TABLE 2.

In vitro activities of 14 antimicrobial agents against 1,077 respiratory tract isolates of H. influenzae from North American medical centers

Antimicrobial agent	MIC (μg/ml)				% by categorya		Breakpointa
	50%	90%	Range	Mode	Susceptible	Resistant	Susceptible	Resistant
Amoxicillin-clavulanate	0.5	2	≤0.06–16	0.25–2	99.8	0.2	≤4/2	≥8/4
Cefaclor	2	32	≤0.25–>32	2	79.6	12.8	≤8	≥32
Cefuroxime	0.5	2	≤0.06–16	0.5	95.7	1.5	≤4	≥16
Cefixime	≤0.03	0.12	≤0.03–1	≤0.03	100.0		≤1
Cefpodoxime	0.06	0.25	≤0.03–1	0.06	100.0		≤2
Cefotaxime	0.015	0.06	≤0.008–0.5	0.015	100.0		≤2
Cefepime	0.12	0.25	≤0.06–2	0.12	100.0		≤2
Azithromycin	2	2	≤0.12–>16	2	99.8	0.2	≤4
Clarithromycin	8	16	≤0.25–>32	8	61.4	3.9	≤8	≥32
Erythromycin	4	8	≤0.25–>32	4
Chloramphenicol	≤2	≤2	≤2–>16	≤2	99.0	0.7	≤2	≥8
Tetracycline	≤2	≤2	≤2–>16	≤2	98.6	0.9	≤2	≥8
TMP-SMX	≤0.25	8	≤0.25–>8	≤0.25	77.3	16.2	≤0.5	≥4
Rifampin	≤1	≤1	≤1–>2	≤1	95.7	0.1	≤1	≥4

^aBreakpoints are those advocated by the NCCLS for use in MIC determinations with H. influenzae (17).