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.

Stereoselective Steady-State Disposition and Bioequivalence of Brand and Generic Bupropion in Adults.

The antidepressant bupropion is stereoselectively metabolized and metabolite enantiomers have differential pharmacologic effects, but steady-state enantiomeric disposition is unknown. Controversy persists about bupropion XL 300 mg generic equivalence to brand product, and whether generics might have different stereoselective disposition leading to enantiomeric non-bioequivalence and, thus, clinical nonequivalence. This preplanned follow-on analysis of a prospective, randomized, double-blinded, crossover study of brand and 3 generic bupropion XL 300 mg products measured steady-state enantiomeric plasma and urine parent bupropion and primary and secondary metabolite concentrations and evaluated bioequivalence and pharmacokinetics. Steady-state plasma and urine bupropion disposition was markedly stereoselective, with up to 40-fold differences in plasma concentrations of the active metabolite S,S-hydroxybupropion vs. R,R,-hydroxybupropion. Urine metabolite glucuronides were prominent, but glucuronidation was metabolite-specific and enantioselective. There were no differences between any generic and brand, or between generics, in plasma enantiomer concentrations of bupropion or the major metabolites. All generic products satisfied formal bioequivalence criteria (peak plasma concentration (Cmax ) and area under the plasma concentration-time curve over 24 hours (AUC0-24 )) using enantiomers for bupropion as well as for metabolites, and generics were comparable to each other, and were considered bioequivalent, based on enantiomeric analysis. Enantiomeric bioequivalence explains the previously observed therapeutic equivalence of bupropion generics and brand in treating major depression. These results have important implications for understanding the clinical therapeutic effects of bupropion based on complex and stereoselective metabolism.

Common Polymorphisms of CYP2B6 Influence Stereoselective Bupropion Disposition.

Bupropion hydroxylation is a bioactivation and metabolic pathway, and the standard clinical CYP2B6 probe. This investigation determined the influence of CYP2B6 allelic variants on clinical concentrations and metabolism of bupropion enantiomers. Secondary objectives evaluated the influence of CYP2C19 and P450 oxidoreductase variants. Healthy volunteers in specific cohorts (CYP2B6*1/*1, CYP2B6*1/*6, CYP2B6*6/*6, and also CYP2B6*4 carriers) received single-dose oral bupropion. Plasma and urine bupropion and hydroxybupropion was quantified. Subjects were also genotyped for CYP2C19 and P450 oxidoreductase variants. Hydroxylation of both bupropion enantiomers, assessed by plasma hydroxybupropion/bupropion AUC ratios and urine hydroxybupropion formation clearances, was lower in CYP2B6*6/*6 but not CYP2B6*1/*6 compared with CYP2B6*1/*1 genotypes, and numerically greater in CYP2B6*4 carriers. CYP2C19 and P450 oxidoreductase variants did not influence bupropion enantiomers hydroxylation or plasma concentrations. The results show that clinical hydroxylation of both bupropion enantiomers was equivalently influenced by CYP2B6 allelic variation. CYP2B6 polymorphisms affect S-bupropion bioactivation, which may affect therapeutic outcomes.

Degradation of Bupropion: Implications for Interpretation of Postmortem Case Data.

The interpretation of postmortem bupropion is often a challenge to the forensic toxicology community because of the instability of the parent compound. At the North Carolina Office of the Chief Medical Examiner (NC OCME) toxicology laboratory, one of the active metabolites, threobupropion, is used as a complementary indicator for the extent of exposure to the parent compound. Metabolite data will address postmortem normal concentrations as well as when bupropion was attributed to the cause of death. For 55 natural cases where bupropion was unattributed to the cause of death, the blood and liver mean threobupropion concentrations were 1.8 mg/L and 12.1 mg/kg, respectively, with median concentrations of 1.5 mg/L and 10 mg/kg, respectively. For the 51 suicidal ingestion cases when bupropion was attributed to the cause of death, the blood and liver mean threobupropion concentrations were 15.8 mg/L and 131.5 mg/kg, respectively, with median concentrations of 13.5 mg/L and 110 mg/kg, respectively. The laboratory completed a stability study over the course of 50 days to evaluate how bupropion and threobupropion degrade in postmortem blood, liver and liver homogenate. The samples were subjected to forensically relevant conditions by storing them at room temperature (RT, 20°C), refrigerated (4°C) and frozen (-20°C). While the concentration of bupropion decreased in all specimens, the rate of degradation of the RT samples was the most dramatic. The threobupropion metabolite appeared to be relatively stable. The postmortem case data along with the evaluation of potential degradation products should provide an overall picture to assist the toxicological community with the interpretation of bupropion found in routine casework.

