Neomycin is typically used as a topical preparation, such as Neosporin.
It can also be given orally, where it is usually combined with other antibiotics. Neomycin is not absorbed from the gastrointestinal tract and has been used as a preventive measure for hepatic encephalopathy and hypercholesterolemia.
By killing bacteria in the intestinal tract, it keeps ammonia levels low and prevents hepatic encephalopathy, especially prior to GI surgery.
It has also been used to treat small intestinal bacterial overgrowth.
It is not given intravenously, as neomycin is extremely nephrotoxic (causes kidney damage), even when compared to other aminoglycosides.
The exception is when neomycin is included, in very small quantities, as a preservative in some vaccines - typically 0.025 mg per dose.