In a randomized study, we evaluated lag time (time from the end of injection of muscle relaxant until the first depression of the train-of-four response [TOF]), onset time (time from the end of injection of muscle relaxant until the maximum depression of the first twitch of the TOF [T1]), neuromuscular block, and endotracheal intubating conditions at 1 min after 1 mg/kg succinylcholine (n = 15) and 1.5 mg/kg Org 9487 (n = 30). Two minutes after administration of Org 9487, 15 of the 30 patients received neostigmine for reversal. Recovery of neuromuscular block after succinylcholine, Org 9487 without and Org 9487 with neostigmine were compared using the time until T1 was 90% for the succinylcholine group, and the time until TOF was 70% for the Org 9487 groups. Neuromuscular transmission was monitored mechanomyographically. Onset time was similar (67 [20] and 83 [38] s for succinylcholine and Org 9487, respectively) and endotracheal intubating conditions were also similar after both muscle relaxants. Times until clinically sufficient recovery of neuromuscular block induced by succinylcholine (time until T1 = 90%: 10.6 [3.3] min) and Org 9487 with neostigmine (time until TOF = 70%: 11.6 [1.4] min) were not different. In contrast, in the Org 9487 without neostigmine group, more time was required until complete recovery (24.1 [6.2] min) (P < 0.05). In conclusion, ORg 9487 is a muscle relaxant suitable for endotracheal intubation and short-lasting interventions.

The dose-response relationship and the time course of action of Org 7617, a short acting non-depolarizing neuromuscular blocking agent, were evaluated during thiopentone, fentanyl, halothane and N2O anaesthesia. Neuromuscular transmission was monitored mechanomyographically. The ED50 and ED90 were calculated after single bolus doses of the drug. Twelve, seven and three patients received 2.5, 3.75 or 5.0 mg.kg-1 Org 7617, respectively. Neuromuscular block was characterized by a short lag time (average 30 s) and rapid development of neuromuscular block (69-84 s). Maximum block approximated to 66%, 91% and 95%, and the duration until clinically adequate recovery (TOF ratio of 0.7) to 7.4, 12.1 and 12.2 min after 2.5, 3.75, 5 mg.kg-1 of Org 7617, respectively. The calculated ED50 and ED90 were 1.8 and 3.4 mg.kg-1. Adverse effects, including a moderate fall in systolic and diastolic arterial blood pressure and a concomitant increase in heart rate appeared to be dose-dependent. Some patients showed flushing. One patient given 5 mg/kg Org 7617 had serious adverse effects suggestive of histamine release, i.e. flushing, urticaria, tachycardia, hypotension and bronchospasm. Therefore further clinical investigations were terminated. Although its low potency and the adverse effects observed will prevent further clinical development of ORG 7617, the results do support the contention that it is feasible to develop short-acting non-depolarizing neuromuscular blocking agents from the steroidal series.

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