The Effect of the Toxic Reaction of the Retina by Liposome-encapsulated Tobramycin in Normal Rabbits

ABSTRACT

To determine whether liposome-encapsulated tobramycin is less toxic than commercial tobramycin and the threshold dose of liposome-encapsulated tobramycin required to produce toxic reactions when it was injected intravitreally in rabbit, we used liposome-encapsulated tobramycin, tobramycin in PBS, mixture of tobramycin and liposome-encapsulated saline, liposome-encapsulated saline and normal saline respectively. After those were injected, we examined the histologic findings and the functional changes of the retina. The final results are summarized as follows; 1. When tobramycin was injected intravitreally alone, there was no toxic reaction of the retina histologically and functionally with dosage 500 micro gram of commercial tobramycin, but dosage more than 750 micro gram produced toxic reaction. 2. When liposome-encapsulated tobramycin was injected intravitreally, there was toxic reaction of the retina histologically and functionally with dosage 1500 micro gram of tobramycin. 3. When a mixture of tobramycin and liposome-encapsulated saline was injected intravitreally, there was similar toxic reaction as tobramycin used alone with dosage more than 750 micro gram of tobramycin. Liposome-encapsulated saline and normal saline did not produce toxic reaction. The above results indicate that liposome encapsulation markedly reduces the ocular toxicity of tobramycin and that as mnch as dosage 1000 micro gram of liposome-encapsulated tobramycin may be tolerated by the intravitreal route in the rabbit eye. Therefore, the results of this study offer some hope that we may use the method of intravitreal injection of liposome-encapsulated tobramycin safely and effeciently for the treatment of bacterial endophthalmitis in near future.