Effects of two benzodiazepines and a benzodiazepine antagonist on neuromuscular blockade in the anaesthetized cat.

The interaction of diazepam and midazolam with non-depolarizing neuromuscular blocking drugs was studied in the sciatic nerve-tibialis anterior muscle preparation of the anaesthetized cat. Both diazepam and midazolam (0.3 mg/kg i.v.) caused a significant enhancement of a constant 50% neuromuscular block, produced by infusions of vecuronium or pancuronium. Increasing the dose of midazolam from 0.3 to 1.5 mg/kg, caused no significant further potentiation of vecuronium, but decreased the onset time of potentiation. Ro 15-1788, a selective benzodiazepine antagonist, did not antagonize the vecuronium potentiation caused by midazolam 0.3 mg/kg. However, when given before midazolam (1.5 mg/kg), Ro 15-1788 delayed the onset of potentiation. Ro 15-1788 antagonized and prevented the considerable blood pressure decrease produced by midazolam 0.3 and 1.5 mg/kg. There appears to exist a ceiling to the benzodiazepine-induced blood pressure decrease and potentiation of vecuronium in the cat.