Neostigmine but not edrophonium prolongs the action of mivacurium.

PURPOSE: To examine the influence of anticholinesterase drugs neostigmine and edrophonium (which have different effects on plasma cholinesterase activity) administered for antagonism of neuromuscular block on the duration of action of mivacurium (a neuromuscular blocking drug metabolised by plasma cholinesterase). METHODS: This was a randomized study where mivacurium 0.15 mg.kg-1 was administered to a control group or after administration of neostigmine 40 micrograms.kg-1 or edrophonium 1 mg.kg-1 (n = 10 for each group) administered 10 min earlier for antagonism of atracurium-induced neuromuscular block. Neuromuscular block was measured by stimulation of the ulnar nerve in a train-of-four mode (TOF) and measuring the force of contraction of the adductor pollicis muscle. Baseline plasma cholinesterase activity was estimated before drug administration in all the groups and following anticholinesterase administration. RESULTS: The times to recovery of T1 (first response in the TOF) to 25 and 90% of control and of the TOF ratio to 0.7 after 0.15 mg.kg-1 of mivacurium were 47, 65 and 70 min in the neostigmine group; 25, 36 and 36 min in the edrophonium group and 17, 29 and 27 min respectively in the control group (P < 0.01). The plasma cholinesterase activity (PCHE) after neostigmine decreased from 6596 to 1959 U.L-1 (P < 0.001) but there was no change after edrophonium (6140 to 6396 U.L-1). CONCLUSIONS: The duration of action of mivacurium is prolonged by previous administration of neostigmine and this is most likely to be due to inhibition of PCHE activity.

Duration of stabilization of control responses affects the onset and duration of action of rocuronium but not suxamethonium.

The effect of the duration of stabilization of control responses on the onset and duration of clinical relaxation of suxamethonium 1 mg kg-1 and rocuronium 0.6 mg kg-1 were investigated in 90 patients. The control responses were allowed to stabilize for 1, 5, 10, 15 or 20 min prior to administration of rocuronium and for 1, 5, 10 or 15 min prior to suxamethonium. The mean onset time for rocuronium decreased from 150 to 46 s as the duration of stabilization increased from 1 to 20 min (P < 0.001) although the maximal effect was observed within the first 5 min. The average duration of clinical relaxation also increased from 25 to 40 min (P < 0.001). No effect was observed for either variable in the case of suxamethonium.

Potency and time course of action of rocuronium during desflurane and isoflurane anaesthesia.

We have studied the potency and onset and duration of action of rocuronium in patients anaesthetized with 1 MAC of desflurane or isoflurane (in 66% nitrous oxide). Potency was estimated using the single bolus dose technique. Neuromuscular block was measured by stimulation of the ulnar nerve and recording the force of contraction of the adductor pollicis muscle. The ED50 and ED95 of rocuronium were estimated as 138 (95% confidence limits 117-162) micrograms kg-1 and 281 (241-328) micrograms kg-1, and 126 (105-151) micrograms kg-1 and 283 (236-339) micrograms kg-1 during desflurane and isoflurane anaesthesia, respectively. The mean times to onset of maximum block after rocuronium 0.6 mg kg-1 were 1.0 (SD 0.10) min and 1.1 (0.15) min, respectively, during anaesthesia with desflurane and isoflurane. The respective times to recovery of T1 (the first response in the train-of-four (TOF) stimulation) to 25% and 90% were 36 (8.3) min and 54 (15.4) min during desflurane anaesthesia and 31 (8.2) min and 45 (12.7) min during isoflurane anaesthesia. The times to recovery of the TOF ratio to 0.7 were 66 (13.4) min and 52 (16.3) min and the 25-75% recovery indices 14 (5.3) min and 10 (3.2) min, respectively, in the desflurane and isoflurane groups. There were no differences in the estimated potency or onset of action of rocuronium during desflurane and isoflurane anaesthesia. However, duration of action tended to be longer curing desflurane anaesthesia although only the differences in times to TOF ratio of 0.7 and the recovery indices were close to being significantly different (P = 0.0503 and 0.0560).

A comparison of the effects of isoflurane and desflurane on the neuromuscular effects of mivacurium.

The effects of 1 MAC of desflurane and isoflurane (in 66% nitrous oxide) on the potency and duration of action of mivacurium were studied in 80 patients. The ED95 of mivacurium was 86 micrograms.kg-1 (74-100) and 88 micrograms.kg-1 (76-103) (mean and 95% confidence intervals) during anaesthesia with desflurane and isoflurane respectively. The onset and duration of recovery to 25, 75 and 90% of T1 (first response in the TOF) of 200 micrograms.kg-1 of mivacurium were 1.4 (0.3) and 1.5 (0.3) min (mean and SD), 22 (4.9) and 19 (4.0), 29 (6.6) and 26 (5.8), and 32 (7.3) and 29 (6.6) min respectively. There was no significant difference in any of the variables between desflurane and isoflurane. It is concluded that the neuromuscular effects of mivacurium are similar during anaesthesia with 1 MAC of desflurane and isoflurane.