Effects of Magnesium Supplementation on Unipolar Depression: A Placebo-Controlled Study and Review of the Importance of Dosing and Magnesium Status in the Therapeutic Response.

Animal studies using tests and models have demonstrated that magnesium exerts an antidepressant effect. The literature contains few studies in humans involving attempts to augment antidepressant therapy with magnesium ions. The purpose of our study was to assess the efficacy and safety of antidepressant treatment, in combination with magnesium ions. A total of 37 participants with recurrent depressive disorder who developed a depressive episode were included in this study. As part of this double-blind study, treatment with the antidepressant fluoxetine was accompanied with either magnesium ions (120 mg/day as magnesium aspartate) or placebo. During an 8-week treatment period, each patient was monitored for any clinical abnormalities. Moreover, serum fluoxetine and magnesium levels were measured, and pharmaco-electroencephalography was performed. The fluoxetine + magnesium and fluoxetine + placebo groups showed no significant differences in either Hamilton Depression Rating Scale (HDRS) scores or serum magnesium levels at any stage of treatment. Multivariate statistical analysis of the whole investigated group showed that the following parameters increased the odds of effective treatment: lower baseline HDRS scores, female gender, smoking, and treatment augmentation with magnesium. The parameters that increased the odds of remission were lower baseline HDRS scores, shorter history of disease, the presence of antidepressant-induced changes in the pharmaco-EEG profile at 6 h after treatment, and the fact of receiving treatment augmented with magnesium ions. The limitation of this study is a small sample size.

Antidepressant polypharmacy and the potential of pharmacokinetic interactions: Doxepin but not mirtazapine causes clinically relevant changes in venlafaxine metabolism.

BACKGROUND: To uncover pharmacokinetic interactions between venlafaxine and doxepin or mirtazapine in a naturalistic sample. METHODS: A therapeutic drug monitoring database containing plasma concentrations of venlafaxine (VEN) and its active metabolite O-desmethylvenlafaxine (ODVEN) was analyzed. We included 1067 of 1594 patients in the analysis. Three study groups were considered; a group of patients under venlafaxine without confounding medications, V0 (n = 905), a group of patients co-medicated with doxepin, VDOX (n = 25) and a second group, co-medicated with mirtazapine, VMIR, n = 137. Plasma concentrations of VEN, ODVEN and the clinically relevant active moiety, sum of venlafaxine and O-desmethylvenlafaxine (ODVEN) (AM), as well as dose-adjusted plasma concentrations (C/D) were compared. RESULTS: Median concentrations in the doxepin group showed 57.7% and 194.4% higher values for AM and VEN respectively; these differences were statistically significant (p < 0.001 for AM and p = 0.002 for VEN). Similar differences were detected for C/D concentrations of active moiety and VEN (p < 0.001 and p = 0.001) with higher values also in the doxepin group. The ratios ODVEN/VEN were lower in the doxepin group (p < 0.001). A co-medication with mirtazapine did not cause any changes in venlafaxine metabolism. CONCLUSIONS: Higher concentrations for VEN and AM imply an inhibiting effect of doxepin on the metabolism of venlafaxine, although the huge variability of concentrations has to be taken into account. It is recommended to monitor plasma concentrations in combination treatment to avoid problems in safety and efficacy. LIMITATIONS: Despite the large size of our study sample, the naturalistic nature of this data may arise some concerns of information bias potentially resulting from non-standardized data recording.

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.

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.

Development and validation of a high-throughput stereoselective LC-MS/MS assay for bupropion, hydroxybupropion, erythrohydrobupropion, and threohydrobupropion in human plasma.

