Pharmacodynamics of mivacurium chloride in 13- to 18-yrs-old adolescents with thermal injury

Abstract

Background. Burned patients demonstrate resistance to the effects of non-depolarizing blocking drugs as a result of acetylcholine receptor changes. They also have decreased activity of plasma cholinesterase (PCHE), which metabolizes mivacurium. We hypothesized that decreased PCHE activity would decrease metabolism of mivacurium, and counteract the receptor-related resistance following burns. Methods. Thirteen burned patients and six controls, aged 13-18 yr were followed in 27 studies. The burned patients were sub-classified as having 10-30% or >30% body surface area burn and were studied whenever possible at ≤6 days, and at 1-12 weeks after the burn. Mivacurium pharmacodynamics were examined following a bolus (0.15 mg kg-1) dose, and during and after a continuous infusion. Results. Following a bolus, the onset time and the maximal effect were similar to controls. Recovery was prolonged in the 10-30% burn group at 1-12 weeks (P<0.008), with a similar trend in the >30% burn group at ≤6 days (P<0.082) compared with controls. The infusion requirements for mivacurium were not increased in the burned groups. The PCHE activity was decreased in all burn groups and was inversely related to recovery following the bolus (r=0.73, P<0.001) and the infusion (r=0.69, P<0.001). Conclusion. In contrast to previous studies with non-depolarizers in burned patients, normal mivacurium doses can produce paralysis, at least as rapidly as in controls, but with a possibility of a prolonged recovery from block. The standard dose of mivacurium in the presence of decreased PCHE activity is in effect, a relative overdose that explains the above findings. Mivacurium is an effective drug for use in burns, irrespective of time after, or magnitude of burn injury.