Disposition of bazedoxifene in rats.

Bazedoxifene acetate (BZA), a novel selective estrogen receptor modulator, is currently being developed for the prevention and treatment of osteoporosis in post-menopausal women. In this study, the disposition of BZA was determined in the rat, a pharmacology and safety model. After a single 0.2 mg/kg intravenous (IV) administration to ovariectomized female rats, the plasma clearance (3.9 L/h/kg) and volume of distribution (16.8 L/kg) of BZA were high and the elimination half-life was short (3.8 h). The bioavailability was low (16%) after a 1 mg/kg oral dose of BZA. Radioactivity was rapidly absorbed (t(max) = 0.35 h), widely distributed into tissues and slowly eliminated (t(1/2) = 29 h) in female rats following a 1 mg/ kg oral dose of [(14)C]BZA. Following a 3 mg/kg oral dose to male rats, the tissue to plasma ratios of radioactivity ranged from 1 to 55 at 2 and 8 h post-dose in ascending order in heart, kidney, lung, and liver. BZA was extensively metabolized in both male and female rats. BZA-5-glucuronide was the major metabolite and BZA-4'-glucuronide was minor in plasma and tissues. Both glucuronides were major metabolites in bile. In vitro metabolite profiles were similar in rat liver and intestinal microsomes and they qualitatively correlated well with bile profiles. Feces was the major route of excretion (>97%) after the IV or oral dose. BZA was the predominant radioactive component in feces.

Etodolac kinetics in the elderly.

The effects of age and chronic dosing on the pharmacokinetics of the anti-inflammatory drug etodolac were evaluated in healthy young subjects, healthy elderly subjects, and elderly patients with osteoarthritis. After either single or chronic (7 days) dosing, both the healthy elderly subjects and the elderly patients with osteoarthritis had values for etodolac peak concentration, time to reach peak concentration, the AUC from 0 to 24 hours, elimination t1/2, and free fraction that did not differ significantly from those in the young (control) subjects. Despite the expected increases in the peak concentration and AUC from 0 to 24 hours for all groups after chronic dosing, there were no changes in etodolac free fraction, time to peak concentration, or t1/2. Because significant accumulation of etodolac was not observed in our elderly participants, adjustment of dosage when elderly subjects receive etodolac therapy is not indicated.

Population distribution and effects on drug metabolism of a genetic variant in the 5' promoter region of CYP3A4.

BACKGROUND: There are large interindividual differences in CYP3A4 expression and in the metabolism of drug substrates for this enzyme. We and others have identified a polymorphism in the 5' promotor region of the CYP3A4 gene; however, its functional significance is not currently known. This study was conducted to determine whether this polymorphism plays a clinically important role in determining CYP3A4 phenotype. METHODS: An adenine (A) to guanine (G) transition was identified in the 5' promotor region of the CYP3A4 gene at position -292 (from the start codon), in a sequence motif known as the nifedipine-specific element. The frequency of this polymorphism was assessed in 802 healthy volunteers from five broadly defined racial groups. The population distribution of the G allele in these groups was as follows: white Americans (3.6%; n = 273), black Americans (54.6%, n = 186), Hispanic Americans (9.3%; n = 188), Japanese Americans (0.0%; n = 77), and Chinese Americans (0.0%; n = 78). In a subsequent study, 90 additional black Americans were genotyped, and a subset of the homozygous subjects (AA, n = 8; GG, n = 23) were given the CYP3A4 probe substrates erythromycin and nifedipine to allow genotype-phenotype comparisons to be made. RESULTS: There was no difference in the rate of CYP3A4-dependent demethylation of erythromycin (erythromycin breath test) or the pharmacokinetics of nifedipine or its CYP3A4-dependent metabolite dehydronifedipine between the two genotype groups (AA or GG). CONCLUSIONS: This promotor region polymorphism does not appear to play a major role in determining constitutive CYP3A4 expression.

Metabolism of equilin sulfate in the dog.