A stereoselective analytical method was developed and validated for the quantification of bupropion, and principle metabolites hydroxybupropion, erythrohydrobupropion and threohydrobupropion in human plasma. Separation of individual enantiomers (R)-bupropion, (S)-bupropion, (R,R)-hydroxybupropion, (S,S-hydroxybupropion), (1S,2S)-threohydrobupropion, (1R,2R)-threohydrobupropion, (1R,2S)-erythrohydrobupropion, and (1S,2R)-erythrohydrobupropion was achieved utilizing an α1-acid glycoprotein column within a 12-min run time. Chromatograph separation was significantly influenced by mobile phase pH and variability between columns. Analytes were quantified by positive ion electrospray tandem mass spectrometry following plasma protein precipitation with 20% trichloroacetic acid. Identification of erythrohydrobupropion enantiomer peaks and threohydrobupropion enantiomer peaks was achieved by sodium borohydride reduction of enantiopure (R)- and (S)-bupropion. Initial assay validation and sensitivity determination was on AB Sciex 3200, 4000 QTRAP, and 6500 mass spectrometers. Accuracy and precision were within 15% for each analyte. The assay was fully validated over analyte-specific concentrations using an AB Sciex 3200 mass spectrometer. Intra- and inter-assay precision and accuracy were within 12% for each analyte. The limits of quantification for bupropion (R and S), hydroxybupropion (R,R and S,S), threohydrobupropion (1S,2S and 1R,2R), and erythrohydrobupropion (1R,2S and 1S,2R) were 0.5, 2, 1, and 1ng/mL, respectively. All analytes were stable following freeze thaw cycles at -80°C and while stored at 4°C in the instrument autosampler. This method was applicable to clinical pharmacokinetic investigations of bupropion in patients. This is the first chromatographic method to resolve erythrohydrobupropion and threohydrobupropion enantiomers, and the first stereoselective LC-MS/MS assay to quantify bupropion, and principle metabolites hydroxybupropion, erythrohydrobupropion, and threohydrobupropion in human plasma.

Decreased Escitalopram Concentrations Post-Roux-en-Y Gastric Bypass Surgery.

BACKGROUND: There is a high coincidence between obesity and psychiatric disorders including depression. Depressive disorders are commonly treated with antidepressants, including the selective serotonin reuptake inhibitor Lexapro (escitalopram). Although candidates for elective Roux-en-Y gastric bypass (RYGB) surgery may be treated with escitalopram, drug dosing strategies are typically not adjusted postoperatively. Therefore, studies are needed to better characterize escitalopram drug concentrations in a postsurgical setting. METHODS: Turbulent flow-liquid chromatographic-tandem mass spectrometric methods were used to quantify escitalopram concentrations in serum in study participants approved for RYGB. Blood was collected from study subjects 2 weeks before surgery, and 2 and 6 weeks postoperatively, to assess the impact of RYGB on systemic drug concentrations. RESULTS: Twelve samples from 4 study participants were collected and analyzed for serum escitalopram concentrations. Two weeks post-RYGB, although there were minimal changes in each participant's body mass index (<5%), drug concentrations were 33% (4%-71%) decreased as compared with presurgical serum concentrations. There were further decreases in drug concentrations 6 weeks postsurgery. All clinical laboratory values were within normal reference intervals. CONCLUSIONS: RYGB significantly alters the gastrointestinal tract and impacts escitalopram drug concentrations, even shortly after surgery.

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.

The comparison of brand-name and generic formulations of venlafaxine: a therapeutic drug monitoring analysis.

OBJECTIVE: Venlafaxine (VEN) is a widely used antidepressant drug, which is available in both brand-name and generic formulations. Bioequivalence studies indicate some pharmacokinetic variability. However, naturalistic therapeutic drug monitoring studies of different generic formulations are lacking. METHODS: In 2010, inpatients of the Department of Psychiatry, Psychosomatics, and Psychotherapy, University Hospital of Würzburg, were treated with either slow-release brand-name VEN (Trevilor) or slow-release generic VEN (Venlafaxin Hexal) depending on the respective inpatient ward. Routine therapeutic drug monitoring analyses of both groups were compared after matching samples regarding dose of VEN, gender, age, smoking habits, and evaluation of co-medication. RESULTS: Both groups did not differ in mean values of VEN, O-desmethyl-VEN (ODV), VEN + ODV serum concentrations, and ODV/VEN ratio. No difference in dose-corrected serum concentrations between generic and brand-name VEN was revealed for males, females, smokers, or nonsmokers. In both groups, Spearman Rho correlation between VEN dose and VEN + ODV serum concentration was moderate but significant (P < 0.001; generic: r = 0.554; brand name: r = 0.668). Within the generic subgroup, females had a significantly higher dose-corrected serum concentration of VEN (U test, P < 0.05), whereas within brand name, no gender influence was detected. Spearman Rho correlation of age and dose-corrected ODV (P < 0.05) and VEN + ODV (P < 0.05) was significant only in the generic group. In the brand-name sample, smokers had significantly lower dose-corrected serum concentrations of ODV (U test, P < 0.01) and VEN + ODV (P < 0.01). In the generic group, smoking habit was without any influence. DISCUSSION: No differences in serum concentrations in dependence of either VEN formulations suggest a safe and efficient treatment of patients using the evaluated generic VEN. However, differences within one formulation regarding gender, age, and smoking status suggest variability of serum concentrations and thus could endanger safety and efficacy of drug use.

