The Change of the Tobramycin Concentration in Aqueous Humor According to the Administration Routes

ABSTRACT

PURPOSE: To determine the best routes of administration of Tobramycin, the intracameral concentrations was assessed as time progressed after administering identical amounts and concentrations of tobramycin through various methods. METHODS: 40 eyes from 20 house rabbits were administered the same amount (200 micro liter) of 0.3% tobramycin. The first group was administered topically, and the second group was administered by subconjunctival injection. Contact lenses were soaked in tobramycin for 30 minutes and were covered over the corneas of the third group. While amniotic membranes were transplanted onto the corneas and tobramycin was topically administered in the fourth group. 100 micro liter of aqueous fluid was extracted 30 min, 1 hr, 2 hr and 3 hr after the administration and intracameral concentrations of tobramycin were measured using FPIA (fluorescence polarization immunoassay). RESULTS: After topical administration and subconjunctival injection, statistically significant decreases of average concentrations were observed after 2~3 hours. The group that was covered with flexible hydrophilic contact lenses showed high concentrations after 30 minutes, and a statistically significant increases of concentration was observed after 2 hours. The group that was topically administered with 0.3% tobramycin after amniotic transplantation on the cornea, showed a gradual increase of concentration as time progressed, and statistically significant increase of concentration was observed after 1~2 hours. CONCLUSIONS: Topical administrations with more frequent instillations increased intracameral concentrations, exceeding the MIC90 concentration of Staphylococcus aureus. while low concentration (0.3%) of subconjunctival injections did not significantly increases intracameral concentrations. Using flexible contact lenses, high concentrations were observed in the early stages, exceeding the MIC90 concentrations of Staphylococcus aureus, Staphylococcus epidermidis, and Pseudomonas aeruginosa. Concentrations exceeded MIC90 concentration of Staphylococcus epidermidis 30 minutes after amniotic membranes transplantation, and continued to increases after 3 hours, Therefore, we can conclude that amniotic membrane can be used as a reservoir for transferring drugs.