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BACKGROUND Bupropion (BUP) is an antidepressant and its pharmacological activity is mediated by its major metabolite, hydroxybupropion (HBUP). We investigated the effects of genetic polymorphisms of CYP2B6 on BUP and HBUP to provide certain evidence on the clinical rational administration of BUP. MATERIAL AND METHODS Plasma BUP and HBUP concentrations were assayed using high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). RESULTS A total of 23 healthy volunteers (eleven participants with CYP2B6*1/*1, 7 participants with CYP2B6*1/*6, 3 participants with CYP2B6*4/*6, and 2 participants with CYP2B6*1/*4) received orally administered 150 mg of BUP according to protocol. Blood samples were obtained up to 96 hours after administration. The whole blood was subject to genotyping by polymerase chain reaction and restriction fragment length polymorphism (PCR-RFLP). The concentration-time curve (AUC(0→96)), maximum plasma concentration (Cmax), and terminal half-life (t1/2) values of BUP in CYP2B6*1/*4 were lower than those of CYP2B6*1/*1. By contrast, the time to Cmax (tmax) value of the former was higher than that of the latter. The HBUP AUC(0→96) values in CYP2B6*4/*6 and CYP2B6*1/*4 increased to values 1.12-fold and 1.98-fold, compared with CYP2B6*1/*1 carriers. However, the HBUP AUC(0→96) value in CYP2B6*1/*1 was 1.51-fold higher than that in CYP2B6*1/*6. Similarly, the HBUP Cmax values in CYP2B6*4/*6 and CYP2B6*1/*4 increased by 1.12-fold and 1.97-fold, whereas the HBUP Cmax value in CYP2B6*1/*6 decreased to a value 1.64-fold lower than that in CYP2B6*1/*1. CONCLUSIONS Genetic polymorphisms of CYP2B6 influence the pharmacokinetic parameters of BUP and HBUP and thus establish rational BUP administration for Chinese patients in clinical settings.

CYP2B subfamily accounts for 2-10% of total hepatic CYP450 enzymes and participate in the metabolism of around 8% of clinical drugs. Borneol has been widely used in traditional Chinese medicine for thousands of years. There are many studies about borneol-induced promoting penetration role for a number of drugs through various physiologic barriers, whereas there is no report involved the effect of borneol on hepatic CYP2B. The present work studied the in vivo effect of borneol on the expression and activity of rat hepatic CYP2B. The results indicated that the oral administration of borneol (33, 100 and 300 mg/kg/d) to rats for consecutive 7 days increased the hepatic CYP2B1/2 activity by 1.4-, 1.7- and 2.8-fold, hepatic CYP2B1 mRNA expression by 6.3-, 8.7- and 18.1-fold, and hepatic CYP2B1/2 protein expression by 1.2-, 1.9- and 2.6-fold, respectively compared to the control. Additionally, in the borneol pre-dosing (300 mg/kg/d for consecutive 7 days) rats, the increased Cl int and decreased AUC 0-24 of bupropion were observed as compared to the control. Moreover, there were no obvious effects on CAR protein level in rat liver microsome and nucleus following the borneol treatment. Taken together, our observations indicate that borneol is an in vivo inducer of rat hepatic CYP2B with different regulatory mechanism from phenobarbital-like inducers which caused CYP2B induction with CAR activation., (Copyright © 2016 Elsevier Ireland Ltd. All rights reserved.)

