Demethyl Metabolite Research Articles

First population pharmacokinetic analysis showing increased quinolone metabolite formation and clearance in patients with cystic fibrosis compared to healthy volunteers

Understanding the pharmacokinetics in patients with cystic fibrosis (CF) is important for dosing. For antibiotics with extensive metabolism, however, a comparison of metabolite formation and elimination between patients with CF and healthy volunteers has never been performed via population modeling. We aimed to compare the population pharmacokinetics of fleroxacin and its N‑oxide and demethyl metabolites between patients with CF and healthy volunteers. Our analysis included eleven adult patients with CF and twelve healthy volunteers who received 800 mg fleroxacin as a single oral dose followed by five doses every 24 h from a previously published study. All plasma concentrations and amounts in urine for fleroxacin and its metabolites were simultaneously modelled. The estimates below accounted for differences in body size and body composition via allometric scaling by lean body mass. Oral absorption was slower in patients with CF than in healthy volunteers. For fleroxacin, the population mean in patients with CF divided by that in healthy volunteers was 1.12 for renal clearance, 1.01 for linear nonrenal clearance, 0.83 for saturable exsorption clearance into intestine, and 0.81 for volume of distribution. The formation clearances of N‑oxide fleroxacin and N‑demethylfleroxacin were 0.520 L/h and 0.496 L/h in patients with CF; these formation clearances were 0.378 L/h and 0.353 L/h in healthy volunteers. Renal clearance in patients with CF divided by that in healthy volunteers was 1.53 for N‑oxide fleroxacin and 1.70 for N‑demethyl fleroxacin. Allometric scaling by lean body mass best explained the variability. While fleroxacin pharmacokinetics was comparable, both formation and elimination clearances of its two metabolites were substantially larger in patients with CF compared to those in healthy volunteers.

Determination of spinetoram and its metabolites in amaranth and parsley using QuEChERS-based extraction and liquid chromatography–tandem mass spectrometry

In this study, a simultaneous method was developed for the determination of spinetoram (XDE-175-J and XDE-175-L) and its demethyl metabolites (N-demethyl-175-J and N-demethyl-175-L) and formyl metabolites (N-formyl-175-J and N-formyl-175-L) in the minor crops; amaranth and parsley. The method uses quick, easy, cheap, effective, rugged, and safe (QuEChERS)-based extraction. Afterwards, the analytes were quantified and confirmed via liquid chromatography-electrospray ionisation tandem mass spectrometry (LC-ESI-MS/MS) in the positive ion mode using multiple reaction monitoring (MRM). Calibration curves were linear over the calibration ranges for all the analytes tested with r(2)>0.993. Limits of detection and quantitation were 0.01 and 0.03 mg/kg for all the tested analytes in amaranth and parsley, respectively. Recovery values, at spiking levels 0.05 and 0.25 mg/kg, ranged from 71.0% to 115.2% with relative standard deviations <15%, except for N-formyl-175-J in both amaranth and parsley. This method was applied to field-incurred samples and was shown to provide an adequate sensitivity and performance for the simultaneous determination of spinetoram and metabolites. To the best of our knowledge, this is the first time spinetoram and its metabolites were quantified using LC-MS/MS in minor crops.

Anti-amnesic and neuroprotective potentials of the mixed muscarinic receptor/sigma1 (σ1) ligand ANAVEX2-73, a novel aminotetrahydrofuran derivative

Tetrahydro-N, N-dimethyl-2, 2-diphenyl-3-furanmethanamine hydrochloride (ANAVEX2-73) binds to muscarinic acetylcholine and sigma(1) (σ(1)) receptors with affinities in the low micromolar range. We characterized its anti-amnesic and neuroprotective potentials in pharmacological and pathological amnesia models. Spatial working memory was evaluated using spontaneous alternation in the Y-maze and non-spatial memory using passive avoidance procedures. ANAVEX2-73 (0.01-3.0 mg/kg i.p.) alleviated the scopolamine- and dizocilpine-induced learning impairments. ANAVEX2-73 (300 µg/kg) also reversed the learning deficits in mice injected with Aβ(25-35) peptide, a non-transgenic Alzheimer's disease model. When the drug was injected simultaneously with Aβ(25-35), 7 days before the tests, it blocked the appearance of learning impairments. This protective activity was confirmed since ANAVEX2-73 blocked the Aβ(25-35)-induced oxidative stress in the hippocampus. This effect was differentially sensitive to the muscarinic receptor antagonist scopolamine or the σ(1) protein antagonist BD1047, confirming the mixed muscarinic/σ(1) pharmacological action. Finally, its unique demethyl metabolite, ANAVEX19-144, was also effective and ANAVEX2-73 presented a longer duration of action, effective 12 h before Aβ(25-35), than its related compound ANAVEX1-41. The neuroprotective activity of ANAVEX2-73, its mixed cholinergic/σ(1) activity, its low active dose range and its long duration of action together reinforce its therapeutic potential in Alzheimer's disease.

