Subtherapeutic bupropion and hydroxybupropion serum concentrations in a patient with CYP2C19*1/*17 genotype suggesting a rapid metabolizer status.

Bupropion is hydroxylated to its primary active metabolite hydroxybupropion by cytochrome P450 enzyme CYP2B6. In vitro data suggest the existence of alternative hydroxylation pathways mediated by the highly polymorphic enzyme CYP2C19. However, the impact of its genetic variants on bupropion metabolism in vivo is still under investigation. We report the case of a 28-year-old male Caucasian outpatient suffering from major depressive disorder who did not respond to a treatment with bupropion. Therapeutic drug monitoring revealed very low serum concentrations of both bupropion and hydroxybupropion. Genotyping identified a heterozygous status for the gain-of-function allele with the genotype CYP2C19*1/*17 predicting enhanced enzymatic activity. The present case shows a reduced bupropion efficacy, which may be explained by a reduced active moiety of bupropion and its active metabolite hydroxybupropion, due to alternative hydroxylation pathways mediated by CYP2C19 in an individual with CYP2C19 rapid metabolizer status. The case report thus illustrates the clinical relevance of therapeutic drug monitoring in combination with pharmacogenetics diagnostics for a personalized treatment approach.

Determination of hydroxybupropion in human serum for routine therapeutic drug monitoring in psychiatry: A tool for dose-individualization in treatment with bupropion.

Therapeutic drug monitoring (TDM) has become a clinical routine in psychiatry. Nevertheless, for bupropion there is only one method available that is suitable for routine use. However, it involves a complex sample clean-up. Owing to the instability of bupropion in serum, the main and active metabolite hydroxybupropion was chosen as the target substance. Therefore, a simple and robust high-performance liquid chromatography method for the quantification of hydroxybupropion in serum was developed and validated. A volume of 30 µL serum was used for easy sample clean-up, based on protein precipitation with acetonitrile followed by online solid-phase extraction. As hydroxybupropion was present in high serum concentrations, UV detection was possible. Owing to the commonly available instrumentation, the method could easily be integrated in routine TDM. The newly developed method was validated following the guidelines for bioanalytical method validation of the European Medicines Agency and US Food and Drug Administration. The lower limit of quantification was 100 ng/mL (0.391 µm) and linearity was shown between 100 and 2500 ng/mL. Intraday and interday precision ranged from 1.17 to 6.79% and from 6.07 to 9.41%, respectively. Intraday and interday accuracy ranged from 89.97 to 110.86% and from 95.05 to 101.2%. The method was shown to be selective, accurate and precise. Additionally, the method was successfully implemented in the therapeutic drug monitoring laboratory of the Department of Psychiatry, Psychosomatics and Psychotherapy at the University Hospital of Würzburg, Germany. Six months of routine analysis showed a rather low correlation between applied dose and serum concentration and therefore the necessity of TDM for dose-individualization in the treatment with bupropion.

Effects of Genetic Polymorphisms of CYP2B6 on the Pharmacokinetics of Bupropion and Hydroxybupropion in Healthy Chinese Subjects.

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.

Chiral Plasma Pharmacokinetics and Urinary Excretion of Bupropion and Metabolites in Healthy Volunteers.