The metabolism of equilin sulfate was determined in female dogs receiving 2.5 mg/kg of [3H]equilin sulfate alone or in a preparation that contained all the components that are present in the conjugated equine estrogen product Premarin. The pharmacokinetic parameters of total radioactivity indicated that the drug is rapidly absorbed and it has a moderate half-life in plasma. The total radioactivity in plasma following administration of [3H]equilin sulfate as part of a mixture of conjugated equine estrogens had significantly lower peak concentration (Cmax), a lower area under the curve (AUC), a longer terminal half-life (t1/2) and a longer mean residence time (MRT) than when [3H]equilin sulfate was given alone, indicating that the other components in the conjugated equine estrogen preparation altered the pharmacokinetics of equilin sulfate. An average of 26.7 +/- 4.4% of the administered radioactive dose was excreted in urine of dogs receiving [3H]equilin sulfate. Again, a significantly lower percentage (21.4 +/- 6.3%, P = 0.023) was eliminated in urine of dogs receiving [3H]equilin sulfate in the conjugated equine estrogen preparation, indicating that the absorption of equilin sulfate was perhaps altered by the other components in the conjugated equine estrogen preparation. Metabolite profiles of plasma and urine were similar. Equilin, equilenin, 17 beta-dihydroequilenin, 17 beta-dihydroequilin, 17 alpha-dihydroequilenin and 17 alpha-dihydroequilin were present in both matrices. 17 beta-Dihydroequilin and equilin were the two major chromatographic peaks in plasma samples. 17 beta-Dihydroequilenin and 17 beta-dihydroequilin were the major metabolites in urine. In conclusion, following oral administration of [3H]equilin sulfate to dogs, the radioactivity is rapidly absorbed. The disposition of equilin sulfate is altered by the other components that are present in the conjugated equine estrogen preparation Premarin. The reduction of the 17-keto group and aromatization of ring-B are the major metabolic pathways of equilin in the dog.

Metabolic disposition of 14C-bromfenac in healthy male volunteers.

The metabolic disposition of 14C-bromfenac, an orally active, potent, nonsteroidal, nonnarcotic, analgesic agent was investigated in six healthy male subjects after a single oral 50-mg dose. The absorption of radioactivity was rapid, producing a mean maximum plasma concentration (Cmax) of 4.9 +/- 1.8 microg x equiv/mL, which was reached 1.0 +/- 0.5 hours after administration. Unchanged drug was the major component found in plasma, and no major metabolites were detected in the plasma. Total radioactivity recovered over a 4-day period from four of the six subjects averaged 82.5% and 13.2% of the dose in the urine and feces, respectively. Excretion into urine was rapid; most of the radioactivity was excreted during the first 8 hours. Five radioactive chromatographic peaks, a cyclic amide and four polar metabolites, were detected in 0- to 24-hour urine samples. Similarity of metabolite profiles between humans and cynomolgus monkeys permitted use of this animal model to generate samples after a high dose for structure elucidation. Liquid chromatography/mass spectrometry (LC/MS) analysis of monkey urine samples indicated that the four polar metabolites were two pairs of diastereoisomeric glucuronides whose molecular weight differed by two daltons. Enzyme hydrolysis, cochromatography, and LC/MS experiments resulted in the identification of a hydroxylated cyclic amide as one of the aglycones, which formed a pair of diastereoisomeric glucuronides after conjugation. Data also suggested that a dihydroxycyclic amide formed by the reduction of the ketone group that joins the phenyl rings formed the second pair of diastereoisomeric glucuronides. Further, incubation of various reference standards in control (blank) urine and buffer with and without creatinine indicated that the hydroxy cyclic amide released from enzyme hydrolysis can undergo ex vivo transformations to a condensation product between creatinine and an alpha-keto acid derivative of the hydroxy cyclic amide that is formed by oxidation and ring opening. Further experiments with a dihydroxylated cyclic amide after reduction of the keto function indicated that it too can form a creatinine conjugate.

