title: Development of a method to measure free and bound ropivacaine in human plasma using equilibrium dialysis and hydrophilic interaction chromatography coupled to high resolution mass spectrometry.
abstract: The pharmacodynamics of absorption of local anaesthetics used during surgical procedures into tissues is governed by the amount of free drug in plasma. Toxicity may occur during continuous infusions if the levels of free drug become too high which may occur if the binding capacity of the α-1-acid glycoprotein present in plasma is exceeded. In order to monitor this a method was developed for the determination of the amount of free and bound ropivacaine in human plasma during knee and hip surgery. Rapid equilibrium dialysis units were used to separate free and bound drug then protein and buffer salts were removed by solvent precipitation. Analysis was carried out using a ZICHILIC HPLC column interfaced with an LTQ Orbitrap mass spectrometer. The following extracted ion ranges ([M+H](+)) were monitored: m/z 275.21-275.22 for ropivacaine and m/z 235.175-235.185 for lidocaine. The method was calibrated by spiking ropivacaine, and a fixed amount of lidocaine as internal standard, into plasma over the range 0.01-1.5 µg/ml. The equation of the line was y=0.886x±4.2% (n=2), forcing the curve through zero since blank plasma was free of the analyte. The values obtained for the accuracy and precision of the analysis of plasma spiked at 0.03 µg/ml and 1.5 µg/ml were 93.2%±2.8% and 95.4%±1.5% respectively (n=5). Repeat analysis of a patient sample for free and bound drug gave the following values for levels of ropivacaine: bound 1.63 µg/ml±1.48%, unbound 0.0671 µg/ml±1.68% (n=5).
authors.affiliation: Strathclyde Institute of Pharmaceutical and Biomedical Sciences, University of Strathclyde, 161 Cathedral Street, Glasgow G4 0RE, United Kingdom.
authors.forename: Muhammad
authors.initials: M
authors.lastname: Abbas
authors.forename: Lateef
authors.initials: L
authors.lastname: Ahmad
authors.forename: Yasar
authors.initials: Y
authors.lastname: Shah
authors.forename: Mike
authors.initials: M
authors.lastname: Gill
authors.forename: David G
authors.initials: DG
authors.lastname: Watson
mesh_terms: D000577:Amides / Q000097:blood* / Q000493:pharmacokinetics; D000779:Anesthetics, Local / Q000097:blood* / Q000493:pharmacokinetics; D019644:Arthroplasty, Replacement, Hip; D019645:Arthroplasty, Replacement, Knee; D002138:Calibration; D057785:Catheters; D002853:Chromatography, Liquid; D003956:Dialysis; D006801:Humans; D057927:Hydrophobic and Hydrophilic Interactions; D008012:Lidocaine / Q000097:blood* / Q000493:pharmacokinetics; D013058:Mass Spectrometry; D009961:Orosomucoid / Q000378:metabolism; D011485:Protein Binding; D015203:Reproducibility of Results; D000077212:Ropivacaine
chemical_list: D000577:Amides; D000779:Anesthetics, Local; D009961:Orosomucoid; D000077212:Ropivacaine; D008012:Lidocaine
keywords: Fourier transform mass spectrometry; Hydrophilic interaction chromatography; Rapid equilibrium dialysis; Ropivacaine