Delayed bupropion cardiotoxicity associated with elevated serum concentrations of bupropion but not hydroxybupropion.

CONTEXT: Bupropion overdose commonly causes generalized seizures and central nervous system depression. Less commonly, cardiotoxicity has been reported. The toxicity of the parent drug compared to its active metabolite hydroxybupropion is uncertain. CASE DETAILS: A 31-year-old man presented to the emergency department with altered mental status after an intentional overdose of bupropion. Three hours after admission he developed status epilepticus requiring intubation, and 13 h after admission he developed marked widening of the QRS complex and prolongation of the QTc interval. Serial serum bupropion levels peaked with the onset of cardiotoxicity (334 ng/mL) and fell into the therapeutic range within 24 h, which coincided with normalization of his ECG intervals. Levels of the metabolite hydroxybupropion peaked later (4302 ng/mL) and remained elevated even after neurological and cardiotoxic symptoms resolved. DISCUSSION: Cardiotoxicity appears to be caused primarily by bupropion rather than its active metabolite hydroxybupropion.

Effect of paroxetine on physiological response to stress and smoking.

OBJECTIVE: Smokers often smoke during stressful events, which leads to large increases in cardiovascular measures such as blood pressure (BP) and heart rate (HR). Because exaggerated cardiovascular response to stress is associated with cardiovascular disease risk, this study examined paroxetine's effect on the physiological response to combining stress and smoking. METHODS: Sixty-two participants completed this randomized, double-blind, crossover study in which BP, HR, plasma epinephrine, norepinephrine, and cortisol concentrations were measured at rest, while smoking, and during a speech and math task. Laboratory sessions occurred after 1 month of paroxetine and after 1 month of placebo. RESULTS: Significant increases occurred for all measures (except cortisol) during smoking, with further increases occurring during the speech task (time effect, p < .001). After 1 month of paroxetine, norepinephrine and HR values were lower and cortisol values were higher (versus placebo) throughout the laboratory session (treatment effect, p < .001). Treatment × time effects were observed for BP and HR (all, p < .01). For systolic and diastolic BP, a smaller increase (from baseline to measures during speech) was observed after paroxetine compared with placebo (both, p < .006). In both measures, the increase in response to smoking was similar for both treatments; however, the further increase during the speech was smaller when taking paroxetine (versus placebo). CONCLUSIONS: This study suggests that paroxetine affects physiological response to stress in smokers. Further research is needed to determine the impact of these results on cardiovascular health. Trial Registration clinicaltrials.gov Identifier: NCT00218439.

The effect of age, sex, smoking and co-medication on serum levels of venlafaxine and O-desmethylvenlafaxine under naturalistic conditions.

INTRODUCTION: Venlafaxine (VEN) is a modern antidepressant which exerts both serotonin and norepinephrine reuptake inhibition. In this study we examined the influence of age, sex, smoking, and co-medication on serum levels of VEN and its metabolite O-desmethylvenlafaxine (ODVEN) in patients treated with VEN under naturalistic conditions. METHODS: We retrospectively evaluated 478 TDM analyses of VEN requested in the Pychiatric University Hospitals of Mainz, Regensburg, and Würzburg. The determination of serum levels was performed by virtually identical chromatographic methods in the TDM laboratories of the participating hospitals. RESULTS: Serum levels varied widely on each dose level. Women had about 30% higher dose-corrected serum levels of VEN and ODVEN than men (p<0.01), and patients older than 60 years showed about 46% higher levels of both compounds than younger ones (p<0.01). In smokers, mean serum levels of ODVEN were 21% lower than in non-smokers. Combining these variables a considerable increase of the differences between the subgroups was found indicating an additive effect. ANOVA over the 8 different groups was significant for ODVEN (p<0.01) and sum (p<0.01), but not for VEN (n.s.). Co-medication with other psychotropic drugs was associated with a decreasing ODVEN/VEN ratio indicating a reduced metabolism in patients receiving polypharmacy. DISCUSSION: These findings show that TDM is useful to identify factors affecting the pharmacokinetic properties of VEN. It is concluded that sex, age and smoking should be considered for optimal dosing of patients with VEN.