Pharmacokinetics, urinary excretion and milk penetration of levofloxacin in lactating goats

Levofloxacin, a recently introduced third-generation fluoroquinolone, is the L-isomer ofloxacin and possesses excellent activity against Gram-positive, Gram-negative and anaerobic bacteria (North et al., 1998). Compared with other fluoroquinolones (FQs), it also has more pronounced bactericidal activity against organisms such as Pseudomonas, Enterobacteriaceae and Klebsiella spp. (Klesel et al., 1995). Several species of staphylococci, streptococci including Streptococcus pneumoniae, bacteroides, clostridium, haemophilus, moraxella, legionella, mycoplasma and chlamydia are susceptible to levofloxacin (Langtry & Lamb, 1998). The bactericidal effect of levofloxacin is achieved through reversible binding to DNA gyrase and subsequent inhibition of bacterial DNA replication and transcription (Fu et al., 1992). Levofloxacin distributes well to target body tissues and fluids in the respiratory tract, skin, urine and prostrate, and its uptake by cells makes it suitable for use against intracellular pathogens. However, it penetrates poorly into the central nervous system (Langtry & Lamb, 1998). FQs act by a concentration-dependent killing mechanism, whereby the optimal effect is attained by the administration of high doses over a short period of time (Drusano et al., 1993). This concentration-dependent killing profile is associated with a relatively prolonged postantibiotic effect (Aliabadi & Lees, 2001). The drug undergoes a limited metabolism in rats and human (Langtry & Lamb, 1998) and is primarily excreted by kidney mainly as active drug. Inactive metabolites (N-oxide and demethyl metabolites) represent <5% of the total dose (Hurst et al., 2002). The pharmacokinetics of levofloxacin has been fully investigated in humans (Chulavatnatol et al., 1999), rabbits (Destache et al., 2001), cats (Albarellos et al., 2005) and calves (Dumka & Srivastava, 2006, 2007). However, there is no information available on the pharmacokinetics of levofloxacin in goats. In view of the marked species variation in the kinetic data of antimicrobial drugs, the present study was undertaken to determine the pharmacokinetics, urinary excretion and milk penetration of levofloxacin following single intravenous (i.v.) and intramuscular (i.m.) administration in lactating goats. Tavanic [100 mL vial of solution of levofloxacin hemihydrate equivalent to 500 mg (5 mg ⁄mL) levofloxacin] was purchased from Aventis, Frankfurt, Germany and Mueller– Hinton agar from Mast Group Ltd., Merseyside, UK. Six adult lactating goats weighing 27–35 kg and aged from 3 to 5 years were determined to be clinically healthy before the study based on physical examination. The goats were fed on barley, alfalfa hay and wheat straw with free access to food and water. The animals did not receive any drug treatment before the study. The study was approved by the Bioethics Committee of the Faculty of Veterinary Medicine, Cairo University. The study was performed in two phases, following a crossover design (2 · 2) with a 15-day washout period between the two phases. Three animals were given a single i.v. injection into the left jugular vein at a dose of 4 mg ⁄kg bodyweight (b.w.) levofloxacin, and the other three were injected i.m. into the semimembranous muscle with the drug at the same dose. Five millilitre venous whole blood samples were taken by jugular venepuncture into 10 mL heparinized Vacutainers (Becton Dickinson Vacutainer Systems, Rutherford, NJ, USA). The sampling times were 0 (blank sample), 0.08, 0.166, 0.33, 0.5, 0.75, 1, 2, 4, 6, 8, 10, 12, 18, 24, 36, 48 and 72 h after treatment. All the blood samples were centrifuged at 3000 g for 15 min to separate the plasma. The plasma samples were frozen at )20 C until analysis. After a washout period of 2 weeks, the animals that had been injected i.v. with the drug were injected i.m. and vice versa. Blood was collected and processed as above. Urine and milk samples were also collected simultaneously from the same animals at various predetermined time intervals of 0.5, 1, 2, 4, 6, 8, 10, 12, 18, 24, 36, 48 and 72 h postadministration. The urine samples were collected via a rubber balloon catheter (Folatex No.12; Sewoon Medical Co., Ltd, Seoul, Korea) previously inserted in the bladder and their volumes were measured. Milk samples were collected by hand stripping both halves of the udder. Complete evacuation of the udder was carried out after each sampling. The concentration of levofloxacin in plasma, urine and milk samples was estimated by a standard microbiological assay (Bennett et al., 1966) using Escherichia coli ATCC 10536 as test micro-organism. This method estimated the level of drug having antibacterial activity, without differentiating between the parent drug and its active metabolites. The reasons why we selected the bioassay are: (i) bioassay measures the total activity which could be more practical for pharmacodynamic evaluations than HPLC (McKellar et al., 1999); (ii) the bioassay method is precise, reproducible and does not require neither J. vet. Pharmacol. Therap. 32, 101–104, doi: 10.1111/j.1365-2885.2008.01001.x. SHORT COMMUNICATION

