[Clinical laboratory approach to estimate effective administrative dose of minocyclin. Reevaluation of in vitro MIC break points in disc susceptibility test].
Antimicrobial activities of minocycline (MINO) against various clinical isolates, 270 strains obtained in 1988, were determined and the reliability of the MINO disc susceptibility test in estimating approximate values of MICs was studied. Clinical significance of a 4 category system for the interpretation of the disc tests, which is widely used in Japan, and that of a 3 category system used in the USA and Europe, were also evaluated to determine which system would be more suitable for the evaluation of proper dose levels of administration. In this study, MICs were determined using the agar dilution method at an inoculum level of 10(6) CFU/ml. MIC80 values of MINO against Staphylococcus aureus, Staphylococcus epidermidis and Streptococcus pneumoniae were all less than or equal to 0.78 micrograms/ml. Those against Haemophilus influenzae, Escherichia coli, Klebsiella pneumoniae, Proteus mirabilis and Proteus vulgaris were 0.39, 6.25, 3.13, 25, 50 micrograms/ml, respectively. MIC80 values against Pseudomonas aeruginosa, Serratia marcescens, Enterobacter spp., and Citrobacter spp. were 50, 100, 50 and 12.5 micrograms/ml, respectively. The inhibition zones obtained with the disc method were compared with MICs. The results of MINO disc susceptibility test either with 200 micrograms disc (Showa) or 30 micrograms disc (prepared in this laboratory) were well correlated with MICs, showing the reliability of the disc method in estimating approximate values of MICs. In the 4 category classification system currently used, break points in MIC values proposed are ( ) MIC less than or equal to 2 micrograms/ml, (++) MIC greater than 2-10 micrograms/ml, (+) greater than 10-50 micrograms/ml, (-) MIC greater than 50 micrograms/ml. The results obtained with 200 micrograms and 30 micrograms discs showed false positive in 26.6% and 20.5% of the samples, and false negative in 5.8% and 23.6% of the samples, respectively. The disc results of S. aureus, S. epidermidis, S. pneumoniae, etc. were relatively well classified, but those of E. coli, K. pneumoniae, Proteus spp. were not, showing more false positive results. Changing the lower 2 MIC break points in the 4 category system to: ( ) MIC less than or equal to 3 micrograms/ml and (++) MIC greater than 3-15 micrograms/ml, the false positive results with both 200 micrograms and 30 micrograms discs were reduced to 12% and 6.2%, respectively. The false negative results were 5.8% and 23.6%, respectively.(ABSTRACT TRUNCATED AT 400 WORDS)
Uete
G
G
Department of Clinical Investigation, Kitano Hospital.
Matsuo
K
K
Uete
T
T
D001419:Bacteria / Q000187:drug effects* / Q000254:growth & development; D004926:Escherichia coli / Q000187:drug effects; D005188:False Negative Reactions; D005189:False Positive Reactions; D008826:Microbial Sensitivity Tests / Q000379:methods; D008911:Minocycline / Q000008:administration & dosage* / Q000494:pharmacology; D011237:Predictive Value of Tests; D013210:Staphylococcus / Q000187:drug effects* / Q000254:growth & development; D013211:Staphylococcus aureus / Q000187:drug effects
D008911:Minocycline