The total antibiotic concentration of penicillin G potassium (benzylpenicillin) and dihydrostreptomycin sulfate were determined in the ocular tissues of rabbits by radioactive tracer methods following systemic and subconjunctival administration. Free, unbound active antibiotic concentrations were determined by a modified disk diffusion assay. Both methods correlated well at concentrations greater than 200μg/gm wet tissue, but below this level the free antibiotic concentrations averaged 30% of the total for penicillin G and 75% for dihydrostreptomycin. After both systemic and subconjunctival administration, the free antibiotic levels in all tissues except lens and vitreous exceeded that in aqueous humor. Thus, the use of aqueous humor assays to determine the intraocular penetration of penicillin G and dihydrostreptomycin is not a valid indication of ocular tissue concentration.
Bloome MA, Golden B, McKee AP. Antibiotic Concentration in Ocular TissuesPenicillin G and Dihydrostreptomycin. Arch Ophthalmol. 1970;83(1):78-83. doi:10.1001/archopht.1970.00990030080015