Transfer of escitalopram and its metabolite demethylescitalopram into breastmilk

To investigate the transfer of escitalopram and its demethyl metabolite into milk, the absolute and relative infant doses via milk and to assess any unwanted effects in the breastfed infant. Multiple samples of blood and milk were obtained over a dose interval at steady state from eight women who were taking escitalopram for postnatal depression. Drug concentrations in plasma and milk were measured by high-performance liquid chromatography and milk/plasma ratio (M/P(AUC)), absolute infant dose and relative infant dose were estimated by standard methods. Their breastfed infants were also examined clinically and in five infants a blood sample was taken for drug analysis. The median dose taken by the women was 10 mg day(-1). The mean (95% confidence interval) M/P(AUC) was 2.2 (2.0, 2.4) for escitalopram and 2.2 (1.9, 2.5) for demethylescitalopram. Absolute infant doses were 7.6 microg kg(-1) day(-1) (5.2, 10.0) for escitalopram and 3.0 microg kg(-1) day(-1) (2.4, 3.6) for demethylescitalopram. The total relative infant dose for escitalopram plus its demethyl metabolite was 5.3% (4.2, 6.4) as escitalopram equivalents. All of the infants had met normal developmental milestones and no adverse effects were seen. Compared with average maternal plasma concentrations (24 microg l(-1)), the concentrations of the parent drug and its metabolite in plasma from five infants were most commonly below the limit of detection (</=3 microg l(-1)). The study shows that escitalopram is safe for use during breastfeeding. Because its absolute infant dose is lower than that for an equivalent antidepressant dose of rac-citalopram, it may be preferred over rac-citalopram in treating depression in lactating women. Nevertheless, each decision to breastfeed should always be made on the basis of an individual risk:benefit analysis.

Pharmacokinetics and safety of mirtazapine in caucasian and japanese young healthy male volunteers

Mirtazapine is a noradrenergic and specific serotonergic antidepressant (NaSSA). In a double-blind, placebo controlled, parallel design multiple dose study, the pharmacokinetics and safety of multiple daily doses of mirtazapine and placebo have been compared in healthy Japanese and Caucasian male volunteers. All subjects received once daily in the evening an oral dose of mirtazapine or placebo over a period of 27 consecutive days. In order to achieve steady-state at every daily dose level, 15 mg mirtazapine or placebo was administered for the first 9 days, followed by 30 mg or placebo for a further 9 days and 45 mg or placebo for the final 9 days. Trough plasma concentrations of mirtazapine and Org 3838 (its demethyl metabolite) were measured while 24 hour plasma profiles were determined after dosing on days 9, 18 and 27; additional samples were collected up to 120 hours after the last 45 mg dose. Eleven Japanese (two on placebo) and 15 Caucasian (two on placebo) subjects completed this study, except for one Caucasian subject (treated with mirtazapine), who dropped out on day 20 for reasons unrelated to the study. The administration of mirtazapine over 27 days in 9 day periods of increasing doses (15 mg, 30 mg and 45 mg) was well tolerated by both Japanese and Caucasian subjects; fatigue was the most frequently reported AE. Liver enzyme increases (particularly ASAT and ALAT) were observed in some subjects in both ethnic groups. In all cases, these increases decreased during the course of the study despite the continued use of increasing doses of mirtazapine. The average plasma concentration of mirtazapine in Japanese subjects was 41% higher than that in Caucasian subjects. After correction for body weight this difference was reduced to 22%. The mean plasma concentrations of Org 3838 in Japanese and in Caucasian subjects were approximately the same. The observed difference of mirtazapine plasma concentrations is considered to be of no practical clinical relevance. Clinical Pharmacology & Therapeutics (2004) 75, P36–P36; doi: 10.1016/j.clpt.2003.11.138

