[In vitro activity of cefaclor (author's transl)]

In vitro activity of Ro 15-8074 and Ro 19-5247 in comparison to cefaclor and cefalexin

805 clinical isolates were investigated for their in vitro sensitivity against Ro 15-8074 and Ro 19-5247 in comparison to cefaclor and cefalexin in a serial dilution test on solid medium. Ro 19-5247 had the strongest activity of all drugs tested against streptococci (except Streptococcus faecalis) and was as active as cefaclor and cefalexin against most strains of Staphylococcus aureus. Ro 19-5247 was the only oral cephalosporin active against Bordetella pertussis. It was on average 160 times more active than cefaclor against Haemophilus influenzae. In its activity against enterobacteria Ro 19-5247 was always superior to cefaclor and cefalexin. Only a few strains of Enterobacter aerogenes, Enterobacter cloacae, Klebsiella pneumoniae, Proteus vulgaris and Serratia marcescens were resistant to Ro 19-5247 as were all strains of Enterobacter agglomerans and Klebsiella ozaenae. Ro 15-8074 was inactive against staphylococci but ten times more active than cefaclor and cefalexin against Streptococcus pyogenes. There was no difference in the activity against Streptococcus pneumoniae and Streptococcus agalactiae. Against Haemophilus influenzae Ro 15-8074 acted 12 times stronger than cefaclor and 100 times stronger than cefalexin. The activity against enterobacteria corresponded to that of Ro 19-5247. Ro 15-8074 was also active against most strains of Enterobacter cloacae and Proteus vulgaris which were resistant to cefaclor and cefalexin.

[Subinhibitory activity of cefaclor and cephalexin (author's transl)]

The determination of the minimal inhibitory concentration (MIC), which is usually performed after 18 to 24 hours of incubation, results in the case of cefaclor in a false picture of the actual activity. Cefaclor is chemically so unstable that after 24 hours only 2-5% of the substance is microbiologically active. In order to compare the activity of cefaclor and cephalexin, the effect of subinhibitory concentrations of both antibiotics against Escherichia coli and Klebsiella pneumoniae strains was studied by means of turbidimetry. After eight hours the absolute inhibitory concentration of cefaclor was lower than that of cephalexin with both methods. At the same time the effect of subinhibitory concentrations of both antibiotics was equal. Automatic measurement over 20 hours showed at the end of the experiment a higher MIC, and also a higher subinhibitory range, for cefaclor than for cephalexin. In our opinion the absolute inhibitory concentration after eight hours should be the criterion used to evaluate the effectiveness of cefaclor and cephalexin, and not the MIC which is usually used. The eight-hour criterion should also be applied in clinical use.