Gentamicin + Dexamethasone is a combination of two medicines: Gentamicin + Dexamethasone1 and Gentamicin + Dexamethasone2. Gentamicin + Dexamethasone1 is an antibiotic. It stops bacterial growth by preventing the synthesis of essential proteins required by bacteria to carry out vital functions. Gentamicin + Dexamethasone2 is a steroid medicine. It blocks the production of certain chemical messengers (prostaglandins) that cause redness, swelling and itching.