Determination of mirtazapine and its demethyl metabolite in plasma by high-performance liquid chromatography with ultraviolet detection: Application to management of acute intoxication

Mirtazapine is a new centrally acting noradrenergic and specific serotonin antidepressant, with an active demethyl metabolite. For toxicological purposes, a specific and accurate RP-HPLC assay was developed for the simultaneous plasma determination of these compounds. A linear response was observed over the concentration range 50–500 ng/ml. A good accuracy (bias <10%) was achieved for all quality controls, with intra-day and inter-day variation coefficients less than 8.3%. The lower limit of quantification was 20 ng/ml, without interferences with endogenous or exogenous components. This rapid method (run time <12 min) was used to manage three intoxications involving mirtazapine.

Mirtazapine and paroxetine: a drug-drug interaction study in healthy subjects.

Paroxetine inhibits cytochrome P(450) 2D6, which is involved in the metabolism of mirtazapine. The possible drug-drug interaction between two pharmacologically distinct antidepressants, mirtazapine and paroxetine, has been investigated in a randomized, three-way crossover study in 24 healthy male and female subjects. After a titration phase of 3 days, each subject received single daily doses of 30 mg mirtazapine, 40 mg paroxetine or the combination for 6 days. Assessments included serial blood sampling for pharmacokinetics at steady state, cognitive testing using the test battery of CDR Ltd, a visual analogue mood rating scale (Bond and Lader) and the Leeds Sleep Evaluation Questionnaire. Paroxetine inhibits the metabolism of mirtazapine, as shown by increases of approximately 17% and 25% of the 24 h AUC's of mirtazapine and its demethyl metabolite, respectively. Mirtazapine did not alter the pharmacokinetics of paroxetine. The combined administration of mirtazapine and paroxetine probably does not alter cognitive functioning or result in major changes on the visual analogue mood rating scale and Sleep Evaluation Questionnaire, compared with the administration of either drug alone. The incidence of adverse events was lower during combined administration of mirtazapine and paroxetine than during administration of either drug alone. Fatigue, dizziness, headache, nausea, anxiety and somnolence were the most common adverse events during combined administration. These data suggest that the combination of mirtazapine and paroxetine is unlikely to lead to clinically relevant drug-drug interactions and can be used without dose adjustment of either drug. The combination may even be better tolerated than either drug alone. Copyright 2001 John Wiley & Sons, Ltd.

Concomitant use of mirtazapine and cimetidine: a drug-drug interaction study in healthy male subjects

The objective of this study was to examine the pharmacokinetics and the tolerability/safety of mirtazapine and cimetidine separately and in combination following oral administration of multiple doses. This was a double-blind, placebo-controlled, two-period cross-over, multiple-dose pharmacokinetic interaction study in 12 healthy male subjects. They received either cimetidine (800 mg b.i.d.) or placebo in combination with (commercially available, racemic) mirtazapine (30 mg nocte). Cimetidine and placebo were administered for 14 days, with mirtazapine added during days 6-12 of each period. Serial blood samples for kinetic profiling were taken on day 5 and day 12 for cimetidine and on days 12-14 for mirtazapine. The co-administration of cimetidine resulted in a statistically significant increase in the area under the curve (AUC(0-24)) and Cmax of mirtazapine (54% and 22% respectively). The AUC(0-24) of demethylmirtazapine increased only slightly, and there was no effect on Cmax. The elimination half-lives for both mirtazapine and its demethyl metabolite were unaffected by cimetidine co-administration. The trough and average plasma concentrations during the steady state were elevated during cimetidine treatment (62% and 54%, respectively). Mirtazapine had no effect on the pharmacokinetics of cimetidine. Co-administration of cimetidine (800 mg b.i.d.) and mirtazapine (30 mg nocte) resulted in increased steady-state plasma levels of mirtazapine (C(ss,min) = +61%, P < 0.05; C(ss,av) = +54%, P < 0.05), probably as a result of increased bio-availability. The Cmax (+22%, P < 0.05) and AUC(0-24) (+54%, P < 0.05) also increased. Due to the variability of the mirtazapine plasma levels in patients, the clinical meaning of these increases is probably limited. Co-administration of mirtazapine did not alter cimetidine pharmacokinetics.

