Browsing by Subject "Stereoselective"

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    Stereoselective disposition of bupropion and its three major metabolites : 4-hydroxybupropion, erythro-dihydrobupropion, and threo-dihydrobupropion
    (2016-02-14) Masters, Andrea Renee; Jones, David R.; Desta, Zeruesenay; Zhang, Jian-Ting
    Bupropion is a dual dopamine-norepinephrine uptake inhibitor and a nicotine receptor antagonist. Clinically, bupropion is given as a racemate for the management of depression, smoking cessation aid, and for the management of weight. Bupropion has also been targeted as a phenotypic probe of CYP2B6 activity. Bupropion metabolites are formed via oxidation (4-hydroxybupropion) through CYP2B6, and reduction (erythro- and threo-dihydrobupropion) through carbonyl reductases. These metabolites exhibit pharmacological activity, but little is known regarding their stereoselective disposition due to the lack of a chiral assay. A novel reversed phase chiral-HPLC-MS/MS method involving a simple liquid-liquid extraction procedure and a small plasma sample volume (50µL) was developed that allowed simultaneous separation and quantification of enantiomers of bupropion, 4-hydroxybupropion, and those of threo- and erythro-dihydrobupropion in human plasma. This method was successfully implemented to determine the unique stereoselective disposition of bupropion and its metabolites in 15 human volunteers administered a single 100 mg oral dose of racemic bupropion. Significant differences (p<0.05) in the stereoselective metabolism were observed for all of the enantiomers. The highest plasma exposure (AUC0-∞) was (2R, 3R)-4-hydoxybupropion, almost 65 fold higher, than (2S, 3S)-4-hydoxybupropion, and over 32 fold greater than the parent R-bupropion. The second highest plasma exposure was threo-dihydrobupropion A, which was almost 5 fold higher than threo-dihydrobupropion B. (Nomenclature of the enantiomers for erythro- and threo-dihydrobupropion was based on the chromatography of the first eluting peak as “A” and the second eluting peak as “B”.) Threo-dihydrobupropion A and B showed the most significant difference between the racemic and enantiomer profiles. Although the AUC was greater for threo-dihydrobupropion B, threo-dihydrobupropion A had a significantly (p<0.05) higher Cmax. The half-life for threo-dihydrobupropion A and erythro-dihydrobupropion A were the longest for all analytes, which could indicate accumulation in multiple dosing. The importance of this study was, for the first time, to be able to characterize the stereoselective metabolism of bupropion and its three major metabolites. This new method and subsequent pharmacokinetic data should enhance further research into bupropion stereoselective metabolism, drug interactions, and effect.
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    Stereoselective method to quantify bupropion and its three major metabolites, hydroxybupropion, erythro-dihydrobupropion, and threo-dihydrobupropion using HPLC-MS/MS
    (Elsevier, 2016-03-15) Masters, Andrea R.; McCoy, Michael; Jones, David R.; Desta, Zeruesenay; Department of Medicine, IU School of Medicine
    Bupropion metabolites formed via oxidation and reduction exhibit pharmacological activity, but little is known regarding their stereoselective disposition. A novel stereoselective liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed to separate and quantify enantiomers of bupropion, 4-hydroxybupropion, and erythro- and threo-dihydrobupropion. Liquid-liquid extraction was implemented to extract all analytes from 50 μL human plasma. Acetaminophen (APAP) was used as an internal standard. The analytes were separated on a Lux 3 μ Cellulose-3 250×4.6 mm column by methanol: acetonitrile: ammonium bicarbonate: ammonium hydroxide gradient elution and monitored using an ABSciex 5500 QTRAP triple-quadrupole mass spectrometer equipped with electrospray ionization probe in positive mode. Extraction efficiency for all analytes was ≥70%. The stability at a single non-extracted concentration for over 48 h at ambient temperature resulted in less than 9.8% variability for all analytes. The limit of quantification (LOQ) for enantiomers of bupropion and 4-hydroxybupropion was 0.3 ng/mL, while the LOQ for enantiomers of erythro- and threo-hydrobupropion was 0.15 ng/mL. The intra-day precision and accuracy estimates for enantiomers of bupropion and its metabolites ranged from 3.4% to 15.4% and from 80.6% to 97.8%, respectively, while the inter-day precision and accuracy ranged from 6.1% to 19.9% and from 88.5% to 99.9%, respectively. The current method was successfully implemented to determine the stereoselective pharmacokinetics of bupropion and its metabolites in 3 healthy volunteers administered a single 100mg oral dose of racemic bupropion. This novel, accurate, and precise HPLC-MS/MS method should enhance further research into bupropion stereoselective metabolism and drug interactions.