Dirithromycin disc susceptibility tests: interpretative criteria and quality control parameters.
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.
Barry
A L
AL
Clinical Microbiology Institute, Tualatin, Oregon 97062.
Pfaller
M A
MA
Fuchs
P C
PC
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
D000900:Anti-Bacterial Agents; D018942:Macrolides; C053853:dirithromycin; D004917:Erythromycin