Activity of ABT-773 against Mycobacterium avium complex in the beige mouse model

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.

Type II pneumocytes in the evaluation of drug antimycobacterial activity

In order to combat the worldwide increase in the prevalence of multi-drug resistant tuberculosis and Mycobacterium avium complex infections, a number of new antimycobacterial drugs has been synthesised and developed. There is great promise for drugs designed by new strategies, especially those based on the information on mycobacterial genome sequences and a host-parasite relationship. Moreover, the development of new protocols for chemotherapy of intractable mycobacterioses is also needed. For this purpose, better in vitro drug activity assay models that enable prediction of therapeutic activity, particularly those predicting the in vivo sterilising activity, are urgently needed, since the ordinary in vitro methods are inefficient indicators of clinical efficacy. In this context, the in vitro models using Type II pneumocytes, which play an important role in the establishment of mycobacterial pulmonary infections as a portal of mycobacterial organisms to the lungs, are considerably useful, especially in predicting the in vivo activity of certain drugs against Mycobacterium avium complex infection.

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.

In vitro activity of ABT-773 against Legionella pneumophila, its pharmacokinetics in guinea pigs, and its use to treat guinea pigs with L. pneumophila pneumonia

The activity of ABT-773 was studied against extracellular and intracellular Legionella pneumophila and for the treatment of guinea pigs with L. pneumophila pneumonia. The ABT-773 MIC at which 50% of isolates are inhibited (MIC(50)) for 20 different Legionella sp. strains was 0.016 microg/ml, whereas the MIC(50)s of clarithromycin and erythromycin were 0.032 and 0.125 microg/ml, respectively. ABT-773 (1 microg/ml) was bactericidal for two L. pneumophila strains grown in guinea pig alveolar macrophages. In contrast, erythromycin and clarithromycin had easily reversible static activity only. Therapy studies of ABT-773 and erythromycin were performed with guinea pigs with L. pneumophila pneumonia. When ABT-773 was given to infected guinea pigs by the intraperitoneal route (10 mg/kg of body weight), mean peak levels in plasma were 0.49 microg/ml at 0.5 h and 0.30 microg/ml at 1 h postinjection. The terminal half-life phase of elimination from plasma was 0.55 h, and the area under the concentration-time curve from 0 to 24 h (AUC(0-24)) was 0.65 microg. h/ml. For the same drug dose, mean levels in the lung were 15.9 and 13.2 microg/g at 0.5 and 1 h, respectively, with a half-life of 0.68 h and an AUC(0-24) of 37.0 microg. h/ml. Ten of 15 L. pneumophila-infected guinea pigs treated with ABT-773 (15 mg/kg/dose given intraperitoneally once daily) for 5 days survived for 9 days post-antimicrobial therapy, as did 14 of 15 guinea pigs treated with erythromycin (30 mg/kg given intraperitoneally twice daily) for 5 days. All of the ABT-773-treated animals that died appeared to do so because of drug-induced peritonitis rather than overwhelming pneumonia. None of 12 animals treated with saline survived. ABT-773 is as effective as erythromycin against L. pneumophila in infected macrophages and in a guinea pig model of Legionnaires' disease. These data support studies of the clinical effectiveness of ABT-773 for the treatment of Legionnaires' disease.

ABT-773: a new ketolide antibiotic

ABT-773 is a new semisynthetic derivative of erythromycin A, the ketolide class of broad spectrum antibacterial agents, in Phase II development by Abbott. With good broad spectrum activity against Gram-positive, some Gram-negative organisms and intracellular bacteria, ABT-773 is being developed as a respiratory agent. Structural changes in the ketolide class agents such as ABT-773 provides expanded activity in vitro against macrolide-resistant strains of Streptococcus pneumoniae and improved activity against MLS(B) (macrolide-lincosamide-streptogramin) constitutive expressing streptococci.