LIX Scientific Papers of the American Otological Society

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Abstract
Comparative antibiotic concentrations were determined in the blood serum, cerebrospinal fluid, and perilymph of 201 cats. Methods for collecting and assaying the specimens were discussed. Penicillin and streptomycin enter the perilymph soon after intramuscular administration. The antibiotic levels attained in ther serum are well above those of the cerebrospinal fluid or perilymph. The penicillin levels in the perilymph rise at a rate nearly identical to those of the cerebrospinal fluid. Slightly higher maximal concentrations in the perilymph are sustained for 4-6 hours longer than those of the cerebrospinal fluid. The concentrations in the cerebrospinal fluid are a better guide to antibiotic therapy of the inner ear since the levels in the perilymph more closely parallel those of the cerebrospinal fluid. There was no demonstrable advantage to the use of procaine penicillin at the dosage levels studied because of the prolonged elevation of the penicillin levels in the perilymph after aqueous penicillin use. The streptomycin levels in the perilymph were well above those in the cerebrospinal fluid with the 2-fold dilution method of assay. Higher streptomycin levels were demonstrated in the perilymph when cats were given repeated injections of streptomycin for several days, than after a single dose. The maximal cumulative effect present after 4 doses did not increase with further injections.