CLINICAL LABORATORY APPROACH FOR ESTIMATING EFFECTIVE

ADMINISTRATIVE DOSE OF CEFSULODIN

Abstract

Reliability of cefsulodin (CFS) disc sensitivity test for estimating approximate values of MICs and its utilization for evaluation of proper administrative dose were studied against 106 strains of Pseudomonas aeruginosa and Staphylococcus aureus isolated from clinical materials using 2 different kind of discs. The disc results were compared with MICs determined using agar dilution method at inoculum level of 10⁶ CFU/ml. The results of CFS disc susceptibility test with 8 mm diameter disc (Showa) and 6 mm diameter disc (Wako), both of them contained 30μ g, were well correlated with MICs. It is capable to use disc results for estima-tion of approximate value of MICs.
For interpretation of CFS disc tests, three category system has been used in USA and Europe, but four category system in Japan. MIC break points proposed for classifying bacteria into three categories of sus-ceptibility: resistant (R) MIC < 32μg/ml, moderately susceptible (MS) MIC 16^-32μg/ml, and susceptible (S) MIC ≤ 8μg/ml. Those in four category system were as follows: (+++) MIC ≤ 3μg/ml,(++) 3μg/ml < MIC ≤ 15μg/ml,(+) 15μg/ml MIC ≤ 60μg/ml,(-) MIC > 60μg/ml. Based on CFS pharmacokinetic data and the recommended dosage schedule (less than 2 g a day), MIC break points < 3μg/ml and < 15μg/ml, appear to be more useful than that of ≤ 8μg/ml and <32μg/ml for evaluating a proper administrative dose level.
In this study, approximately 73 and 94% of strains of P. aeruginosa and S. aureus isolated from clinical materials, respectively, were inhibited at a concentration of 12.5μg/ml CFS. This susceptibility result well indicate usefulness of this drug.