- Bacteriologic response to cefuroxime axetil and cefaclor administered for 10 days was evaluated in acute otitis media (AOM) in patients aged 6 ‐ 36 months. Middle ear fluid culture was obtained by tympanocentesis before treatment, on day 4 or 5 after initiation of treatment, and if clinical relapse occurred before day 17. Bacteriologic failure was observed in 32% of patients receiving cefaclor versus 15% of patients receiving cefuroxime axetil (PA .009). Failure rates increased with increasing MIC: For Streptococcus pneumoniae, 0.5 mg/mL (established as cutoff value for cefuroxime by the National Committee for Clinical Laboratory Standards [NCCLS]) discriminated between success and failure. For Haemophilus influenzae, high failure rates were observed for cefaclor, even with low MICs (£1.0 mg/mL), and with both drugs they tended to increase with increasing MIC, even for values below the cutoff suggested by the NCCLS (8.0 and 4.0 mg/mL for cefaclor and cefuroxime, respectively). Thus, for AOM caused by H. influenzae, lower susceptibility cutoff levels for MICs should be established. Acute otitis media (AOM) is the most common cause of ation between MIC and bacteriologic failure rate for the above drugs.