to moderate, with gastrointestinal effects (diarrhea, nausea, vomiting) being the most commonly reported, followed by headache and dizziness. Telithromycin has been associated with elevations in hepatic transaminases and prolongation of the electrocardiographic QTc interval, although the significance of these findings is not known. Telithromycin is also a strong inhibitor of and substrate for the cytochrome P450 (CYP) 3A4 isozyme. Therefore, it is important to monitor for potential drug interactions with medications that prolong the QTc interval or are metabolized by the CYP system.

CONCLUSIONS

Telithromycin appears to be a useful option for the empiric treatment of community-acquired RTIs in adults. It may be particularly useful in the outpatient setting in areas with high rates of penicillin- and macrolide-resistant S pneumoniae; it may also be an alternative agent for patients who are allergic to beta-lactams and live in areas with a high prevalence of multidrug-resistant S pneumoniae or for those who have failed to respond to beta-lactam- or macrolide-based therapy.

Ketolides in the treatment of community-acquired respiratory tract infections: A review

BACKGROUND

The increasing prevalence of resistance to established antibiotics among key respiratory bacterial pathogens highlights a need for new antibacterial agents for the treatment of community-acquired respiratory tract infections (RTIs). Ketolides are a new class of antibiotics specifically developed for the treatment of RTIs.

OBJECTIVE

The aim of this review was to present the current status of treatment of RTIs with ketolides, focusing on telithromycin-the first ketolide to be approved by the US Food and Drug Administration for clinical use.

METHODS

TO GATHER EVIDENCE ON THE CURRENT STATUS OF KETOLIDES, A LITERATURE SEARCH WAS CONDUCTED USING MEDLINE (YEARS: 1990-2005; key terms: ketolides, telithromycin, and HMR3647).

RESULTS

Telithromycin shows strong in vitro activity against the major respiratorypathogens, including strains resistant to other antibiotics, as well as the atypical respiratory pathogens. The pharmacokinetic properties of telithromycin are compatible with once-daily dosing. Clinical trials have demonstrated that telithromycin 800 mg QD for 5 to 10 days is effective in the treatment of acute bacterial sinusitis, acute bacterial exacerbations of chronic bronchitis, and mild to moderate community-acquired pneumonia. Overall, telithromycin is well tolerated by patients. Drug-drug interactions are similar to those reported for macrolides.

CONCLUSION

Evidence to date indicates that telithromycin is an effective andwell-tolerated empiric treatment for community-acquired RTIs.

Telithromycin for the treatment of acute exacerbations of chronic bronchitis

Pooled data from three randomized, double-blind, multi- centre studies evaluated the efficacy and tolerability of telithromycin 800 mg once daily for 5 days vs. standard comparators (10-day amoxicillin-clavulanate 500/125 mg three times daily, clarithromycin 500 mg or cefuroxime axetil 500 mg twice daily) in the outpatient treatment for acute exacerbations of chronic bronchitis. Per-protocol clinical cure rates at post-therapy/test of cure (days 17-24) were 86.0 and 85.8% for telithromycin and comparators, respectively, and 79.1 and 78.7%, respectively, at late post-therapy (days 31-36). Clinical cure rates were comparable for patients at increased risk, including those of > or =65 years and those with severe infection or significant airway obstruction (telithromycin, > or =77.1%; comparators, > or =75.0%). Telithromycin was well tolerated. Most adverse events considered possibly related to study medication were gastrointestinal and of mild intensity. In conclusion, 5-day telithromycin therapy is as effective and well tolerated as 10-day treatment with standard comparators.

Pharmacodynamic profile of telithromycin against macrolide- and fluoroquinolone-resistant Streptococcus pneumoniae in a neutropenic mouse thigh model

The new ketolide telithromycin has potent in vitro activity against Streptococcus pneumoniae, including strains resistant to penicillin, macrolides, and fluoroquinolones. The aim of the present study was to define the pharmacodynamic profile of telithromycin against S. pneumoniae strains with various resistance profiles in an in vivo system. Ten S. pneumoniae strains were studied; seven exhibited penicillin resistance, six demonstrated macrolide resistance, and two exhibited gatifloxacin resistance. The telithromycin MICs for all isolates were < or =0.5 microg/ml. Using the murine thigh infection model, CD-1/ICR mice were rendered neutropenic and were then inoculated with 10(5) to 10(6) CFU of S. pneumoniae per thigh. Telithromycin was administered orally at doses ranging from 25 to 800 mg/kg of body weight/day, with the doses administered one, two, three, or four times a day. The activity of telithromycin was assessed by determination of the change in the bacterial density in thigh tissue after 24 h of treatment for each treatment group and the untreated controls. Pharmacokinetic studies of telithromycin were conducted in infected, neutropenic animals. The levels of protein binding by telithromycin in mice ranged from 70 to 95% over the observed range of pharmacokinetic concentrations. By using either the total or the free concentrations of telithromycin, the area under the concentration-time curve (AUC)/MIC ratio was a strong determinant of the response against S. pneumoniae, regardless of the phenotypic resistance profile. The maximal efficacy (the 95% effective dose) against this cohort of S. pneumoniae strains and bacterial inhibition (stasis) of telithromycin were predicted by ratios of the AUC for the free drug concentration/MIC of approximately 1,000 and 200, respectively.

Nonresponses and treatment failures with conventional empiric regimens in patients with community-acquired pneumonia

Although most patients with suspected CAP respond to empiric therapy,a small number of patients do not respond in the expected fashion. Age and underlying comorbid conditions have a strong influence on the course of illness. Less common causes of treatment failures include overwhelming infection, antimicrobial resistance, and misdiagnosis. It is a common practice for empiric antimicrobial treatment of CAP to be initiated without microbiologic studies. Clinicians carefully should observe these patients for unusual or slow responses and should be ready to pursue a more extensive search for the cause of treatment failure.

Macrolides and ketolides: azithromycin, clarithromycin, telithromycin

The advanced macrolides, azithromycin and clarithromycin, and the ketolide telithromycin are structural analogues of erythromycin. They have several distinct advantages when compared with erythromycin including enhanced spectrum of activity, more favorable pharmacokinetics and pharmacodynamics, once daily administration, and improved tolerability. This article reviews the pharmacokinetics, antimicrobial activity, clinical use, and adverse effects of these antimicrobial agents.

