Objective: The aim of the study was to assess rocuronium pharmacodynamics following a single bolus dose. Design: Clinical prospective randomized controlled study. Setting: Department of Anaesthesiology and Intensive Care, University Hospital. Material and Methods: Following the ethics committee approval and obtaining informed consent 210 patients scheduled for elective surgery under general anaesthesia with tracheal intubation were randomized into 7 groups with different rocuronium doses administered (0.30, 0.45, 0.60, 0.75, 0.90, 1.05, 1.20 mg•kg-1, respectively). After setting up neuromuscular transmission monitoring (Datex-Ohmeda S5 Anaesthesia Monitor with NMT module, ulnar nerve stimulation, TOF pattern, electromyographic evaluation of evoked response of the adductor pollicis muscle), tracheal intubation was performed after 80%depression of T1. For each consecutive patient the onset time for 80 (95) % effect, clinical duration and recovery index were determined. The recorded data were subjected to statistical analysis. Results: The onset time 80 was 123.3 ± 15.4, 94.7 ± 14.6, 71.3 ± 12.9, 59.2 ± 10.6, 54.7 ± 8.4, 50.8 ± 8.0, 47.0 ± 8.1 seconds, respectively, the onset time 95 was 162.8 ± 14.7, 119.3 ± 13.4, 92.8 ± 13.0, 82.0 ± 16.3, 74.5 ± 13.6, 67.2 ± 12.3, 63.2 ± 9.6 seconds. The clinical duration was 15.0 ± 3.7, 23.4 ± 3.8, 35.6 ± 6.1, 45.5 ± 6.6, 53.5 ± 10.5, 62.8 ± 13.1, 70.6 ± 15.0 minutes. The recovery index was 12.5 ± 3.9, 13.3 ± 4.3, 14.9 ± 3.8, 17.9 ± 3.8, 18.5 ± 4.6, 18.8 ± 5.6, 19.9 ± 5.8 minutes. When 80 % depression of T1 was reached the quality of intubating conditions was the same in all groups. Conclusion: Rocuronium is a rapid-onset neuromuscular blocker with a predictable effect. By decreasing the intubating dose by 50 % the clinical duration is shortened by more than 50 %. If we accept the simultaneous onset time prolongation during this anaesthetic strategy a low-dose rocuronium can be used for the neuromuscular block of about 15-minute duration. However, comparable intubating conditions (as assesed from NMT measurements and the clinical picture) are reached after two or more minutes.

        Key words: neuromuscular blocker – rocuronium – onset time – clinical duration – recovery index