Reassessment of the cefaclor breakpoint for Streptococcus pneumoniae

Discrepancies between proven clinical success of cefaclor and its relatively poor activity in vitro were investigated against eight pneumococcal isolates. The bacteriostatic minimum inhibitory concentration (MIC) (the concentration resulting in no growth/kill relative to the starting inoculum) was derived from time kill studies. Bioassay results demonstrated an in vitro half-life of >24 and 9 h for cefuroxime and cefaclor, respectively. The mean NCCLS MIC for cefaclor was 1.4 and 0.3 mg/l for cefuroxime. The corresponding mean bacteriostatic MICs were 0.24 and 0.16 mg/l. Whilst cefaclor NCCLS MICs were significantly higher compared with cefuroxime MICs (P = 0.00058) there was no statistical differences between the bacteriostatic MICs (P = 0.259). Bacteriostatic MIC determination established that cefaclor and cefuroxime are equally active against pneumococci. (C) 2004 Elsevier B.V. and the International Society of Chemotherapy. All rights reserved.