The comparative neuromuscular blocking effects of some aminoglycoside antibiotics

The neuromuscular blocking effects of aminoglycoside antibiotics were tested in the isolated phrenic nervediaphragm preparation of the rat. The neuromuscular blocking potencies were netilmicin equals sisomicin much greater than neomycin much greater than gentamicin much greater than tobramycin. The EC 50's (concentration resulting in 50 percent depression of the original twitch tension) were respectively 13.3 x 10(-4); 13.4 x 10(-4); 13.6 x 10(-4); 15.1 x 10(-4); and 95.3 x 10(-4) Mol/l for netilmicin, sisomicin, neomycin, gentamicin and tobramycin. When a threshold dose of pancuronium was added to the bathing fluid the EC 50's were diminished respectively by a factor of 0.4 (sisomicin and neomycin) 0.5 (tobramycin) and 0.6 (netilmicin and gentamicin). Addition of a threshold dose of Org-NC45, a new steroidal non-depolarizing muscle relaxant, diminished the EC 50's to the same extent. The neuromuscular blocking effects of pancuronium and Org-NC45 themselves were potentiated by pretreatment of the preparations with a threshold dose of the aminoglycoside. Comparison of the results demonstrated the following potentiating effects: netilmicin equals sisomicin much greater than neomycin much greater than gentamicin greater than tobramycin. Which is in the same sequence s the neuromuscular blocking potencies of these drugs.