Enantioselective capillary electrophoresis for pharmacokinetic analysis of methadone and 2‐ethylidene‐1,5‐dimethyl‐3,3‐diphenylpyrrolidine in equines anesthetized with ketamine and isoflurane

Abstract

An enantioselective assay for the determination of methadone and its main metabolite 2‐ethylidene‐1,5‐dimethyl‐3,3‐diphenylpyrrolidine in equine plasma based on capillary electrophoresis with highly sulfated γ‐cyclodextrin as chiral selector and electrokinetic analyte injection is described. The assay is based on liquid/liquid extraction of the analytes at alkaline pH from 0.1 mL plasma followed by electrokinetic sample injection of the analytes from the extract across a buffer plug without chiral selector. Separation occurs cationically at normal polarity in a pH 3 phosphate buffer containing 0.16% (w/v) of highly sulfated γ‐cyclodextrin. The developed assay is precise (intra‐ and interday RSD < 4% and < 7%, respectively), is capable to determine enantiomer levels of methadone and 2‐ethylidene‐1,5‐dimethyl‐3,3‐diphenylpyrrolidine in plasma down to 2.5 ng/mL, and was successfully applied to monitor enantiomer drug and metabolite levels in plasma of a pony that was anesthetized with racemic ketamine and isoflurane and received a bolus of racemic methadone and a bolus followed by constant rate infusion of racemic methadone. The data suggest that the assay is well suited for pharmacokinetic purposes.

Antinociceptive effects of levomethadone in standing horses sedated with romifidine

“…Plasma concentrations of levomethadone and romifidine were determined by capillary electrophoresis. This method was a modification of assays described for the enantioselective determination of ketamine and its metabolites (Theurillat et al 2016) and methadone and its main metabolite (Theurillat et al 2019) in plasma. In order to be able to monitor romifidine, methadone and its main metabolite in one assay, the amount of highly sulfated γ-cyclodextrin in the pH 3.0 running buffer had to be lowered to 0.14 % (Diez Bernal et al 2019).…”

Bioanalysis of drugs and their metabolites by chiral electromigration techniques (2010–2020)

“…As in the previous decade, there are again a number of CE‐based investigations that dealt with the elucidation of the pharmacokinetics via analysis of the drug or metabolite enantiomers in plasma (Table 2). Examples studied included the drugs ibuprofen [51], mirtazapine [52], ketamine [45,53], chlorpheniramine [54], brompheniramine [55], methadone [56], and S ‐ketamine [57]. Three of the used assays are capable of measuring simultaneously the enantiomers of the parent compound and two or three chiral metabolites and many assays use FASI or CSEI of the analytes from the plasma extracts to enable the determination of ppb blood levels of the compounds of interest.…”

“…The work described revealed stereoselectivities of the investigated metabolic pathways, including the demethylation of mirtazapine [52] and the conversion of methadone to 2‐ethylidene‐1,5‐dimethyl‐3,3‐diphenylpyrrolidine (EDDP) in equines under isoflurane anesthesia [56]. In the latter work, R‐methadone (also referred to as l ‐methadone) plasma levels were found to be larger than those of S‐methadone ( d ‐methadone) and R‐EDDP ( l ‐EDDP) concentrations were higher than those of S‐EDDP ( d ‐EDDP).…”

Stereoselective methadone disposition after administration of racemic methadone to anesthetized Shetland ponies assessed by capillary electrophoresis

“…Enantiospecific analysis by CE has been found to be an attractive tool to investigate the stereoselectivity of drug disposition, metabolism, and pharmacokinetics [ 14 , 15 , 16 , 17 , 18 ]. Recently, we described an enantioselective assay for the determination of ppb enantiomer levels of methadone and EDDP in equine plasma based on CE with highly sulfated γ‐cyclodextrin as chiral selector and electrokinetic analyte injection [ 19 ]. Its format is similar to that developed for the enantiomers of methadone in human plasma [ 20 ] and to that for ketamine and its metabolites in canine plasma [ 21 ].…”

“…Lower LOQ of the enantiomers of methadone and EDDP were 25 and 5 ng/mL, respectively. Intra‐ and interday precisions for the determined compound concentrations were <4% ( n = 6) and <7% ( n = 6), respectively [ 19 ].…”