Mivacurium-induced prolonged neuromuscular block

We report a case of prolonged neuromuscular block after administrationof mivacurium 0.2 mg kg^–1 to a 16-yr-old patient wherethe duration of block was 2.5 h. The interesting points in thiscase were that the patient had homozygous atypical plasma cholinesterasedeficiency (both parents had a normal phenotype) following livertransplantation. Investigations showed low plasma cholinesteraseactivity (343 iu litre^–1 normal 600–1400) and dibucainenumber was 25 (normal 76–83). Despite possessing atypicalenzyme normally associated with markedly prolonged durationof suxamethonium, on two occasions the patient received suxamethoniumand responded normally. This had not previously been reported.The patient demonstrated prolonged block with mivacurium asa result of atypical enzyme (despite normal metabolism of suxamethonium).