Metabolic disposition and pharmacokinetics of pelrinone, a new cardiotonic drug, in laboratory animals and man.

The metabolic disposition of pelrinone, a cardiotonic drug, was studied in mouse, rat, rabbit, dog, monkey and man. Pelrinone was rapidly and extensively absorbed in rodents, dogs, monkeys and man. Except in rabbits, the major portion of the serum radioactivity was due to parent drug. Pelrinone was moderately bound to human serum proteins and weakly bound to serum proteins from animals. Radioactive compounds were rapidly eliminated from rat tissues with the highest concentrations found in organs associated with absorption and elimination. After a 1.0 mg/kg i.v. dose, the rapid elimination of pelrinone from mouse, rat and dog serum precluded estimation of an elimination half life (t1/2). However, after higher oral or i.v. doses, a more prolonged elimination phase was apparent and the t1/2 of pelrinone ranged from 8-10 h in rodents and dogs. In human subjects given escalating oral or i.v. doses of pelrinone, the elimination t1/2 was independent of dose and averaged 1-2 h. The serum AUC of pelrinone was linearly dose-related following oral doses up to 20 mg/kg in dogs and 100 mg in man. In mice, a greater proportional increase in AUC occurred between oral doses of 2-100 mg/kg while in rats, the serum AUC increased in less than proportional manner from 10-200 mg/kg p.o. In all species, radioactive compounds were excreted mainly in the urine. No metabolites were detected in dog and human urine while small amounts of unconjugated metabolites were excreted in mouse and rat urine.

Effects of ertiprotafib on hepatic cytochrome P450 and peroxisomal enzymes in rats and dogs, and in rat and human primary hepatocytes.

Ertiprotafib (ERTI) significantly increased liver weights in male and female rats, and moderately increased liver weights in male dogs after treatment for 28 days. The present study tested the hypotheses that the organ weight increases were associated with peroxisome proliferation in rats and induction of hepatic enzymes in rats and dogs, and would have limited impacts on humans. At a dosage of 200 mg kg-1 day-1, CYP4A was induced by tenfold in male rats and 2.4-fold in female rats. In male rats, CYP2B was induced by 1.2-fold and CYP3A was induced by 1.7-fold. Palmitoyl CoA oxidase was induced by 5.1-fold in male rats and 2.9-fold in female rats; carnitine acetyltransferase was induced by 10.4-fold in male rats and 5.2-fold in female rats. CYP3A, CYP4A and peroxisomal enzymes were not induced in dogs at 150/200 mg kg-1 day-1. ERTI at 50 microM markedly induced the mRNA level of CYP4A by up to fivefold in rat hepatocytes, but not in human primary hepatocytes. In conclusion, the liver weight increases observed in rats treated with ERTI appears to be due to rodent-specific peroxisome proliferation and the substantial induction of CYP4A1. ERTI is not a potent P450 inducer in dogs or in human hepatocytes. Therefore, ERTI is not expected to exert any significant effects on hepatic drug-metabolizing enzymes in humans.

The effect of Alcide, a new antimicrobial drug, on rat blood glutathione and erythrocyte osmotic fragility, in vitro.

Alcide is an antimicrobial drug which has been demonstrated to kill a variety of common pathogenic bacteria as well as fungi, in vitro. This agent is supplied in liquid and gel forms and consists of two parts, one of which contains sodium chlorite, while the other contains lactic acid as the active ingredients. Mixing of the two parts prior to use produces chlorine dioxide (ClO2), a strong oxidizing agent. A dose-dependent decrease in glutathione content and erythrocyte osmotic fragility occurred after incubation of whole blood with Alcide. Glutathione concentration and erythrocyte osmotic fragility approached the control values after 240 min of incubation with Alcide containing 1 mM NaClO2. The addition of exogenous glutathione (50 mg 100 ml-1) or glutathione reductase and NADPH to rat blood in the presence of Alcide returned erythrocyte osmotic fragility to control values. Treatment of rat blood with Alcide did not change glutathione reductase or glutathione peroxidase activities after 1 h of incubation.

