Data are presented on the ocular, humor, and tissue concentrations of gentamicin administered by subTenon's and intramuscular routes. The microgram per milliliter concentration of the absorbed antibiotic exceeds the minimum inhibitory concentrations for the majority of organisms commonly infecting the eye at 1 and 24 hours after a subTenon's injection. Intramuscular injections alone do not give detectable antibiotic in the vitreous or lens at any time or in the other ocular tissues, with the exception of conjunctiva, after six hours. While there is not a direct corollary between these experiments done in rabbits and humans, these data indicate that subTenon's injections from 20 to 40 mg should be adequate for most ocular infections if given every 24 hours. Higher levels of ocular tissue concentration may be obtained with concomitant use of gentamicin administered intramuscularly.
Golden B, Coppel SP. Ocular Tissue Absorption of Gentamicin. Arch Ophthalmol. 1970;84(6):792-796. doi:10.1001/archopht.1970.00990040794020