Pharmacokinetics and pharmacodynamics of l-methadone in isoflurane-anaesthetized and mechanically ventilated ponies

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

The enantioselectivity of the pharmacokinetics of methadone was investigated in anesthetized Shetland ponies after a single intravenous (0.5 mg/kg methadone hydrochloride; n = 6) or constant rate infusion (0.25 mg/kg bolus followed by 0.25 mg/kg/h methadone hydrochloride; n = 3) administration of racemic methadone. Plasma concentrations of l‐methadone and d‐methadone and their major metabolites, l‐ and d‐2‐ethylidene‐1,5‐dimethyl‐3,3‐diphenylpyrrolidine (EDDP), respectively, were analyzed by CE with highly sulfated γ‐cyclodextrin as chiral selector and electrokinetic analyte injection from liquid/liquid extracts prepared at alkaline pH. In both trials, the d‐methadone concentrations were lower than those of l‐methadone and the d‐EDDP levels were lower than those of L‐EDDP. For the case of a single intravenous bolus injection, the plasma concentration versus time profile of methadone enantiomers was analyzed with a two‐compartment pharmacokinetic model. l‐methadone showed a slower elimination rate constant, a lower body clearance, and a smaller steady‐state volume of distribution than d‐methadone. d‐methadone and d‐EDDP were eliminated faster than their respective l‐enantiomers. This is the first study that outlines that the disposition of racemic methadone administered to anesthetized equines is enantioselective.

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

The further development and application of capillary electromigration techniques for the enantioselective determination of drugs and their metabolites in body fluids, tissues, and in vitro preparations during the 2010 to 2020 time period continued to proof their usefulness and attractiveness in bioanalysis. This review discusses the principles and important aspects of capillary electrophoresis- based chiral drug bioassays, provides a survey of the assays reported during the past 10 years and presents an overview of the key achievements encountered in that time period. For systems with charged chiral selectors, special attention is paid on assays that feature field-amplified sample injection to enable the determination of ppb levels of analytes and optimized online incubation procedures for the rapid assessment of a metabolic pathway. Applications discussed encompass the pharmacokinetics of drug enantiomers in vivo and in vitro, the impact of inhibitors on metabolic steps, the elucidation of the stereoselectivity of drug metabolism in vivo and in vitro, and drug enantiomers in toxicological, forensic, and doping analysis.