Accumulation and activity of cethromycin (ABT-773) within human polymorphonuclear leucocytes

Cethromycin: A New Ketolide Antibiotic

OBJECTIVE

To review the pharmacology, chemistry, microbiology, in vitro susceptibility, mechanism of resistance, pharmacokinetics, pharmacodynamics, clinical efficacy, safety, drug interactions, dosage, and administration of cethromycin, a new ketolide antibiotic.

DATA SOURCES

Literature was obtained through searching PubMed (1950-October 2012), International Pharmaceutical Abstracts (1970-October 2012), and a bibliographic review of published articles. Search terms included cethromycin, ABT-773, ketolide antibiotic, and community-acquired pneumonia.

STUDY SELECTION AND DATA EXTRACTION

All available in vitro and preclinical studies, as well as Phase 1, 2, and 3 clinical studies published in English were evaluated to summarize the pharmacology, chemistry, microbiology, efficacy, and safety of cethromycin in the treatment of respiratory tract infections.

DATA SYNTHESIS

Cethromycin, a new ketolide, has a similar mechanism of action to telithromycin with an apparently better safety profile. Cethromycin displays in vitro activity against selected gram-positive, gram-negative, and atypical bacteria. The proposed indication of cethromycin is treatment of mild to moderate community-acquired bacterial pneumonia in patients aged 18 years or older. Based on clinical studies, the recommended dose is 300 mg orally once a day without regard to meals. Cethromycin has an orphan drug designation for tularemia, plague, and anthrax prophylaxis. The Food and Drug Administration denied approval for the treatment of community-acquired pneumonia in 2009; a recent noninferiority trial showed comparable efficacy between cethromycin and clarithromycin. Preliminary data on adverse effects suggest that cethromycin is safe and gastrointestinal adverse effects appear to be dose-related.

CONCLUSIONS

Cethromycin appears to be a promising ketolide for the treatment of mild to moderate community-acquired pneumonia. It was denied approval by the FDA in 2009 pending more evidence to show its efficacy, with more recent studies showing its noninferiority to antibiotics for the same indication.

Advances in MRSA drug discovery: where are we and where do we need to be?

INTRODUCTION

Methicillin-resistant Staphylococcus aureus (MRSA) have been on the increase during the past decade, due to the steady growth of the elderly and immunocompromised patients, and the emergence of multidrug-resistant (MDR) bacterial strains. Although there are a limited number of anti-MRSA drugs available, a number of different combination antimicrobial drug regimens have been used to treat serious MRSA infections. Thus, the addition of several new antistaphylococcal drugs into clinical practice should broaden clinician's therapeutic options. As MRSA is one of the most common and problematic bacteria associated with increasing antimicrobial resistance, continuous efforts for the discovery of lead compounds as well as development of alternative therapies and faster diagnostics are required.

AREAS COVERED

This article summarizes the FDA-approved drugs to treat MRSA infections, the drugs in clinical trials, and the drug leads for MRSA and related Gram-positive bacterial infections. In addition, the article discusses the mode of action of antistaphylococcal molecules and the resistant mechanisms of some molecules.

EXPERT OPINION

The number of pipeline drugs presently undergoing clinical trials is not particularly encouraging. There are limited and rather expensive therapeutic options for MRSA infections in the critically ill. Further research efforts are required for effective phage therapy on MRSA infections in clinical use, which seem to be attractive therapeutic options for the future.

