Mivacurium in infants and children.

Mivacurium is the only available short-acting nondepolarizing muscle relaxant in clinical use. It is a bis-quaternary benzylisoquinolinium ester hydrolysed by plasma-cholinesterase into inactive compounds. The ED50 and ED95 in children are about 50 micrograms.kg-1 and 90 micrograms.kg-1 respectively. In infants, they have a tendency to be lower. A standard intubating dose of 0.25 mg.kg-1 causes complete neuromuscular depression in 1.5-2 min, recovery to 5% in 6-10 min, and complete recovery in 15-20 min. The recent tendency is to use 0.3 mg.kg-1 to obtain better intubating conditions with slight prolongation of effect. Since the recovery profile of mivacurium is independent of the dose and duration, it is most suitable for administration by continuous infusion. The infusion requirement in children is 10-16 micrograms.kg-1 min-1, which is about twice that of adults. Cutaneous flushes from histamine release are commonly seen with the larger doses of mivacurium; however, the associated hypotensive effects are minimal and counteracted by the tracheal intubation. The duration of action of mivacurium is prolonged in patients with cholinesterase deficiency. Mivacurium's neuromuscular effects can be satisfactorily antagonized by edrophonium or neostigmine.