Review of macrolides and ketolides: focus on respiratory tract infections

The use of macrolides in treatment of upper respiratory tract infections

Antimicrobial resistance is a growing problem among upper respiratory tract pathogens. Resistance to beta-lactam drugs among Streptococcus pneumoniae, Haemophilus influenzae, and Streptococcus pyogenes is increasing. As safe and well-tolerated antibiotics, macrolides play a key role in the treatment of community-acquired upper respiratory tract infections (RTIs). Their broad spectrum of activity against gram-positive cocci, such as S. pneumoniae and S. pyogenes, atypical pathogens, H. influenzae (azithromycin and clarithromycin), and Moraxella catarrhalis, has led to the widespread use of macrolides for empiric treatment of upper RTIs and as alternatives for patients allergic to beta-lactams. Macrolide resistance is increasing among pneumococci and recently among S. pyogenes, and is associated with increasing use of the newer macrolides, such as azithromycin. Ribosomal target modification mediated by erm(A) and erm(B) genes and active efflux due to mef(A) and mef(E) are the principal mechanisms of resistance in both S. pneumoniae and S. pyogenes. Recently, ribosomal protein and RNA mutations have been found to be responsible for acquired resistance to macrolides in S. pneumoniae, S. pyogenes, and H. influenzae. Although macrolides are only weakly active against macrolide-resistant streptococci species, producing an efflux pump (mef), and are inactive against pathogens with ribosomal target modification (erm), treatment failures are uncommon. Therefore, macrolide therapy, for now, remains a good alternative for treatment of upper RTIs; however, continuous monitoring of the local resistance patterns is essential.

[Clinically significant toxicity and tolerance of the main antibiotics used in lower respiratory tract infections]

The purpose of this article was not to review all reported adverse reactions of antibiotics used in the treatment of lower respiratory tract infections but rather to focus either on those which might have an impact on observance, efficacy, and resistance, or on rare but life-threatening adverse effects such as torsade de pointe. The latter are mostly predictable and prescribers should adhere to precautions and contraindications. For new antibiotics, the number of patients enrolled in phase I to III clinical trials is far to small to detect such rare adverse effects and large post registration tolerance surveys are mandatory. ss-lactams are well tolerated. The risk of anaphylactic reaction is magnified by patient reports and can be reduced by skin testing. Macrolides are well tolerated as well. The risk of cardiac toxicity should be reduced by assessing individual susceptibility and avoiding drug interactions. The tolerance to telithromycin, a new ketolide, is similar to that of macrolides. Serious toxic reactions such as convulsions, tendon rupture, torsade de pointe, and hypoglycemia are associated with the use of fluoroquinolones. Most of these adverse reactions can be often circumvented by avoiding exposure patients at risk. Quinupristin/dalfopristin can induce arthralgia and myalgia and the major adverse effects of linezolid are IMAO like reactions, reversible myelosuppression, and peripheral neuropathy. Most of the adverse antibiotic reactions are reported when precautions of use in susceptible patients are not taken into account. When they are, the safety/risk ratio is good.

Anti-inflammatory activity of azithromycin attenuates the effects of lipopolysaccharide administration in mice

Macrolide antibacterials inhibit the production of various cytokines and the migration of inflammatory cells. These anti-inflammatory actions of macrolides may be beneficial in attenuating inflammatory processes involved in bacterial sepsis. Therefore, we investigated the ability of azithromycin to attenuate the deleterious effects of lipopolysaccharide (LPS), in three different LPS-induced inflammatory models. Our results show that azithromycin (10 and 100 mg/kg) significantly attenuated the intraperitoneal LPS-induced increase in plasma TNF-alpha concentration. It also increased survival rate in a septic shock model in mice challenged with intravenous LPS. Oral treatment with azithromycin (up to 300 mg/kg) was less effective in suppressing neutrophil infiltration into the lungs 24 h after intranasal LPS challenge, possibly because of a slower onset of action or inadequate dosing. In the same model, azithromycin given intraperitoneally significantly improved inflammatory markers (total cell number, neutrophil percentage and MIP-2 concentration) in bronchoalveolar lavage fluid. In conclusion, azithromycin exhibits significant anti-inflammatory properties but the potency of such effects varies depending on the experimental model and route of administration.

Managing acute lower respiratory tract infections in an era of antibacterial resistance

Respiratory tract infections account for more than 116 million office visits and an estimated 3 million visits to hospital EDs annually. Patients presenting at EDs with symptoms suggestive of lower respiratory tract infections of suspected bacterial etiology are often severely ill, thus requiring a rapid presumptive diagnosis and empiric antimicrobial treatment. Traditionally, clinicians have relied on beta-lactam or macrolide antibiotics to manage community-acquired lower respiratory tract infections. However, the emerging resistance of Streptococcus pneumoniae to beta-lactams and/or macrolides may affect the clinical efficacy of these agents. Inappropriate use of antibiotics and use of agents with an overly broad spectrum of antimicrobial activity have contributed to the emergence of antibiotic resistance. When treating respiratory infections, clinicians need to prescribe antimicrobial agents only for those individuals with infections of suspected bacterial etiology; to select agents with a targeted spectrum of activity that ensures coverage against typical S pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis strains, including antibiotic-resistant strains and atypical pathogens; and to consider agents with specific chemical properties that limit the development of antimicrobial resistance and that achieve concentrations at sites of infection that exceed those required for bactericidal activity. Newer classes of antimicrobial agents, such as the oxazolidinones and ketolides, will likely play a significant role in this era of antimicrobial resistance.

Effect of efflux on telithromycin and macrolide susceptibility in Haemophilus influenzae

This study investigated the presence of telithromycin and azithromycin efflux in 58 clinical strains of Haemophilus influenzae with various susceptibilities to macrolides, azalides, and ketolides. Efflux pumps were studied by measuring accumulation of radioactive [3H]telithromycin and [N-methyl-3H]azithromycin in the presence and absence of carbonyl m-chlorophenylhydrazone (CCCP), a protonophore. In 17 strains for which the telithromycin MICs were 0.06 to 0.5 microg/ml (azithromycin MICs, < or = 0.06 to 0.125 microg/ml; clarithromycin MICs, < or = 0.06 to 2 microg/ml), telithromycin and azithromycin accumulations were high without CCCP and not affected by its addition, which indicates absence of efflux. In 22 strains for which the telithromycin MICs were 0.25 to 4 microg/ml (azithromycin MICs, 0.25 to 1 microg/ml; clarithromycin MICs, 1 to 8 microg/ml), initially low levels of telithromycin accumulation became higher after addition of CCCP, indicating a functioning efflux pump. Nineteen strains for which the telithromycin MICs were > or = 2 microg/ml had efflux as well as various mutations in ribosomal proteins L4, L22, and/or 23S rRNA (domains II and V). Of these 19 strains, the telithromycin MICs (> or = 8 microg/ml) for 17 of them were significantly raised (azithromycin, MICs 4 to >32 microg/ml; clarithromycin MICs, 8 to >32 microg/ml). From these results we conclude that telithromycin efflux with or without additional ribosomal alterations is present in all H. influenzae strains, except for those for which the telithromycin MICs were very low.

