Telithromycin: an oral ketolide for respiratory infections

Structure-based drug designing against Leishmania donovani using docking and molecular dynamics simulation studies: exploring glutathione synthetase as a drug target

In the pursuit of developing novel anti-leishmanial agents, we conducted an extensive computational study to screen inhibitors from the FDA-approved ZINC database against Leishmania donovani glutathione synthetase. The three-dimensional structure of Leishmania donovani glutathione synthetase was constructed by homology modeling, using the crystallographic structure of Trypanosoma brucei glutathione synthetase as a template. Subsequently, molecular docking studies were carried out for a large number of compounds using AutoDock Vina. Among the screened compounds, we selected the top five with strong binding affinity to Leishmania donovani glutathione synthetase but having a very low affinity to its human homolog. Further investigations on protein-ligand complexes were done by conducting molecular dynamics (MD) simulation and MM/PBSA analysis. The results revealed that Olysio (Simeprevir) exhibited the lowest binding energy (-89.21 kcal/mol), followed by Telithromycin (-45.34 kcal/mol). These findings showed that these compounds have the potential to act as inhibitors of glutathione synthetase. Hence, our study provides valuable insights for the development of a novel therapeutic strategy against Leishmania donovani by targeting the glutathione synthetase enzyme.Communicated by Ramaswamy H. Sarma.

Alterations in regulatory regions of erm(B) genes from clinical isolates of enterococci resistant to telithromycin

We determined rates of resistance to the ketolide telithromycin in 56 Enterococcus faecalis isolates and 44 Enterococcus faecium isolates collected from hospitals in Korea between 2005 and 2006. Twenty nine (51.8%) isolates of E. faecalis and 35 (79.5%) isolates of E. faecium were resistant to telithromycin (minimum inhibitory concentrations, ≥ 4 μg/mL). All of the telithromycin-resistant E. faecalis carried the erm(B) gene only. Of the telithromycin-resistant E. faecium, 29 resistant strains carried erm(B) only, the other six carried erm(A) and erm(B) together. The nucleotide sequence of the erm(B) regulatory regions from 29 E. faecalis and 29 E. faecium isolates with erm(B) only was analyzed. Five types of alterations were detected. The first and second types had point mutations that destabilize the secondary structure of erm(B) mRNA sequestering the translation initiation region of the structural gene. The third type was identical to erm(Bv1), a previously reported variant of erm(B) with different induction specificity. The fourth and fifth types had point mutations within the critical sequence for induction and a point mutation destabilizing the stem-loop of erm(B) mRNA sequestering the translation initiation region of the structural gene.

Nortriptyline Cardiac Toxicity Resulting from a Probable Interaction with Telithromycin

Objective

To report a case of probable nortriptyline toxicity associated with a combination of telithromycin and nortriptyline.

Case Summary

A 50-year-old white woman was admitted to the hospital with new-onset palpitations after taking 5 days of telithromycin in combination with nortriptyline. On admission her electrocardiograph showed atrioventricular nodal reentry tachycardia. The patient was also hypotensive, with a blood pressure of 90/45 mm Hg. She had been taking nortriptyline 150 mg daily at bedtime for 10 years without complications. The final day of telithromycin therapy was completed, and nortriptyline was discontinued on admission. The tachycardia subsided with a dose of diltiazem.

Discussion

It is suspected that the cardiovascular symptoms observed in the patient are the result of nortriptyline toxicity caused by inhibition of CYP2D6 by telithromycin. Limited evidence shows that telithromycin may be an inhibitor of CYP2D6. An assessment of causation of the adverse effects using the Drug Interaction Probability Scale suggests a probable interaction between telithromycin and nortriptyline.

Conclusion

It is recommended that clinicians remain aware of possible interactions between telithromycin and known CYP2D6 substrates such as nortriptyline. Should telithromycin therapy be required, close monitoring of the potential adverse effects and/or plasma drug levels of patients taking interacting drugs is warranted.

Antibiotics for treatment of resistant gram-positive coccal infections

Vancomycin is considered the workhorse for the treatment of most drug-resistant gram-positive bacterial infections. However, concerns have been raised regarding the increasing rates of vancomycin-resistant enterococci and the clinical shortcomings of vancomycin in the treatment of invasive Staphylococcus aureus infections. Resources have been committed to the development of antimicrobial agents with activity against these organisms. This review will focus on the newer antibacterial agents that have been developed for the treatment of resistant gram-positive pathogens. Included in this review are the agents: quinupristin-dalfopristin, linezolid, daptomycin, telithromycin, and tigecycline.