Ketolides: an emerging treatment for macrolide-resistant respiratory infections, focusing on S. pneumoniae

Resistance to antibiotics in community acquired respiratory infections is increasing worldwide. Resistance to the macrolides can be class-specific, as in efflux or ribosomal mutations, or, in the case of erythromycin ribosomal methylase (erm)-mediated resistance, may generate cross-resistance to other related classes. The ketolides are a new subclass of macrolides specifically designed to combat macrolide-resistant respiratory pathogens. X-ray crystallography indicates that ketolides bind to a secondary region in domain II of the 23S rRNA subunit, resulting in an improved structure-activity relationship. Telithromycin and cethromycin (formerly ABT-773) are the two most clinically advanced ketolides, exhibiting greater activity towards both typical and atypical respiratory pathogens. As a subclass of macrolides, ketolides demonstrate potent activity against most macrolide-resistant streptococci, including ermB- and macrolide efflux (mef)A-positive Streptococcus pneumoniae. Their pharmacokinetics display a long half-life as well as extensive tissue distribution and uptake into respiratory tissues and fluids, allowing for once-daily dosing. Clinical trials focusing on respiratory infections indicate bacteriological and clinical cure rates similar to comparators, even in patients infected with macrolide-resistant strains.

Comparative in vitro activity of antiribosomal agents on penicillin-susceptible and -resistant Streptococcus pneumoniae in relation to their resistance genotypes

A collection of 326 strains of Streptococcus pneumoniae isolated from blood, cerebrospinal fluid, bronchoalveolar lavage, transtracheal aspirate or sputum from January 1996-June 2002 were included in this study. The activity of clarithromycin, clindamycin, telithromycin, linezolid and quinupristin/dalfopristin against penicillin G and erythromycin A susceptible and resistant pneumococci were determined; the erythromycin A resistance phenotypes and genotypes were identified and susceptibilities of these agents were assessed according to the resistance genotypes. MICs were determined for all strains of pneumococci using an agar dilution method. MLS(B) resistance phenotypes were determined by the double disk (erythromycin A and clindamycin) diffusion method. Genetic determinants for macrolide resistance were identified by PCR using primers specific for erm(B) and mef(A). Erythromycin A resistance was detected in 13.8% of the strains. MLS(B) resistance phenotype was observed in 82% of these (60% being cMLS(B) and 40% being iMLS(B)), and M type resistance in about 18%. All the MLS(B) phenotype strains except four, revealed the presence of erm(B) gene and all except one M phenotype strains revealed the mef(A) gene. Of the erythromycin A resistant pneumococci about 49% were also resistant to clindamycin. No strains were resistant to telithromycin, quinupristin/dalfopristin and linezolid. Telithromycin had the lowest MIC values for both erythromycin A resistant and susceptible strains of all the antiribosomal agents tested. The most prevalent mechanism of macrolide resistance was mediated by the erm(B) gene leading to the expression of MLS(B) phenotype. Telithromycin was the most active antiribosomal agent, regardless of the macrolide resistance genotype of the pneumococci tested.

Activities of cethromycin and telithromycin against recent North American isolates of Streptococcus pneumoniae

The in vitro activities of two investigational ketolides, cethromycin (formerly ABT-773) and telithromycin, were determined for a selected group of 312 Streptococcus pneumoniae isolates from a national surveillance program. The MIC of cethromycin at which 50% of the isolates were inhibited was 0.008 micro g/ml, and the MIC at which 90% of the isolates were inhibited was 0.06 micro g/ml; the corresponding values for telithromycin were </=0.015 and 0.25 micro g/ml, respectively. For six quinupristin-dalfopristin-resistant strains, the cethromycin MICs were 0.25 to 16 micro g/ml and the telithromycin MICs were 1 to 4 micro g/ml. However, there was only 0.3% resistance to telithromycin.

Fluoroquinolone and macrolide treatment failure in pneumococcal pneumonia and selection of multidrug-resistant isolates

Streptococcus pneumoniae serotype 3, isolated from a penicillin-allergic patient and initially susceptible to fluoroquinolones, macrolides, lincosamides, quinupristin-dalfopristin, and telithromycin, became resistant to all these drugs during treatment. Mutations in the parC and gyrA and in the 23S rRNA and the ribosomal protein L22 genes were detected in the resistant isolates.

In vitro activities of telithromycin and 10 oral agents against aerobic and anaerobic pathogens isolated from antral puncture specimens from patients with sinusitis

A study of the comparative in vitro activity of telithromycin, a new ketolide, against 155 aerobic and 171 anaerobic antral sinus puncture isolates showed it to be active against a broad range of sinus pathogens. All pneumococci, including erythromycin-resistant strains, were susceptible to telithromycin at < or = 0.5 microg/ml; all Haemophilus influenzae and Eikenella corrodens strains were inhibited by < or = 4 microg of telithromycin/ml; all Moraxella spp. and beta-lactamase-producing Prevotella species strains were inhibited by < or = 0.25 and 0.5 microg of telithromycin/ml, respectively. Among all anaerobes tested, 94% (160 of 171 strains) were susceptible to < or = 4 microg of telithromycin/ml; however, 8 of 17 (47%) Fusobacterium strains, 2 Veillonella strains, and 1 Peptostreptococcus micros strain required > 4 microg of telithromycin/ml for inhibition. Telithromycin may offer a therapeutic alternative for sinus infections, including those due to erythromycin-resistant pneumococci.

Dead bugs don't mutate: susceptibility issues in the emergence of bacterial resistance

The global emergence of antibacterial resistance among common and atypical respiratory pathogens in the last decade necessitates the strategic application of antibacterial agents. The use of bactericidal rather than bacteriostatic agents as first-line therapy is recommended because the eradication of microorganisms serves to curtail, although not avoid, the development of bacterial resistance. Bactericidal activity is achieved with specific classes of antimicrobial agents as well as by combination therapy. Newer classes of antibacterial agents, such as the fluoroquinolones and certain members of the macrolide/lincosamine/streptogramin class have increased bactericidal activity compared with traditional agents. More recently, the ketolides (novel, semisynthetic, erythromycin-A derivatives) have demonstrated potent bactericidal activity against key respiratory pathogens, including Streptococcus pneumoniae, Haemophilus influenzae, Chlamydia pneumoniae, and Moraxella catarrhalis. Moreover, the ketolides are associated with a low potential for inducing resistance, making them promising first-line agents for respiratory tract infections.

