KINETICS OF GENTAMICIN UPTAKE IN THE INNER-EAR OF CHINCHILLA LANGIER AFTER MIDDLE-EAR ADMINISTRATION IN A SUSTAINED-RELEASE VEHICLE

The search for a safe, effective treatment for the vertigo associated with Meniere's disease has long been an important topic in otolaryngol ogy. In recent years many groups have begun using intratympanic gentam icin to treat this vertigo. Although reported cure rates are as high a s 90%, many questions remain regarding this type of treatment. Current limitations are the necessity for repeated treatments and a lack of c lear dosing guidelines. In addition, the gentamicin must be delivered in a manner that allows maximal vestibulotoxic effect without injury t o hearing. Until investigators can control the exact amount of medicin e that is placed in the ear and have an understanding of the kinetics of gentamicin absorption, adequate dosing guidelines will be difficult to establish, and therapy will continue to rely on empiric data. We d escribe the use of a fibrin-based sustained-release vehicle, impregnat ed with gentamicin, injected into the middle ear of chinchillas. This allows for a prolonged effect without repeated dosing. Using this mode l, we studied the absorption kinetics of gentamicin at time points ran ging from 8 hours to 1 week after injection. We used our findings to c reate a kinetics curve of gentamicin absorption. We discuss the shape and characteristics of this kinetics curve and examine the effects of the fibrin-based sustained-release vehicle and gentamicin on the middl e ear. We noted no absorption in the contralateral (untreated ear) or blood. Through better understanding of the actions of gentamicin in th is animal model, we hope to facilitate safer use of intratympanic medi cines in our patient population and initiate programs for the use of t his sustained-release vehicle in human beings.