Bupropion, widely used as an antidepressant and smoking cessation aid, undergoes complex metabolism to yield numerous metabolites with unique disposition, effect, and drug-drug interactions (DDIs) in humans. The stereoselective plasma and urinary pharmacokinetics of bupropion and its metabolites were evaluated to understand their potential contributions to bupropion effects. Healthy human volunteers (n = 15) were administered a single oral dose of racemic bupropion (100 mg), which was followed by collection of plasma and urine samples and determination of bupropion and metabolite concentrations using novel liquid chromatography-tandem mass spectrometry assays. Time-dependent, elimination rate-limited, stereoselective pharmacokinetics were observed for all bupropion metabolites. Area under the plasma concentration-time curve from zero to infinity ratios were on average approximately 65, 6, 6, and 4 and Cmax ratios were approximately 35, 6, 3, and 0.5 for (2R,3R)-/(2S,3S)-hydroxybupropion, R-/S-bupropion, (1S,2R)-/(1R,2S)-erythrohydrobupropion, and (1R,2R)-/(1S,2S)-threohydrobupropion, respectively. The R-/S-bupropion and (1R,2R)-/(1S,2S)-threohydrobupropion ratios are likely indicative of higher presystemic metabolism of S- versus R-bupropion by carbonyl reductases. Interestingly, the apparent renal clearance of (2S,3S)-hydroxybupropion was almost 10-fold higher than that of (2R,3R)-hydroxybupropion. The prediction of steady-state pharmacokinetics demonstrated differential stereospecific accumulation [partial area under the plasma concentration-time curve after the final simulated bupropion dose (300-312 hours) from 185 to 37,447 nM⋅h] and elimination [terminal half-life of approximately 7-46 hours] of bupropion metabolites, which may explain observed stereoselective differences in bupropion effect and DDI risk with CYP2D6 at steady state. Further elucidation of bupropion and metabolite disposition suggests that bupropion is not a reliable in vivo marker of CYP2B6 activity. In summary, to our knowledge, this is the first comprehensive report to provide novel insight into mechanisms underlying bupropion disposition by detailing the stereoselective pharmacokinetics of individual bupropion metabolites, which will enhance clinical understanding of bupropion's effects and DDIs with CYP2D6.

Bupropion therapy during pregnancy: the drug and its major metabolites in umbilical cord plasma and amniotic fluid.

BACKGROUND: Bupropion is used for treatment of depression during pregnancy. However, its use as a smoking cessation aid for pregnant women is currently under evaluation. OBJECTIVE: The aim of this opportunistic study was to investigate the transfer of bupropion and its major pharmacologically active metabolites, hydroxybupropion and threohydrobupropion, across the placenta in vivo. In addition, the concentrations of the drug and its metabolites were determined in the amniotic fluid. STUDY DESIGN: The following samples were collected at deliveries from 22 women taking bupropion: maternal blood (n = 22), umbilical cord venous blood (n = 22), and amniotic fluid (n = 9). The concentrations of the drug and its metabolites in blood plasma and amniotic fluid were determined by means of liquid chromatography-mass spectrometry. Placental passage was calculated as a ratio of umbilical cord venous plasma to maternal plasma concentrations. RESULTS: The levels of hydroxybupropion and threohydrobupropion in umbilical cord venous plasma were invariably lower than their corresponding concentrations in maternal plasma. The concentrations of bupropion in umbilical cord plasma were lower than in maternal plasma in the majority of the maternal-cord blood pairs. The median values of the umbilical cord venous plasma to maternal plasma ratios were: bupropion, 0.53 (interquartile range 0.35, n = 18), hydroxybupropion, 0.21 (interquartile range 0.12, n = 18), and threohydrobupropion, 0.61 (interquartile range 0.11, n = 21). In umbilical cord venous plasma, the median concentration of bupropion was 5.3 ng/mL; hydroxybupropion, 103.6 ng/mL; and threohydrobupropion, 59.6 ng/mL. Bupropion and its metabolites were detectable in the amniotic fluid but the concentrations of threohydrobupropion were higher than those in the corresponding umbilical cord venous plasma. CONCLUSION: Bupropion and its active metabolites cross the placenta to the fetal circulation. The concentrations of hydroxybupropion and threohydrobupropion in umbilical cord venous plasma were higher than bupropion concentrations suggesting a higher fetal exposure to the metabolites than the parent drug. The higher levels of threohydrobupropion in the amniotic fluid than those in umbilical cord venous plasma suggest that enzymes involved in the metabolism of bupropion to threohydrobupropion are most likely active in the fetus. The biological consequences of fetal exposure to maternally administered bupropion and/or its active metabolites via placental transfer and recirculation of the amniotic fluid are yet to be determined.

The P450 oxidoreductase (POR) rs2868177 and cytochrome P450 (CYP) 2B6*6 polymorphisms contribute to the interindividual variability in human CYP2B6 activity.

