NEOSTIGMINE BUT NOT EDROPHONIUM PROLONGS THE ACTION OF MIVACURIUM

Purpose: To examine the influence of anticholinesterase drugs neostigm ine and edrophonium (which have different effects on plasma cholineste rase activity) administered for antagonism of neuromuscular block on t he duration of action of mivacurium (a neuromuscular blocking drug met abolised by plasma cholinesterase). Methods: This was a randomized stu dy where mivacurium 0.15 mg . kg(-1) was administered to a control gro up or after administration of neostigmine 40 mu g . kg(-1) or edrophon ium I mg . kg(-1) (n = 10 for each group) administered 10 min earlier for antagonism of atracurium-induced neuromuscular block. Neuromuscula r block was measured by stimulation of the ulnar nerve in a train-of-f our 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 anticholin esterase administration. Results: The times to recovery of T-1 (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 plasm a cholinesterase activity (PCHE) after neostigmine decreased from 6596 to 1959 U . L(-1) (P < 0.001) but there was no change after edrophoni um (6140 to 6396 U . L(-1)). Conclusions: The duration of action of mi vacurium is prolonged by previous administration of neostigmine and th is is most likely to be due to inhibition of PCHE activity.