Neuromuscular block by neomycin in the cat

Mechanisms of aminoglycoside ototoxicity and targets of hair cell protection

Aminoglycosides are commonly prescribed antibiotics with deleterious side effects to the inner ear. Due to their popular application as a result of their potent antimicrobial activities, many efforts have been undertaken to prevent aminoglycoside ototoxicity. Over the years, understanding of the antimicrobial as well as ototoxic mechanisms of aminoglycosides has increased. These mechanisms are reviewed in regard to established and potential future targets of hair cell protection.

Anesthesia for craniotomy in a patient with previous paralytic polio

Poliomyelitis remains endemic in many developing nations. Patients may develop residual muscle weakness in one or more limbs after an attack of poliomyelitis in childhood. We report an adult patient who presented for right temporal cortical grid placement. He had childhood poliomyelitis and, while showing no evidence of postpolio syndrome, demonstrated excessive sensitivity to nondepolarizing muscle relaxants and developed prolonged muscle weakness during the postoperative period.

Failure of neuromuscular blockade reversal after rocuronium in a patient who received oral neomycin

PURPOSE

Because the aminoglycoside antibiotics and nondepolarizing muscle relaxants have interactions that vary, it is necessary to update the potential for such interactions when new drugs are introduced clinically. Rocuronium is a newly released steroidal nondepolarizing muscle relaxant with an intermediate duration of action. The following report is the first description of prolonged neuromuscular blockage after rocuronium in a patient who had received oral neomycin in anticipation of open bowel resection.

CLINICAL FEATURES

A 71-yr-old woman with a two week history of bleeding pr was scheduled for exploratory laparotomy and right hemicolectomy. She received two standard bowel preparations consisting of oral erythromycin and neomycin over a two day period. Rocuronium was used to facilitate tracheal intubation and maintain muscle relaxation during a two hour operation. Despite clinical appearance of reversal of neuromuscular blockade after neostigmine and glycopyrolate, the patient complained of dyspnoea and weakness upon tracheal extubation and required reintubation twice. The reason for prolonged muscle relaxation was thought to be secondary to a rocuronium and neomycin interaction.

CONCLUSION

Rocuronium, a new nondepolarizing muscle relaxant, has potential interactions with other drugs including the aminoglycoside antibiotics. This clinical report describes the failure of neuromuscular blockade reversal in a patient who received oral neomycin in anticipation of open bowel resection.

Aminoglycoside antibiotics block voltage-dependent calcium channels in intact vertebrate nerve terminals

Intrinsic and extrinsic optical signals recorded from the intact nerve terminals of vertebrate neurohypophyses were used to investigate the anatomical site and physiological mechanism of the antagonistic effects of aminoglycoside antibiotics on neurotransmission. Aminoglycoside antibiotics blocked the intrinsic light scattering signal closely associated with neurosecretion in the mouse neurohypophysis in a concentration-dependent manner with an IC50 of approximately 60 microM and the block was relieved by increasing [Ca2+]o. The rank order potency of different aminoglycoside antibiotics for blocking neurosecretion in this preparation was determined to be: neomycin greater than gentamicin = kanamycin greater than streptomycin. Optical recordings of rapid changes in membrane potential using voltage-sensitive dyes revealed that aminoglycoside antibiotics decreased the Ca(2+)-dependent after-hyperpolarization of the normal action potential and both the magnitude and after-hyperpolarization of the regenerative Ca2+ spike. The after-hyperpolarization results from a Ca-activated potassium conductance whose block by aminoglycoside antibiotics was also reversed by increased [Ca2+]o. These studies demonstrate that the capacity of aminoglycoside antibiotics to antagonize neurotransmission can be attributed to the block of Ca channels in the nerve terminal.

Influence of extracellular calcium in the effects of dibekacin and diltiazem on indirectly elicited tetanic responses in the rat phrenic-hemidiaphragm preparation

1. Dibekacin (70 microM-3 mM) produced a decrease of peak tetanic tension in a concentration-dependent manner and this effect was dependent on extracellular calcium (0.3-2.5 mM Ca2+). Only minimal fade was observed and it was not related with extracellular calcium concentrations. 2. Diltiazem (30-300 microM) decreased peak tetanic tension and produced tetanic fade. Both effects were independent of extracellular calcium, although a significant potentiation was observed at 0.3 mM calcium. 3. It is concluded that tetanic parameters are related differently to extracellular calcium.

The neuromuscular blocking effect of dibekacin and its reversal by Ca2+ and drugs in the isolated rat phrenic-hemidiaphragm preparation

1. Dibekacin (0.3-3 mM) reduced indirectly elicited twitches in rat phrenic-hemidiaphragm. This effect was potentiated in low extracellular calcium media. 2. The blockade induced by dibekacin (3 mM) could be reversed by calcium (2.5 mM), 3,4-diamino-pyridine (3,4-DAP, 10 microM) or guanidine (3 mM), whereas neostigmine (3 microM), eserine (25 microM) or tetraethylammonium (100 microM) were less potent. 3. Dibekacin (3 mM) blocked directly-elicited twitches. Low concentrations were unable to obtain any effect. 4. It is concluded that dibekacin exerts its blocking action by limiting the calcium entry at motor nerve terminals, but a postsynaptic effect is also present. 3,4-DAP, guanidine and calcium were the most potent drugs in reversing the blockade.

Neuromuscular and cardiovascular depression produced by prolonged exposure to Polymyxin B

It has been reported previously that in cats pre-treatment for 24 to 48 hours with neomycin sulphate resulted in a change in the pattern of neuromuscular block subsequently produced with this antibiotic. The unique characteristics of neomycin-induced neuromuscular block observed during acute exposure gave way to a pattern of block usually observed with tubocurarine. In a similar experiment on six cats we have demonstrated that with polymyxin B prolonged exposure did not result in a comparable time-dependent change in the nature of the neuromuscular block it produced, in terms of train-of-four, tetanic, and post-tetanic behaviour of the neurally-elicited muscle response. The differing characteristics of neuromuscular block seen with various antibiotics, e.g. the aminoglycoside neomycin as opposed to the polypeptide polymyxin B, during acute and sub-chronic exposure is stressed. Previously observed ability of 4 aminopyridine 0.6 mg/kg to reverse the neuromuscular and cardiovascular depression during acute exposure to polymyxin B persisted in prolonged exposure.