Well look at this, a question that hits home with my day job!!!!.....In the wonderful world of Pharmacy, the vast number of medications do not adhere to plastics. Almost all of them in fact. There are a few notable exceptions such as nitroglycerin (not used in aquaria of course, but it is a notable exception). Nitro needs to kept in a glass or a metal container. Think of it this way, when you go to the pharmacy, how many times do you get meds in anything BUT a plastic vial? I cannot think of ANY antibiotic that can not be stored in plastic.......