Intraocular penetration of sisomicin in rabbits

The intraocular penetration of sisomicin, an aminoglycoside antibiotic, was studied in 47 normal rabbits following subconjunctival and/or intramuscular (IM) injections. Sisomicin levels were determined in the cornea and the aqueous humor of the injected eye as well as in the aqueous of the fellow eye by means of the cylinder-plate bioassay technique. When the IM route alone was used, the eye tissue concentrations remained negligible. One hour after subconjunctival injection, highly therapeutic sisomicin concentrations were achieved in the aqueous humor of both injected and fellow eyes, but the level dropped to very low concentrations 12 hours after the injection. The concomitant administration of sisomicin intramuscularly and subconjunctivally resulted in a significant delay of the clearance of sisomicin from the eye tissues. The use of the combined subconjunctival-IM regimen for administering aminoglycoside antibiotics needs further evaluation.