Bupropion sustained release is used to promote smoking cessation in males and nonpregnant females. However, its efficacy as a smoking cessation aid during pregnancy is not reported. The pregnancy-associated changes in maternal physiology may alter the pharmacokinetics and pharmacodynamics of bupropion and consequently its efficacy in pregnant smokers. Therefore, the aims of this study were to determine the steady-state pharmacokinetics of bupropion during pregnancy and the effect of functional genetic variants of CYP2B6 and CYP2C19 on bupropion pharmacokinetics in pregnant women. Plasma and urine concentrations of bupropion and its metabolites hydroxybupropion (OHBUP), threohydrobupropion, and erythrohydrobupropion were determined by liquid chromatography-mass spectrometry. Subjects were genotyped for five nonsynonymous single-nucleotide polymorphisms that result in seven CYP2B6 alleles, namely *2, *3, *4, *5, *6, *7, and *9, and for CYP2C19 variants *2, *3, and *17 The present study reports that the isoform-specific effect of pregnancy on bupropion-metabolizing enzymes along with the increase of renal elimination of the drug could collectively result in a slight decrease in exposure to bupropion in pregnancy. In contrast, pregnancy-induced increase in CYP2B6-catalyzed bupropion hydroxylation did not impact the plasma levels of OHBUP, probably due to a higher rate of OHBUP glucuronidation, and renal elimination associated with pregnancy. Therefore, exposure to OHBUP, a pharmacologically active metabolite of the bupropion, appears to be similar to that of the nonpregnant state. The predicted metabolic phenotypes of CYP2B6*6 and variant alleles of CYP2C19 in pregnancy are similar to those in the nonpregnant state., (Copyright © 2016 by The American Society for Pharmacology and Experimental Therapeutics.)

Bupropion is a widely used antidepressant, smoking cessation aid, and weight-loss therapy. It is administered as a racemic mixture, but the pharmacokinetics and activity of bupropion are stereoselective. The activity and side effects of bupropion are attributed to bupropion and its metabolites S,S- and R,R-OH-bupropion, threohydrobupropion, and erythrohydrobupropion. Yet the stereoselective metabolism in vitro and the enzymes contributing to the stereoselective disposition of bupropion have not been characterized. In humans, the fraction of bupropion metabolized (fm) to the CYP2B6 probe metabolite OH-bupropion is 5-16%, but ticlopidine increases bupropion exposure by 61%, suggesting a 40% CYP2B6 and/or CYP2C19 fm for bupropion. Yet, the CYP2C19 contribution to bupropion clearance has not been defined, and the enzymes contributing to overall bupropion metabolite formation have not been fully characterized. The aim of this study was to characterize the stereoselective metabolism of bupropion in vitro to explain the stereoselective pharmacokinetics and the effect of drug-drug interactions (DDIs) and CYP2C19 pharmacogenetics on bupropion exposure. The data predict that threohydrobupropion accounts for 50 and 82%, OH-bupropion for 34 and 12%, erythrohydrobupropion for 8 and 4%, and 4'-OH-bupropion for 8 and 2% of overall R- and S-bupropion clearance, respectively. The fm,CYP2B6 was predicted to be 21%, and the fm,CYP2C19, 6% for racemic bupropion. Importantly, ticlopidine was found to inhibit all metabolic pathways of bupropion in vitro, including threohydrobupropion, erythrohydrobupropion, and 4'OH-bupropion formation, explaining the in vivo DDI. The stereoselective pharmacokinetics of bupropion were quantitatively explained by the in vitro metabolic clearances and in vivo interconversion between bupropion stereoisomers., (Copyright © 2016 by The Author(s).)

Although CYP2B6 catalyzes the biotransformation of many drugs used clinically for children and adults, information regarding the effects of development on CYP2B6 expression and activity are scarce. Utilizing a large panel of human liver samples (201 donors: 24 fetal, 141 pediatric, and 36 adult), we quantified CYP2B6 mRNA and protein expression levels, characterized CYP2B6 (bupropion hydroxylase) activity in human liver microsomes (HLMs), and performed an extensive genotype analysis to differentiate CYP2B6 haplotypes such that the impact of genetic variation on these parameters could be assessed. Fetal livers contained extremely low levels of CYP2B6 mRNA relative to postnatal samples and fetal HLMs did not appear to catalyze bupropion hydroxylation; however, fetal CYP2B6 protein levels were not significantly different from postnatal levels. Considerable interindividual variation in CYP2B6 mRNA expression, protein levels, and activity was observed in postnatal HLMs (mRNA, ∼40,000-fold; protein, ∼300-fold; activity, ∼600-fold). The extremely wide range of interindividual variability in CYP2B6 expression and activity was significantly associated with age (P < 0.01) following log transformation of the data. Our data suggest that CYP2B6 activity appears as early as the first day of life, increases through infancy, and by 1 year of age, CYP2B6 levels and activity may approach those of adults. Surprisingly, CYP2B6 interindividual variability was not significantly associated with genetic variation in CYP2B6, nor was it associated with differences in gender or ethnicity, suggesting that factors other than these are largely responsible for the wide range of variability in CYP2B6 expression and activity observed among a large group of individuals/samples., (Copyright © 2016 by The American Society for Pharmacology and Experimental Therapeutics.)

