The effect of colymycin m, gentamycin and kanamycin on depression of neuromuscular transmission induced by pancuronium bromide

In summation, the effect of three mycin antibiotics on pancuronium bromide-induced depression of neuromuscular transmission was studied, using a sciatic nerve tibialis anterior muscle preparation of anaesthetized dogs. Muscle twitch responses were recorded before and after administration of non-paralysing doses of the muscle relaxant and the test antibiotic. It was inferred from the results that colymycin, gentamycin and kanamycin potentiated the neuromuscular blockade induced by pancuronium. Colymycin showed the least potency while kanamycin induced the most effective blockade. Calcium and neostigmine had limited effect in reversing the neuromuscular blockade due to gentamycin and kanamycin. The antibiotics are believed to depress neuromuscular transmission by depleting acetylcholine at the motor endplate, through inhibition of its release. With decreased calcium levels in the motor nerve terminal membranes, non-depolarizing muscle relaxants exert a similar effect. At the post-synaptic membrane the antibiotic desensitizes the receptors to acetylcholine, while the muscle relaxant acts by occupying the receptor. The mode of action of the antibiotic and muscle relaxant at the presynaptic membrane is similar to that of magnesium ions. The resistance to reversal of the neuromuscular blockade by both calcium and neostigmine finds explanation in its multifocal nature.