Murine models of pneumococcal pneumonia and their applicability to the study of tissue-directed antimicrobials

Animal models have long played a crucial role in the preclinical and postmarketing evaluation of antimicrobial drug efficacy. With the alarming rise of antibiotic resistance in Streptococcus pneumoniae, such models have received increased attention as tools for deriving pharmacodynamic data and for determining the clinical significance of drug resistance. This information helps us to make therapeutic decisions to optimize efficacy and restrict the further promotion of drug resistance. Until now, however, insufficient attention has been paid to the special issues that arise in the evaluation of antimicrobials that are concentrated in tissue relative to serum or plasma. This article reviews the utility of animal models in the evaluation of these tissue-directed antibiotics, citing recent attempts to use murine models of pneumococcal pneumonia to determine the importance of macrolide resistance. A promising new, low-dose aerosol model of pneumonia is briefly presented, as is a discussion of the limitations of existing models.

Pharmacokinetics of azithromycin after i.v. and i.m. administration to sheep

The pharmacokinetics (PK) of azithromycin after i.v. and i.m. injection at a single dosage of 20 mg/kg bodyweight was studied in sheep. Blood samples were collected from the jugular vein until 120 h after dosing for both routes. Plasma concentrations of azithromycin were determined by bioassay. The plasma concentration-time data of azithromycin best fitted a three-compartment model after i.v. administration and a two-compartment model with first-order absorption after i.m. administration. The elimination half-life (t(1/2lambdaz)) was 47.70 +/- 7.49 h after i.v. administration and 61.29 +/- 13.86 h after i.m. administration. Clearance value after i.v. dosing was 0.52 +/- 0.08 L/kg.h. After i.m. administration a peak azithromycin concentration (C(max)) of 1.26 +/- 0.19 mg/L was achieved at 1.24 +/- 0.31 h (t(max)). Area under the curve (AUC) were 38.85 +/- 5.83 mg.h/L and 36.03 +/- 1.52 mg.h/L after i.v. and i.m. administration respectively. Bioavailability obtained after i.m. administration was 94.08 +/- 11.56%. The high tolerability of this i.m. preparation and the favourable PK behaviour such as the long half-life and high bioavailability make azithromycin likely to be effective in sheep.

Chlamydophila pneumoniae and Mycoplasma pneumoniae: a role in asthma pathogenesis?

The potential role of atypical bacterial infection in the pathogenesis of asthma is a subject of continuing debate. There is an increasing body of literature concerning the association between the atypical bacteria Chlamydophila pneumoniae and Mycoplasma pneumoniae and asthma pathogenesis; however, many studies investigating such a link have been uncontrolled and have provided conflicting evidence, in part due to the difficulty in accurately diagnosing infection with these atypical pathogens. This article reviews the evidence for an association between atypical bacterial respiratory pathogens and the pathogenesis of asthma, and discusses the biological mechanisms that could account for such a link. The possible role of antibacterial therapy in the management of asthma and the need for well-designed studies to investigate this is also discussed.

Pharmacodynamic activity of telithromycin at simulated clinically achievable free-drug concentrations in serum and epithelial lining fluid against efflux (mefE)-producing macrolide-resistant Streptococcus pneumoniae for which telithromycin MICs vary

The present study, using an in vitro model, assessed telithromycin pharmacodynamic activity at simulated clinically achievable free-drug concentrations in serum (S) and epithelial lining fluid (ELF) against efflux (mefE)-producing macrolide-resistant Streptococcus pneumoniae. Two macrolide-susceptible (PCR negative for both mefE and ermB) and 11 efflux-producing macrolide-resistant [PCR-positive for mefE and negative for ermB) S. pneumoniae strains with various telithromycin MICs (0.015 to 1 microg/ml) were tested. The steady-state pharmacokinetics of telithromycin were modeled, simulating a dosage of 800 mg orally once daily administered at time 0 and at 24 h (free-drug maximum concentration [C(max)] in serum, 0.7 microg/ml; half-life [t(1/2)], 10 h; free-drug C(max) in ELF, 6.0 microg/ml; t(1/2), 10 h). Starting inocula were 10(6) CFU/ml in Mueller-Hinton Broth with 2% lysed horse blood. Sampling at 0, 2, 4, 6, 12, 24, and 48 h assessed the extent of bacterial killing (decrease in log(10) CFU/ml versus initial inoculum). Free-telithromycin concentrations in serum achieved in the model were C(max) 0.9 +/- 0.08 microg/ml, area under the curve to MIC (AUC(0-24 h)) 6.4 +/- 1.5 microg . h/ml, and t(1/2) of 10.6 +/- 0.6 h. Telithromycin-free ELF concentrations achieved in the model were C(max) 6.6 +/- 0.8 microg/ml, AUC(0-24 h) 45.5 +/- 5.5 microg . h/ml, and t(1/2) of 10.5 +/- 1.7 h. Free-telithromycin S and ELF concentrations rapidly eradicated efflux-producing macrolide-resistant S. pneumoniae with telithromycin MICs up to and including 0.25 microg/ml and 1 microg/ml, respectively. Free-telithromycin S and ELF concentrations simulating C(max)/MIC > or = 3.5 and AUC(0-24 h)/MIC > or = 25 completely eradicated (> or =4 log(10) killing) macrolide-resistant S. pneumoniae at 24 and 48 h. Free-telithromycin concentrations in serum simulating C(max)/MIC > or = 1.8 and AUC(0-24 h)/MIC > or = 12.5 were bacteriostatic (0.1 to 0.2 log(10) killing) against macrolide-resistant S. pneumoniae at 24 and 48 h. In conclusion, free-telithromycin concentrations in serum and ELF simulating C(max)/MIC > or = 3.5 and AUC(0-24 h)/MIC > or = 25 completely eradicated (> or =4 log(10) killing) macrolide-resistant S. pneumoniae at 24 and 48 h.

An Efficient Synthesis of Gougerotin and Related Analogues Using Solid- and Solution-Phase Methodology

The first solid-phase synthesis of the natural product gougerotin has been accomplished. The synthetic route is versatile and allows for diversification at position C-4 of the heterocycle, C-6' of the sugar ring, and both residues of the peptidic moiety at N-4' in a parallel fashion. [structure: see text]

Hidden epidemic of macrolide-resistant pneumococci

Community-acquired respiratory tract infections (RTIs) account for a substantial proportion of outpatient antimicrobial drug prescriptions worldwide. Concern over the emergence of multidrug resistance in pneumococci has largely been focused on penicillin-resistant Streptococcus pneumoniae. Macrolide antimicrobial drugs have been widely used to empirically treat community-acquired RTIs because of their efficacy in treating both common and atypical respiratory pathogens, including S. pneumoniae. However, increased macrolide use has been associated with a global increase in pneumococcal resistance, which is leading to concern over the continued clinical efficacy of the macrolides to treat community-acquired RTIs. We provide an overview of macrolide-resistant S. pneumoniae and assess the impact of this resistance on the empiric treatment of community-acquired RTIs.

