Interaction of Neuromuscular Blocking Effects ofNeomycin and Polymyxin B

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Abstract
In neuromuscular pharmacology, while interactions between antibiotics and other drugs have been well studied, interactions among antibiotics are relatively unclear. Neomycin, the most potent neuromuscular blocking aminoglycoside, and polymyxin B, the most potent polypeptide, block neuromuscular transmission by different mechansisms of action and produce blocks whose features are different. The interaction of the neuromuscular blocking effects of these 2 antibiotics is described. Neomycin and polymyxin B produce neuromuscular blocks with distinct features by different mechanisms of action. In 8 anesthetized cats their interaction was studied by examining the neuromuscular block produced by an equipotent mixture. Values of onset, potency, dose-response relations, duration and reversibility of block, the train-of-four and tetanic responses during block, the frequency-block relationships, and the posttetanic twitch behavior were well approximated by averaging the corresponding values previously reported for each antibiotic. Edrophonium, 0.2 mg/kg, reversed the block by 8-35%; 4-aminopyridine, 0.6 mg/kg, completely reversed the block and caused a long-lasting overshoot of the twitch response. Neomycin and polymyxin B are evidently additive in neuromuscular effects, not only in terms of potency and duration, but also in terms of the characteristics of the blocks produced.