High-performance liquid chromatographic assay with fluorescence detection for the routine monitoring of the antidepressant mirtazapine and its demethyl metabolite in human plasma

A validated HPLC method for the simultaneous quantitative analysis of the antidepressant mirtazapine and its demethyl metabolite in human plasma is described. The active constituents including internal standard were extracted from 1 ml of plasma with hexane and separated on a μBondapak Phenyl column with fluorescence detection. The lower limit of quantification was 0.5 ng/ml, without significant interferences with endogenous or exogenous components. Inter- and intra-assay accuracy determined at quality control levels of 2, 10 and 80 ng/ml were, respectively, 104.6–113.7% and 105.1–117.7% for mirtazapine, and 91.7–99.3% and 89.9–103.7% for demethylmirtazapine. In all cases the precision was below 6.8%.

Comparison of the effects of antidepressants and their metabolites on reuptake of biogenic amines and on receptor binding.

1. The present survey compares the effects of antidepressants and their principal metabolites on reuptake of biogenic amines and on receptor binding. The following antide-pressants were included in the study: the tricyclic antidepressants amitriptyline, dothiepin, and lofepramine and the atypical antidepressant bupropion, which all have considerable market shares in the UK and/or US markets; the selective serotonin reuptake inhibitors (SSRIs) citalopram, fluoxetine, fluvoxamine, paroxetine, and sertraline; and the recently approved antidepressants venlafaxine and nefazodone. 2. Amitriptyline has similar in vitro reuptake inhibitory potencies for 5-HT and NA, whereas the metabolite nortriptyline is preferentially a NA reuptake inhibitor. Both amitriptyline and nortriptyline are also 5-HT2 receptor antagonists. 3. Dothiepin has equipotent 5-HT and NA reuptake inhibitory activity, whereas northiaden shows a slight selectivity for NA reuptake inhibition. Dothiepin and northiaden are also 5-HT2 receptor antagonists. The slow elimination rate of northiaden (36-46 hr) compared to dothiepin (14-24 hr) suggests that northiaden contributes significantly to the therapeutic effect of dothiepin. 4. Lofepramine is extensively metabolized to desipramine. Desipramine plays an important role in the antidepressant activity of lofepramine, as the plasma elimination half-life of lofepramine (4-6 hr) is much shorter than that of desipramine (24 hr). Both compounds are potent and selective inhibitors of NA reuptake. 5. The five approved SSRIs, citalopram, fluoxetine, fluvoxamine, paroxetine, and sertraline, are potent 5-HT reuptake inhibitors, and the demethyl metabolites, norfluoxetine, demethylsertraline, and demethylcitalopram, also show selectivity. Paroxetine and sertraline are the most potent inhibitors of 5-HT reuptake, whereas citalopram is the most selective. Fluoxetine is the least selective and the metabolite of fluoxetine, norfluoxetine, is a more selective and more potent 5-HT reuptake inhibitor than the parent compound and has an extremely long half-life (7-15 compared to 1-3 days). Thus the metabolite plays an important role for the therapeutic effect of fluoxetine. Fluoxetine is also a 5-HT2C receptor antagonist. Demethylsertraline is a weaker and less selective 5-HT reuptake inhibitor in vitro than sertraline, but demethylsertraline has a very long half-life (62-104 hr) compared to the parent compound (24 hr) and it might play a role in the therapeutic effects of sertraline. Demethylcitalopram has about a 10 times lower 5-HT reuptake inhibitory potency in vitro than citalopram, and the elimination half-lives are approximately 1.5 and 2 days, respectively. 6. Bupropion and hydroxybupropion are weak inhibitors of biogenic amine reuptake. The mechanisms of action responsible for the clinical effects of bupropion are not fully understood, but it has been suggested that both dopaminergic and noradrenergic components play a role and that the hydroxybupropion metabolite contributes significantly to the antidepressant activity. 7. Venlafaxine and O-demethylvenlafaxine are weak inhibitors of 5-HT and NA reuptake, and the selectivity ratios are close to one. O-Demethylvenlafaxine is eliminated more slowly than venlafaxine (plasma half-lives of 5 and 11 hr, respectively), and it is likely that it contributes to the overall therapeutic effect of venlafaxin. 8. Nefazodone and alpha-hydroxynefazodone are equipotent 5-HT and NA reuptake inhibitors. Both compounds are also 5-HT2 receptor antagonists. Both parent compound and metabolite have short elimination half-lives.