AIM: To investigate whether single-nucleotide polymorphisms (SNPs) in the P450 oxidoreductase (POR) gene were correlated with interindividual variations in cytochrome P450 (CYP) 2B6 activity. METHODS: Thirty-six healthy volunteers who tested CYP2B6 and POR polymorphisms were enrolled in the study. CYP2B6 activity was measured by bupropion hydroxylation with LC/MS/MS. The ratio of hydroxybupropion versus bupropion (AUC_hyd/AUC_bup) in terms of area under the time-concentration curve (AUC) was used to represent the CYP2B6 activity. RESULTS: The volunteers carrying CYP2B6*1/*1 showed a significantly higher mean AUC_hyd/ AUC_bup than those CYP2B6*1/*6 and CYP2B6*6/*6 variants (15.66 ± 1.65 vs. 9.25 ± 1.92, P = 0.008 and 15.66 ± 1.65 vs. 8.21 ± 1.74, P = 0.006, respectively). POR rs2868177 (6593 A > G) AA homozygotes showed a significantly lower mean AUC_hyd/ AUC_bup than that of POR rs2868177 AG heterozygotes or GG homozygotes (8.13 ± 1.37 vs. 12.15 ± 2.97, P = 0.005 and 8.13 ± 1.37 vs. 17.59 ± 3.25, P = 0.001, respectively). Moreover, POR rs2868177 AG heterozygotes and GG homozygotes showed a significantly increased mean AUC_hyd/AUC_bup than AA homozygotes in the CYP2B6*1/*1 and CYP2B6*6 carriers (16.40 ± 2.01 vs. 12.40 ± 1.45, P = 0.006 and 10.65 ± 1.47 vs. 6.54 ± 1.25, P = 0.004, respectively). Meanwhile, a strong correlation between the genetic variations (POR rs2868177 and CYP2B6*6) and AUC_hyd/ AUC_bup was found (P = 0.009 and P = 0.001, respectively). There was no significant difference in the mean AUC_hyd/AUC_bup among different POR *28 genotypes (P > 0.05). CONCLUSION: POR rs2868177 and CYP2B6*6 variants contribute to the interindividual variability in human CYP2B6 activity, which may affect the disposition and interaction of other CYP2B6 substrate drugs.

Assessment of a Potential Pharmacokinetic Interaction between Nebivolol and Bupropion in Healthy Volunteers.

BACKGROUND/AIMS: The study aimed at investigating the effects of multiple-dose bupropion (potent inhibitor of CYP2D6) on the pharmacokinetics (PKs) of single-dose nebivolol (CYP2D6 substrate) and to evaluate the clinical relevance of this potential drug interaction. METHODS: This open-label, nonrandomized clinical study had a 2-period design: during period 1 (reference), a single dose of 5 mg nebivolol was administered, while during period 2 (test), 5 mg nebivolol + 300 mg bupropion were ingested concomitantly, after a pretreatment regimen with bupropion (7 days). The PK parameters of nebivolol and its active metabolite were analyzed by noncompartmental modeling, while the pharmacodynamic (PD) parameters (blood pressure and heart rate) were assessed at rest. RESULTS: Bupropion plus nebivolol increased the mean peak plasma concentrations (Cmax) of nebivolol (1.67 ± 0.69 vs. 3.80 ± 1.70 ng/ml) and its active metabolite (0.68 ± 0.22 vs. 1.13 ± 0.38 ng/ml) compared to nebivolol alone. After bupropion pretreatment, the exposure to nebivolol was increased by 7.2-fold for the parent drug and 4-fold for the hydroxylated active metabolite. The difference between the PD parameters measured during the 2 periods was not significant. CONCLUSION: The study concluded that bupropion influenced the PKs of nebivolol in healthy volunteers, but a clinical relevance was not established. However, this latter aspect requires further investigation.

Identification of non-reported bupropion metabolites in human plasma.

