Postantibiotic suppression of growth of erythromycin A-susceptible and -resistant gram-positive bacteria by the ketolides telithromycin (HMR 3647) and HMR 3004

In vitro killing of multidrug/extensively drug-resistant Pseudomonas aeruginosa by fosfomycin alone or in combination with antipseudomonal antibiotics

Pseudomonas aeruginosa is a leading cause of nosocomial infections. Given the constant rise in resistance, adequate therapy is increasingly demanding. Fosfomycin recently became an appealing treatment option of bacterial infections due to multidrug-resistant bacteria (MDR). So far, fosfomycin synergy with other antibiotics has been assessed in studies, but only a limited number focused on MDR P. aeruginosa and on the effect of these combinations on the duration of the postantibiotic effect (PAE). We investigated synergy of fosfomycin with an array of antipseudomonal antibiotics using gradient diffusion strip cross method and time-kill method, and their effect on the duration of PAE against 51 variously resistant P. aeruginosa isolates. The highest rate of synergy was observed for combination with ceftazidime (23.4%) and gentamicin (19.1%). The PAE of antibiotic combinations was superior to that of the drugs alone. Our findings indicate that fosfomycin combination therapy may be a valuable treatment alternative.

Progress in Niobium Oxide-Containing Coatings for Biomedical Applications: A Critical Review

Typically, pure niobium oxide coatings are deposited on metallic substrates, such as commercially pure Ti, Ti6Al4 V alloys, stainless steels, niobium, TiNb alloy, and Mg alloys using techniques such as sputter deposition, sol-gel deposition, anodizing, and wet plasma electrolytic oxidation. The relative advantages and limitations of these coating techniques are considered, with particular emphasis on biomedical applications. The properties of a wide range of pure and modified niobium oxide coatings are illustrated, including their thickness, morphology, microstructure, elemental composition, phase composition, surface roughness and hardness. The corrosion resistance, tribological characteristics and cell viability/proliferation of the coatings are illustrated using data from electrochemical, wear resistance and biological cell culture measurements. Critical R&D needs for the development of improved future niobium oxide coatings, in the laboratory and in practice, are highlighted.

A novel ketolide class: Synthesis and antibacterial activity of a lead compound

Synthesis and antibacterial activity of a new class of ketolide antibiotics, exemplified by the prototype GW680788X (1), are described. The structure of (1) has been elucidated by spectroscopic analysis. The good antibacterial activity shown by (1) in comparison with clarithromycin prompted us to consider this compound as a lead molecule for further exploration.

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: 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.

Telithromycin

Telithromycin, the first member of the ketolide antibacterials, has good activity against community-acquired respiratory pathogens, including multiple-drug-resistant strains of Streptococcus pneumoniae. Telithromycin 800 mg once daily has been US FDA approved for the treatment of acute bacterial sinusitis (ABS; treatment duration 5 days), acute bacterial exacerbations of chronic bronchitis (AECB; 5 days) and mild-to-moderate community-acquired pneumonia (CAP; 7-10 days). In patients with CAP, telithromycin was as effective as amoxicillin 1000 mg three times daily for 10 days, clarithromycin 500 mg twice daily for 10 days or trovafloxacin 200 mg once daily for 7-10 days. In patients with AECB, telithromycin was as effective as a 10-day regimen of amoxicillin/clavulanic acid 500/125 mg three times daily, cefuroxime axetil 500 mg twice daily or clarithromycin 500 mg twice daily. In patients with ABS, telithromycin was as effective as a 10-day course of amoxicillin/clavulanic acid 500/125 mg three times daily or cefuroxime axetil 250 mg twice daily. Telithromycin was generally well tolerated and most adverse events were of mild-to-moderate severity and transitory. The most common adverse events with telithromycin were diarrhoea and nausea (10.8% and 7.9% of 2702 patients in clinical trials); these events occurred in 8.6% and 4.6% of 2139 comparator-treated patients.

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.

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.

Postantibiotic effects of ABT-773 and amoxicillin-clavulanate against Streptococcus pneumoniae and Haemophilus influenzae

This study determined the postantibiotic effect (PAE) of ABT-773 versus that of amoxicillin-clavulanate against clinical isolates of Streptococcus pneumoniae and Haemophilus influenzae. The PAEs of ABT-773 and amoxicillin-clavulanate ranged from 2.3 to 6.0 h and 0 to 2.2 h against S. pneumoniae and from 2.7 to 9.1 h and 0 to 0.8 h against H. influenzae, respectively.

Telithromycin

Telithromycin is the first member of a new family of the macrolide-lincosamide-streptogramin-B (MLS(B)) class of antimicrobials, the ketolides. It has a good spectrum of activity against respiratory pathogens, including penicillin- and erythromycin-resistant pneumococci, as well as intracellular and atypical bacteria. Furthermore, it has a low potential to select for resistance or induce cross-resistance among other MLS(B) antimicrobials. At the recommended dosage of 800 mg orally once daily, telithromycin reaches maximal plasma concentrations of about 2 mg/L. It penetrates rapidly into bronchopulmonary, tonsillar, sinus and middle ear tissues and/or fluids and achieves high concentrations at sites of infection. It also concentrates within polymorphonuclear neutrophils. In clinical trials in patients with community-acquired pneumonia (CAP), acute exacerbations of chronic bronchitis (AECB) or pharyngitis/tonsillitis caused by group A beta-haemolytic streptococci, telithromycin 800 mg once daily achieved clinical cure rates of 86 to 95%. In acute maxillary sinusitis (AMS), cure rates were 73 to 91%. A 7- to 10-day regimen of telithromycin was as effective as a 10-day course of amoxicillin 1000 mg 3 times daily, clarithromycin 500 mg twice daily or a 7- to 10-day course of trovafloxacin 200 mg once daily for treating CAP. A 5-day regimen of telithromycin was as effective as a 10-day regimen of cefuroxime axetil 500 mg twice daily or amoxicillin/clavulanic acid 500/125 mg 3 times daily in AECB. A 5-day regimen of telithromycin was as effective as a 10-day regimen of clarithromycin 250 mg twice daily or phenoxymethylpenicillin 500 mg 3 times daily in pharyngitis/tonsillitis, or a 10-day regimen of amoxicillin/clavulanic acid 500/125 mg 3 times daily in patients with AMS. Telithromycin was well tolerated across all patient populations. Adverse events associated with telithromycin were generally mild to moderate in intensity and seldom led to treatment discontinuation. The most frequent adverse events were diarrhoea (13.3%) and nausea (8.1%). Other adverse events included dizziness and vomiting.

Telithromycin: an oral ketolide for respiratory infections

The ketolides represent a new subclass of antibiotics among the macrolide-lincosamide-streptogramin group. Telithromycin, the first ketolide to be awarded approvable status for clinical use, demonstrates in vitro activity against community-acquired respiratory pathogens including penicillin- and erythromycin-resistant Streptococcus pneumoniae. An extended half-life permits once-daily oral administration. Telithromycin is a substrate for cytochrome P450 (CYP) 3A4 and also inhibits drugs metabolized by CYP3A4. A relatively high frequency of mild-to-moderate gastrointestinal adverse effects has been reported. Similar clinical and microbiologic efficacy has been demonstrated with oral dosing in comparative clinical trials for community-acquired pneumonia, acute sinusitis, acute exacerbations of chronic bronchitis, and pharyngitis. Although limited data on penicillin-resistant S. pneumoniae and erythromycin-resistant Streptococcus pyogenes are available from clinical trials, this drug appears promising for respiratory infections caused by these pathogens.