Venlafaxine: in vitro inhibition of CYP2D6 dependent imipramine and desipramine metabolism; comparative studies with selected SSRIs, and effects on human hepatic CYP3A4, CYP2C9 and CYP1A2.

AIMS: In order to anticipate drug-interactions of potential clinical significance the ability of the novel antidepressant, venlafaxine, to inhibit CYP2D6 dependent imipramine and desipramine 2-hydroxylation was investigated in human liver microsomes. The data obtained were compared with the selective serotonin re-uptake inhibitors, fluoxetine, sertraline, fluvoxamine and paroxetine. Venlafaxine's potential to inhibit several other major P450 s was also studied (CYP3A4, CYP2D6, CYP1A2). METHODS: Ki values for venlafaxine, paroxetine, fluoxetine, fluvoxamine and sertraline as inhibitors of imipramine and desipramine 2-hydroxylation were determined from Dixon plots of control and inhibited rate data in human hepatic microsomal incubations. The inhibitory effect of imipramine and desipramine on liver microsomal CYP2D6 dependent venlafaxine O-demethylation was determined similarly. Venlafaxine's IC50 values for CYP3A4, CYP1A2 CYP2C9 were determined based on inhibition of probe substrate activities (testosterone 6 beta-hydroxylation, ethoxyresorufin O-dealkylase and tolbutamide 4-hydroxylation, respectively). RESULTS: Fluoxetine, paroxetine, and fluvoxamine were potent inhibitors of imipramine 2-hydroxylase activity (Ki values of 1.6 +/- 0.8, 3.2 +/- 0.8 and 8.0 +/- 4.3 microM, respectively; mean +/- s.d., n = 3), while sertraline was less inhibitory (Ki of 24.7 +/- 8.9 microM). Fluoxetine also markedly inhibited desipramine 2-hydroxylation with a Ki of 1.3 +/- 0.5 microM. Venlafaxine was less potent an inhibitor of imipramine 2-hydroxylation (Ki of 41.0 +/- 9.5 microM) than the SSRIs that were studied. Imipramine and desipramine gave marked inhibition of CYP2D6 dependent venlafaxine O-demethylase activity (Ki values of 3.9 +/- 1.7 and 1.7 +/- 0.9 microM, respectively). Venlafaxine did not inhibit ethoxyresorufin O-dealkylase (CYP1A2), tolbutamide 4-hydroxylase (CYP2C9) or testosterone 6 beta-hydroxylase (CYP3A4) activities at concentrations of up to 1 mM. CONCLUSIONS: It is concluded that venlafaxine has a low potential to inhibit the metabolism of substrates for CYP2D6 such as imipramine and desipramine compared with several of the most widely used SSRIs, as well as the metabolism of substrates for several of the other major human hepatic P450s.

The inhibitory effect of Alcide, an antimicrobial drug, on protein synthesis in Escherichia coli.

Alcide, a broad-spectrum antimicrobial drug, has been shown to kill a wide range of common pathogenic bacteria as well as fungi, in vitro. This agent consists of Part A and Part B which contain sodium chlorite and lactic acid as the active ingredients, respectively. The mixing of these two parts immediately prior to use results in the formation of chlorine dioxide (ClO2), a potent germicidal compound. Exposure of exponentially growing E. coli cells to Alcide resulted in a rapid inhibition of growth as well as loss of viability. Alcide inhibited DNA, RNA, and protein synthesis; however, RNA and protein synthesis were affected at much lower concentrations. The accumulation of the amino acid analog amino-isobutyric acid into growing cultures of E. coli was only partially impaired by Alcide. Cell-free protein synthesis using an RNA directed system was inhibited by Alcide and this effect was lessened in the presence of mercaptoethanol. Higher concentrations of Alcide (1 mM) oxidized 25% of the methionine to methionine sulfoxide. Aminoacylation of E. coli bulk tRNA was decreased in vitro and the aminoacylation of tRNAfMet was particularly sensitive to Alcide.

