Neomycin concentrations in inner ear tissues and other organs of the guinea pig after chronic drug administration.

The kinetics of neomycin entry into tissues, including those of the inner ear, was studied in the guinea pig. The animals received daily subcutaneous injections of 100 mg neomycin/kg body weight and were killed after 1, 3, and 6 days and 1, 2, and 3 weeks. In agreement with previous studies, kidney accumulated the drug rapidly and to a high level (450 micrograms neomycin/g tissue at day 7) while levels in heart, liver, lung, and spleen were lower by more than one order of magnitude. The drug was virtually absent from brain at all times. The salient finding was that neomycin content of cochlear tissues was relatively low. For instance, at 2 weeks, concentrations in organ of Corti (0.7 micrograms/mg protein) and lateral wall tissues (0.4 microgram) were similar to those in heart (0.3 microgram), liver (0.5 microgram), lung (0.8 microgram) and spleen (0.6 microgram) while the concentration in kidney was 6.8 micrograms neomycin/mg protein. The results show that mechanisms of drug entry are different for kidney and cochlea. They also show that the frequently discussed 'accumulation' of aminoglycosides in perilymph is apparently not reflected in tissue levels of the drug.