No percutaneous absorption was detected using a bioassay method sensitive to 0.0333μg/ml for serum following topical application of neomycin sulfate ointment in groups of normal male volunteers who had neomycin sulfate ointment applied to their bodies. Treatment areas ranged from coverage of all of the "wet" body areas on one side of the body to complete body coverage (excluding the genitalia) for a period of six hours. Results of urine and blood samples at various intervals were consistently negative for neomycin sulfate as determined by a sensitive bioassay method. No sensitization was found when subjects were patch and intradermally tested one to two months following treatment.
Panzer JD, Epstein WL. Percutaneous Absorption Following Topical Application of Neomycin. Arch Dermatol. 1970;102(5):536-539. doi:10.1001/archderm.1970.04000110052009