The use of macrolides in treatment of upper respiratory tract infections

Antimicrobial resistance is a growing problem among upper respiratory tract pathogens. Resistance to beta-lactam drugs among Streptococcus pneumoniae, Haemophilus influenzae, and Streptococcus pyogenes is increasing. As safe and well-tolerated antibiotics, macrolides play a key role in the treatment of community-acquired upper respiratory tract infections (RTIs). Their broad spectrum of activity against gram-positive cocci, such as S. pneumoniae and S. pyogenes, atypical pathogens, H. influenzae (azithromycin and clarithromycin), and Moraxella catarrhalis, has led to the widespread use of macrolides for empiric treatment of upper RTIs and as alternatives for patients allergic to b-lactams. Macrolide resistance is increasing among pneumococci and recently among S. pyogenes, and is associated with increasing use of the newer macrolides, such as azithromycin. Ribosomal target modification mediated by erm(A) and erm(B) genes and active efflux due to mef(A) and mef(E) are the principal mechanisms of resistance in S. pneumoniae and S. pyogenes. Recently, ribosomal protein and RNA mutations have been found responsible for acquired resistance to macrolides in S. pneumoniae, S. pyogenes, and H. influenzae. Although macrolides are only weakly active against macrolide-resistant streptococci species producing an efflux pump (mef) and are inactive against pathogens with ribosomal target modification (erm), treatment failures are uncommon. Therefore, macrolide therapy, for now, remains a good alternative for treatment of upper RTIs; however, continuous monitoring of the local resistance patterns is essential.

Efflux-mediated antimicrobial resistance

Antibiotic resistance continues to plague antimicrobial chemotherapy of infectious disease. And while true biocide resistance is as yet unrealized, in vitro and in vivo episodes of reduced biocide susceptibility are common and the history of antibiotic resistance should not be ignored in the development and use of biocidal agents. Efflux mechanisms of resistance, both drug specific and multidrug, are important determinants of intrinsic and/or acquired resistance to these antimicrobials, with some accommodating both antibiotics and biocides. This latter raises the spectre (as yet generally unrealized) of biocide selection of multiple antibiotic-resistant organisms. Multidrug efflux mechanisms are broadly conserved in bacteria, are almost invariably chromosome-encoded and their expression in many instances results from mutations in regulatory genes. In contrast, drug-specific efflux mechanisms are generally encoded by plasmids and/or other mobile genetic elements (transposons, integrons) that carry additional resistance genes, and so their ready acquisition is compounded by their association with multidrug resistance. While there is some support for the latter efflux systems arising from efflux determinants of self-protection in antibiotic-producing Streptomyces spp. and, thus, intended as drug exporters, increasingly, chromosomal multidrug efflux determinants, at least in Gram-negative bacteria, appear not to be intended as drug exporters but as exporters with, perhaps, a variety of other roles in bacterial cells. Still, given the clinical significance of multidrug (and drug-specific) exporters, efflux must be considered in formulating strategies/approaches to treating drug-resistant infections, both in the development of new agents, for example, less impacted by efflux and in targeting efflux directly with efflux inhibitors.

Effect of cirrhosis on antibiotic efficacy in a rat model of pneumococcal pneumonia

A rat model was used to study the effects of cirrhosis on antibiotic therapy of pneumococcal pneumonia. Cirrhotic and control male Sprague-Dawley rats were infected transtracheally with type 3 Streptococcus pneumoniae. Treatment began 18 h later with phosphate-buffered saline (PBS), azithromycin (50 mg/kg), trovafloxacin (50 mg/kg), or ceftriaxone (100 mg/kg) injected subcutaneously twice daily for 5 days. Antibiotic concentrations were measured by high-performance liquid chromatography. Azithromycin, trovafloxacin, and ceftriaxone were all equally effective at preventing mortality in both cirrhotic and normal rats. Free fraction area under the curve to minimum inhibitory concentration ratio (AUC/MIC) and maximum calculated serum concentration to MIC ratio (C(max)/MIC) and percent time that the serum concentration exceeded the MIC (%T > MIC) were greater for ceftriaxone compared with azithromycin or trovafloxacin. Azithromycin achieved higher concentrations in bronchoalveolar lavage fluid (BALF), epithelial lining fluid (ELF), and BAL white blood cells than ceftriaxone or trovafloxacin in cirrhotic rats. Macrolide, beta-lactam, or fluoroquinolone antibiotic efficacy in a pneumococcal pneumonia model does not appear to be affected by hepatic cirrhosis.

Antibiotic multiresistance plasmid pRSB101 isolated from a wastewater treatment plant is related to plasmids residing in phytopathogenic bacteria and carries eight different resistance determinants including a multidrug transport system

Ten different antibiotic resistance plasmids conferring high-level erythromycin resistance were isolated from an activated sludge bacterial community of a wastewater treatment plant by applying a transformation-based approach. One of these plasmids, designated pRSB101, mediates resistance to tetracycline, erythromycin, roxythromycin, sulfonamides, cephalosporins, spectinomycin, streptomycin, trimethoprim, nalidixic acid and low concentrations of norfloxacin. Plasmid pRSB101 was completely sequenced and annotated. Its size is 47 829 bp. Conserved synteny exists between the pRSB101 replication/partition (rep/par) module and the pXAC33-replicon from the phytopathogen Xanthomonas axonopodis pv. citri. The second pRSB101 backbone module encodes a three-Mob-protein type mobilization (mob) system with homology to that of IncQ-like plasmids. Plasmid pRSB101 is mobilizable with the help of the IncP-1alpha plasmid RP4 providing transfer functions in trans. A 20 kb resistance region on pRSB101 is located within an integron-containing Tn402-like transposon. The variable region of the class 1 integron carries the genes dhfr1 for a dihydrofolate reductase, aadA2 for a spectinomycin/streptomycin adenylyltransferase and bla(TLA-2) for a so far unknown Ambler class A extended spectrum beta-lactamase. The integron-specific 3'-segment (qacEDelta1-sul1-orf5Delta) is connected to a macrolide resistance operon consisting of the genes mph(A) (macrolide 2'-phosphotransferase I), mrx (hydrophobic protein of unknown function) and mphR(A) (regulatory protein). Finally, a putative mobile element with the tetracycline resistance genes tetA (tetracycline efflux pump) and tetR was identified upstream of the Tn402-specific transposase gene tniA. The second 'genetic load' region on pRSB101 harbours four distinct mobile genetic elements, another integron belonging to a new class and footprints of two more transposable elements. A tripartite multidrug (MDR) transporter consisting of an ATP-binding-cassette (ABC)-type ATPase and permease, and an efflux membrane fusion protein (MFP) of the RND-family is encoded between the replication/partition and the mobilization module. Homologues of the macrolide resistance genes mph(A), mrx and mphR(A) were detected on eight other erythromycin resistance-plasmids isolated from activated sludge bacteria. Plasmid pRSB101-like repA amplicons were also obtained from plasmid-DNA preparations of the final effluents of the wastewater treatment plant indicating that pRSB101-like plasmids are released with the final effluents into the environment.

The effect of oral clarithromycin on health status and sputum bacteriology in stable COPD

BACKGROUND

Chronic obstructive pulmonary disease (COPD) is characterised by airway inflammation, poor health status and recurrent infective exacerbations. Macrolide antibiotics have been shown to improve symptoms and exacerbation rate in chronic lung disease, particularly cystic fibrosis (CF) and diffuse pan-bronchiolitis. The effect of long-term oral clarithromycin on health status, sputum bacterial numbers and exacerbation rate in subjects with clinically stable COPD is undetermined.