Determination of bupropion using liquid chromatography with fluorescence detection in pharmaceutical preparations, human plasma and human urine.

A novel pre-column derivatization reversed-phase high-performance liquid chromatography with fluorescence detection is described for the determination of bupropion in pharmaceutical preparation, human plasma and human urine using mexiletine as internal standard. The proposed method is based on the reaction of 4-chloro-7-nitrobenzofurazan (NBD-Cl) with bupropion to produce a fluorescent derivative. The derivative formed is monitored on a C18 (150 mm × 4.6 mm i.d., 5 µm) column using a mobile phase consisting of methanol-water 75:25 (v/v), at a flow-rate of 1.2 mL/min and detected fluorimetrically at λ(ex) = 458 and λ(em) = 533 nm. The assay was linear over the concentration ranges of 5-500 and 10-500 ng/mL for plasma and urine, respectively. The limits of detection and quantification were calculated to be 0.24 and 0.72 ng/mL for plasma and urine, respectively (inter-day results). The recoveries obtained for plasma and urine were 97.12% ± 0.45 and 96.00% ± 0.45, respectively. The method presents good performance in terms of precision, accuracy, specificity, linearity, detection and quantification limits and robustness. The proposed method is applied to determine bupropion in commercially available tablets. The results were compared with an ultraviolet spectrophotometry method using t- and F-tests.

Sensitive, selective and rapid determination of bupropion and its major active metabolite, hydroxybupropion, in human plasma by LC-MS/MS: application to a bioequivalence study in healthy Indian subjects.

A sensitive, selective and rapid liquid chromatography tandem mass spectrometry (LC-MS/MS) method was developed for the simultaneous determination of bupropion (BUP) and its major active metabolite hydroxybupropion (HBUP) in human plasma. Separation of both the analytes and venlafaxine as internal standard (IS) from 50 µL human plasma was carried out by solid-phase extraction. The chromatographic separation of the analytes was achieved on a Zorbax Eclipse XDB C(18) (150 × 4.6 mm, 5 µm) analytical column using isocratic mobile phase consisting of 20 mm ammonium acetate-methanol (10:90, v/v), with a resolution factor of 3.5. The method was validated over a wide dynamic concentration range of 0.1-350 ng/mL for BUP and 0.1-600 ng/mL for HBUP. The matrix effect was assessed by post-column infusion and the mean process efficiency was 96.08 and 94.40% for BUP and HBUP, respectively. The method was successfully applied to a bioequivalence study of 150 mg BUP (test and reference) extended release tablet formulation in 12 healthy Indian male subjects under fed conditions.

Determination of bupropion and its main metabolite in rat plasma by LC-MS and its application to pharmacokinetics.

A sensitive and selective liquid chromatograpy-mass spectrometry method for the determination of bupropion and its main metabolite, hydroxubupropion, in rat plasma was developed and validated. After addition of carbamazepine as internal standard (IS) and precipitation of protein with acetonitrile, the plasma samples were analyzed on an Agilent Zorbax SB-C18 (2.1 mm x 50 mm, 3.5 microm) column at 30 degrees C, with acetonitrile-0.1% formic acid as mobile phase at a flow rate of 0.4 mL min(-1). The detection was carried out in the selective ion monitoring mode with a positive electrospray ionization interface. The calibration curve was linear over the 10-2000 ng mL(-1) for bupropion and 5-1000 ng mL(-1) for hydroxybupropion in plasma. RSD of inter-day and intra-day precision was less than 7% for bupropion, 9% for hydroxybupropion. The developed method was successfully applied to pharmacokinetic studies after single intragastric administration of bupropion 15 mg kg(-1) to rats.