Stereoselective high-performance liquid chromatographic assay with fluorometric detection for the isomers of mivacurium in human plasma.
A high-performance liquid chromatographic assay with fluorometric detection was developed for the analysis of the stereoisomers of mivacurium, a new short-acting neuromuscular blocker, in plasma. The isomers were isolated from plasma by solid-phase extraction with C18 and anion-exchange cartridges. The extracts were chromatographed on a LiChrosphere 60 RP Select B column (125 mm x 4.6 mm I.D.) using a mobile phase of acetonitrile-water (4:6, v/v) containing 0.005 M octanesulfonic acid. The fluorescence excitation and emission wavelengths were 202 and 320 nm, respectively. The accuracy and precision of the assay, expressed as the percentage deviation of measured values from true values and the percentage coefficient of variation, respectively, were less than or equal to 10% at all concentrations except for the percentage coefficient of variation at the lower limit of quantitation (5 ng/ml). The assay has been successfully used for the analysis of plasma samples from a pharmacokinetic study in human volunteers.
Effect of Edrophonium and Neostigmine on the Pharmacokinetics and Neuromuscular Effects of Mivacurium
Background: Previous studies demonstrated that both edrophonium and neostigmine affect mivacurium’s pharmacokinetics, thereby potentially affecting its recovery profile. However, those studies were not clinically relevant because mivacurium was still infused after the antagonists were given. In the present study, the authors gave antagonists (or placebo) after discontinuing a mivacurium infusion, thereby obtaining data that are more clinically relevant. Methods: In 18 patients, mivacurium was infused at 10 &mgr;g · kg−1 · min−1 for 40 min, the infusion was discontinued for 15 min and then restarted at the same rate for another 40 min. Patients were randomized to receive 500 &mgr;g/kg edrophonium, 50 &mgr;g/kg neostigmine, or saline at discontinuation of the second infusion; all subjects received 1 mg atropine. Plasma was sampled during the final 10 min of each infusion to determine steady state mivacurium concentrations and for 15 min after each infusion. Twitch tension was recorded. Mivacurium concentrations after each of the two infusions were compared. Results: After discontinuation of the second infusion, mivacurium concentrations were larger than those after the first infusion at 2 min with edrophonium and at 2, 4, and 7 min with neostigmine. With both neostigmine and edrophonium, twitch tension recovered after infusion #2 more rapidly than after infusion #1; however, the magnitude of this effect was small. Conclusion: Edrophonium transiently slows the rate at which mivacurium concentrations decrease; this is consistent with our previous findings. Neostigmine has a similar, although longer, effect. Despite altering mivacurium’s elimination characteristics, both drugs facilitate neuromuscular recovery, although their benefit is small.
Assay of serum cholinesterase with succinylcholine and propionylthiocholine as substrates.
Serum cholinesterase (E.C. 3.1.1.8) was assayed with succinylcholine as a substrate. The reaction was coupled with choline oxidase and peroxidase in the presence of 4-aminoantipyrine and phenol to produce a red quinone dye that was measured spectrophotometrically. The method requires 25 microliter of sample in a total volume of 1.0 ml. The mean activity for 35 adults of the usual genotype was 74.4 +/- 28 U/l (range 24-125 U/l). Succinylcholine-sensitive individuals had activities below 18 U/l. The same serum samples also were assayed with propionylthiocholine as a substrate. Activities with the two substrates showed a coefficient of correlation of 0.980 (n = 68). However, the method using propionylthiocholine showed more overlap between the activities of succinylcholine-sensitive and insensitive individuals. Assay with succinylcholine thus may offer a more effective method of screening for sensitive individuals, since some escape detection by conventional genotyping with dibucaine and fluoride.