METHODS

Subjects with moderate-to-severe COPD were recruited into a prospective, double-blind, randomised-controlled trial of 3-months oral clarithromycin (Klaricid XL) or placebo once-daily. The effect of clarithromycin on health status (St. George respiratory and Short Form-36 questionnaires), sputum quantitative bacterial numbers and exacerbation rate were investigated.

RESULTS

Sixty-seven subjects (46 males) were recruited; 31 and 36 subjects received clarithromycin and placebo, respectively. There were 7(10%) withdrawals. Compared to placebo, clarithromycin did not significantly improve health status, sputum bacterial numbers, or exacerbation rate.

CONCLUSIONS

Three months of oral clarithromycin given to subjects with stable COPD does not improve health status, sputum bacterial numbers or exacerbation rate. Treatment of COPD with clarithromycin during the clinical stable state yields no clinical advantages and therefore cannot be recommended as means of eliminating sputum bacteria or preventing infective exacerbations.

Update on treatment guidelines for acute bacterial sinusitis

Acute bacterial sinusitis (ABS) is a common complication of viral upper respiratory tract infections and represents a considerable social burden both in terms of diminished quality of life for the patient and the economic implications of decreased productivity and treatment costs. Several national health authorities have developed guidelines for the management of ABS, which aim to promote rational selection of anti-bacterial therapy to optimise clinical outcomes while minimising the potential for selection of anti-bacterial resistance as a result of inappropriate anti-bacterial usage. This article provides an overview of current guidelines, with particular focus on the clinical significance of variations in treatment recommendations and new treatment options, such as the ketolide telithromycin, which was recently added to a number of national treatment guidelines.

[Guidelines for the management of community pneumonia in adult who needs hospitalization]

Community acquired pneumonia is still an important health problem. In Spain the year incidence is 162 cases per 100,000 inhabitants with 53,000 hospital admission costing 115 millions of euros per year. In the last years there have been significant advances in the knowledge of: aetiology, diagnostic tools, treatment alternatives and antibiotic resistance. The Spanish Societies of Intensive and Critical Care (SEMICYUC), Infectious Diseases and Clinical Microbiology (SEIMC) and Pulmonology and Thoracic Surgery (SEPAR) have produced these evidence-based Guidelines for the management of community acquired pneumonia in Adults. The main objective is to help physicians to make decisions about this disease. The different points that have been developed are: aetiology, diagnosis, treatment and prevention.

Telithromycin new product overview

Community-acquired respiratory tract infections (CARTIs), including community-acquired pneumonia, acute exacerbations of chronic bronchitis, and acute bacterial sinusitis, contribute substantially to health care costs in the United States. Although many prescriptions for antibiotics are written each year for the treatment of CARTIs, most are prescribed on an empiric basis. Concerns about the increasing prevalence of antimicrobial resistance and the changing pattern of pathogens isolated from subjects with CARTIs have raised questions about the empiric treatment paradigm. When choosing appropriate antimicrobial therapy for CARTIs, physicians must consider not only the spectrum of activity of antibiotics but also the potential risk of resistance. Telithromycin is the first member of the ketolide class, a new family of antimicrobials structurally related to the macrolides, to be approved by the US Food and Drug Administration for the treatment of CARTIs. The spectrum of activity of telithromycin includes common typical and atypical causative pathogens associated with community-acquired respiratory tract infections, including antibiotic-resistant strains of Streptococcus pneumoniae. Clinical trials have shown that telithromycin is as effective as traditionally used antimicrobial agents in the treatment of mild-to-moderate community-acquired pneumonia, acute exacerbations of chronic bronchitis, and acute bacterial sinusitis.

Role of antimicrobial agents in the management of exacerbations of COPD

Acute exacerbations of chronic obstructive pulmonary disease (AECOPD) are a common occurrence and characterize the natural history of the disease. Over the past decade, new knowledge has substantially enhanced our understanding of the pathogenesis, outcome and natural history of AECOPD. The exacerbations not only greatly reduce the quality of life of these patients, but also result in hospitalization, respiratory failure, and death. The exacerbations are the major cost drivers in consumption of healthcare resources by COPD patients. Although bacterial infections are the most common etiologic agents, the role of viruses in COPD exacerbations is being increasingly recognized. The efficacy of antimicrobial therapy in acute exacerbations has established a causative role for bacterial infections. Recent molecular typing of sputum isolates further supports the role of bacteria in AECOPD. Isolation of a new strain of Haemophilus influenzae, Moraxella catarrhalis, or Streptococcus pneumoniae was associated with a considerable risk of an exacerbation. Lower airway bacterial colonization in stable patients with COPD instigates airway inflammation, which leads to a protracted self-perpetuating vicious circle of progressive lung damage and disease progression. A significant proportion of patients treated for COPD exacerbation demonstrate incomplete recovery, and frequent exacerbations contribute to decline in lung function. The predictors of poor outcome include advanced age, significant impairment of lung function, poor performance status, comorbid conditions and history of previous frequent exacerbations requiring antibacterials or systemic corticosteroids. These high-risk patients, who are likely to harbor organisms resistant to commonly used antimicrobials, should be identified and treated with antimicrobials with a low potential for failure. An aggressive management approach in complicated exacerbations may reduce costs by reducing healthcare utilization and hospitalization.

Synthesis and antibacterial activity of 6-O-arylpropargyl-9-oxime-11,12-carbamate ketolides

A series of novel 6-O-arylpropargyl-9-oxime-ketolides was synthesized and evaluated against various pathogens. These new compounds show promising in vitro antibacterial potency and in vivo efficacy against macrolide resistant strains.

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.

Molecular basis of intrinsic macrolide resistance in clinical isolates of Mycobacterium fortuitum

OBJECTIVES

Some clinical isolates of Mycobacterium fortuitum are naturally resistant to macrolides, e.g. clarithromycin. Thus, the aim of this study was to identify the gene(s) conferring this resistance.

METHODS

M. fortuitum ATCC 6841T DNA libraries were screened for plasmids that complemented the macrolide-susceptible phenotype of Mycobacterium smegmatis variant ermKO4 [erm(38)-negative]. Macrolide-resistant M. smegmatis transformants were selected on agar containing 128 mg/L erythromycin.

RESULTS

Genetic complementation identified an M. fortuitum rRNA methylase gene, termed erm(39), 69% identical to erm(38) of M. smegmatis. In addition, erm(39) was found to be in the same chromosomal location as erm(38) in their respective hosts. Like erm(38), erm(39) conferred resistance (MIC >128 mg/L) to macrolide-lincosamide (ML) agents, but not to streptogramin B. Analysis of erm gene expression in M. fortuitum showed that ML agents increased erm(39) RNA levels, reaching a steady state level approximately 20-fold higher than baseline. Screening of 32 M. fortuitum clinical isolates by PCR showed that all were positive for erm(39), irrespective of clarithromycin susceptibility. A majority of clarithromycin-susceptible (MIC < or = 2 mg/L) isolates were postulated to carry a disabled erm(39) gene as they had a GTG-->CTG mutation in the putative initiation codon of the erm(39) gene.