In Vitro and In Vivo Studies on the Disposition of Mirtazapine in Humans

The novel antidepressant mirtazapine is a racemate with both noradrenergic and serotonergic potentiating effects. In vitro metabolism of racemic mirtazapine was studied in (a) microsomes from cells expressing different cytochrome P450 (CYP) enzymes and (b) human liver microsomes from 10 subjects and compared with the rate of metabolism of 4 substrates of specific CYP enzymes: ethoxyresorufin (CYP1A2), diclofenac (CYP2C9), bufuralol (CYP2D6) and testosterone (CYP3A4). These experiments suggested that the 8-hydroxylation of mirtazapine is catalysed by CYP2D6, and that the N(2)-demethylation and N(2)-oxidation are catalysed by CYP3A4. Mirtazapine was shown to be a competitive inhibitor of the CYP2D6 mediated hydroxylation of bufuralol in vitro, but with a 10 times higher inhibition constant (Ki) than for fluoxetine, i.e. mirtazapine is a much weaker inhibitor. To investigate the importance of CYP2D6 for the in vivo disposition of mirtazapine, a single oral dose of racemic mirtazapine was given to 7 extensive (EM) and 7 poor metabolisers (PM) of debrisoquine. Plasma concentrations (sum of enantiomers) of mirtazapine and its demethyl metabolite were monitored over 3 days. Oral plasma clearance of mirtazapine was very similar in EM and PM of debrisoquine (0.51 ±0.18 and 0.49 ± 0.22 L/h/kg, respectively; NS). In addition, the mean half-lives were almost identical: 23.4 and 23.3 hours, respectively. Plasma concentrations of demethylmirtazapine were also very similar in EM and PM. This in vivo study indicates that the major enantiomer of mirtazapine in plasma is not metabolised by CYP2D6, but it cannot be excluded that the minor one is. A study using a chiral analysis of the 2 enantiomers is currently ongoing. From a clinical point of view it is unlikely that mirtazapine would inhibit the metabolism of coadministered drugs metabolised by CYP1A2, CYP2D6 or CYP3A4. The panel study on EM and PM shows that strong inhibitors of CYP2D6 would not be expected to affect the concentration of the major mirtazapine enantiomer, but the effect on the minor enantiomer cannot be predicted.

Diazepam metabolism in native Chinese poor and extensive hydroxylators of S-mephenytoin: Interethnic differences in comparison with white subjects

A single oral 5 mg dose of diazepam was given to 16 healthy native Chinese Han volunteers. Eight volunteers were extensive metabolizers of S-mephenytoin, and eight were poor metabolizers of S-mephenytoin. Plasma levels of diazepam and its demethyl metabolite were determined by HPLC in blood samples drawn during 4 weeks. There was no difference in diazepam disposition between the two phenotypes. However, the plasma half-life of demethyldiazepam was longer in poor metabolizers than in extensive metabolizers of mephenytoin (mean +/- SD: 161 +/- 37 and 116 +/- 29 hours, respectively; p less than 0.02). The plasma concentrations of demethyldiazepam at 7, 14, and 21 days after intake of diazepam were significantly higher in poor metabolizers than in extensive metabolizers. We compared the pharmacokinetic parameters of diazepam in Chinese subjects with our previously reported data from white subjects. The mean plasma half-life values of diazepam in Chinese extensive metabolizers (85.1 hours) and poor metabolizers (88.3 hours) were very similar to those in white subjects who were poor metabolizers (88.3 hours), and more than twice those in white subjects who were extensive metabolizers (40.8 hours). In parallel, the mean clearance of diazepam in Chinese subjects (independent of phenotype) was similar to that in white subjects who were poor metabolizers, but half that in white subjects who were extensive metabolizers. Chinese subjects had a slightly larger volume of distribution of diazepam than white subjects.(ABSTRACT TRUNCATED AT 250 WORDS)

