TENTATIVE CRITERIA FOR DETERMINING THE IN-VITRO SUSCEPTIBILITIES OF HAEMOPHILUS-INFLUENZAE, INCLUDING QUALITY-CONTROL PARAMETERS, TO 2 FLUOROQUINOLONES (GREPAFLOXACIN AND PD-131628)

Grepafloxacin (OPC 17116) and PD 131628 were evaluated against 150 Hae mophilus influenzae isolates to propose susceptibility testing criteri a for both broth dilution and disk diffusion procedures using haemophi lus test medium. Grepafloxacin-susceptible isolates are defined as tho se for which minimum inhibitory concentrations (MICs) are less than or equal to 0.06 mu g/ml and zones of inhibition are greater than or equ al to 27 mm. PD 131628-susceptible strains of H. influenzae included t hose that exhibited MICs less than or equal to 0.03 mu g/ml, and the z ones were greater than or equal to 32 mm. All MICs were well below con centrations that can be achieved in the blood and tissues of patients treated with either study drug. Criteria for defining a resistant cate gory cannot be determined until strains with elevated MICs are availab le for study. The proposed quality control guidelines for H. influenza e ATCC 49247 and the disk test are 32-39 mm in diameter for grepafloxa cin and 34-42 mm for PD 131628. The preliminary broth microdilution MI C control limits for this strain are 0.002-0.016 mu g/ml for grepaflox acin and 0.002-0.008 mu g/ml for PD 131628.