Bupropion and its three active metabolites exhibit clinical efficacy in the treatment of major depression, seasonal depression and smoking cessation. The pharmacokinetics of bupropion in humans is highly variable. It is not known if there are any non-reported metabolites formed in humans in addition to the three known active metabolites. This paper reports newly identified and non-reported metabolites of bupropion in human plasma samples. Human subjects were dosed with a single oral dose of 75 mg of an immediate release bupropion HCl tablet. Plasma samples were collected and analysed by LC-MS/MS at 0, 6 and 24 h. Two non-reported metabolites (M1 and M3) were identified with mass-to-charge (m/z) ratios of 276 (M1, hydration of bupropion) and 258 (M3, hydroxylation of threo/erythrohydrobupropion) from human plasma in addition to the known hydroxybupropion, threo/erythrohydrobupropion and the glucuronidation products of the major metabolites (M2 and M4-M7). These new metabolites may provide new insight and broaden the understanding of bupropion's variability in clinical pharmacokinetics. © 2016 The Authors Biopharmaceutics & Drug Disposition Published by John Wiley & Sons Ltd.

Effect of CYP2B6*6 on Steady-State Serum Concentrations of Bupropion and Hydroxybupropion in Psychiatric Patients: A Study Based on Therapeutic Drug Monitoring Data.

BACKGROUND: The clinical effect of bupropion is mediated by its active metabolite hydroxybupropion. Previous studies have reported conflicting impact of the CYP2B6*6 variant allele on the formation of hydroxybupropion from bupropion. The aim of this study was to clarify the effect of CYP2B6*6 and secondarily CYP2D6 genotype on steady-state serum concentrations of bupropion and hydroxybupropion in a large population of psychiatric patients. METHODS: Retrospective information about dose-adjusted serum concentrations (C/D ratios) of bupropion and hydroxybupropion, CYP2B6 genotype (ie, data on the 2B6*6 polymorphisms 516G>T and 785A>G) and CYP2D6 genotype, was obtained from a therapeutic drug monitoring database (n = 132 patients). C/D ratios of bupropion and hydroxybupropion, and metabolic ratios, were compared between CYP2B6 genotype subgroups by multivariate mixed-model analyses (2B6*1/*1 was defined as control group). In the analyses, CYP2D6 genotype was also included as a covariate. RESULTS: Homozygous 2B6*6 carriers (n = 7) had significantly lower C/D ratios of hydroxybupropion compared with controls (n = 79), that is, estimated mean 5.8 versus 13.0 nmol·L·mg (P < 0.001). C/D ratio of hydroxybupropion in heterozygous *6 carriers (12.1 nmol·L·mg; n = 46) did not significantly differ compared with controls (P = 0.32). The hydroxybupropion/bupropion metabolic ratios in heterozygous and homozygous 2B6*6 carriers were significantly lower than in controls (P = 0.001 and P < 0.001, respectively). CYP2D6 genotype did not significantly alter the hydroxybupropion C/D ratio, but higher bupropion values were observed in poor versus extensive CYP2D6 metabolizers (P = 0.020). CONCLUSIONS: This study shows that the CYP2B6*6 variant allele is associated with significantly reduced formation of the active bupropion metabolite in psychiatric patients. Our findings suggest that dose-adjusted serum concentrations of hydroxybupropion at steady state is approximately halved in homozygous CYP2B6*6 carriers, which might imply risk of reduced clinical response in this patient subgroup. The CYP2D6 genotype does not affect hydroxybupropion concentrations and is therefore unlikely to impact bupropion treatment.

Development and validation of a high-performance liquid chromatography-tandem mass spectrometric method for simultaneous determination of bupropion, quetiapine and escitalopram in human plasma.

In the present study, an effective high performance liquid chromatography-tandem mass spectrometric (HPLC/MS/MS) method was developed and validated to simultaneously determine bupropion (BUP), quetiapine (QUE) and escitalopram (ESC) in human plasma using carbidopa as the internal standard. Chromatographic separation was achieved on a Waters Sun Fire C18 column using reversed-phase chromatography. The MS/MS experiment was performed in positive ion multiple reaction monitoring mode to produce product ions of m/z 240.3 → 184.2 for BUP, 384.2 → 253.1 for QUE, 325.3 → 109.3 for ESC and 227.2 → 181.2 for the internal standard. The method showed good linearity (R(2) ≥ 0.997), precision (relative standard deviation ≤7.5%), satisfactory intra- and interday accuracy (88.4-113.0%) and acceptable extraction recovery (87.2-115.0%), matrix effect (84.5.5-108.7%) and stability (92.3-103.5%). The method was successfully applied to determine the concentrations of BUP, QUE and ESC in human plasma samples.