Involvement of the drug transporters p glycoprotein and multidrug resistance-associated protein Mrp2 in telithromycin transport

The present study aims to investigate the role of P glycoprotein and multidrug resistance-associated protein (Mrp2) in the transport of telithromycin, a newly developed ketolide antibiotic, in vitro and in vivo. The in vitro experiments revealed that the intracellular accumulation of telithromycin in adriamycin-resistant human chronic myelogenous leukemia cells (K562/ADR) overexpressing P glycoprotein was significantly lower than that in human chronic myelogenous leukemia cells (K562/S) not expressing P glycoprotein. Cyclosporine significantly increased the intracellular accumulation of telithromycin in K562/ADR cells. When telithromycin was coadministered intravenously with cyclosporine in Sprague-Dawley (SD) rats, cyclosporine significantly delayed the disappearance of telithromycin from plasma and decreased its systemic clearance to 60% of the corresponding control values. Hepatobiliary excretion experiments revealed that cyclosporine almost completely inhibited the biliary clearance of telithromycin, suggesting that telithromycin is a substrate of P glycoprotein and a potential substrate of Mrp2. Moreover, the biliary clearance of telithromycin was significantly decreased by 80% in Eisai hyperbilirubinemic mutant rats with a hereditary deficiency in Mrp2, indicating that Mrp2, as well as P glycoprotein, plays an important role in the biliary excretion of telithromycin. When the effect of telithromycin on the biliary excretion of doxorubicin, a substrate of P glycoprotein and Mrp2, was examined in SD rats, telithromycin significantly decreased the biliary clearance of doxorubicin by 80%. Results obtained from this study indicate that telithromycin is a substrate of both P glycoprotein and Mrp2, and these transporters are involved in the hepatobiliary transport of telithromycin.

Telithromycin: a novel agent for the treatment of community-acquired upper respiratory infections

The ketolides are a new subclass of macrolides, and telithromycin is the first of these agents to be approved. Modifications to the basic macrolide structure result in enhanced activity against penicillin- and erythromycin resistant respiratory pathogens. It is therefore an option in the treatment of mild to moderate community-acquired respiratory infections, such as pneumonia, acute exacerbations of chronic bronchitis, pharyngitis/tonsillitis, and sinusitis. Telithromycin also offers the advantages of once-daily dosing and a shorter course of therapy in certain infections. Comparative clinical trials, although limited and involving only a small number of resistant organisms, showed the equivalence of telithromycin to existing therapies, although telithromycin generally had a higher frequency of mild to moderate gastrointestinal adverse effects. Further clinical and safety data, especially in patients with resistant organisms, are needed.

Telithromycin for the Treatment of Acute Bacterial Maxillary Sinusitis: A Review of a New Antibacterial Agent

OBJECTIVE

Telithromycin, the first approved ketolide antibiotic, was developed to treat community-acquired respiratory tract infections, including acute bacterial maxillary sinusitis (ABMS). A previously published study showed that a 5-day course of 800 mg telithromycin once daily is as effective as a 10-day course in the treatment of ABMS.

MATERIALS AND METHODS

Data were pooled from two controlled, multinational, prospective, randomized, double-blinded ABMS trials comparing 5-day telithromycin (800 mg once daily) with 10-day amoxicillin-clavulanate (500/125 mg 3 times daily) and cefuroxime axetil (250 mg twice daily). Clinical cure and bacteriologic eradication rates were compared by means of descriptive statistics.

RESULTS

The clinical cure rate for telithromycin was 80.9% versus 77.4% for comparators; bacteriologic eradication rate for telithromycin was 84.9% versus 81.7% for comparators. Most adverse events were mild to moderate in intensity and, most commonly, gastrointestinal in nature.

CONCLUSIONS

These results support the conclusion that 5 days of treatment with telithromycin is as safe and effective in patients with ABMS as a 10-day course of treatment with amoxicillin-clavulanate or cefuroxime axetil.

