Alteration of aminoglycoside antibiotic ototoxicity by hyper- and hypohydration

The ototoxicities of tobramycin sulfate and gentamicin sulfate were investigated in guinea pigs under conditions of normal, increased, and decreased hydration. Increased hydration was associated with no decline in the amplitude of the cochlear microphonics, a lesser decline in the eighth nerve action potentials and lesser damage to the organ of Corti. Decreased hydration was associated with an increase in the threshold of the cochlear microphonics and the eighth nerve action potentials, a decline in the amplitude of the cochlear microphonics, a greater decline in the eighth nerve action potentials, and greater damage to the organ of Corti. Tobramycin sulfate was substantially less toxic than gentamicin sulfate with normal, increased and decreased hydration. These findings suggest the preferential use of tobramycin sulfate for patients with normal renal function, and especially patients with renal impairment.