THE EFFECT OF PLASMA CHOLINESTERASE ACTIVITY ON MIVACURIUM INFUSION RATES

Although mivacurium is eliminated by plasma cholinesterase, previous i nvestigations have revealed either no relationship or limited correlat ion between mivacurium infusion rates (IRs) and plasma cholinesterase activity. Assuming that such a relationship should exist, we used a no vel approach to better demonstrate the relationship in humans. Fourtee n isoflurane-anesthetized adults underwent standard neuromuscular moni toring. Mivacurium was then infused at 1.0 mu g . kg(-1). min(-1) unti l twitch tension stabilized. The LR 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 t witch depression, the IRs expected to produce 50% and 90% twitch depre ssion (IR(50) and IR(90), respectively) were estimated by nonlinear re gression. Both IR(50) (r(2) = 0.51, P < 0.005) and IR(90) (r(2) = 0.48 , P < 0.01) were related to plasma cholinesterase activity; the coeffi cient of the Hill equation did not vary with plasma cholinesterase act ivity. We conclude that mivacurium IRs are, as expected, influenced by the activity of the enzyme responsible for its elimination.