antibiotic sensitivity disc shelf life

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emmafiori's picture
antibiotic sensitivity disc shelf life

I was wondering if anyone can tell me the actual shelf-life of your average Kirby-bauer antibiotic sensitivity disc would be. I recently found a whole bunch in the back of a fridge in my lab, and they are way past expiration. But I know that printed expiration dates are usually very conservative, and many products can be used long past the suggested date. But I'm not sure what the case would be for these antibiotic discs... would the drug degrade and therefore not be active in the disc and so give underestimation of sensitivity? Or are the drugs pretty stable and likely to last long after the expiration date? Any suggestions for how long after the date? A few months? A year? A few years? FYI these have ben stored at 4oC (refrigerator).
Thanks for your help!