Effect of repeated administrations of neomycin on the neuromuscular functions and the enhancement of d-tubocurarine action in mice.

Effects of repeated s.c. treatments with 50 mumol (approx. 31 mg)/kg/day of neomycin for 10 or 15 days were examined in mice. There were no significant differences between saline and neomycin treatment groups in the motor coordination assessed by rota-rod test and traction test. On tension recordings, an in vitro addition of d-tubocurarine inhibited the twitch tensions evoked by the nerve stimulations in both cases of saline or neomycin treatment. Neomycin treatments shifted the concentration-response curve between twitch tension and d-tubocurarine to the left, dependently on its injection days. These results suggest that repeated treatments with neomycin enhance the inhibitory effect of d-tubocurarine on the neuromuscular transmission in mice without eliciting motor incoordination and muscle relaxation.