Key takeaways
Polytrim (polymyxin B / trimethoprim) and Tobrex (tobramycin) are both antibiotics used to treat bacterial eye infections, but they belong to different classes and have some key differences. Polytrim is a combination of two antibiotics, polymyxin B and trimethoprim, which work together to kill bacteria by breaking their protective covering and stopping them from making folic acid. Tobrex, on the other hand, is an aminoglycoside antibiotic that kills bacteria by blocking their ability to make proteins and damaging their protective covering. Polytrim is typically used every 3 hours for 7 to 10 days, while Tobrex can be used as eye drops every 4 hours for mild infections or more frequently for severe infections, and also comes in an ointment form that requires fewer doses per day. Both medications can cause temporary eye irritation and swelling. Polytrim is available only as a generic, while Tobrex is available in both brand-name and generic versions. Neither medication should be used longer than prescribed to avoid new infections or resistance.