Clinical efficacy of newer agents in short-duration therapy for community-acquired pneumonia

Streptococcus pneumoniae, the most important respiratory tract pathogen implicated in community-acquired pneumonia (CAP), is becoming increasingly resistant in vitro to the beta -lactams and macrolides, and fluoroquinolone resistance has been detected. A growing body of evidence suggests that prolonged antimicrobial use may contribute directly and indirectly to increased antimicrobial resistance among common respiratory pathogens. Long-term exposure to antimicrobial agents, especially less-potent agents, directly increases selection pressure for resistance. Indirectly, poor patient compliance, multiple daily dosing, and the increased risk of adverse events further complicate the resistance issue and diminish the efficacy of long-term antimicrobial use. Controlled clinical trials addressing the appropriate duration of therapy for CAP are lacking. However, available data suggest that with appropriate antibiotic selection, based on appropriate spectrum, potency, and pharmacokinetic/pharmacodynamic profile, lower respiratory tract infections in outpatients can be successfully treated in <7 days rather than the 7-14 days currently recommended.

Antibiotic Resistance

Resistance to antibiotics is economically and physiologically costly. Control of antibiotic resistance will require aggressive implementation of numerous strategies. Ongoing surveillance is needed to monitor known antibiotic types and to be able to identify the development of other potential types. Early intervention is needed to combat the rising rate of resistance. Persistent use of hygiene measures and controlled use of antibiotics will limit the spread of antibiotic resistance. Health care providers need to monitor adherence to control measures. Hand and environmental control measures remain a critical component of staff education activities. Active management of infections with non-pharmacologic treatments should be promoted. Motivational campaigns will reinforce positive infection control behaviors. Consistent surveillance of antibiotic use will help fulfill the CDC directive to combat antibiotic resistance and keep the population healthy.

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.

Efficacy and safety of oral telithromycin once daily for 5 days versus moxifloxacin once daily for 10 days in the treatment of acute bacterial rhinosinusitis

OBJECTIVE

To compare the clinical and bacteriologic efficacy and safety of short-duration treatment with telithromycin given for 5 days with moxifloxacin given for 10 days in adults with acute bacterial rhinosinusitis (ABRS).

STUDY DESIGN

In this prospective, double-blind, parallel-group, randomized, multicenter study, adult patients (N = 349) with ABRS were randomized to oral telithromycin (800 mg once daily for 5 days) or to oral moxifloxacin (400 mg once daily for 10 days) and followed for 31 to 36 days. Clinical outcome was determined by the investigator at the posttherapy/test of cure (TOC) visit. Bacteriologic outcome was determined by comparing cultures taken at the pretreatment visit with cultures obtained at the posttherapy/TOC visit. The primary objective was to demonstrate equivalence of clinical cure rates in the per-protocol population between treatment groups at the posttherapy/TOC visit.

RESULTS

Clinical success at TOC (primary endpoint) was achieved in 87.4% of patients in the telithromycin group compared with 86.9% for moxifloxacin (per-protocol patients; 0.5% difference between treatment groups; 95% confidence interval [CI], -8.1, 9.2; P = 0.8930). The bacteriologic success rates were 94.1% and 93.9%, respectively (0.2% difference between treatment groups; 95% CI, -14.2, 14.5; P = 0.9734). Overall treatment-emergent adverse events for both drugs (mostly gastrointestinal) were mild to moderate in intensity.

CONCLUSION AND SIGNIFICANCE

The clinical and bacteriologic efficacy of telithromycin 800 mg once daily for 5 days was equivalent to that of moxifloxacin 400 mg once daily for 10 days, establishing telithromycin as an important treatment option for ABRS.

Chemometric Studies on the Bactericidal Activity of Quinolones via an Extended VolSurf Approach

An extended VolSurf approach, that additionally includes SHAPE descriptors, was applied to a dataset of 55 quinolones. Bactericidal activity was measured at Bayer AG, Germany, for Gram-negative (Escherichia coli and Pseudomonas aeruginosa) and Gram-positive bacteria (Staphylococcus aureus and Enterococcus faecalis). Chemometric analysis was first approached via a classical VolSurf approach. The following descriptors were found most important: bactericidal activity particularly increases with high values of the best volume (BV11(OH2)) and the minimum energy (Emin1(OH2)) of the water probe, high values of the integy moment (ID(DRY)) of the lipophilic probe, and high values of the hydrophilic region (W(O)) of the hydrogen bond acceptor probe. Best volume (BV31(OH2)) of the water probe and best volume (BV12(DRY)) and lipophilic regions (D(DRY)) of the lipophilic probe as well as H-bonding capacity derived with the CO probe (HB(O)) are inversely related to activity. PLS analysis yields a five-component model with an r(2) of 0.83 and a q(2) of 0.43 after variable selection via fractional factorial design (FFD). Chemometric modeling could be improved by including newly derived SHAPE descriptors, which were merged with the VolSurf descriptors and subjected to PLS analysis. The global model of this extended VolSurf approach is optimal with two components and exhibits a significantly improved statistical quality; a marginally reduced r(2) (0.75 versus 0.83) is more than compensated by a highly improved predictivity with a q(2) of 0.63 versus 0.43. To prove model quality, external prediction of seven test set quinolones was performed. The precise prediction of all test set molecules nicely demonstrates the robustness and statistical significance of the obtained chemometric model using the extended VolSurf approach.

