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

The research article is about the development of an accurate assay for determining levels of methadone and its metabolite within the plasma of horses. The assay was successfully tested in a matter involving an anesthetized pony.

Research Objective

• The study aimed to develop an enantioselective assay that can accurately determine the concentrations of methadone and its main metabolite, 2-ethylidene-1,5-dimethyl-3,3-diphenylpyrrolidine, in equine plasma.

Methodology

• There were several steps involved in performing the assay. First, a capillary electrophoresis with highly sulfated γ-cyclodextrin as a chiral selector and electrokinetic analyte injection was utilized.
• The next step involved extracting the analytes from 0.1 mL of equine plasma at alkaline pH.
• Then, an electrokinetic sample injection of the analytes was performed from the extract across a buffer plug without a chiral selector.
• The separation of the analytes occurred cationically at normal polarity in a pH 3 phosphate buffer containing 0.16% (w/v) of highly sulfated γ-cyclodextrin.

Results

• The developed assay showed precision, with intra- and interday Relative Standard Deviation (RSD) being less than 4% and 7% respectively.
• The assay demonstrated the ability to determine enantiomer levels of methadone and 2-ethylidene-1,5-dimethyl-3,3-diphenylpyrrolidine in plasma down to 2.5 ng/mL.
• The assay was successfully applied to monitor levels of the drug and metabolite in the plasma of an anesthetized pony. The pony 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.

Conclusions

• The researchers concluded that the developed assay is well suited for pharmacokinetic purposes, suggesting it could be used for measuring the presence and concentration of methadone and its metabolite in equine plasma.