The effect of plasma cholinesterase activity on mivacurium infusion rates

Although mivacurium is eliminated by plasma cholinesterase, previous investigations have revealed either no relationship or limited correlation between mivacurium infusion rates (IRs) and plasma cholinesterase activity. Assuming that such a relationship should exist, we used a novel approach to better demonstrate the relationship in humans. Fourteen isoflurane-anesthetized adults underwent standard neuromuscular monitoring. Mivacurium was then infused at 1.0 micrograms.kg-1.min-1 until twitch tension stabilized. The IR was then adjusted, using the Hill equation, to produce approximately steady state 50% (n = 14) or 90% (n = 13) twitch depression. Using these values for IR and steady-state twitch depression, the IRs expected to produce 50% and 90% twitch depression (IR50 and IR90, respectively) were estimated by on nonlinear regression. Both IR50 (r2 = 0.51, P < 0.005) and IR90 (r2 = 0.48, P < 0.01) were related to plasma cholinesterase activity; the coefficient of the Hill equation did not vary with plasma cholinesterase activity. We conclude that mivacurium IRs are, as expected, influenced by the activity of the enzyme responsible for its elimination.