Simultaneous determination of bupropion, metroprolol, midazolam, phenacetin, omeprazole and tolbutamide in rat plasma by UPLC-MS/MS and its application to cytochrome P450 activity study in rats.

A specific ultra-performance liquid chromatography tandem mass spectrometry method is described for the simultaneous determination of bupropion, metroprolol, midazolam, phenacetin, omeprazole and tolbutamide in rat plasma with diazepam as internal standard, which are the six probe drugs of the six cytochrome P450 isoforms CYP2B6, CYP2D6, CYP3A4, CYP1A2, CYP2C19 and CYP2C9. Plasma samples were protein precipitated with acetonitrile. The chromatographic separation was achieved using a UPLC® BEH C18 column (2.1 × 100 mm, 1.7 µm). The mobile phase consisted of acetonitrile and water (containing 0.1% formic acid) with gradient elution. The triple quadrupole mass spectrometric detection was operated by multiple reaction monitoring in positive electrospray ionization. The precisions were <13%, and the accuracy ranged from 93.3 to 110.4%. The extraction efficiency was >90.5%, and the matrix effects ranged from 84.3 to 114.2%. The calibration curves in plasma were linear in the range of 2-2000 ng/mL, with correlation coefficient (r(2) ) >0.995. The method was successfully applied to pharmacokinetic studies of the six probe drugs of the six CYP450 isoforms and used to evaluate the effects of erlotinib on the activities of CYP2B6, CYP2D6, CYP3A4, CYP1A2, CYP2C19 and CYP2C9 in rats. Erlotinib may inhibit the activity of CYP2B6 and CYP3A4, and may induce CYP2C9 of rats.

Gene variants in CYP2C19 are associated with altered in vivo bupropion pharmacokinetics but not bupropion-assisted smoking cessation outcomes.

Bupropion is used clinically to treat depression and to promote smoking cessation. It is metabolized by CYP2B6 to its active metabolite hydroxybupropion, yet alterations in CYP2B6 activity have little impact on bupropion plasma levels. Furthermore, less than 10% of a bupropion dose is excreted as urinary bupropion and its characterized metabolites hydroxybupropion, threohydrobupropion, and erythrohydrobupropion, suggesting that alternative metabolic pathways may exist. In vitro data suggested CYP2C19 could metabolize bupropion. The current study investigated the impact of functional CYP2C19 genetic variants on bupropion pharmacokinetics and treatment outcomes. In 42 healthy volunteers, CYP2C19*2 (a reduced activity allele) was associated with higher bupropion area under the plasma concentration-time curve (AUC), but similar hydroxybupropion AUC. The mean bupropion AUC was 771 versus 670 hours⋅ng/ml in individuals with and without CYP2C19*2, respectively (P = 0.017). CYP2C19*2 was also associated with higher threohydrobupropion and erythrohydrobupropion AUC (P < 0.005). Adjusting for CYP2B6 genotype did not alter these associations, and CYP2C19 variants did not alter the utility of the hydroxybupropion/bupropion ratio as a measure of CYP2B6 activity. Finally, in a clinical trial of 540 smokers, CYP2C19 genotype was not associated with smoking cessation outcomes, supporting the hypothesis that bupropion response is mediated by hydroxybupropion, which is not altered by CYP2C19. In conclusion, our study reports the first in vivo evidence that reduced CYP2C19 activity significantly increases the steady-state exposure to bupropion and its reductive metabolites threohydrobupropion and erythrohydrobupropion. These pharmacokinetic changes were not associated with differences in bupropion's ability to promote smoking cessation in smokers, but may influence the side effects and toxicity associated with bupropion.

Metabolism and disposition of bupropion in pregnant baboons (Papio cynocephalus).

