title: Dirithromycin disc susceptibility tests: interpretative criteria and quality control parameters.
abstract: Dirithromycin and its bioactive metabolite (erythromycylamine) were compared in vitro to erythromycin against 450 bacterial isolates. Dirithromycin and erythromycylamine did not differ in their in-vitro activity and the two compounds were additive when combined in equal proportions. Both compounds were active against erythromycin-susceptible bacteria but erythromycin was two to four times more potent on a weight-to-weight basis. Interpretive criteria for dirithromycin were not based on achievable blood concentrations since tissue concentrations may be 20-30 times greater than peak serum levels. Dirithromycin-susceptible strains were those with zones > or = 19 mm in diameter (15 micrograms dirithromycin disc) or MIC < or = 2.0 mg/L and resistance was defined as a zone < or = 15 mm or MIC > or = 8.0 mg/L. Interpretive criteria for testing Haemophilus influenzae on Haemophilus Test Medium (HTM) agar were not defined because of the drug's poor activity in the test system used. Two multi-laboratory studies were also undertaken, one to define quality control limits for disc diffusion tests and the other to define broth microdilution MIC control limits for tests with dirithromycin.
authors: Clinical Microbiology Institute, Tualatin, Oregon 97062.
authors: A L
authors: AL
authors: Barry
authors: M A
authors: MA
authors: Pfaller
authors: P C
authors: PC
authors: Fuchs
mesh_terms: D000900:Anti-Bacterial Agents; D001419:Bacteria / Q000187:drug effects*; D004353:Drug Evaluation, Preclinical; D013293:Enterococcus faecalis / Q000187:drug effects; D004917:Erythromycin / Q000031:analogs & derivatives* / Q000494:pharmacology; D006193:Haemophilus influenzae / Q000187:drug effects; D018942:Macrolides; D008826:Microbial Sensitivity Tests / Q000592:standards*; D011786:Quality Control; D013211:Staphylococcus aureus / Q000187:drug effects
chemical_list: D000900:Anti-Bacterial Agents; D018942:Macrolides; C053853:dirithromycin; D004917:Erythromycin