Administration of bupropion [(±)-2-(tert-butylamino)-1-(3-chlorophenyl)propan-1-one] and its preformed active metabolite, hydroxybupropion [(±)-1-(3-chlorophenyl)-2-[(1-hydroxy-2-methyl-2-propanyl)amino]-1-propanone], to rats with measurement of unbound concentrations by quantitative microdialysis sampling of plasma and brain extracellular fluid was used to develop a compartmental pharmacokinetics model to describe the blood-brain barrier transport of both substances. The population model revealed rapid equilibration of both entities across the blood-brain barrier, with resultant steady-state brain extracellular fluid/plasma unbound concentration ratio estimates of 1.9 and 1.7 for bupropion and hydroxybupropion, respectively, which is thus indicative of a net uptake asymmetry. An overshoot of the brain extracellular fluid/plasma unbound concentration ratio at early time points was observed with bupropion; this was modeled as a time-dependent uptake clearance of the drug across the blood-brain barrier. Translation of the model was used to predict bupropion and hydroxybupropion exposure in human brain extracellular fluid after twice-daily administration of 150 mg bupropion. Predicted concentrations indicate that preferential inhibition of the dopamine and norepinephrine transporters by the metabolite, with little to no contribution by bupropion, would be expected at this therapeutic dose. Therefore, these results extend nuclear imaging studies on dopamine transporter occupancy and suggest that inhibition of both transporters contributes significantly to bupropion's therapeutic efficacy., (Copyright © 2016 by The American Society for Pharmacology and Experimental Therapeutics.)

Knowledge about the cytochrome P450 (CYP) inhibition potential of new drug candidates is important for drug development because of its risk of interactions. For novel psychoactive substances (NPS), corresponding data are not available. For developing a general drug inhibition cocktail assay, a liquid-chromatography high-resolution tandem mass spectrometry multi-analyte approach was developed and validated for quantifying low concentrations of O-diethyl phenacetin for CYP 1A2, 7-hydroxy coumarin for CYP 2A6, 4-hydroxy bupropion for CYP 2B6, N-diethyl amodiaquine for CYP 2C8, 4-hydroxy diclofenac for CYP 2C9, 5-hydroxy omeprazole for CYP 2C19, O-dimethyl dextromethorphan for CYP 2D6, 6-hydroxy chlorzoxazone for CYP 2E1, and 6-beta-hydroxy testosterone for CYP 3A in the incubation mixture in the presence of substrates and inhibitors. The tested matrix effects ranged from 63 to 141 % and the recoveries from 95 to 110 %. Time-saving one-point calibration allowed sufficient quantification, although some of the validation results for 7-hydroxy coumarin, 4-hydroxy bupropion, 4-hydroxy diclofenac, and 6-beta-hydroxy testosterone were outside the acceptance criteria (AC) but without influence of the IC50 calculation. Validation showed also that the approach was sensitive and selective using mass spectral multiplexing. In conclusion, the presented assay was suitable for the quantification of the model substrate metabolites and could be used for the development of a CYP inhibition assay for testing most CYPs and a wide range of drugs of abuse.

