Ketolide ABT-773 is active against Toxoplasma gondii

Cethromycin

Cethromycin [ABT 773, A-195773, Abbott-195773, A-1957730, A-195773-0] is a once-daily ketolide antibiotic that originated from Abbott Laboratories' research into next-generation compounds to the macrolide antibacterial, clarithromycin. The aim of the research programme was to maintain the positive attributes of clarithromycin and to add the property of efficacy against macrolide-resistant organisms. Cethromycin acts by binding to the 23S molecule of the 50S ribosomal subunit. Advanced Life Sciences is conducting multinational, pivotal phase III trials of cethromycin for the treatment of mild-to-moderate community-acquired pneumonia, phase II/III trials for treatment of acute bacterial sinusitis, as well as preclinical trials for the treatment of anthrax. Advanced Life Sciences plans to advance discussions with prospective commercialisation partners for cethromycin during 2006. Abbott Laboratories and Taisho Pharmaceutical entered a collaboration to develop and commercialise new macrolide antibacterials in October 1997. Each company brought its existing macrolides into the collaboration and both companies were to jointly develop novel new macrolides. Abbott was to have exclusive marketing, manfacturing and supply rights worldwide (except in Japan) to any compounds resulting from this collaboration. Taisho was to receive royalties on Abbott's sales in consideration of granted rights. In Japan, the two companies were to co-market any resulting macrolide antibacterials. This agreement extended to the development of cethromycin; however, the agreement was suspended in April 2004 and appears to have been terminated. Abbott exclusively licensed cethromycin to Advanced Life Sciences worldwide excluding Japan in December 2004. Advanced Life Sciences initiated commercial manufacturing agreements for cethromycin with DSM and Cardinal Health in May 2006. In March 2006, Advanced Life Sciences completed private placement of $US36 million from which the net proceeds will be used to advance development of cethromycin. The company plans to submit an NDA for cethromycin in 2007. In Japan, phase II trials were being conducted with Abbott's partner, Taisho Pharmaceutical. Although development in the US had been put on hold, Abbott was to continue to support product development in Japan by Taisho. However, in April 2004, Taisho and Abbott Japan decided to suspend co-development activities for cethromycin. A patent has been granted for cethromycin (US patent number 5 866 549) that expires in September 2016.

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.

Standardised in vitro susceptibility testing of Borrelia burgdorferi against well-known and newly developed antimicrobial agents--possible implications for new therapeutic approaches to Lyme disease

Lyme disease represents a disorder of potentially chronic proportions, and relatively little is known about the in vivo pharmacodynamic interactions of antimicrobial agents with borreliae. So far, evidence-based drug regimens for the effective treatment of Lyme disease have not been definitively established. Moreover, therapeutic failures have been reported for almost every suitable antimicrobial agent currently available. Resistance to treatment and a protracted course of the disease, therefore, continue to pose problems for clinicians in the management of patients suffering from chronic Lyme disease. Further characterisation of the antibiotic susceptibility pattern and a better understanding of the interactions of B. burgdorferi with antimicrobial agents are urgently needed and continue to be crucial owing to considerable differences in the experimental conditions and test methods applied. The development of easily performed, new techniques for the sensitivity testing of B. burgdorferi provides the opportunity to study factors affecting the bacteriostatic and bactericidal action of recently introduced chemotherapeutic agents under more standardised conditions. For the first time, these studies provide direct evidence that, in addition to beta-lactams, macrolides, and tetracyclines which are recommended for stage-dependent treatment of Lyme borreliosis, other recently introduced substances, such as fluoroquinolones, everninomycins, and the ketolide family of antimicrobial agents, also show enhanced in vitro activity against borreliae. Some of these compounds, if effective in vivo as well, may prove to be useful agents in the treatment of certain manifestations of Lyme disease. As such, their potential role should be evaluated further by in vivo experiments and clinical trials. Finally, these antimicrobial agents may turn out to be very effective therapeutic alternatives on account of their oral availability, favourable pharmacodynamic profiles, and high tissue levels in cases where beta-lactames or tetracyclines cannot be administered without detrimental side-effects.

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.

Atovaquone nanosuspensions show excellent therapeutic effect in a new murine model of reactivated toxoplasmosis

Immunocompromised patients are at risk of developing toxoplasma encephalitis (TE). Standard therapy regimens (including sulfadiazine plus pyrimethamine) are hampered by severe side effects. While atovaquone has potent in vitro activity against Toxoplasma gondii, it is poorly absorbed after oral administration and shows poor therapeutic efficacy against TE. To overcome the low absorption of atovaquone, we prepared atovaquone nanosuspensions (ANSs) for intravenous (i.v.) administration. At concentrations higher than 1.0 microg/ml, ANS did not exert cytotoxicity and was as effective as free atovaquone (i.e., atovaquone suspended in medium) against T. gondii in freshly isolated peritoneal macrophages. In a new murine model of TE that closely mimics reactivated toxoplasmosis in immunocompromised hosts, using mice with a targeted mutation in the gene encoding the interferon consensus sequence binding protein, i.v.-administered ANS doses of 10.0 mg/kg of body weight protected the animals against development of TE and death. Atovaquone was detectable in the sera, brains, livers, and lungs of mice by high-performance liquid chromatography. Development of TE and mortality in mice treated with 1.0- or 0.1-mg/kg i.v. doses of ANS did not differ from that in mice treated orally with 100 mg of atovaquone/kg. In conclusion, i.v. ANSs may prove to be an effective treatment alternative for patients with TE.

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.