Telithromycin is as effective as amoxicillin/clavulanate in acute exacerbations of chronic bronchitis

This randomized, double-blind study evaluated the efficacy and safety of a short, 5-day course of telithromycin, a new ketolide antibacterial, compared with a standard 10-day course of amoxicillin/clavulanate, in the treatment of acute exacerbations of chronic bronchitis (AECB). The study enrolled 325 adult patients with AECB and a history of chronic obstructive pulmonary disease (COPD). Patients received either telithromycin 800 mg once daily (qd) for 5 days (followed by placebo for 5 days) or amoxicillin/clavulanate 500/125 mg three times daily (tid) for 10 days. Clinical cure rates for telithromycin post-therapy (Days 17-21, test-of-cure) and late post-therapy (Days 31-36) were 86.1 and 78.1%, respectively; 82.1 and 75.0% for amoxicillin/clavulanate. Excellent clinical cure rates were also observed for high-risk patients. Bacteriologic outcome was satisfactory for 69.2% of telithromycin recipients vs 70.0% for amoxicillin/clavulanate recipients. Both treatments were generally well tolerated, although the frequency of drug-related adverse events was almost two-fold higher for amoxicillin/clavulanate (25.0 vs. 13.1%). Thus, a 5-day course of telithromycin 800 mg qd is an effective and well-tolerated alternative to a standard 10-day course of amoxicillin/clavulanate 500/125 mg tid for first-line empiric treatment of AECB in adults with COPD.

Comparative in vitro activity of penicillin G, levofloxacin, moxifloxacin, telithromycin, pristinamycin, quinupristin-dalfopristin and linezolid against ofloxacin-intermediate and -resistant Streptococcus pneumoniae

Screening by ofloxacin disk was carried out on 1158 strains of Streptococcus pneumoniae in order to investigate the in vitro bacteriostatic activity of penicillin G, levofloxacin, moxifloxacin, telithromycin, linezolid, pristinamycin and quinupristin-dalfopristin against ofloxacin-intermediate and -resistant S. pneumoniae strains. It was concluded that these new antimicrobial agents could be useful for the treatment of pneumococcal infections caused by penicillin-sensitive and -resistant S. pneumoniae, and would represent a valid therapeutic option for patients allergic to beta-lactams, should they prove to be potent in vivo.

The ketolides: a critical review

Ketolides are a new class of macrolides designed particularly to combat respiratory tract pathogens that have acquired resistance to macrolides. The ketolides are semi-synthetic derivatives of the 14-membered macrolide erythromycin A, and retain the erythromycin macrolactone ring structure as well as the D-desosamine sugar attached at position 5. The defining characteristic of the ketolides is the removal of the neutral sugar, L-cladinose from the 3 position of the ring and the subsequent oxidation of the 3-hydroxyl to a 3-keto functional group. The ketolides presently under development additionally contain an 11, 12 cyclic carbamate linkage in place of the two hydroxyl groups of erythromycin A and an arylalkyl or an arylallyl chain, imparting in vitro activity equal to or better than the newer macrolides. Telithromycin is the first member of this new class to be approved for clinical use, while ABT-773 is presently in phase III of development. Ketolides have a mechanism of action very similar to erythromycin A from which they have been derived. They potently inhibit protein synthesis by interacting close to the peptidyl transferase site of the bacterial 50S ribosomal subunit. Ketolides bind to ribosomes with higher affinity than macrolides. The ketolides exhibit good activity against Gram-positive aerobes and some Gram-negative aerobes, and have excellent activity against drug-resistant Streptococcus pneumoniae, including macrolide-resistant (mefA and ermB strains of S. pneumoniae). Ketolides such as telithromycin display excellent pharmacokinetics allowing once daily dose administration and extensive tissue distribution relative to serum. Evidence suggests the ketolides are primarily metabolised in the liver and that elimination is by a combination of biliary, hepatic and urinary excretion. Pharmacodynamically, ketolides display an element of concentration dependent killing unlike macrolides which are considered time dependent killers. Clinical trial data are only available for telithromycin and have focused on respiratory infections including community-acquired pneumonia, acute exacerbations of chronic bronchitis, sinusitis and streptococcal pharyngitis. Bacteriological and clinical cure rates have been similar to comparators. Limited data suggest very good eradication of macrolide-resistant and penicillin-resistant S. pneumoniae. As a class, the macrolides are well tolerated and can be used safely. Limited clinical trial data suggest that ketolides have similar safety profiles to the newer macrolides. Telithromycin interacts with the cytochrome P450 enzyme system (specifically CYP 3A4) in a reversible fashion and limited clinically significant drug interactions occur. In summary, clinical trials support the clinical efficacy of the ketolides in upper and lower respiratory tract infections caused by typical and atypical pathogens including strains resistant to penicillins and macrolides. Considerations such as local epidemiology, patterns of resistance and ketolide adverse effects, drug interactions and cost relative to existing agents will define the role of these agents. The addition of the ketolides in the era of antibacterial resistance provides clinicians with more options in the treatment of respiratory infections.

Antibiotic susceptibilities of Parachlamydia acanthamoeba in amoebae

Parachlamydia acanthamoeba are intracellular bacteria of amoebae and are considered potential etiological agents of human pneumonia. We have determined the in vitro antibiotic susceptibilities of two strains (strain Bn(9) and Hall's coccus) in Acanthamoeba polyphaga. The two strains were susceptible to tetracyclines, macrolides, and rifampin, but resistant to fluoroquinolones.

Resistance among Streptococcus pneumoniae: Implications for drug selection

Streptococcus pneumoniae is an important pathogen in many community-acquired respiratory infections in the United States and a leading cause of morbidity and mortality worldwide. Unfortunately, S. pneumoniae is becoming increasingly resistant to a variety of antibiotics. Results of recent surveillance studies in the United States show that the prevalence of penicillin-nonsusceptible S. pneumoniae ranges from 25% to >50%, and rates of macrolide resistance among pneumococci are reported to be as high as 31%. A high prevalence of resistance to other antimicrobial classes is found among penicillin-resistant strains. Newer quinolones (e.g., gatifloxacin, gemifloxacin, and moxifloxacin) that have better antipneumococcal activity in vitro are the most active agents and therefore are attractive options for treatment of adults with community-acquired respiratory infections. Efforts should be made to prevent pneumococcal infections in high-risk patients through vaccination.