Bupropion is widely used as an antidepressant drug and also as a smoking cessation aid. In humans, this drug is extensively metabolized to form several metabolites. Oxidised hydroxybupropion and two reduced metabolites, threohydrobupropion and erythrohydrobupropion, are major metabolites. All of these metabolites are considered to be active. Although the oxidative metabolic pathway and the central role of CYP2B6 are known, the enzymes that participate in the reduction have not been identified to date. The aim of this study was to confirm the role of human liver subcellular fractions in the metabolism of bupropion and elucidate the contribution of particular carbonyl-reducing enzymes. An HPLC method for the determination of bupropion metabolites was utilised. Bupropion is reduced to threohydrobupropion and less to erythrohydrobupropion in human liver cytosol, microsomes and also mitochondria. Surprisingly, intrinsic clearance for formation of both metabolites is the highest in mitochondrial fraction. Moreover this study provides the first direct evidence that 11β-hydroxysteroid dehydrogenase 1, AKR1C1, AKR1C2, AKR1C3 and CBR1 participate in the reducing biotransformation of bupropion in vitro. The enzyme kinetics of all of these reductases was investigated and kinetic parameters were calculated.

Unlabelled: This study investigated the effects of pregnane X receptor (PXR/NR1I2) and CYP2B6 genetic variants on sodium ferulate (SF)-mediated induction of bupropion hydroxylation. The pharmacokinetics of bupropion and hydroxybupropion were evaluated after an oral dose of bupropion (150 mg) administered with and without SF pretreatment for 14 days in 33 healthy subjects. The area under the time-concentration curve (AUC) ratio of AUC&#95;hyd (AUC(0-∞) of hydroxybupropion)/AUC&#95;bup (AUC(0-∞) of bupropion) represents the CYP2B6 hydroxylation activity, which was significantly lower in CYP2B6*6 carriers (NR1I2 TGT noncarriers or carriers) than in noncarriers in both the basal and SF-induced states (p-value<0.05). AUC ratio and AUC&#95;hyd of NR1I2 -24113AA variant were markedly lower than GA and GG genotypes (7.5±2.1 versus 14.5±3.3 and 20.6±1.1, and 8873±1431 versus 14,504±2218 and 17,586±1046) in the induced states. However, -24020(-)/(-) variant didn't show significant difference in the induction of CYP2B6 hydroxylation activity by SF compared with other -24020[GAGAAG]/(-) genotypes. NR1I2 TGT haplotype (-25385T+g.7635G+g.8055T) carriers exhibited a significantly decreased AUC ratio, compared with TGT noncarriers, in the basal states (7.6±1.0 versus 9.7±1.0), while this result wasn't observed in CYP2B6*6 noncarriers. Moreover, individuals with complete mutation-type [CYP2B6*6/*6+NR1I2 TGT+ -24113AA+ -24020 (-)/(-)] showed even lower percent difference of AUC ratio (8.7±1.2 versus 39.5±8.2) than those with complete wild-type. In conclusion, it is suggested that NR1I2 variants decrease the bupropion hydroxylation induced by SF treatment, particularly in CYP2B6*6 carriers., Trial Registration: ChiCTR.org ChiCTR-TRC-11001285.

