In vitro activity of ABT-773 versus macrolides and quinolones against resistant respiratory tract pathogens

ABT-773, a novel ketolide, was compared to erythromycin, azithromycin, clarithromycin, ciprofloxacin, ofloxacin, levofloxacin, moxifloxacin, gatifloxacin, and gemifloxacin against antibiotic-resistant strains recently isolated from patients with respiratory tract infections. MICs were determined by agar dilution using standard NCCLS methodology. ABT-773 (MIC 90 0.06 mg/L) was more active than the macrolides (MIC 90 ≥ 2 mg/L) and fluoroquinolones (MIC 90 ≥ 0.5 mg/L) against penicillin-resistant Streptococcus pneumoniae. The fluoroquinolones were the most active agents tested against β-lactamase-positive Haemophilus influenzae (MIC 90 ≤ 0.01–0.06 mg/L), against which ABT-773 (MIC 90 4 mg/L) was comparable to azithromycin and two- and four-fold more active than erythromycin and clarithromycin, respectively. Against β-lactamase positive Moraxella catarrhalis, the activity of ABT-773 (MIC 90 0.06 mg/L) was comparable to gemifloxacin, trovafloxacin, levofloxacin, and ciprofloxacin (MIC 90 0.03–0.06 mg/L) and 4- to eightfold greater than that of clarithromycin, gatifloxacin, and erythromycin. These data suggest ABT-773 could be a valuable compound for the treatment of respiratory tract infections, including those resistant to usual oral therapy.