MIC analysis of dosage form antibiotics - (Jun/28/2014 )

Hi, 

I am currently facing problem on determining the MIC of dosage form of antibiotics. I am using broth microdilution method for the determination of MIC. I have no problem with this method as I have been getting MIC using it. However, when I used the same method to evaluate the MIC of dosage form of antibiotics, if failed, all the dosage form antibiotics did not have antimicrobial activity. I have no experience in testing the antimicrobial activity of dosage form antibiotics, they are all in tablet form. Due to their form, I had to crush and grind them into powder form before dissolving them with solvents (as suggested by CLSI). After that, I diluted them to desired concentrations and performed broth microdilution in a two-fold manner to find the MIC. I had done this twice and I got negative result for the two independent experiments. 

I have no idea what had gone wrong here and I seriously need some advice on this matter. Thanks. 

I do usually have the same problem when testing antimicrobials that come in powder form because most of the times they are not dissolved in water, and the powder form might not be in same concentration (the one you need ) to achieve an MIC.

try and get it liquid form