THE DIFFICULTY OF DETERMINING THE ROUTE OF INTRAOCULAR PENETRATION OF GENTAMICIN AFTER SUB-CONJUNCTIVAL INJECTION IN THE RABBIT

  • 1 January 1981
    • journal article
    • research article
    • Vol. 20  (4) , 509-514
Abstract
In small animals i.e., the rabbit the ratio of eye size to body size is much larger than it is in humans. Accordingly, periocular injection of antibiotics in this animal model causes significantly higher serum concentrations than does a comparable dose in a human. To assess the effect of the systemic drug component on ocular penetration, the levels of gentamicin in ocular tissues and fluids of the rabbit were compared following injection of 20 mg by subconjunctival or intramuscular routes. Blood levels of gentamicin were similar with the 2 routes of administration. In normal rabbit eyes, no antibiotic was detectable in the vitreous humor for the first 3 h after subconjunctival or i.m. injection. By 6 h, low vitreous levels of drug were detectable after subconjunctival, but not after i.m., injection. As the concentrations were so close to the threshold of sensitivity of the assay, it was not clear that the difference between the routes was significant in normal eyes. In infected eyes, the concentrations of gentamicin in the vitreous were similar after subconjunctival and i.m. injection. The penetration of gentamicin into the infected vitreous humor of rabbits after subconjunctival injection could be attributed to hematogenous carriage as to direct penetration. The problem in distinguishing systemic from direct transport with periocular injections may be inherent in any small animal model in which the ratio of eye size to body size is high.

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