PRE- AND POSTJUNCTIONAL BLOCKING EFFECTS OF AMINOGLYCOSIDE, POLYMYXIN, TETRACYCLINE AND LINCOSAMIDE ANTIBIOTICS

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Abstract
The effects of seven antibiotics (streptomycin, amikacin, polymyxin B, lincomycin, clindamycin, tetracyc-line and oxytetracycline) were compared with those of magnesium, tubocurarine and lignocaine in the frog sciatic nerve - sartorius muscle preparation, using intraceUular recording techniques All compounds except tubocuranne decreased end-plate potential quantal content. The prejunctional effects of magnesium, streptomycin, amikacin, polymyxin B and oxytetracydine (but not the other drugs) were well reversed by increasing the calcium concentration At concentrations which depressed quantal content, only magnesium, tetracycline and oxytetracydine did not reduce postjunctional sensitivity. Further postjunctional effects of the drugs were revealed by alterations in the time-courses of end-plate potentials. All the drugs tested except magnesium, tubocurarine and lincomycin produced changes in muscle action potentials. None of the compounds had anticholinesterase activity. The results confirm that aminogrycoside, polymyxin, tetracyc-Une and lincosamide antibiotics produce neuromuscular block by a combination of both pre- and postjunctional actions.