Plectasin shows intracellular activity against Staphylococcus aureus in human THP-1 monocytes and in a mouse peritonitis model

Antimicrobial therapy of infections with Staphylococcus aureus can pose a challenge due to slow response to therapy and recurrence of infection. These treatment difficulties can partly be explained by intracellular survival of staphylococci, which is why the intracellular activity of antistaphylococcal compounds has received increased attention within recent years. The intracellular activity of plectasin, an antimicrobial peptide, against S. aureus was determined both in vitro and in vivo. In vitro studies using THP-1 monocytes showed that some intracellular antibacterial activity of plectasin was maintained (maximal relative efficacy [E(max)], 1.0- to 1.3-log reduction in CFU) even though efficacy was inferior to that of extracellular killing (E(max), >4.5-log CFU reduction). Animal studies included a novel use of the mouse peritonitis model, exploiting extra- and intracellular differentiation assays, and assessment of the correlations between activity and pharmacokinetic (PK) parameters. The intracellular activity of plectasin was in accordance with the in vitro studies, with an E(max) of a 1.1-log CFU reduction. The parameter most important for activity was fC(peak)/MIC, where fC(peak) is the free peak concentration. These findings stress the importance of performing studies of extra- and intracellular activity since these features cannot be predicted from traditional MIC and killing kinetic studies. Application of both the THP-1 and the mouse peritonitis models showed that the in vitro results were similar to findings in the in vivo model with respect to demonstration of intracellular activity. Therefore the in vitro model was a good screening model for intracellular activity. However, animal models should be applied if further information on activity, PK/pharmacodynamic parameters, and optimal dosing regimens is required.

Delivery systems to increase the selectivity of antibiotics in phagocytic cells

Many infectious diseases are caused by facultative organisms that are able to survive in phagocytic cells. The intracellular location of these microorganisms protects them from the host defence systems and from some antibiotics with poor penetration into phagocytic cells. One strategy used to improve the penetration of antibiotics into phagocytic cells is the use of carrier systems that deliver these drugs directly to the target cell. Delivery systems such as liposomes, micro/nanoparticles, lipid systems, conjugates, and biological carriers such as erythrocyte ghosts may contribute to increasing the therapeutic efficacy of antibiotics and antifungal agents in the treatment of infections caused by intracellular microorganisms. The main objective of this review is to analyze recent advances and current perspectives in the use of antibiotic delivery systems in the treatment of intracellular infections such as mycobacterial infections, brucellosis, salmonellosis, listeriosis, fungal infections, visceral leishmaniasis, and HIV.

Pharmacodynamic evaluation of the intracellular activities of antibiotics against Staphylococcus aureus in a model of THP-1 macrophages

The pharmacodynamic properties governing the activities of antibiotics against intracellular Staphylococcus aureus are still largely undetermined. Sixteen antibiotics of seven different pharmacological classes (azithromycin and telithromycin [macrolides]; gentamicin [an aminoglycoside]; linezolid [an oxazolidinone]; penicillin V, nafcillin, ampicillin, and oxacillin [beta-lactams]; teicoplanin, vancomycin, and oritavancin [glycopeptides]; rifampin [an ansamycin]; and ciprofloxacin, levofloxacin, garenoxacin, and moxifloxacin [quinolones]) have been examined for their activities against S. aureus (ATCC 25923) in human THP-1 macrophages (intracellular) versus that in culture medium (extracellular) by using a 0- to 24-h exposure time and a wide range of extracellular concentrations (including the range of the MIC to the maximum concentration in serum [C(max); total drug] of humans). All molecules except the macrolides caused a net reduction in bacterial counts that was time and concentration/MIC ratio dependent (four molecules tested in detail [gentamicin, oxacillin, moxifloxacin, and oritavancin] showed typical sigmoidal dose-response curves at 24 h). Maximal intracellular activities remained consistently lower than extracellular activities, irrespective of the level of drug accumulation and of the pharmacological class. Relative potencies (50% effective concentration or at a fixed extracellular concentration/MIC ratio) were also decreased, but to different extents. At an extracellular concentration corresponding to their C(max)s (total drug) in humans, only oxacillin, levofloxacin, garenoxacin, moxifloxacin, and oritavancin had truly intracellular bactericidal effects (2-log decrease or more, as defined by the Clinical and Laboratory Standards Institute guidelines). The intracellular activities of antibiotics against S. aureus (i) are critically dependent upon their extracellular concentrations and the duration of cell exposure (within the 0- to 24-h time frame) to antibiotics and (ii) are always lower than those that can be observed extracellularly. This model may help in rationalizing the choice of antibiotic for the treatment of S. aureus intracellular infections.

