TABLE 3.

In vitro activities of 14 antimicrobial agents against 503 respiratory tract isolates of M. catarrhalis from North American medical centers

Antimicrobial agent	MIC (μg/ml)				% by categorya		Breakpointa
	50%	90%	Range	Mode	Susceptible	Resistant	Susceptible	Resistant
Amoxicillin-clavulanate	0.12	0.25	≤0.06–4	0.25	100.0	0.0	≤8/4	≥16/8
Cefaclor	1	2	≤0.25–32	0.50	99.6	0.2	≤8	≥32
Cefuroxime	1	2	0.12–8	1	99.2	0.0	≤4	≥32
Cefixime	0.25	0.5	≤0.03–2	0.25	99.4	0.0	≤1	≥4
Cefpodoxime	1	2	≤0.03–>4	1	99.0	0.2	≤2	≥8
Cefotaxime	0.5	1	≤0.008–2	0.5	100.0	0.0	≤8	≥64
Cefepime	1	4	≤0.06–8	1	100.0	0.0	≤8	≥32
Azithromycin	≤0.12	≤0.12	≤0.12–0.25	≤0.12	100.0	0.0	≤2	≥8
Clarithromycin	≤0.25	≤0.25	≤0.25–1	≤0.25	100.0	0.0	≤2	≥8
Erythromycin	≤0.25	0.5	≤0.25–1	≤0.25	99.0	0.0	≤0.5	≥8
Chloramphenicol	≤2	≤2	≤2	≤2	100.0	0.0	≤8	≥32
Tetracycline	≤2	≤2	≤2	≤2	100.0	0.0	≤4	≥16
TMP-SMX	≤0.25	0.5	≤0.25–8	≤0.25	99.2	0.2	≤2/38	≥8/152
Rifampin	≤1	≤1	≤1	≤1	100.0	0.0	≤1	≥4

^aBreakpoints are those advocated by the NCCLS for use in MIC determinations with nonfastidious bacteria that grow well on unsupplemented Mueller-Hinton medium (17).