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

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Abstract
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 μg/ml, whereas the MIC 50 s of clarithromycin and erythromycin were 0.032 and 0.125 μg/ml, respectively. ABT-773 (1 μg/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 μg/ml at 0.5 h and 0.30 μg/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 μg · h/ml. For the same drug dose, mean levels in the lung were 15.9 and 13.2 μg/g at 0.5 and 1 h, respectively, with a half-life of 0.68 h and an AUC 0–24 of 37.0 μg · 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.

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