Clomipramine Metabolism

A steady-state model is here developed as a framework for the analysis of blood concentrations of clomipramine, obtained during routine drug monitoring. A model is proposed to account for its major metabolic pathways, hydroxylation and demethylation, including first-pass effect. Impaired hydroxylation capacity is shown to lead to a dramatic increase in the concentration of demethyl-clomipramine, with a concomitant moderate increase in that of the parent drug. Deficient demethylation capacity is associated with a reduced ratio of demethyl metabolite to parent drug. A nomogram is provided to allow easy determination of hydroxylation and demethylation capacities from routinely measured blood concentrations. Data from 150 patients are analysed in order to identify interindividual variability factors. Average pseudo-clearances, calculated from trough blood concentrations at steady-state, are 17 L/h for hydroxylation, 23 L/h for demethylation and 40 L/h for elimination of hydroxylated metabolites. Maximum to minimum ratios are 8, 27 and 11, respectively. The metabolising capacity through either process significantly decreases with increasing age, clearance estimates being 40 to 50% lower for patients 75 years or older than for those 40 years or younger. Tobacco smoking and chronic alcohol consumption induce and reduce the demethylation clearance, respectively. Inhibition of hydroxylation in the presence of phenothiazine comedication is also shown. Finally, small but significant differences according to sex are observed. Potential implications of the proposed model-based approach include adaptation of the dosage regimen to individual characteristics at the very beginning of antidepressant therapy, and early detection of patients with impaired metabolising capacities.

Contributions of the enantiomers of mirtazapine (Org 3770) and of its demethyl metabolite to its neurophamacological profile in rats

Contributions of the enantiomers of mirtazapine (Org 3770) and of its demethyl metabolite to its neurophamacological profile in rats

Pharmacokinetics of toremifene

The pharmacokinetics of toremifene has been investigated in man after single and multiple oral doses. Toremifene was completely absorbed without first-pass metabolism. Peak concentration in serum was achieved in 4 h. Mean half-lives of distribution and elimination were 4 h and 5 days, respectively. Kinetics was linear in the studied dose-range of 10–680 mg. Toremifene was over 99% bound to plasma proteins and extensively metabolized. The main metabolites in serum were demethyl- and deaminohydroxytoremifene. In patients receiving multiple dosing of 60 mg/day serum steady-state level of toremifene was 0.8 μg/ml on average. The level of demethyl metabolite was twice and that of deaminohydroxy metabolite was one tenth of toremifene.

High-performance liquid chromatographic assay of fenflumizole and its demethyl metabolites in biological samples

This paper describes sensitive, selective and precise methods for the assay of fenflumizole and its chromatographically verified demethyl and didemethyl metabolitesin whole blood, isolated red blood cells, plasma, saliva, urine and tissue (skin and fat) from human subjects. Also conjugates of the two metabolites with glucuronic acid and sulphate were assayable. The compounds were quantitated by means of reversed-phase liquid chromatography after diethyl ether extraction, followed by fluorescence and/or electrochemical detection. The assay using fluorescence detection is quantitative down to ca. 150 pg/ml; with electrochemically this limit was ca. 600 pg/ml and included the demethyl metabolites only. Proteinaceous materials show an extraction yield of 70–75%, whereas analytes in sample materials without proteins show yields of better than 95%. The precision at concentration levels of ca. 50 ng/ml for the parent compound and ca. 5 ng/ml for the metabolites is at most 6% (relative standard deviation) with both detection modes. The analytical procedures developed were applied after both single and repetitive administration of fenflumizole. The administration of 14C-labelled fenflumizole in the single-dose study revealed the presence in plasma and urine of as yet unknown metabolites. The in vivo retention time of 14C activity was substantially greater in the blood cells than in plasma. Measurements of 14C activity in excreta demonstrated that excretion via the faeces is the preferred route.