Antimicrobial resistance among clinical isolates of Streptococcus pneumoniae in Canada during 2000

A total of 2,245 clinical isolates of Streptococcus pneumoniae were collected from 63 microbiology laboratories from across Canada during 2000 and characterized at a central laboratory. Of these isolates, 12.4% were not susceptible to penicillin (penicillin MIC, >or=0.12 microg/ml) and 5.8% were resistant (MIC, >or=2 microg/ml). Resistance rates among non-beta-lactam agents were the following: macrolides, 11.1%; clindamycin, 5.7%; chloramphenicol, 2.2%; levofloxacin, 0.9%; gatifloxacin, 0.8%; moxifloxacin, 0.4%; and trimethoprim-sulfamethoxazole, 11.3%. The MICs at which 90% of the isolates were inhibited (MIC90s) of the fluoroquinolones were the following: gemifloxacin, 0.03 microg/ml; BMS-284756, 0.06 microg/ml; moxifloxacin, 0.12 microg/ml; gatifloxacin, 0.25 microg/ml; levofloxacin, 1 microg/ml; and ciprofloxacin, 1 microg/ml. Of 578 isolates from the lower respiratory tract, 21 (3.6%) were inhibited at ciprofloxacin MICs of >or=4 microg/ml. None of the 768 isolates from children were inhibited at ciprofloxacin MICs of >or=4 microg/ml, compared to 3 of 731 (0.6%) from those ages 15 to 64 (all of these >60 years old), and 27 of 707 (3.8%) from those over 65. The MIC90s for ABT-773 and telithromycin were 0.015 microg/ml for macrolide-susceptible isolates and 0.12 and 0.5 microg/ml, respectively, for macrolide-resistant isolates. The MIC of linezolid was <or=2 microg/ml for all isolates. Many of the new antimicrobial agents tested in this study appear to have potential for the treatment of multidrug-resistant strains of pneumococci.

Therapies in development for community-acquired pneumonia

The current use of antimicrobials has become more complex due to the extensive emergence of antibiotic resistance. The single most important approach in resistance control is probably the judicious use of chemotherapeutic agents. New agents that may be of use in the treatment of community-acquired pneumonia are currently in development. Antimicrobials can be grouped according to their mechanism of action. These include protein synthesis inhibitors (ketolides, oxazolidinones, streptogramins and glycylcyclines), nucleic acid synthesis inhibitors (fluoroquinolones), peptidoglycan synthesis inhibitors (beta-lactams and glycopeptides) and agents interfering with membrane function (cationic peptides and lipopeptides). Among those agents under development, only the oxazolidinones, the cationic peptides and the lipopeptide antibiotics can be truly regarded as structurally novel inhibitors as the other agents are analogues of existing compounds which have been in clinical use for many years.

Telithromycin: the first of the ketolides

OBJECTIVE

To review the chemistry, spectrum of activity, pharmacology, clinical efficacy, and safety of telithromycin.

DATA SOURCES

A MEDLINE search from 1966 to December 2000 was performed via OVID and PubMed using the following search terms: HMR 3647, HMR3647, Ketek, RU 66647, and telithromycin. An extensive review of retrieved literature, abstracts from international scientific conferences, and minutes from regulatory authority meetings was also performed.

DATA EXTRACTION

Medicinal chemistry, in vitro, animal, and human trials were reviewed for information on the antimicrobial activity, clinical efficacy, pharmacology, and safety of telithromycin.

DATA SYNTHESIS

Several chemical modifications to the macrolide structure have led to the development of telithromycin, the first ketolide antimicrobial that demonstrates improved activity against penicillin- and macrolide/azalide-resistant Streptococcus pneumoniae due to its unique binding to the ribosomal target site. Although telithromycin may be useful in the treatment of community-acquired respiratory tract infections due to its activity against common typical and atypical pathogens, questions concerning its reliable activity against Haemophilus influenzae need to be addressed. Telithromycin's pharmacokinetics permit once-daily dosing for abbreviated periods and good distribution into lung tissue and phagocytic cells. Clinical and bacteriologic cure rates have been similar to those of comparator agents in human efficacy trials; however, the incidence of adverse gastrointestinal events were generally higher with telithromycin patients. Like other macrolides and many newer fluoroquinolones, telithromycin's ability to prolong the QTc interval is a potential safety issue, especially in elderly patients with predisposing conditions or those who are concurrently receiving drugs that are substrates for CYP2D6 and 3A4. Liver function test elevations demonstrated during clinical trials, although not overtly severe, may warrant monitoring in some patients taking multiple hepatically metabolized/cleared agents.

CONCLUSIONS

Telithromycin offers potential advantages over traditional macrolides/azalides for community-acquired respiratory tract infections caused by macrolide-resistant pathogens. Further studies are needed to elucidate its clinical efficacy against H. influenzae, potential drug interactions, and safety in various subpopulations.

Ketolides in the treatment of respiratory infections

The ketolides are a new class of macrolides specifically designed to combat respiratory tract pathogens that have acquired resistance to macrolides. The ketolides are semi-synthetic derivatives of the 14-membered macrolide erythromycin A. There are currently two ketolides in the late stages of clinical development in the US (telithromycin [HMR-364, Kelek; Aventis] and ABT-773 [Abbot Laboratories]), as well as newer compounds in earlier stages of testing. Ketolides have a mechanism of action very similar to that of erythromycin A. They potently inhibit protein synthesis by interacting close to the peptidyl transferase site of the bacterial 50S ribosomal subunit. Ketolides bind to ribosomes with higher affinity than macrolides. The ketolides exhibit good activity against Gram-positive and some Gram-negative aerobes and have are active against macrolide-resistant Streptococcus species, including most mef A and erm B strains of Streptococcus pneumoniae. Ketolides have pharmacokinetics which allow once-daily dosing and extensive tissue distribution with very high uptake into respiratory tissues and fluids relative to serum. Evidence suggests the ketolides are primarily metabolised by the cytochrome P450 (CYP) enzyme system in the liver and that elimination is a combination of biliary, hepatic and urinary excretion. Clinical trial data are only available for telithromycin and have focused on respiratory tract infections (RTIs) including community-acquired pneumonia (CAP), acute exacerbations of chronic bronchitis (AECB), sinusitis and streptococcal pharyngitis. Bacteriological and clinical cure rates have been similar to comparators. Ketolides have similar safety profiles to the newer macrolides. In summary, early clinical trials support the clinical efficacy of the ketolides in common RTIs, including activity against macrolide-resistant pathogens.

