title: Determination of in vitro synergy when three antimicrobial agents are combined against Mycobacterium tuberculosis.
abstract: We determined the in vitro antimycobacterial activity of rifampicin, isoniazid and a third agent in combination using a three-dimensional chequerboard in Middlebrook 7H9 broth microdilutions. Of 28 agents screened, ethambutol, streptomycin, clarithromycin, minocycline, ciprofloxacin, levofloxacin, sparfloxacin, gatifloxacin and sitafloxacin were potentially synergistic. A further three-dimensional chequerboard assay quantitatively looked for synergy against ten clinical isolates of Mycobacterium tuberculosis, including seven multidrug-resistant isolates. Sitafloxacin, gatifloxacin and clarithromycin showed significant synergy, with fractional inhibitory concentration indices ranging from 0.41 to 0.79, 0.39 to 0.90 and 0.48 to 0.95, respectively. It is concluded that three-dimensional chequerboard assay can quantitatively determine antimycobacterial synergy, and that fluoroquinolones and antibacterial agents such as clarithromycin are effective against multidrug-resistant isolates of M. tuberculosis when combined with rifampicin and isoniazid.
authors.affiliation: Department of Laboratory Medicine, Graduate School and Faculty of Medicine, University of the Ryukyus, Nishihara-Nakagami, Okinawa, Japan. f011144@med.u-ryukyu.ac.jp
authors.forename: Y
authors.initials: Y
authors.lastname: Bhusal
authors.forename: C M
authors.initials: CM
authors.lastname: Shiohira
authors.forename: N
authors.initials: N
authors.lastname: Yamane
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D000904:Antibiotics, Antitubercular / Q000494:pharmacology; D000995:Antitubercular Agents / Q000494:pharmacology; D002939:Ciprofloxacin / Q000494:pharmacology; D017291:Clarithromycin / Q000494:pharmacology; D004357:Drug Synergism; D004977:Ethambutol / Q000494:pharmacology; D024841:Fluoroquinolones / Q000494:pharmacology*; D006801:Humans; D007538:Isoniazid / Q000494:pharmacology; D064704:Levofloxacin; D008826:Microbial Sensitivity Tests; D008911:Minocycline / Q000494:pharmacology; D009169:Mycobacterium tuberculosis / Q000187:drug effects*; D015242:Ofloxacin / Q000494:pharmacology; D012293:Rifampin / Q000494:pharmacology; D014376:Tuberculosis / Q000382:microbiology
chemical_list: D000900:Anti-Bacterial Agents; D000904:Antibiotics, Antitubercular; D000995:Antitubercular Agents; D024841:Fluoroquinolones; D002939:Ciprofloxacin; D064704:Levofloxacin; D004977:Ethambutol; D015242:Ofloxacin; D008911:Minocycline; D017291:Clarithromycin; D007538:Isoniazid; D012293:Rifampin