What does tobradex (tobramycin and dexamethasone) antibiotic do?

2 things. Tobradex (tobramycin and dexamethasone) is an antibiotic / steroid combination and is good for conditions where you have both a bacterial infection and inflammation. Or it can be used to treat inflammation and prevent an infection. The steroid part does have potential side effects (glaucoma, cataracts, etc) so use with caution.