What Is Already Known About This Subject: Woohwangcheongsimwon suspension has traditionally been used for the treatment and prevention of stroke, hypertension, palpitations, convulsions and unconsciousness in various Asian countries. Woohwangcheongsimwon suspensions showed an inhibitory effect on CYP2B6 activity in vitro. Two terpenoids, borneol and isoborneol, are major constituents of woohwangcheongsimwon suspension, and show a competitive inhibition of CYP2B6 with K(i) values of 9.5 and 5.9 microM, respectively. Bupropion undergoes metabolic transformation to the active metabolite, 4-hydroxybupropion, primarily via CYP2B6 both in vivo and in vitro. It is often used as a CYP2B6 substrate for clinical drug-drug interaction studies. Drug interactions may occur between woohwangcheongsimwon suspension and bupropion., What This Study Adds: Co-administration with woohwangcheongsimwon suspension did not alter the pharmacokinetics of bupropion or its metabolite, 4-hydroxybupropion. Dosage adjustment of bupropion is unnecessary in patients concomitantly administered the highest recommended daily dose of woohwangcheongsimwon suspension., Aims: To examine the effects of woohwangcheongsimwon suspension on the pharmacokinetics of bupropion and its active metabolite, 4-hydroxybupropion, formed via CYP2B6 in vivo., Methods: A two-way crossover clinical trial with a 2 week washout period was conducted in 14 healthy volunteers. In phases I and II, subjects received 150 mg bupropion with or without woohwangcheongsimwon suspension four times (at -0.17, 3.5, 23.5 and 47.5 h, with the time of bupropion administration taken as 0 h) in a randomized balanced crossover order. Bupropion and 4-hydroxybupropion plasma concentrations were measured for up to 72 h by LC-MS/MS. Urine was collected up to 24 h to calculate the renal clearance. In addition, the CYP2B6*6 genotype was also analyzed., Results: The geometric mean ratios and 90% confidence interval of bupropion with woohwangcheongsimwon suspension relative to bupropion alone were 0.976 (0.917, 1.04) for AUC(0,infinity) and 0.948 (0.830,1.08) for C(max), respectively. The corresponding values for 4-hydroxybupropion were 0.856 (0.802, 0.912) and 0.845 (0.782, 0.914), respectively. The t(max) values of bupropion and 4-hydroxybupropion were not significantly different between the two groups (P > 0.05). The pharmacokinetic parameters of bupropion and 4-hydroxybupropion were unaffected by woohwangcheongsimwon suspension., Conclusions: These results indicate that woohwangcheongsimwon suspension has a negligible effect on the disposition of a single dose of bupropion in vivo. As a result, temporary co-administration with woohwangcheongsimwon suspension does not seem to require a dosage adjustment of bupropion.

A selective and sensitive ultra-performance liquid chromatography (UPLC)-electrospray ionization-tandem mass spectrometry (MS) method for simultaneous determination of bupropion and its main metabolites, hydroxybupropion, erythrohydrobupropion, and threohydrobupropion, in human whole blood is presented. The sample preparation consists of cleanup protein precipitation with methanol combined with a solid-phase extraction on Oasis HLB cartridges. Analytes were separated on a Waters Acquity UPLC((R)) BEH phenyl column using a binary mobile phase consisting of ammonium formate buffer (2 mM, pH 4) and acetonitrile. Detection was performed on a Waters Acquity UPLC system coupled to a Quattro Premier triple-quadrupole MS in positive ion selected reaction monitoring. Internal standards were bupropion-d(9) and hydroxybupropion-d(6). Linearity was from 5 to 1000 ng/mL for bupropion and from 10 to 2000 ng/mL for metabolites. Accuracy profiles (80-120%), precision (< 15%), and limits of detection (1 ng/mL for bupropion and 2 ng/mL for metabolites) were also evaluated and responded to all criteria of validation. The aim of this study was to compare this presented method with a previously described method developed on a classic liquid chromatography-tandem MS system.

Aims: To assess the effects of Ginkgo biloba extract on the pharmacokinetics of bupropion in healthy volunteers., Methods: Fourteen healthy male volunteers (age range 19-25 years) received orally administered bupropion (150 mg) alone and during treatment with G. biloba 240 mg day(-1) (two 60-mg capsules taken twice daily) for 14 days. Serial blood samples were obtained over 72 h after each bupropion dose, and used to derive pharmacokinetic parameters of bupropion and its CYP2B6-catalysed metabolite, hydroxybupropion., Results: Ginkgo biloba extract administration resulted in no significant effects on the AUC(0-infinity) of bupropion and hydroxybupropion. Bupropion mean AUC(0-infinity) value was 1.4 microg.h ml(-1)[95% confidence interval (CI) 1.2, 1.6] prior to G. biloba treatment and 1.2 microg.h ml(-1) (95% CI 1.1, 1.4) after 14 days of treatment. Hydroxybupropion mean AUC(0-infinity) value was 8.2 microg.h ml(-1) (95% CI 6.5, 10.4) before G. biloba administration and 8.7 microg.h ml(-1) (95% CI 7.1, 10.6) after treatment. The C(max) of hydroxybupropion increased from 221.8 ng ml(-1) (95% CI 176.6, 278.6) to 272.7 ng ml(-1) (95% CI 215.0, 345.8) (P = 0.038) and the t(1/2) of hydroxybupropion fell from 25.0 h (95% CI 22.7, 27.5) to 21.9 h (95% CI 19.9, 24.1) (P = 0.000)., Conclusions: Ginkgo biloba extract administration for 14 days does not significantly alter the basic pharmacokinetic parameters of bupropion in healthy volunteers. Although G. biloba extract treatment appears to reduce significantly the t(1/2) and increase the C(max) of hydroxybupropion, no bupropion dose adjustments appear warranted when the drug is administered orally with G. biloba extract, due to the lack of significant change observed in AUC for either bupropion or hydroxybupropion.