Prevention and management of antibacterial resistance for primary care patients with respiratory tract infections

This review examines the problem of increasing antibacterial resistance among the pathogens commonly associated with community-acquired respiratory tract infections, particularly Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis. The increases in morbidity, mortality, and treatment cost associated with increased resistance to available antibiotics are challenging prescribers to find more effective therapeutic strategies. A MEDLINE search of the literature from 1966 to the present was performed to seek data relevant to the issue of resistance, especially the negative effects on patient outcomes and costs of therapy. Several observations and conclusions emerged. Data are lacking on local resistance patterns, broad-spectrum agents are overprescribed when narrower-spectrum choices would be more appropriate, a need exists for educational programs to encourage restricting drug use and changing prescribing habits, and there is a need for new antibiotic choices. The best antibiotic options are agents with a tailored spectrum of activity that are targeted at particular respiratory tract pathogens and have low potential to select for resistant organisms.

Fluoroquinolone AUIC Break Points and the Link to Bacterial Killing Rates Part 2: Human Trials

OBJECTIVE

To review clinical trials with fluoroquinolones and the pharmacokinetic and pharmacodynamic parameters predictive of clinical and microbiologic outcomes and resistance. Data on fluoroquinolones are summarized and the premise that a single AUIC target >125 may be used for all fluoroquinolones against all target organisms is examined.

DATA SOURCES

Primary articles were identified by a MEDLINE search (1966-February 2002) and through secondary sources.

STUDY SELECTION AND DATA EXTRACTION

All of the articles identified from the data sources were evaluated and all information deemed relevant was included.

DATA SYNTHESIS

The fluoroquinolones exhibit concentration-dependent killing. This effect clearly depends upon concentrations achieved and outcomes depend upon endpoints established by individual investigators. With AUIC values <60, the actions of fluoroquinolones are essentially bacteriostatic; any observed bacterial killing is the combined effect of low concentrations in relation to minimum inhibitory concentration and the action of host factors such as neutrophils and macrophages. AUIC values >100 but <250 yield bacterial killing at a slow rate, but usually by day 7 of treatment. AUICs >250 produce rapid killing, and bacterial eradication occurs within 24 hours. Disagreements regarding target endpoints are the expected consequences of comparing microbial and clinical outcomes across animal models, in vitro experiments (Part 1), and humans when the endpoints are clearly not equivalent. Careful attention to time-related events such as speed of bacterial killing versus global endpoints such as bacteriologic cure allows optimal break points to be defined.

CONCLUSIONS

Evidence from human trials favors the use of AUIC values >250 for rapid bactericidal action, regardless of whether the organism is gram-negative or gram-positive.

Novel antibacterial agents for the treatment of serious Gram-positive infections

With the continuing development of clinical drug resistance among bacteria and the advent of resistance to the recently released agents quinupristin-dalfopristin and linezolid, the need for new, effective agents to treat multi-drug-resistant Gram-positive infections remains important. This review focuses on agents presently in clinical development for the treatment of serious multidrug-resistant staphylococcal, enterococcal and pneumococcal infections, including methicillin-resistant Staphylococcus aureus, vancomycin-resistant enterococci and penicillin-resistant Streptococcus pneumoniae. Agents to be discussed that affect the prokaryotic cell wall include the antimethicillin-resistant S. aureus cephalosporins BAL9141 and RWJ-54428, the glycopeptides oritavancin and dalbavancin and the lipopeptide daptomycin. Topoisomerase inhibitors include the fluoroquinolones gemifloxacin, sitafloxacin and garenoxacin. Protein synthesis inhibitors are represented by the ketolides telithromycin and cethromycin, the oxazolidinones and the glycylcycline tigecycline. Although each of these compounds has demonstrated antibacterial activity against antibiotic-resistant pathogens, their final regulatory approval will depend on an acceptable clinical safety profile.