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January 1970

Antibiotic Concentration in Ocular Tissues: Penicillin G and Dihydrostreptomycin

Author Affiliations

Iowa City
From the Department of Ophthalmology, Laboratory of Experimental Ophthalmic Microbiology and Immunology, University of Iowa, Iowa City.

Arch Ophthalmol. 1970;83(1):78-83. doi:10.1001/archopht.1970.00990030080015

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.