Recent in vitro data obtained in our laboratory revealed similarities between baboons and humans in the biotransformation of bupropion (BUP) by both hepatic and placental microsomes. These data supported the use of baboons to study BUP biotransformation during pregnancy. The aim of this investigation was to determine the pharmacokinetics of BUP in baboons during pregnancy and postpartum, as well as fetal exposure to the drug after intravenous administration. Pregnant baboons (n = 5) received a single intravenous bolus dose of bupropion hydrochloride (1 mg/kg) at gestational ages 94-108 days (midpregnancy), 142-156 days (late pregnancy), and 6 weeks postpartum. Blood and urine samples were collected for 12 and 24 hours, respectively. The concentrations of BUP, hydroxybupropion (OH-BUP), threohydrobupropion, and erythrohydrobupropion in plasma were determined by liquid chromatography-tandem mass spectrometry. Relative to the postpartum period, the average midpregnancy clearance of BUP trended higher (3.6 ± 0.15 versus 2.7 ± 0.28 l/h per kg) and the average C(max) (294 ± 91 versus 361 ± 64 ng/ml) and the area under the curve (AUC) of BUP values (288 ± 22 versus 382 ± 42 h·ng/ml) trended lower. AUC(OH-BUP) also tended to be lower midpregnancy compared with postpartum (194 ± 76 versus 353 ± 165 h·ng/ml). Whereas the observed trend toward increased clearance of BUP during baboon pregnancy could be associated with a pregnancy-induced increase in its biotransformation, the trend toward increased renal elimination of OH-BUP may overshadow any corresponding change in the hydroxylation activity of CYP2B.

Serum concentrations of hydroxybupropion for dose optimization of depressed patients treated with bupropion.

BACKGROUND: Bupropion is a dopamine and norepinephrine reuptake inhibitor approved for the treatment of depression and smoking cessation. According to the recently published reviews, it is a candidate for therapeutic drug monitoring (TDM) to improve therapeutic outcomes and reduce risks of intolerability or intoxication. In practice, however, the use of TDM is limited due to the chemical instability of bupropion. This investigation sought to determine if the major, active, and chemically stable metabolite 4-hydroxybupropion is a suitable measure to guide antidepressant drug therapy with bupropion. METHODS: 4-Hydroxybupropion serum levels were measured using a newly developed and validated high-performance liquid chromatography assay with ultraviolet detection. They correlated with therapeutic effects measured by the clinical global impression scale for improvement. RESULTS: The study included 52 patients (50% women). Patients who were markedly improved according to the clinical global impression scale score had significantly (P = 0.042) higher 4-hydroxybupropion serum levels than those with moderate or minimal improvement (mean ± SD, 1113 ± 576, 825 ± 398, and 475 ± 331 ng/mL, respectively). Analysis of receiver operating characteristics revealed significant predictive properties of 4-hydroxybupropion serum levels (P = 0.002) for marked improvement with a lower threshold level of 858 ng/mL. Under similar mean doses (265 ± 107 versus 239 ± 100 mg, respectively), women attained significantly higher serum levels than men (1050 ± 524 versus 589 ± 352 ng/mL, respectively) and exhibited a better therapeutic effect (P = 0.018). CONCLUSIONS: Despite multiple limitations of this naturalistic study, evidence could be given that the measurement of 4-hydroxybupropion in serum is suitable to perform TDM for bupropion. Blood levels should be above 860 ng/mL to attain therapeutic improvement. Potential sex differences in bupropion pharmacokinetics, probably due to differential activities of CYP2B6, should be taken into account when the drug is prescribed.

Validation of a bupropion, dextromethorphan, and omeprazole cocktail for simultaneous phenotyping of cytochrome P450 2B11, 2D15, and 3A12 activities in dogs.

