Activity of a novel series of acylides active against community-acquired respiratory pathogens

Resistance to macrolides and β-lactams has increased sharply amongst key respiratory pathogens, leading to major concern. A novel series of acylides was designed to overcome this resistance and was evaluated for in vitro and in vivo activity. This series of acylides was designed starting from clarithromycin by changing the substitution on the desosamine nitrogen, followed by conversion to 3-O-acyl and 11,12-carbamate. Minimum inhibitory concentrations (MICs) of acylides were determined against susceptible as well as macrolide–lincosamide–streptogramin B (MLSB)- and penicillin-resistant Streptococcus pneumoniae, Streptococcus pyogenes and Moraxella catarrhalis by the agar dilution method. Microbroth MICs for Haemophilus influenzae were determined according to Clinical and Laboratory Standards Institute guidelines. In vivo efficacy was determined by target organ load reduction against S. pneumoniae 3579 (ermB). The bactericidal potential of promising acylides was also determined. MICs of these compounds against S. pneumoniae, S. pyogenes, H. influenzae and M. catarrhalis were in the range of 0.06–2, 0.125–1, 1–16 and 0.015–0.5 μg/mL, respectively, irrespective of their resistance pattern. Mycoplasma pneumoniae and Legionella pneumophila showed MIC ranges of 0.004–0.125 μg/mL and 0.004–0.03 μg/mL, respectively. The acylides also showed better activity against telithromycin-resistant S. pneumoniae strains. Compounds with a 4-furan-2-yl-1H-imidazolyl side chain on the carbamate (RBx 10000296) showed a target organ load reduction of >3 log10 colony-forming units/mL and concentration-dependent bactericidal potential against S. pneumoniae 994 mefA and H. influenzae strains. This novel and potent series of acylides active against antibiotic-resistant respiratory pathogens should be further investigated.