Objective: To characterize the effect of efavirenz on bupropion hydroxylation as a marker of cytochrome P450 (CYP) 2B6 activity in healthy subjects., Methods: Thirteen subjects received a single oral dose of bupropion SR 150 mg before and after 2 weeks of efavirenz administration for comparison of bupropion and hydroxybupropion pharmacokinetics. Efavirenz plasma concentrations were also assessed. Subjects were genotyped for CYP2B6 (G516T, C1459T, and A785G), CYP3A4 (A-392G), CYP3A5 (A6986G), and multidrug resistance protein 1 (C3435T)., Results: The area under the concentration vs. time curve ratio of hydroxybupropion:bupropion increased 2.3-fold after efavirenz administration (P=0.0001). Bupropion area under the concentration vs. time curve and Cmax decreased by 55% and 34%, respectively (P<0.002). None of the CYP2B6 or CYP3A genotypes evaluated were associated with a difference in bupropion or efavirenz clearance. The 2 individuals homozygous for multidrug resistance protein 1 3435-T/T had 2.5- and 1.8-fold greater bupropion and efavirenz clearance, respectively, relative to C/C and C/T individuals (P<0.05)., Conclusions: Our results confirm that efavirenz induces CYP2B6 enzyme activity in vivo, as demonstrated by an increase in bupropion hydroxylation after 2 weeks of efavirenz administration.

Ritonavir is the most potent and efficacious inhibitor of cytochrome P4503A (CYP3A), and it is used accordingly for the pharmacoenhancement of other antiretrovirals. Paradoxically, ritonavir induces the clinical metabolism and clearance of many drugs. The mechanism by which ritonavir inhibits and induces clinical drug metabolism is unknown. Ritonavir induces CYP2B6 in human hepatocytes. This investigation tested the hypothesis that ritonavir induces human CYP2B6 in vivo. Thirteen healthy human immunodeficiency virus-negative volunteers underwent a three-way sequential crossover protocol, receiving racemic bupropion after nothing (control), 3 days of treatment with ritonavir, and 2.5 weeks of treatment with ritonavir (400 mg twice a day). Stereoselective bupropion hydroxylation was used as an in vivo probe for CYP2B6 activity. Plasma and urine (R)- and (S)-bupropion and (R,R)- and (S,S)-hydroxybupropion concentrations were measured by liquid chromatography-mass spectrometry. Racemic, (R)-, and (S)-bupropion plasma ratios of the area under the concentration-time curve from 0 h to infinity (AUC(0-infinity)) (ritonavir/control) were significantly reduced to 0.84, 0.86, and 0.80, respectively, after 3 days of ritonavir treatment and to 0.67, 0.69, and 0.60 after steady-state ritonavir treatment. Apparent oral clearances for racemic, (R)-, and (S)-bupropion all were significantly increased by 1.2-fold after 3 days of ritonavir treatment and by 1.4-, 1.7-, and 1.5-fold after steady-state ritonavir treatment. The plasma (S,S)-hydroxybupropion/(S)-bupropion AUC(0-72) ratio was significantly increased by ritonavir. Formation clearances of both (R,R)- and (S,S)-hydroxybupropion were increased 1.8-fold after 3 days of ritonavir treatment and 2.1-fold after steady-state ritonavir treatment. These results show that ritonavir induces human CYP2B6 activity. Induction is rapid, occurring after only 3 days of ritonavir, and is sustained for at least 2 weeks. The ritonavir induction of CYP2B6 activity may have significant implications for drug interactions and clarify previously unexplained interactions.