CONCLUSIONS

The similarity of the erm genes of M. smegmatis and M. fortuitum suggests that they were inherited from a common ancestor. Although the clinical impact of erm(39) on the therapeutic utility of clarithromycin is unclear, induction of this gene is consistent with the trailing end-points commonly seen during susceptibility testing of M. fortuitum isolates against macrolides.

Pharmacodynamic activity of telithromycin against macrolide-susceptible and macrolide-resistant Streptococcus pneumoniae simulating clinically achievable free serum and epithelial lining fluid concentrations

BACKGROUND

The association between macrolide resistance mechanisms and ketolide bacteriological eradication of Streptococcus pneumoniae remains poorly studied. The present study, using an in vitro model, assessed telithromycin pharmacodynamic activity against macrolide-susceptible and macrolide-resistant S. pneumoniae simulating clinically achievable free serum and epithelial lining fluid (ELF) concentrations.

MATERIALS AND METHODS

Two macrolide-susceptible [PCR-negative for both mef(A) and erm(B)] and six macrolide-resistant [five mef(A)-positive/erm(B)-negative displaying various degrees of macrolide resistance and one mef(A)-negative/erm(B)-positive] S. pneumoniae were tested. Telithromycin was modelled simulating a dosage of 800 mg by mouth once daily [free serum: maximum concentration (C(max)) 0.7 mg/L, t(1/2) 10 h; and free ELF: C(max) 6.0 mg/L, t(1/2) 10 h]. Starting inocula were 1 x 10(6) cfu/mL in Mueller-Hinton broth with 2% lysed horse blood. Sampling at 0, 2, 4, 6, 12, 24 and 48 h assessed the extent of bacterial killing (decrease in log(10) cfu/mL versus initial inoculum).

RESULTS

Telithromycin free serum concentrations achieved in the model were: C(max) 0.9+/-0.08 mg/L, AUC(0-24) 6.4+/-1.5 mg.h/L and t(1/2) of 10.6+/-1.6 h. Telithromycin free ELF concentrations achieved in the model were: C(max) 6.6+/-0.8 mg/L, AUC(0-24) 45.5+/-5.5 mg.h/L and t(1/2) of 10.5+/-1.7 h. At 2 h, free serum telithromycin concentrations achieved a 1.0-1.9 log(10) reduction in inoculum compared with a 3.0-3.3 log(10) reduction with free ELF versus macrolide-susceptible and macrolide-resistant S. pneumoniae. Free telithromycin serum and ELF concentrations simulating C(max)/MIC > or =14.1 and area under the curve to MIC (AUC(0-24)/MIC) > or =100 [time above the MIC (t > MIC) of 100%], were bactericidal (> or =3 log(10) killing) at 4, 6, 12, 24 and 48 h versus macrolide-susceptible and macrolide-resistant S. pneumoniae.

CONCLUSION

Telithromycin serum and ELF concentrations rapidly eradicated macrolide-susceptible and macrolide-resistant S. pneumoniae regardless of resistance phenotype. Achieving C(max)/MIC > or =14.1 and AUC(0-24)/MIC > or =100 resulted in bactericidal activity at 4 h with no regrowth over 48 h.

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.

A review of clinical failures associated with macrolide-resistant Streptococcus pneumoniae

The emerging reports of clinical failures using macrolides and their associations with macrolide-resistant Streptococcus pneumoniae prompted us to review the literature describing these cases. Thirty-three cases reporting macrolide treatment failure during treatment of pneumococcal infections were available for review. The most prevalent diagnosis (24/27 or 88.8% of available diagnoses) was community-acquired pneumonia (CAP). Previous medical history included cardiopulmonary disease in eight (24.2%) and immunocompromised states in five (15.1%) patients. The majority, 31/33 (93.9%) of patients received oral macrolide treatment in an outpatient setting. S. pneumoniae was isolated from the blood in 26 (78.8%) of 33 patients, three (9.1%) patients had bacteria present in both blood and cerebrospinal fluid, two (6%) patients grew S. pneumoniae from blood and bronchial washings and two (6%) patients had positive sputum cultures. The MLS(B) phenotype was the most predominant phenotype present in 12 (63.2%) of 19 patients. After failing initial macrolide treatment, 26 (78.8%) of 33 patients received parenteral antibiotic treatment. Of 33 patients admitted to hospital, 29 (87.8%) had their outcome described as 'survived'.

Pharmacokinetics and lung tissue concentrations of tulathromycin in swine

The absolute bioavailability and lung tissue distribution of the triamilide antimicrobial, tulathromycin, were investigated in swine. Fifty-six pigs received 2.5 mg/kg of tulathromycin 10% formulation by either intramuscular (i.m.) or intravenous (i.v.) route in two studies: study A (10 pigs, i.m. and 10 pigs, i.v.) and study B (36 pigs, i.m.). After i.m. administration the mean maximum plasma concentration (C(max)) was 616 ng/mL, which was reached by 0.25 h postinjection (t(max)). The mean apparent elimination half-life (t(1/2)) in plasma was 75.6 h. After i.v. injection plasma clearance (Cl) was 181 mL/kg.h, the volume of distribution at steady-state (V(ss)) was 13.2 L/kg and the elimination t(1/2) was 67.5 h. The systemic bioavailability following i.m. administration was >87% and the ratio of lung drug concentration for i.m. vs. i.v. injection was > or =0.96. Following i.m. administration, a mean tulathromycin concentration of 2840 ng/g was detected in lung tissue at 12 h postdosing. The mean lung C(max) of 3470 ng/g was reached by 24 h postdose (t(max)). Mean lung drug concentrations after 6 and 10 days were 1700 and 1240 ng/g, respectively. The AUC(inf) was 61.4 times greater for the lung than for plasma. The apparent elimination t(1/2) for tulathromycin in the lung was 142 h (6 days). Following i.m. administration to pigs at 2.5 mg/kg body weight, tulathromycin was rapidly absorbed and highly bioavailable. The high distribution to lung and slow elimination following a single dose of tulathromycin, are desirable pharmacokinetic attributes for an antimicrobial drug indicated for the treatment of respiratory disease in swine.

