Stability of imipenem in Mueller-Hinton agar stored at 4 degrees C

The purpose of the present study was to measure the stability of imipenem in Mueller-Hinton agar stored at 4 degrees C over time. MICs for Staphylococcus aureus ATCC 25923, Streptococcus faecalis ATCC 29212, Escherichia coli ATCC 25922, and Pseudomonas aeruginosa ATCC 27853 were determined in triplicate daily for up to 15 days. The calculated mean time to observe a shift of one dilution in MIC endpoints was 4.33 +/- 1.25 days. For routine work, imipenem agar dilution plates should be prepared within 48 to 72 h of the test.