Pharmacokinetics of Dothiepin in Humans: A Single Dose Dose–Proportionality Study

Dothiepin hydrochloride (N,N-dimethyldibenzo[b,e]thiepin-Δ11(6 H),γ-propylamine hydrochloride) is a tricyclic antidepressant which is structurally similar to amitriptyline. Twenty-seven healthy men received three single oral doses of 50-, 100-, and 150-mg dothiepin hydrochloride capsules in a three-way randomized, crossover dose–proportionality study. Plasma concentration-time profiles of dothiepin (1) were described by both one- and two-compartment models with first-order absorption. The total intrinsic clearance of dothiepin decreased from 165.5 to 121.1L/h as the dose was increased from 50 to 150mg, but there was no significant effect on the terminal half-life (∼20 h). Plasma concentration-time profiles of the three major metabolites of dothiepin, the S-oxide derivative of dothiepin, N,N-dimethyl[b,e]thiepin-Δ11(6 H),γ-propylamine 5-oxide (2), the demethyl derivative, N-methyldi-benzo[b,e]thiepin-Δ11(6 H),γ-propylamine (3) and the demethyl S-oxide derivative N-methyldibenzo[b,e]thiepin-Δ11(6 H),γ-propylamine 5-oxide (4), were described by a one-compartment model with apparent first-order formation. The AUC∞ values of the S-oxide 2 and the demethyl S-oxide 4 increased proportionally with dose. The dose proportionality of the demethyl metabolite 3 may not be ascertained from the data in this study. The corresponding half-lives of the three metabolites, which are dose independent, were approximately 24, 28, and 40 h, respectively.

Determination of Trimipramine and Metabolites in Plasma by Liquid Chromatography with Electrochemical Detection

A procedure for the determination of trimipramine, the demethyl, 2-hydroxy, and 2-hydroxy demethyl metabolites in plasma by liquid chromatography with electrochemical detection is described. A 1-mL plasma sample is made alkaline with a carbonate buffer (pH 9.8) and extracted with 20% ethyl acetate in n-heptane. After back-extraction into an acid phosphate buffer, an aliquot is injected onto a reverse-phase trimethylsilyl-packed column and eluted with a phosphate buffer-acetonitrile mobile phase (65:35) containing n-butylamine. The peaks were detected at +1.1 V versus the silver-silver chloride reference electrode. The method provides absolute recoveries of 60–91% and a day-to-day precision of <9% for all compounds. The minimum quantifiable level for all compounds was 3 ng/mL. Steady-state plasma concentration data for 29 depressed patients receiving either 75 mg or 150 mg/d is reported.

Serotonin and noradrenaline uptake inhibitors in the treatment of depression--relationship to 5-HIAA in spinal fluid.

Evidence is accumulating that endogenous depression, in spite of its relatively uniform clinical picture, may have different pathophysiological correlates, and that these may predict the outcome of treatment. The distribution of the serotonin (5‐HT) metabolite, 5‐hydroxyindoleacetic acid (5‐HIAA) in the spinal fluid (CSF) from depressed patients has repeatedly been shown to be bimodal, provided that sufficiently sensitive biochemical methods (mass fragmentography) are used for the analysis.A study of nortriptyline revealed a poor antidepressant effect of this typical noradrenaline (NA) uptake blocker in patients with low pretreatment CSF 5‐HIAA. Chlorimipramine (CI), which is a potent 5‐HT uptake blocker in vitro and in animals was therefore given to depressed patients. The serotonin effects were borne out by a profound decrease in CSF 5‐HIAA. This effect, which is presumably mediated by feed‐back inhibition of 5‐HT synthesis was correlated to the plasma concentration of CI, but only up to a certain plasma level. Above this, there was little effect on 5‐HIAA, suggesting that high concentrations of CI may block 5‐HT receptors. The concentration of the NA metabolite, 4‐hydroxy‐3‐methoxyphenyl glycol (HMPG) in CSF decreased in proportion to the demethyl metabolite (DMCI) concentration in plasma. DMCI is a potent NA uptake blocker in vitro. Patients with low pretreatment CSF 5‐HIAA reacted equally well to treatment with CI as those with high levels, but only in the latter group was there a correlation to plasma levels (between DMCI and antidepressant effect). The antidepressant effect was also correlated to HMPG reduction in CSF, suggesting that these patients recover in proportion to drug effect on NA