Advances in the research and development of chemotherapeutic agents for respiratory tract bacterial infections

The activity of existing antibiotics is diminishing due to the increasing number of resistant strains and by the increase of infections with naturally resistant microorganisms. New agents are urgently needed to meet this challenge and the molecular strategies adopted for the discovery of these compounds must focus on minimizing the emergence of future resistance to them. Novel compounds can be grouped on the basis of their mechanism of action: inhibitors of nucleic acid synthesis (fluoroquinolones), inhibitors of protein synthesis (ketolides, oxazolidinones, streptogramins, and glycylcyclines), inhibitors of peptidoglycan synthesis (beta-lactams and glycopeptides), and agents interfering with membrane function (cationic peptides, and lipopeptides). Regarding the agents that are already in the research and development pipeline, only the oxazolidinones, the cationic peptides and the lipopeptide antibiotics can be truly considered as structurally novel inhibitors because the other agents are analogues of existing compounds that have been in use for many years.

Bronchopulmonary disposition of the ketolide telithromycin (HMR 3647)

Telithromycin (HMR 3647) is the first member of a new family of antimicrobials, the ketolides, developed specifically for the treatment of community-acquired respiratory tract infections. Telithromycin has proven in vitro activity against both common and atypical respiratory tract pathogens. The penetration of telithromycin into bronchopulmonary tissues and subsequent elimination from these sites were evaluated in four groups (groups A, B, C, and D) of six healthy male subjects who received telithromycin at 800 mg once daily for 5 days. Subjects in groups A, B, C, and D underwent fiberoptic bronchoscopy and bronchoalveolar lavage 2, 8, 24, and 48 h after receipt of the last dose, respectively. The concentration of telithromycin in the alveolar macrophages, epithelial lining fluid (ELF), and plasma was determined by the agar diffusion method with Bacillus subtilis ATCC 6633 as the test organism. The concentration of telithromycin in alveolar macrophages markedly exceeded that in plasma, reaching up to 146 times the concentration in plasma 8 h after dosing (median concentration, 81 mg/liter). Telithromycin was retained in alveolar macrophages 24 h after dosing (median concentration, 23 mg/liter), and it was still quantifiable 48 h after dosing (median concentration, 2.15 mg/liter). Telithromycin median concentrations in ELF also markedly exceeded concentrations in plasma (median concentration in ELF, 3.7 mg/liter 8 h after dosing). Telithromycin achieves high and sustained concentrations in ELF and in alveolar macrophages, while it maintains adequate levels in plasma, providing an ideal pharmacokinetic profile for effective treatment of community-acquired respiratory tract infections caused by either common or atypical, including intracellular, respiratory tract pathogens.

In vitro activity of the ketolide ABT-773

The in vitro activities of ABT-773, azithromycin, erythromycin, and clindamycin were compared by testing 1,223 clinical isolates selected to represent different species and phenotypes. ABT-773 was particularly potent against staphylococci (the MIC at which 90% of the strains tested were inhibited [MIC(90)] was < or =0.06 microg/ml), including all strains that were macrolide resistant but clindamycin susceptible. Streptococcus pneumoniae and other streptococci were inhibited by low concentrations of ABT-773, and that included most erythromycin-resistant strains. Against Haemophilus influenzae, ABT-773 and azithromycin were similar in their antibacterial potency (MIC(90), 4.0 and 2.0 microg/ml, respectively).

Activity of quinupristin-dalfopristin in invasive isolates of Streptococcus pneumoniae from Italy

Eighty-five recent isolates of Streptococcus pneumoniae from patients with invasive disease were examined for their susceptibility to erythromycin, clindamycin, penicillin and quinupristin-dalfopristin by E test. A novel duplex PCR assay was used to detect the presence of the erm(B) or mef(A) genes in all of the erythromycin-resistant isolates. All of the strains tested were susceptible to the combination quinupristin-dalfopristin, regardless of their susceptibility to penicillin or to erythromycin. By duplex PCR, two-thirds of the erythromycin-resistant strains harbored erm, and one-third harbored mef. The activity of quinupristin-dalfopristin was not influenced by the genetic determinant of erythromycin resistance. The in vitro susceptibility of S. pneumoniae to quinupristin-dalfopristin is promising for future use; however, it is important to monitor the possible emergence of resistance.

Novel streptogramin antibiotics

Streptogramins represent a unique class of antibiotics remarkable for their antibacterial activity and their unique mechanism of action. These antibiotics are produced naturally as secondary metabolites by a number of Streptomyces species and have been classified into two main groups. They consist of at least two structurally unrelated compounds, group A or M (macrolactones) and group B or S (cyclic hexadepsipeptides). Both groups bind bacterial ribosomes and inhibit protein synthesis at the elongation step and they act synergistically in vitro against many microorganisms. Streptogramins A and B act synergistically in vivo; the mixture of the two compounds is more powerful than the individual components and their combined action is irreversible. The pharmacokinetic parameters of group A and B streptogramins in blood are similar. The major gap, limiting the therapeutic use of the natural compounds, was represented by the lack dissolution in water. The synthesis of water-soluble derivatives of pristinamycin I(A) and II(B) has allowed the development of injectable, first represented by quinupristin/dalfopristin (Synercid) and oral formulations, represented by RPR-106972, streptogramins with fixed compositions. Streptogramins have demonstrated activity against Gram-positive microorganisms in vitro and in vivo, including those with multi-drug resistance. Moreover, the absence of cross-resistance to macrolides in many of these microorganisms and the rarity of cross-resistance between the two groups of antibiotics associated with the rapid bacterial killing are the principal features of the streptogramins, offering the possibility for treating the rising number of infections that are caused by multi-resistant Gram-positive bacteria.

