Is 2% pen strep too much for cell culture? - will my cells die a painful death? (May/27/2011 )
I was making DMEM with 10% FBS and 1% pen-strep, but accidentally made it 2% pen strep. Is this too much? I will be using this on HeLa cells. Will it kill them?
I don't know but I certainly wouldn't chance it. Cell culture media isn't expensive enough to warrant the frustration of dead cells.
Neither antibiotic will kill eukaryotic cells. However, as kfunk said, chancing something like this and then getting a funny result will (at least, should) result in you thinking to yourself "Is that result because of the change in antibiotic or is it a real result?".. which basically means that you should just make up a fresh lot of medium rather than waste time and money trying to figure out odd results.
The general rule is "If in doubt, throw it out".
Ideally you would not be using any antibiotics in your cell culture. They tend to hide poor technique and cryptic infections which can alter how your cells behave.
If you're that worried you could just get some more media and combine the two together to double the volume and create a 1% solution (remembering to add extra FCS to keep that at 10%)