Uptake and intracellular activity of voriconazole in human polymorphonuclear leucocytes

OBJECTIVES

The intracellular penetration of voriconazole into human polymorphonuclear leucocytes (PMNs) and its intracellular activity against Candida spp. were evaluated.

METHODS

The intracellular penetration of voriconazole into PMNs was evaluated by a radiometric assay. The effect of cell viability, environmental conditions, metabolic inhibitors and membrane stimulation was also studied. The intracellular activity was determined by incubation of PMNs containing intracellular blastospores in the presence of voriconazole for 3 h.

RESULTS

The uptake of voriconazole by PMNs was rapid and not saturable. The cellular to extracellular concentration (C/E) ratio for voriconazole was 8.5+/-1.3. Voriconazole was rapidly released from loaded PMNs. The uptake of voriconazole was not affected by environmental temperature and cell viability. Neither the external pH nor the metabolic inhibitors affected the uptake of voriconazole. The ingestion of opsonized zymosan, but not of opsonized Candida spp., significantly decreased the levels of PMN-associated voriconazole. At the extracellular concentrations evaluated, voriconazole did not affect the intracellular survival of Candida.

CONCLUSIONS

Voriconazole reached high intracellular concentrations within human PMNs. The uptake was rapid and not saturable but it did not affect the intracellular killing of Candida spp.

Steady-state plasma and intrapulmonary pharmacokinetics and pharmacodynamics of cethromycin

The objective of this study was to determine the steady-state plasma and intrapulmonary pharmacokinetic parameters of orally administered cethromycin in healthy volunteers. The study design included administering 150 or 300 mg of cethromycin once daily to 25 or 35 healthy adult subjects, respectively, for a total of five doses. Standardized and timed bronchoalveolar lavage (BAL) was performed after the last dose. Blood was obtained for drug assay prior to the first and last dose, at multiple time points following the last dose, and at the time of BAL. Cethromycin was measured in plasma, BAL, and alveolar cell (AC) by using a combined high-performance liquid chromatography-mass spectrometric technique. Plasma, epithelial lining fluid (ELF), and AC pharmacokinetics were derived by noncompartmental methods. C(max)/90% minimum inhibitory concentration (MIC(90)) ratios, area under the concentration-time curve (AUC)/MIC(90) ratios, intrapulmonary drug exposure ratios, and percent time above MIC(90) during the dosing interval (%T > MIC(90)) were calculated for recently reported respiratory pathogens. The kinetics were nonlinear, i.e., not proportional to dose. In the 150-mg-dose group, the C(max) (mean +/- standard deviations), AUC(0-24), and half-life for plasma were 0.181 +/- 0.084 microg/ml, 0.902 +/- 0.469 microg. h/ml, and 4.85 +/- 1.10 h, respectively; for ELF the values were 0.9 +/- 0.2 microg/ml, 11.4 microg. h/ml, and 6.43 h, respectively; for AC the values were 12.7 +/- 6.4 microg/ml, 160.8 microg. h/ml, and 10.0 h, respectively. In the 300-mg-dose group, the C(max) (mean +/- standard deviations), AUC(0-24), and half-life for plasma were 0.500 +/- 0.168 microg/ml, 3.067 +/- 1.205 microg. h/ml, and 4.94 +/- 0.66 h, respectively; for ELF the values were 2.7 +/- 2.0 microg/ml, 24.15 microg. h/ml, and 5.26 h, respectively; for AC the values were 55.4 +/- 38.7 microg/ml, 636.2 microg. h/ml, and 11.6 h, respectively. We concluded that the C(max)/MIC(90) ratios, AUC/MIC(90) ratios, %T > MIC(90) values, and extended plasma and intrapulmonary half-lives provide a pharmacokinetic rationale for once-daily administration and are favorable for the treatment of cethromycin-susceptible pulmonary infections.