Pharmacodynamics of telithromycin In vitro against respiratory tract pathogens

Telithromycin (HMR 3647) is a new ketolide that belongs to a new class of semisynthetic 14-membered-ring macrolides which have expanded activity against multidrug-resistant gram-positive bacteria. The aim of the present study was to investigate different basic pharmacodynamic properties of this new compound. The following studies of telithromycin were performed: (i) studies of the rate and extent of killing of respiratory tract pathogens with different susceptibilities to erythromycin and penicillin exposed to a fixed concentration that corresponds to a dose of 800 mg in humans, (ii) studies of the rate and extent of killing of telithromycin at five different concentrations, (iii) studies of the rate and extent of killing of the same pathogens at three different inocula, (iv) studies of the postantibiotic effect and the postantibiotic sub-MIC effect of telithromycin, and (v) determination of the rate and extent of killing of telithromycin in an in vitro kinetic model. In conclusion, telithromycin exerted an extremely fast killing of all strains of Streptococcus pneumoniae both with static concentrations and in the in vitro kinetic model. A slower killing of the strains of Streptococcus pyogenes was noted, with regrowth in the kinetic model of a macrolide-lincosamide-streptogramin B-inducible strain. The strains of Haemophilus influenzae were not killed at all at a concentration of 0.6 mg/liter due to high MICs. A time-dependent killing was seen for all strains. No inoculum effect was seen for the strains of S. pneumoniae, with a 99.9% reduction in the numbers of CFU for all inocula at both 8 h and 24 h. The killing of the strains of S. pyogenes was reduced by 1 log(10) CFU at 8 h and 2 to 3 log(10) CFU at 24 h when the two lower inocula were used but not at all at 8 and 24 h when the highest inoculum was used. For both of the H. influenzae strains there was an inoculum effect, with 1 to 2 log(10) CFU less killing for the inoculum of 10(8) CFU/ml in comparison to that for the inoculum of 10(6) CFU/ml. Overall, telithromycin exhibited long postantibiotic effects and postantibiotic sub-MIC effects for all strains investigated.

Pharmacokinetics of the new ketolide telithromycin (HMR 3647) administered in ascending single and multiple doses

Telithromycin (HMR 3647) is a novel ketolide antimicrobial with good activity against both common and atypical respiratory pathogens, including many resistant strains. This randomized, three-period crossover study determined the dose proportionality of telithromycin pharmacokinetics after single and multiple dosing in healthy subjects. In each treatment period, subjects received a single oral dose of 400, 800 or 1,600 mg of telithromycin followed 4 days later by the same dose once daily for 7 days. Blood and urine samples were taken throughout the study for determination of pharmacokinetic parameters for telithromycin and RU 76363, its main metabolite. Telithromycin and RU 76363 achieved steady state within 2 to 3 days of once-daily dosing. A slight accumulation of telithromycin was observed after 7 days of therapy, with values of the area under the concentration-time curve from 0 to 24 h approximately 1.5 times higher than those achieved with the single dose. The pharmacokinetics of telithromycin and RU 76363 deviated moderately from dose proportionality. At a dose of 800 mg/day, telithromycin attained mean maximal and trough plasma concentrations of 2.27 and 0. 070 mg/liter respectively. Elimination was biphasic; initial and terminal half-lives were 2.87 and 9.81 h for the 800-mg dose. Study medication was well tolerated, although adverse events tended to be more frequent at the 1,600-mg dose. This study showed that telithromycin was generally well tolerated and suggests that a once-daily 800-mg oral dose of telithromycin maintains an effective concentration in plasma for the treatment of respiratory tract infections involving the key respiratory pathogens.

Quinupristin/dalfopristin: a therapeutic review

BACKGROUND

The proliferation of multidrug-resistant gram-positive bacteria, including methicillin-resistant Staphylococcus aureus and vancomycin-resistant Enterococcus faecium (VREF), has created a pressing need for effective alternative antibiotics. Quinupristin/dalfopristin is a new combination streptogramin product with a selective spectrum of antibacterial activity, mainly against gram-positive aerobic bacteria. It has been assessed primarily in emergency-use protocols, in hospitalized patients with skin and skin-structure infections, and in patients with VREF bacteremia.

OBJECTIVES

The objectives of this review were to summarize important results of in vitro microbiologic studies; to provide information on relevant pharmacokinetic parameters, drug interactions, and Y-site compatibility; and to assess efficacy and safety data from clinical studies of quinupristin/dalfopristin.

METHODS

Articles included in this review were identified by a MEDLINE search of the literature published between 1966 and September 2000 using the terms Synercid, quinupristin, and dalfopristin. Additional articles were retrieved from the reference lists of articles identified in the MEDLINE search.

RESULTS

In vitro analysis of the spectrum of activity of quinupristin/dalfopristin has confirmed its relatively selective coverage of gram-positive aerobic bacteria. Both quinupristin and dalfopristin undergo hepatic metabolism and are extensively excreted in the feces. Combination quinupristin/dalfopristin inhibits the cytochrome P450 3A4 pathway, and caution is warranted with concomitant use of other medications eliminated via this pathway. In trials in patients with VREF infections, treatment success with quinupristin/dalfopristin varied depending on the site of infection, ranging from 51.9% in bacteremia of unknown origin to 88.9% in urinary tract infections. The results of comparative clinical trials suggest that quinupristin/dalfopristin has similar efficacy to that of commonly used antibiotics, including cefazolin, oxacillin, and vancomycin, in patients with skin and skin-structure infections or nosocomial pneumonia. The most frequently reported adverse effects with administration of quinupristin/dalfopristin were infusion-site inflammation, pain, and edema; other infusion-site reactions; and thrombophlebitis. Arthralgia, myalgia, nausea, diarrhea, vomiting, and rash occurred in 2.5% to 4.6% of patients and were the most frequently reported systemic adverse events.

CONCLUSIONS

Outcomes data from clinical trials indicate that quinupristin/dalfopristin has the potential to play an important role in the treatment of bacteremia, complicated skin and skin-structure infections, and nosocomial pneumonia caused by VREF. Issues of bacterial resistance to quinupristin/dalfopristin and other appropriate uses of this combination agent remain to be elucidated.