QT prolongation with antimicrobial agents: understanding the significance

Cardiac toxicity has been relatively uncommon within the antimicrobial class of drugs, but well described for antiarrhythmic agents and certain antihistamines. Macrolides, pentamidine and certain antimalarials were traditionally known to cause QT-interval prolongation, and now azole antifungals, fluoroquinolones and ketolides can be added to the list. Over time, advances in preclinical testing methods for QT-interval prolongation and a better understanding of its sequelae, most notably torsades de pointes (TdP), have occurred. This, combined with the fact that five drugs have been removed from the market over the last several years, in part because of QT-interval prolongation-related toxicity, has elevated the urgency surrounding early detection and characterisation methods for evaluating non-antiarrhythmic drug classes. With technological advances and accumulating literature regarding QT prolongation, it is currently difficult or overwhelming for the practising clinician to interpret these data for purposes of formulary review or for individual patient treatment decisions. Certain patients are susceptible to the effects of QT-prolonging drugs. For example, co-variates such as gender, age, electrolyte derangements, structural heart disease, end organ impairment and, perhaps most important, genetic predisposition, underlie most if not all cases of TdP. Between and within classes of drugs there are important differences that contribute to delayed repolarisation (e.g. intrinsic potency to inhibit certain cardiac ion currents or channels, and pharmacokinetics). To this end, a risk stratification scheme may be useful to rank and compare the potential for cardiotoxicity of each drug. It appears that in most published cases of antimicrobial-associated TdP, multiple risk factors are present. Macrolides in general are associated with a greater potential than other antimicrobials for causing TdP from both a pharmacodynamic and pharmacokinetic perspective. The azole antifungal agents also can be viewed as drugs that must be weighed carefully before use since they also have both pharmacodynamic and pharmacokinetic characteristics that may trigger TdP. The fluoroquinolones appear less likely to be associated with TdP from a pharmacokinetic perspective since they do not rely on cytochrome P450 (CYP) metabolism nor do they inhibit CYP enzyme isoforms, with the exception of grepafloxacin and ciprofloxacin. Nonetheless, patient selection must be carefully made for all of these drugs. For clinicians, certain responsibilities are assumed when prescribing antimicrobial therapy: (i) appropriate use to minimise resistance; and (ii) appropriate patient and drug selection to minimise adverse event potential. Incorporating information learned regarding QT interval-related adverse effects into the drug selection process may serve to minimise collateral iatrogenic toxicity.

Dual Effects of MLS Antibiotics

The macrolide-lincosamide-streptogramin (MLS) antibiotics are an important group of translation inhibitors that act on the 50S ribosome. We show that, at subinhibitory concentrations, members of the MLS group modulate specific groups of bacterial promoters, as detected by screening a library of promoter-luxCDABE reporter clones of Salmonella enterica serovar Typhimurium. The patterns of transcription permit identification of classes of promoters having differential responses to antibiotics of related structure and mode-of-action; studies of antibiotic synergy or antagonism showed that eukaryotic translation inhibitors may act on the 50S ribosome. The mechanism of transcriptional modulation is not known but may involve bacterial stress responses and/or the disturbance and subsequent compensation of metabolic networks as a result of subtle interference with ribosome function. Transcriptional patterns detected with promoter-lux clones provide a novel approach to antibiotic discovery and mode-of-action studies.

Evaluation of 5-day therapy with telithromycin, a novel ketolide antibacterial, for the treatment of tonsillopharyngitis

A pooled analysis of two double-blind, multicentre, Phase III studies compared oral telithromycin 800 mg once-daily for 5 days with penicillin V 500 mg three-times-daily or clarithromycin 250 mg twice-daily for 10 days in the treatment of Streptococcus pyogenes (group A beta-haemolytic streptococcus; GABHS) tonsillopharyngitis. Patients aged > or = 13 years with acute GABHS tonsillopharyngitis were randomised to receive telithromycin (n = 430), penicillin (n = 197) or clarithromycin (n = 231). Clinical isolates of S. pyogenes (n = 590) obtained from throat swab samples on study entry were tested for their in-vitro susceptibility to telithromycin, clarithromycin and azithromycin. Telithromycin demonstrated in-vitro activity against the clinical isolates of S. pyogenes (MIC50/90 0.03/0.06 mg/L) higher than clarithromycin or azithromycin (MIC50/90 0.06/0.06 mg/L and 0.12/0.25 mg/L, respectively), including erythromycin-resistant strains. At the post-therapy/test of cure (TOC) visit (days 16-23), satisfactory bacteriological outcome was demonstrated for 88.3% (234/265) and 88.6% (225/254) of telithromycin- and comparator-treated patients, respectively (per-protocol population). Overall, GABHS eradication rates were 88.7% (235/265) for telithromycin and 89.0% (226/254) for comparators. The clinical cure rates at the post-therapy/TOC visit were 93.6% (248/265) and 90.9% (220/242) for telithromycin and pooled comparators, respectively. Telithromycin was generally well-tolerated. Most adverse events considered to be possibly related to study medication were gastrointestinal and of mild intensity. Discontinuations as a result of adverse events were few in both treatment groups. In conclusion, telithromycin 800 mg once-daily for 5 days was as effective as penicillin V or clarithromycin for 10 days in the treatment of GABHS tonsillopharyngitis.

The Use of Ketolides in Treatment of Upper Respiratory Tract Infections

Recent surveillance studies suggest that the incidence of resistance to macrolide antibiotics in common community-acquired respiratory tract pathogens, particularly Streptococcus pneumoniae and Streptococcus pyogenes, is increasing and limiting the usefulness of these drugs. The ketolides, of which telithromycin is the first to be available for clinical use (but not yet in the United States), represent a new class of antibacterials developed specifically to combat respiratory tract pathogens that have acquired resistance to macrolides. The ketolides possess innovative structural modifications, a 3-keto group and a large N-substituted C11, C12-carbamate side chain. This novel structure allows ketolides, which are inhibitors of protein synthesis, to exert a more effective interaction with domain II of the 23S rRNA, enhancing binding to bacterial ribosomes and allowing binding to macrolide-lincosamide-streptogramin B-resistant ribosomes. This novel chemical structure also promotes greater stability of telithromycin in acid conditions, providing the potential for greater stability in gastric fluid and at cellular/tissue levels. Early clinical trials support the bacteriologic and clinical efficacy of telithromycin in the treatment of upper respiratory tract infections (RTIs) such as streptococcal pharyngitis and acute sinusitis, including infections caused by macrolide-resistant S. pneumoniae and S. pyogenes. Common adverse side effects associated with telithromycin are predominantly gastrointestinal, usually of mild to moderate severity, and rarely involve withdrawal of the drug. Telithromycin represents an attractive option for the empiric treatment of upper RTIs, especially as resistance to macrolides is likely to continue to increase.

Synthesis and Antibacterial Activity of a Novel Class of 4‘-Substituted 16-Membered Ring Macrolides Derived from Tylosin

Novel 4'-substituted 16-membered ring macrolides were synthesized by the cleavage of the mycarose sugar of tylosin and subsequent modification of 4'-hydroxyl group. This new class of macrolide antibiotics exhibited potent activity against some key erythromycin-resistant pathogens.

Evaluation of the Medical and Surgical Treatment Of Chronic Rhinosinusitis: A Prospective, Randomised, Controlled Trial

OBJECTIVES

To conduct the first prospective, randomized, controlled trial evaluating and comparing the medical and surgical treatment of polypoid and nonpolypoid chronic rhinosinusitis (CRS).

MATERIALS AND METHODS

Ninety patients with CRS were equally randomized either to medical or surgical therapy. All patients underwent pre- and posttreatment assessments of visual analogue score (VAS), the Sinonasal Outcome Test-20 (SNOT-20), the Short Form 36 Health Survey (SF-36), nitric oxide (NO), acoustic rhinometry, saccharine clearance time (SCT), and nasal endoscopy. Each patient had three assessments: before starting the treatment, after 6 months, and, finally, after 1 year.

RESULTS

Both the medical and surgical treatment of CRS significantly improved almost all the subjective and objective parameters of CRS (P <.01), with no significant difference being found between the medical and surgical groups (P >.05), except for the total nasal volume in CRS (P <.01) and CRS without polyposis (P <.01) groups, in which the surgical treatment demonstrated greater changes.