OBJECTIVE: Develop a cytochrome P450 (CYP) phenotyping cocktail for dogs using specific substrates for hepatic P450 enzymes CYP2B11, CYP2D15, and CYP3A12 and determine whether alternative sampling methods (saliva and urine) or single time point samples could be used instead of multiple blood sampling. ANIMALS: 12 healthy client-owned dogs (8 females and 4 males) from February 2019 to May 2019. METHODS: In a randomized crossover study, dogs received oral administration of the probe drug bupropion (75 mg), dextromethorphan (30 mg), or omeprazole (40 mg) alone or as a 3-drug combination (Program in Individualized Medicine [PrIMe] cocktail) to evaluate simultaneous phenotyping of CYP2B11, CYP2D15, and CYP3A12. Pharmacokinetic profiles for the probe drugs and metabolites were determined using plasma, saliva, and urine. Dogs received probe drugs alone or combined. Pharmacokinetic profiles up to 6 hours postdose for the probe drugs and metabolites were determined using plasma, saliva, and urine. RESULTS: The PrIMe cocktail was well tolerated. There was no statistically significant interaction between the probe drugs when administered together. Single time point plasma metabolic ratios at 4 hours postdose for all probe drugs strongly correlated with the corresponding area under the plasma concentration-versus-time curve (AUC) ratios. Saliva AUC metabolic ratios for CYP3A12 and CYP2D15 and 6-hour urine for CYP2B11 and CYP2D15 were correlated with plasma AUC ratios. CONCLUSIONS: The PrIMe cocktail can be used for simultaneous CYP phenotyping using plasma 4-hour single time point sample metabolic ratios. Saliva and urine sampling are suitable for specific CYPs. CLINICAL RELEVANCE: The PrIMe cocktail has potential as a useful tool in dogs to detect clinically important CYP-mediated drug-drug interactions, identify novel pharmacogenes, determine the drug-metabolizing phenotype of individual dogs, aid in individualized dose selection, and evaluate the effects of various physiological states on drug metabolism.

Influence of CYP2B6 genetic variants on plasma and urine concentrations of bupropion and metabolites at steady state.

BACKGROUND: Bupropion, an antidepressant and smoking cessation medication, is metabolized to hydroxybupropion (HB), an active metabolite, primarily by CYP2B6. OBJECTIVES: To compare plasma concentrations of bupropion and metabolites at steady state in healthy volunteers with and without CYP2B6 genetic variants. METHODS: In a genotype-guided study of 42 healthy individuals, we measured the plasma and urine concentrations of bupropion and its metabolites, HB, threohydrobupropion, and erythrohydrobupropion after 7 days of sustained-release bupropion dosing. RESULTS: CYP2B6*6 and *18 gene variants were associated with ~33% reduced concentrations of HB, with no effects on concentrations of bupropion or other metabolites. We could account for 50% of the variation in HB concentrations in a model including genotype and sex. CONCLUSION: As HB is active and its steady-state concentrations are more than 10 times higher than bupropion, CYP2B6 variants are likely to affect pharmacological activity. Because of the large individual variation within the genotype group, the use of therapeutic drug monitoring for dose optimization may be necessary.

The influence of sex, ethnicity, and CYP2B6 genotype on bupropion metabolism as an index of hepatic CYP2B6 activity in humans.

The effects of sex, ethnicity, and genetic polymorphism on hepatic CYP2B6 (cytochrome P450 2B6) expression and activity were previously demonstrated in vitro. Race/ethnic differences in CYP2B6 genotype and phenotype were observed only in women. To identify important covariates associated with interindividual variation in CYP2B6 activity in vivo, we evaluated these effects in healthy volunteers using bupropion (Wellbutrin SR GlaxoSmithKline, Research Triangle Park, NC) as a CYP2B6 probe substrate. A fixed 150-mg oral sustained-release dose of bupropion was administered to 100 healthy volunteers comprising four sex/ethnicity cohorts (n = 25 each): Caucasian men and Caucasian, African American, and Hispanic women. Blood samples were obtained at 0 and 6 hours postdose for the measurement of serum bupropion (BU) and hydroxybupropion (HB) concentrations. Whole blood was obtained at baseline for CYP2B6 genotyping. To characterize the relationship between CYP2B6 activity and ethnicity, sex, and genotype when accounting for serum BU concentrations (dose-adjusted log(10)-transformed), analysis of covariance model was fitted in which the dependent variable was CYP2B6 activity represented as the log(10)-transformed, metabolic ratio of HB to BU concentrations. Several CYP2B6 polymorphisms were associated with CYP2B6 activity. Evidence of dependence of CYP2B6 activity on ethnicity or genotype-by-ethnicity interactions was not detected in women. These results suggest that CYP2B6 genotype is the most important patient variable for predicting the level of CYP2B6 activity in women, when measured by the metabolism of bupropion. The bupropion metabolic ratio appears to detect known differences in CYP2B6 activity associated with genetic polymorphism, across different ethnic groups. Prospective studies will be needed to validate the use of bupropion as a probe substrate for clinical use.