[Problems with gram-positive bacteria: resistance in staphylococci, enterococci, and pneumococci to antimicrobial drugs]

The resistance in staphylococci, enterococci, and pneumococci is reviewed. The author also recalls the first cases, and presents an overview of the distribution of cases in the world, the genetic and molecular mechanisms of resistance, the importance in Brazil and therapeutic alternatives. The factors that contribute to the dissemination of these problem bacteria and the measures for their control are emphasized.

Frequency of occurrence and antimicrobial susceptibility patterns for pathogens isolated from latin american patients with a diagnosis of pneumonia: results from the SENTRY antimicrobial surveillance program (1998)

The correct empiric choice of antimicrobial therapy in the treatment of pneumonia in hospitalized patients has established itself as a major therapeutic challenge to clinicians. Selection of an inappropriate antimicrobial agent could lead to increased rates of mortality and morbidity. Characteristics of pathogens responsible for this infection such as species prevalence, overall antimicrobial resistance rates, and mechanisms of detected resistance could serve as an invaluable resource to clinicians in making such therapeutic selections. This report addresses the aforementioned problems/needs by analysis of 712 strains isolated from the lower respiratory tract of patients hospitalized with a diagnosis of pneumonia in 10 Latin American medical centers in the SENTRY Antimicrobial Surveillance Program (1998). The four most frequently isolated pathogens (no/% of total) were: Pseudomonas aeruginosa (191/26.8%), Staphylococcus aureus (171/24.0%), Klebsiella spp. (86/12.1%), and Acinetobacter spp. (75/10.5%); representing nearly 75.0% of all isolates. More than 40 antimicrobial agents (23 reported) were tested against these isolates by reference broth microdilution methodology, and susceptibility profiles were established. The nonfermentative Gram-negative bacteria (P. aeruginosa and Acinetobacter spp.) exhibited high levels of resistance to the agents tested. Amikacin (77.5% susceptible) was the most active drug tested against P. aeruginosa 50.0% against the Acinetobacter spp. isolates. Based on published interpretive criteria, over 22.0% of the Klebsiella spp. and 12.5% of the Escherichia coli were classified as extended spectrum beta-lactamase (ESBL) producers. Of the cephalosporin class compounds tested against the Klebsiella spp. and E. coli isolates, cefepime demonstrated the highest rates of susceptibility (84.9% and 91.7%, respectively). This compound also fared well against the Enterobacter spp. isolates, inhibiting 88.2% of the isolates tested, many of which were resistant to ceftazidime and ceftriaxone. Resistance to oxacillin among the S. aureus isolates was nearly 50. 0%, with vancomycin, teicoplanin, and the streptogramin combination quinupristin/dalfopristin inhibiting all isolates. Several clusters of multiply resistant organisms were also observed, and further characterization by ribotyping and pulsed-field gel electrophoresis established possible patient-to-patient spread. The results of this study indicate that rates of resistance among respiratory tract pathogens continue to rise in Latin America, with specific concerns for the high prevalence of nonfermentative Gram-negative bacteria isolated, oxacillin resistance rates in S. aureus, and the epidemic dissemination of multiply-resistant strains in several medical centers. International surveillance programs (SENTRY) should assist in the control of escalating antimicrobial resistance in this geographic area.

In vitro activity of telithromycin (HMR3647), a new ketolide, against clinical isolates of Mycoplasma pneumoniae in Japan

The in vitro activity of telithromycin (HMR3647), a new ketolide, against Mycoplasma pneumoniae was determined by the broth microdilution test using 41 clinical isolates obtained in Japan, as compared with those of five macrolides (erythromycin, clarithromycin, roxithromycin, azithromycin, and josamycin), minocycline, and levofloxacin. Telithromycin was less potent than azithromycin, but it was more active than four other macrolides, minocycline, and levofloxacin; its MICs at which 50 and 90% of the isolates tested were inhibited were both 0.00097 microg/ml, justifying clinical studies to determine its efficacy for treatment of M. pneumoniae.

Serious streptococcal infections produced by isolates resistant to streptogramins (quinupristin/dalfopristin): case reports from the SENTRY antimicrobial surveillance program

The emergence and sustained prevalence of Gram-positive organisms resistant to antimicrobials has been of interest for over a decade. Quinupristin/dalfopristin (formerly RP 59500 or Synercid) is a new injectable streptogramin combination that has been reported to have activity against Gram-positive organisms, even those with documented MLS(B) resistance. However, the two case reports presented here illustrate three well-documented Streptococcus spp. strains (S. mitis, S. pneumoniae) to be resistant to quinupristin/dalfopristin (MICs at 3, 8, and 12 microg/ml) following referral as routine isolates in the SENTRY Antimicrobial Surveillance Program. The S. pneumoniae pleural fluid isolate was cross-resistant to erythromycin. Both bacteremic S. mitis strains were resistant to macrolides (erythromycin, azithromycin, clarithromycin), lincosamides (clindamycin), and fluoroquinolones. Patient histories indicated no prior use of MLS class antimicrobials for the S. mitis case, but the patient having the S. pneumoniae isolate did receive prior treatment of erythromycin and clindamycin. All isolates had modestly increased penicillin MICs of 0.12 microg/ml. The mode of resistance to quinupristin/dalfopristin was not evident (sat A-negative by PCR); and these cases illustrate the existence of streptogramin-resistant isolates before the introduction of this antimicrobial class into human clinical practice.

In vitro development of resistance to telithromycin (HMR 3647), four macrolides, clindamycin, and pristinamycin in Streptococcus pneumoniae

The ability of 50 sequential subcultures in subinhibitory concentrations of telithromycin (HMR 3647), azithromycin, clarithromycin, erythromycin A, roxithromycin, clindamycin, and pristinamycin to select for resistance was studied in five macrolide-susceptible and six macrolide-resistant pneumococci containing mefE or ermB. Telithromycin selected for resistance less often than the other drugs.

