Loading Doses and Extended Dosing Intervals in Topical Gentamicin Therapy

Loading doses and extended dosing intervals were studied in a rabbit model using topically applied gentamicin in a concentration of 13.6 mg/ml. Loading doses consisting of one drop every minute for five minutes produced significantly higher gentamicin concentrations in the cornea during the early hours of treatment than regimens using one drop every hour and one drop every 30 minutes. Extended dosing intervals of two and four hours, when used in conjunction with an initial loading dose, produced peak gentamicin levels above 125 μg/g of cornea. However, trough levels with these extended dosing intervals were significantly lower than troughs during hourly gentamicin administration. An extended dosing interval regimen consisting of three drops every two hours maintained peak and trough levels equal to those produced by one drop an hour.