Factors associated with discontinuation of bupropion and counseling among African American light smokers in a randomized clinical trial.

BACKGROUND: African Americans are at risk of inadequate adherence to smoking cessation treatment, yet little is known about what leads to treatment discontinuation. PURPOSE: The purpose of this study was to examine the factors associated with discontinuation of treatment in African American light smokers (≤10 cigarettes per day). METHODS: Bupropion plasma levels and counseling attendance were measured among 540 African American light smokers in a placebo-controlled randomized trial of bupropion. RESULTS: By week 3, 28.0 % of subjects in the bupropion arm had discontinued bupropion, and only moderate associations were found between the plasma levels and self-reported bupropion use (r s = 0.38). By week 16, 36.9 % of all subjects had discontinued counseling. Males had greater odds of discontinuing medication (OR = 2.02, 95% CI = 1.10-3.71, p = 0.02), and older adults had lower odds of discontinuing counseling (OR = 0.96, 95% CI = 0.94-0.97, p < 0.0001). CONCLUSIONS: Bupropion and smoking cessation counseling are underutilized even when provided within the context of a randomized trial. Future research is needed to examine strategies for improving treatment utilization among African American smokers.

Assessment of effects of chronic hydrogen sulfide poisoning on cytochrome P450 isoforms activity of rats by cocktail approach.

Hydrogen sulfide (H2S) is one of the neurotoxic gases with suffocating and irritating. Its main target organs of toxic effects are the central nervous system and respiratory system. Cocktail method was used to evaluate the influence of chronic hydrogen sulfide poisoning on the activities of cytochrome P450 (CYP450) isoforms CYP1A2, CYP2C9, CYP2B6 and CYP2D6, which were reflected by the changes of pharmacokinetic parameters of 4 specific probe drugs phenacetin, tolbutamide bupropion and metroprolol, respectively. The experimental rats were randomly divided into two groups, control group and chronic hydrogen sulfide poisoning group. The chronic hydrogen sulfide poisoning group rats were inhaled 20 ppm for 1 h twice a day for 40 d. The mixture of 4 probes was given to rats through sublingual veins and the blood samples were obtained at a series of time-points through the caudal vein. The concentrations of probe drugs in rat plasma were measured by liquid chromatography-mass spectrometry (LC-MS). In the experiment for chronic hydrogen sulfide poisoning and control group, there was a statistically significant difference in the area under the plasma concentration-time curve from zero to infinity (AUC(0-∞)), plasma clearance (CL) and maximum plasma concentration (C(max)) for phenacetin and bupropion, while there was no statistical pharmacokinetics difference for tolbutamide and metoprolol. Chronic hydrogen sulfide poisoning could induce the activity of CYP1A2 and CYP2B6 of rats.

The effects of H2S on the activities of CYP2B6, CYP2D6, CYP3A4, CYP2C19 and CYP2C9 in vivo in rat.

Hydrogen sulfide (H2S) is a colorless, flammable, extremely hazardous gas with a "rotten egg" smell. The human body produces small amounts of H2S and uses it as a signaling molecule. The cocktail method was used to evaluate the influence of H2S on the activities of CYP450 in rats, which were reflected by the changes of pharmacokinetic parameters of five specific probe drugs: bupropion, metroprolol, midazolam, omeprazole and tolbutamide, respectively. The rats were randomly divided into two groups, control group and H2S group. The H2S group rats were given 5 mg/kg NaHS by oral administration once a day for seven days. The mixture of five probes was given to rats through oral administration and the blood samples were obtained at a series of time-points through the caudal vein. The concentrations of probe drugs in rat plasma were measured by LC-MS. In comparing the H2S group with the control group, there was a statistically pharmacokinetics difference for midazolam and tolbutamide; the area under the plasma concentration-time curve (AUC) was decreased for midazolam (p < 0.05) and increased for tolbutamide (p < 0.05); while there was no statistical pharmacokinetics difference for bupropion, metroprolol and omeprazole. H2S could not influence the activities of CYP2B6, CYP2D6 and CYP2C19 in rats, while H2S could induce the activity of CYP3A4 and inhibit the activity of CYP2C9 in rats.