Macrolide resistance and erythromycin resistance determinants among Belgian Streptococcus pyogenes and Streptococcus pneumoniae isolates

Resistance of streptococci to macrolide antibiotics is caused by target-site modification or drug efflux. The phenotypic expression of target-site modification can be inducible or constitutive. The prevalence of the three phenotypes among Belgian erythromycin-resistant Group A streptococci (GAS) and Streptococcus pneumoniae isolates was surveyed, their MICs for seven antibiotics were determined and the clonality of the isolates was explored. Of the 2014 GAS isolates tested 131(6.5%) were erythromycin resistant (MIC > 1 mg/L): 110 (84.0%) showed the M-resistance phenotype whereas the remaining 21 strains (16.0%) were constitutively resistant. No inducibly resistant strains were detected. Of 100 S. pneumoniae isolates, 33 were erythromycin resistant (MIC > 1 mg/L). In contrast to the GAS isolates, only 9.1% of the 33 erythromycin-resistant S. pneumoniae isolates showed the M-resistance phenotype. The presence of mefA/E and ermB genes in the M-resistant and constitutively and inducibly resistant strains, respectively, was confirmed by PCR analysis. Genomic analysis based on pulsed-field gel electrophoresis (PFGE) using the restriction enzyme SfiI, revealed 54 different PFGE patterns among the 131 erythromycin-resistant GAS isolates, of which an M6 clone represented 16.0% of the strains; all other clones, exhibiting different M-types, represented <7% of the strains. The S. pneumoniae isolates also appeared to be polyclonally based, as determined by arbitrarily primed PCR. The macrolides miocamycin and rovamycin, the lincosamide clindamycin and the ketolide HMR 3647 showed excellent activity against the M-resistant GAS and S. pneumoniae strains.

Quinupristin/dalfopristin: a review of its use in the management of serious gram-positive infections

Quinupristin/dalfopristin is the first parenteral streptogramin antibacterial agent, and is a 30:70 (w/w) ratio of 2 semisynthetic pristinamycin derivatives. The combination has inhibitory activity against a broad range of gram-positive bacteria including methicillin-resistant staphylococci, vancomycin-resistant Enterococcus faecium (VREF), drug-resistant Streptococcus pneumoniae, other streptococci, Clostridium perfringens and Peptostreptococcus spp. The combination also has good activity against selected gram-negative respiratory tract pathogens including Moraxella catarrhalis, Legioniella pneumophila and Mycoplasma pneumoniae. Quinupristin/dalfopristin has poor activity against E. faecalis. The combination is bactericidal against staphylococci and streptococci, although constitutive erythromycin resistance can affect its activity. As for many other agents, quinupristin/dalfopristin is generally bacteriostatic against E. faecium. In patients with methicillin-resistant S. aureus (MRSA) or VREF infections participating in prospective emergency-use trials, quinupristin/dalfopristin 7.5 mg/kg every 8 or 12 hours achieved clinical or bacteriological success in > or =64% of patients. Emergence of resistance to quinupristin/dalfopristin was uncommon (4% of patients) in those with VREF infections. Quinupristin/dalfopristin 7.5 mg/kg 8- or 12-hourly also achieved similar clinical success rates to comparator agents in patients with presumed gram-positive complicated skin and skin structure infections or nosocomial pneumonia (administered in combination with aztreoman) in 3 large multicentre randomised trials. Systemic adverse events associated with quinupristin/dalfopristin include gastrointestinal events (nausea, vomiting and diarrhoea), rash and pruritus. Myalgias and arthralgias also occur at an overall incidence of 1.3%, although higher rates (2.5 to 31%) have been reported in patients with multiple comorbidities. Venous events are common if the drug is administered via a peripheral line; however, several management options (e.g. use of central venous access, increased infusion volume) may help to minimise their occurrence. Hyperbilirubinaemia has been documented in 3.1% of quinupristin/dalfopristin recipients versus 1.3% of recipients of comparator agents. Quinupristin/dalfopristin inhibits cytochrome P450 3A4 and therefore has the potential to increase the plasma concentrations of substrates of this enzyme.

CONCLUSIONS

Quinupristin/dalfopristin, the first parenteral streptogramin, offers a unique spectrum of activity against multidrug-resistant gram-positive bacteria. In serious gram-positive infections for which there are other treatment options available, the spectrum of activity and efficacy of quinupristin/ dalfopristin should be weighed against its tolerability and drug interaction profile. However, in VREF or unresponsive MRSA infections, where few proven treatment options exist, quinupristin/dalfopristin should be considered as a treatment of choice for these seriously ill patients.

Recent developments in macrolides and ketolides

Emergence of bacterial resistance to macrolide antibiotics, particularly in Gram-positive bacteria, has been observed. Novel macrolides having C-4" carbamate functional groups and ketolides, the 3-keto derivatives of macrolides, have been found to have activities against macrolide-resistant strains. Several potential non-antibacterial activities of macrolides have been reported, such as inhibition of cytokine production, neutrophil attachment to human bronchial epithelial cells and vesicular transport.

What's new in the antibiotic pipeline

Many advances have recently been made in the development of chemotherapeutic agents for bacterial infections. As a consequence of problematic antimicrobial-resistant bacteria, research is now directed towards narrow-spectrum agents rather than broad-spectrum agents. Further, orally active agents have always been desirable, but today's cost-saving environment, in line with a desire to minimize treatment costs, values reduced administration costs and keeping patients out of the hospital. There has been a recent increase in research into orally active antibacterial agents, such as carbapenems and cephalosporins, and non-glycopeptide natural products.

In vitro activity of the novel ketolide HMR 3647 and comparative oral antibiotics against Canadian respiratory tract isolates of Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis

The in vitro activities of HMR 3647, erythromycin A, clarithromycin, azithromycin, roxithromycin, penicillin G, ampicillin, cefuroxime, trimethoprim/sulfamethoxazole, tetracycline, ciprofloxacin, and levofloxacin were determined for 1179 Streptococcus pneumoniae, 1438 Haemophilus influenzae, and 428 Moraxella catarrhalis isolated from respiratory tract specimens by 18 medical centers across Canada during 1997-1998. On a per weight basis, HMR 3647 was the most active agent tested against S. pneumoniae with MIC90s of < or = 0.12 microgram/mL for both penicillin susceptible and penicillin intermediate isolates and 0.25 microgram/mL for penicillin-resistant isolates. HMR 3647 was also highly active against M. catarrhalis (MIC90, < or = 0.12 microgram/mL), but less active against H. influenzae (MIC90, 4 micrograms/mL).