ABSTRACT
The tympanic membrane [TM] and external auditory canal [EAC] of the rabbits were studied microscopically after application of Bonain's solution [local anaesthetic] on 21 rabbits including six controls. Bonain's solution was administered into both sides of the rabbits and was massaged for at least 3 minutes. Experimental animals were divided into three groups of 5 rabbits each. The rabbits of first, second and third group were sacrified at 48 hour, 10 days and 20 days respectively. The specimens taken at 48 hours after exposure of Bonain's solution showed intraepithelial hemorrhage in the squamous epithelium of the EAC, and the TM showed hemorrhage and curvatures. The specimens taken at 10 days showed split of the basal membrane in the epidermal layer and intraepithelial mononuclear cell infiltration in the EAC. Thickening in the epidermal layer and mononuclear cell infiltration were also seen in the TM. The specimens taken at 20th day showed degeneration and pus on the epithelial layer in the EAC, thickening and hyperplasia in the epidermal layer of TM were observed as well. Controls were normal. This study confirms that Bonain's solution damages the TM and EAC when used as a local anaesthetics in rabbits and similar damage may be caused in humans thus its use should be limited and with caution