CONCLUSION

CRS should be initially targeted with maximal medical therapy (e.g., a 3 month course of a macrolide antibiotic, douche, and topical steroid), with surgical treatment being reserved for cases refractory to medical therapy. The presence of nasal polyps is not a poor prognostic factor for the efficacy of CRS therapy, either surgical or medical.

Synthesis of novel 4'-substituted 16-membered ring macrolide antibiotics derived from leucomycins

A series of novel 4'-substituted 16-membered ring macrolides was synthesized by the cleavage of the mycarose sugar and subsequent modification of 4'-hydroxyl group. This new class of macrolides antibiotics is acid stable. The synthetic methodology described here is expected to find application in the synthesis of new generation of macrolides that target the emerging bacterial resistance.

New developments in antibacterial choice for lower respiratory tract infections in elderly patients

Elderly patients are at increased risk of developing lower respiratory tract infections compared with younger patients. In this population, pneumonia is a serious illness with high rates of hospitalisation and mortality, especially in patients requiring admission to intensive care units (ICUs). A wide range of pathogens may be involved depending on different settings of acquisition and patient's health status. Streptococcus pneumoniae is the most common bacterial isolate in community-acquired pneumonia, followed by Haemophilus influenzae, Moraxella catarrhalis and atypical pathogens such as Chlamydia pneumoniae, Legionella pneumophila and Mycoplasma pneumoniae. However, elderly patients with comorbid illness, who have been recently hospitalised or are residing in a nursing home, may develop severe pneumonia caused by multidrug resistant staphylococci or pneumococci, and enteric Gram-negative bacilli, including Pseudomonas aeruginosa. Moreover, anaerobes may be involved in aspiration pneumonia. Timely and appropriate empiric treatment is required in order to enhance the likelihood of a good clinical outcome, prevent the spread of antibacterial resistance and reduce the economic impact of pneumonia. International guidelines recommend that elderly outpatients and inpatients (not in ICU) should be treated for the most common bacterial pathogens and the possibility of atypical pathogens. The algorithm for therapy is to use either a selected beta-lactam combined with a macrolide (azithromycin or clarithromycin), or to use monotherapy with a new anti-pneumococcal quinolone, such as levofloxacin, gatifloxacin or moxifloxacin. Oral (amoxicillin, amoxicillin/clavulanic acid, cefuroxime axetil) and intravenous (sulbactam/ampicillin, ceftriaxone, cefotaxime) beta-lactams are agents of choice in outpatients and inpatients, respectively. For patients with severe pneumonia or aspiration pneumonia, the specific algorithm is to use either a macrolide or a quinolone in combination with other agents; the nature and the number of which depends on the presence of risk factors for specific pathogens. Despite these recommendations, clinical resolution of pneumonia in the elderly is often delayed with respect to younger patients, suggesting that optimisation of antibacterial therapy is needed. Recently, some new classes of antibacterials, such as ketolides, oxazolidinones and streptogramins, have been developed for the treatment of multidrug resistant Gram-positive infections. However, the efficacy and safety of these agents in the elderly is yet to be clarified. Treatment guidelines should be modified on the basis of local bacteriology and resistance patterns, while dosage and/or administration route of each antibacterial should be optimised on the basis of new insights on pharmacokinetic/pharmacodynamic parameters and drug interactions. These strategies should be able to reduce the occurrence of risk factors for a poor clinical outcome, hospitalisation and death.

The clinical significance of macrolide-resistant Streptococcus pneumoniae: it's all relative

Macrolides are currently recommended as first-line agents for the empirical treatment of community-acquired pneumonia. Heavy use of these agents for a variety of indications has resulted in an increasing incidence of macrolide resistance among pneumococcal isolates. Although several case reports and small case series have suggested that in vitro macrolide resistance is associated with treatment failure in cases of pneumococcal pneumonia, other observational data suggest that drug susceptibility testing may not correlate with treatment failure. In this article, we review current information on the mechanisms of macrolide resistance and the pharmacodynamics of macrolide therapy, together with efficacy data from animal models and clinical observations, to begin to gauge the clinical significance of macrolide resistance in Streptococcus pneumoniae. Areas for further investigation are highlighted.

A guide to selection and appropriate use of macrolides in skin infections

Dermatologists must be aware of the adverse effects of antimicrobial agents as well as various drug interactions that may influence the choice of drug as well as specific drug schedules. The development of modern antibacterials has improved the treatment of cutaneous bacterial infections. Macrolide antibacterials continue to be an important therapeutic class of drugs with established efficacy in a variety of skin infections. All macrolides inhibit protein synthesis by reversibly binding to the 23S ribosomal RNA in the 50S-subunit. Erythromycin, the prototype of macrolide antibacterials, was isolated from the metabolic products of a strain of Streptomyces erytherus in 1952. Originally, erythromycin was introduced as an alternative to penicillin because of its activity against the Gram-positive organisms. Numerous studies have demonstrated the efficacy and safety of erythromycin for various infectious diseases. Unfortunately, erythromycin is associated with a number of drawbacks including a narrow spectrum of activity, unfavorable pharmacokinetic properties, poor gastrointestinal tolerability, and a significant number of drug-drug interactions. Newer macrolides have been developed to address these limitations. The pharmacokinetics of azithromycin and clarithromycin allow for shorter dosing schedules because of prolonged tissue levels. The efficacy of azithromycin for the treatment of skin and soft tissue infections in adults and children is well established. The unique pharmakinetics of azithromycin makes it a suitable agent for the treatment of acne. Clarithromycin represents a clear advance in the macrolide management of patients with leprosy and skin infections with atypical mycobacteria. Dirithromycin and roxithromycin display no clinical or bacteriological adcantage over erythromycin despite a superior pharmacokinetic profile. An area of concern is the increasing macrolide resistance that is being reported with some of the common pathogens which may limit the clinical usefulness of this class of antimicrobial agents in future.

Current Management Issues Associated with Community-Acquired Pneumonia

Community-acquired pneumonia (CAP) is a significant cause of morbidity, mortality, and increased cost. Despite numerous managementguidelines, CAP continues to existas a challenge to the learned clinician. Due to a lack of sensitive diagnostic testing, causative pathogens are often not identified, making most therapy empiric. Increasing levels of bacterial resistance to available antimicrobials worldwide has been implicated in driving up the costs of treatment and adversely effecting clinical outcomes. Pharmacists can be part of the solution by encouraging appropriate antimicrobial selection based on resistance patterns in their communities and ensuring appropriate vaccines are employed to prevent CAP.

Macrolide resistance: an increasing concern for treatment failure in children

BACKGROUND

Antimicrobial treatment of pediatric respiratory tract infections has evolved during the past 30 years as a result of antimicrobial resistance. The focus of antimicrobial therapy in these conditions has shifted from penicillins to other agents because of the dramatic increase in antimicrobial resistance among common respiratory pathogens, including Streptococcus pneumoniae, Haemophilus influenzae and Moraxella catarrhalis. It is important for clinicians to understand how resistance develops so that they can help prevent this phenomenon from occurring with other antimicrobials.

