[Clinical laboratory approach for estimating effective administrative dose of cefuzonam. Evaluation of disc susceptibility test and its interpretation system].
In vitro activities of cefuzonam (CZON) against 273 clinical isolates were studied through the evaluation of MIC's and the results of disc susceptibility test. The MIC's were determined using the agar dilution method at an inoculum level of 10(6)CFU/ml. The MIC80's of CZON against Streptococcus pneumoniae, Escherichia coli, Klebsiella pneumoniae, Proteus mirabilis, Proteus vulgaris, Haemophilus influenzae and Citrobacter spp. were less than 0.20 microgram/ml. The MIC80's against Serratia marcescens and Enterobacter aerogenes were both 6.25 micrograms/ml, and that against Pseudomonas aeruginosa was 100 micrograms/ml. The MIC80's against Staphy-lococcus epidermidis were 25 and 6.25 micrograms/ml, respectively. Approximately 70% of strains of S. aureus were inhibited at concentrations less than 1.56 microgram/ml. For the interpretation of the CZON Showa 30 micrograms disc susceptibility test a 4 category system was used. In the 4 category system for Showa disc containing CZON, the following classification inhibitory zone diameters has been proposed: ( ) MIC less than or equal to 3 micrograms/ml, (++) MIC greater than 3-15 micrograms/ml, (+) MIC greater than 15-60 micrograms/ml, (-) MIC less than 60 micrograms/ml. Reliability of the CZON disc tests in estimating approximate MIC values was studied using Showa 30 micrograms discs and discs prepared in this laboratory containing 1-10 micrograms CZON. A good negative correlation was observed between inhibitory zone diameters and MIC's, showing the reliability of the disc method. The results of the test using Showa 30 micrograms disc against various clinical isolates were accurately classified into the 4 groups except those against P. aeruginosa. Some strains of P. aeuruginosa showed false positive results, exhibiting relatively larger inhibitory zone diameters compared with MIC's against these organisms. As CZON is not effective against P. aeruginosa a much better overall correlation between MIC's and the disc test would result when P. aeruginosa was excluded. With Showa 30 micrograms discs of various cephalosporins, sub-classification of strains with MIC less than 3 micrograms/ml cannot be achieved. In this study, however, it was demonstrated that differentiation of strains with MIC's less than 0.5-1.56 micrograms/ml was possible when discs containing 1-10 micrograms of CZON were used. According to recent concepts on pharmacokinetics for antibiotics including penetration of drugs into tissues and inflammatory fluids, serum protein binding of drugs appears to be one of the important determinants of drug distribution in the body.(ABSTRACT TRUNCATED AT 400 WORDS)
Uete
T
T
Department of Clinical Investigation, Kitano Hospital, Tazuke Kofukai Medical Research Institute.
Matsuo
K
K
D015296:Ceftizoxime / Q000008:administration & dosage / Q000031:analogs & derivatives* / Q000493:pharmacokinetics / Q000494:pharmacology; D006090:Gram-Negative Bacteria / Q000187:drug effects*; D006094:Gram-Positive Bacteria / Q000187:drug effects*; D006801:Humans; D008826:Microbial Sensitivity Tests / Q000379:methods
C049934:cefuzonam; D015296:Ceftizoxime