METHODS

This article reviews the published literature on resistance to macrolide antimicrobials among common pediatric respiratory tract pathogens and clinical and bacteriologic outcomes of infections with these pathogens.

RESULTS

Resistance among common pediatric respiratory tract pathogens to macrolides occurs through two main mechanisms, alteration of the target site and active efflux. Although resistance patterns vary by geographic region, the widespread use of macrolides has contributed to the emergence of both types of macrolide-resistant organisms. Conditions that favor the selection and proliferation of resistant strains include children with repeated, close contact who frequently receive antimicrobial treatment or prophylaxis, such as children who attend day care. Recent US surveillance data show that 20 to 30% of S. pneumoniae are resistant to macrolides, with approximately two-thirds of macrolide-resistant strains associated with an efflux mechanism and the remainder associated with a ribosomal methylase. Additionally, although less well-known, virtually all strains of H. influenzae have an intrinsic macrolide efflux pump. As resistance to macrolides has increased, clinical failures have resulted, and these agents are no longer considered appropriate for empiric first line antimicrobial therapy of acute otitis media and sinusitis unless patients are truly penicillin-allergic. Therefore, other antimicrobials are recommended for the empiric treatment of children with respiratory tract infections, including higher doses of amoxicillin and amoxicillin/clavulanate (90 mg/kg/day amoxicillin), cefuroxime axetil and intramuscular ceftriaxone.

CONCLUSIONS

As resistance to macrolides increases and clinical failures in children become more common with this class of antimicrobials, judicious use of antimicrobials is needed. This includes limiting antimicrobial use for viral infections and using the most effective agents when antimicrobials are clinically indicated, such as higher doses of amoxicillin and amoxicillin/clavulanate. Application of these principles may prevent proliferation and further development of resistance.

Antimicrobial resistance in respiratory tract Streptococcus pneumoniae isolates: results of the Canadian Respiratory Organism Susceptibility Study, 1997 to 2002

A total of 6,991 unique patient isolates of Streptococcus pneumoniae were collected from October 1997 to June 2002 from 25 medical centers in 9 of the 10 Canadian provinces. Among these isolates, 20.2% were penicillin nonsusceptible, with 14.6% being penicillin intermediate (MIC, 0.12 to 1 microg/ml) and 5.6% being penicillin resistant (MIC, > or =2 microg/ml). The proportion of high-level penicillin-resistant S. pneumoniae isolates increased from 2.4 to 13.8% over the last 3 years of the study, and the proportion of multidrug-resistant S. pneumoniae isolates increased from 2.7 to 8.8% over the 5-year period. Resistant rates (intermediate and resistant) among non-beta-lactam agents were as follows: macrolides, 9.6 to 9.9%; clindamycin, 3.8%; doxycycline, 5.5%; chloramphenicol, 3.9%; and trimethoprim-sulfamethoxazole, 19.0%. Rates of resistance to non-beta-lactam agents were higher among penicillin-resistant strains than among penicillin-susceptible strains. No resistance to vancomycin or linezolid was observed; however, 0.1% intermediate resistance to quinupristin-dalfopristin was observed. The rate of macrolide resistance (intermediate and resistant) increased from 7.9 to 11.1% over the 5 years. For the fluoroquinolones, the order of activity based on the MICs at which 50% of isolates are inhibited (MIC(50)s) and the MIC(90)s was gemifloxacin > clinafloxacin > trovafloxacin > moxifloxacin > grepafloxacin > gatifloxacin > levofloxacin > ciprofloxacin. The investigational compounds ABT-773 (MIC(90), 0.008 microg/ml), ABT-492 (MIC(90), 0.015 microg/ml), GAR-936 (tigecycline; MIC(90), 0.06 microg/ml), and BMS284756 (garenoxacin; MIC(90), 0.06 micro g/ml) displayed excellent activities. Despite decreases in the rates of antibiotic consumption in Canada over the 5-year period, the rates of both high-level penicillin-resistant and multidrug-resistant S. pneumoniae isolates are increasing in Canada.

Synthesis of new 14-membered macrolide antibiotics via a novel ring contraction metathesis

[reaction: see text] A novel ring opening ring closing metathesis (ROM-RCM) was demonstrated for cyclic conjugated dienes, effecting the excision of a C(2)H(2) unit and a net ring contraction. Applying the ring contraction metathesis, new 14-membered ring macrolide antibiotics were synthesized in a single step from existing 16-membered ring macrolides. This new class of macrolide antibiotics will provide access to new therapeutics for the treatment of macrolide-resistant bacterial infections.

A comparison of 5-day courses of dirithromycin and azithromycin in the treatment of acute exacerbations of chronic obstructive pulmonary disease

BACKGROUND

Short-term use of antibiotics has become a common component of the management of acute exacerbations of chronic bronchitis (AECB), particularly in complex cases with productive cough or purulent phlegm. The macrolide antibiotics, particularly second-generation agents such as dirithromycin and azithromycin, are among the antibiotic classes frequently recommended and used to treat upper and lower respiratory infections, including AECB.

OBJECTIVE

This study compared the clinical efficacy and tolerability of 5-day courses of dirithromycin and azithromycin given once daily for the treatment of acute exacerbations of chronic obstructive pulmonary disease (COPD).

METHODS

This randomized, investigator-blinded, parallel-group clinical trial was conducted at 5 centers in the United States. Eligible patients were adult (age >35 years) smokers or ex-smokers (smoking history of at least 10 pack-years) with chronic bronchitis and an acute exacerbation, defined by the occurrence of increased dyspnea and/or productive cough and feverishness within 48 hours of enrollment. Before randomization, an attempt was made to obtain a sputum specimen from each patient for Gram's staining and culture. Patients were randomized to receive dirithromycin 500 mg QD for 5 days or azithromycin 500 mg QD on day 1 and 250 mg QD on days 2 to 5. Clinical efficacy was assessed separately by patients and physicians at early (days 7-10) and late (days 25-35) posttreatment visits.

RESULTS

Eighty-six patients (48 women, 38 men; mean age, 55 years) with a mean smoking history of 31 pack-years were included in the intent-to-treat analysis. Forty-six (54%) patients were randomized to dirithromycin and 40 (47%) patients to azithromycin. Clinical efficacy was reported in a high proportion of patients in both treatment groups, both at the early posttreatment visit (84.8% dirithromycin, 75.7% azithromycin; difference dirithromycin - azithromycin, 9.1%; 95% CI, -8.2 to 26.4) and the late posttreatment visit (95.5% and 86.5%, respectively; difference dirithromycin - azithromycin, 9.0%; 95% CI, -3.7 to 21.6). A similar proportion of patients required a second course of antibiotics over the study period (20.5% dirithromycin, 27.0% azithromycin; difference dirithromycin - azithromycin, -6.6%; 95% CI, -25.2 to 12.1). Only 42 (48.8%) patients were able to produce a sputum sample before receiving study treatment, and of these, only 20 (47.6%) demonstrated a preponderance of neutrophils on Gram's staining. Both treatments were well tolerated.

CONCLUSIONS

The results of this study suggest comparable clinical efficacy between 5-day courses of once-daily dirithromycin and azithromycin in acute exacerbations of COPD. There were insufficient data to permit meaningful comparison of the bacteriologic efficacy of these macrolide antibiotics.