Pharmacokinetics of Alcide, a germicidal compound in rat.

Alcide is a germicidal compound which is currently being used as a liquid sterilizer. This agent has the ability to kill a wide range of bacteria, viruses and fungi in vitro within 1 min. The active ingredients in this sterilizer are sodium chlorite and lactic acid. The kinetics of 36Cl-labelled liquid Alcide were studied in rats. After oral administration, the peak plasma level was obtained in 8 h. The half life for 36Cl absorption from plasma was 8.03 h, corresponding to a rate constant of 0.086 h-1, while the half life for 36Cl elimination from plasma was 48.02 h, corresponding to a rate constant of 0.014 h-1. At 144 h, radioactivity was highest in plasma followed by lung, kidney, skin, bone marrow, stomach, ovary, duodenum, ileum, spleen, fat, brain, liver and carcass. The greatest amount of activity in whole blood was present in plasma. Subcellular distribution revealed that 85% of the activity in the liver homogenate resided in the cytosol. Seventy per cent of total activity in plasma was located in the trichloroacetic acid (TCA) supernant, with 30% bound to the precipitated protein fraction. Urinary excretion accounted for most of the 36Cl eliminated. Radioactivity was excreted as chloride and chlorite in urine.

Pharmacodynamics of alcide, a new antimicrobial compound, in rat and rabbit.

Alcide is a germicidal preparation which has been shown to kill a wide range of common pathogenic bacteria as well as fungi, in vitro. This preparation is composed of Part A and Part B which contains sodium chlorite (NaClO2) and lactic acid as the active ingredients, respectively. The two parts are combined in equal volumes immediately prior to application resulting in the formation of chlorine dioxide (ClO2). Alcide gel was applied to the shaven backs of 18 female Sprague-Dawley rats in a 2.0-g/kg dose by combining 1 g of each part immediately prior to administration. This dose was applied for a period of 10 days to reach a steady state. On the 11th day, 36Cl-labeled Alcide gel, which contained Na36ClO2 in Part A, was administered to the animals in a 0.6-g dose (2.0 g/kg) containing 0.1 microCi. The half-life for 36Cl absorption was 22.1 hr while the elimination half-life was 64.0 hr. 36Cl was excreted by the kidneys with chloride (Cl-) and chlorite as the metabolites. Ninety-six hours after Alcide administration, radioactivity was highest in whole blood and lowest in fat. In a 90-day subchronic dermal toxicity study in rabbits, exposure to Alcide gel resulted in decreased glutathione concentrations in blood of the group receiving 2.0 g/kg Alcide as well as in the placebo gel group which received the same dose of gel.

The application of in vitro models of drug metabolism and toxicity in drug discovery and drug development.

In vitro models are being used increasingly during all phases of the drug development process in concert with the more traditional in vivo toxicological and pharmacokinetic evaluations. These in vitro models may be classified empirically as either validated in vitro screens, value-added screens or 'ad-hoc' mechanistic screens. The application of these screens is discussed with respect to their level of validation, standardization, uses of human tissue, level of iteration with in vivo studies, regulatory position and utility in the drug discovery and development process. The predictability and reproducibility of these screens is discussed, as well as future trends in regard to emerging technology and its application.

The disposition of venlafaxine enantiomers in dogs, rats, and humans receiving venlafaxine.

A stereospecific high-performance liquid chromatographic (HPLC) method was developed for the quantitation of the enantiomers of venlafaxine, an antidepressant, in dog, rat, and human plasma. The procedure involves derivatization of venlafaxine with the chiral reagent, (+)-S-naproxen chloride, and a postderivatization procedure. The method was linear in the range of 50 to 5,000 ng of each enantiomer per ml of plasma. No interference by endogenous substances or known metabolites of venlafaxine occurred. Studies to characterize the disposition of the enantiomers of venlafaxine were conducted in dog, rat, and human, following oral administration of venlafaxine. The Cmax, area under the curve (AUC) and (S)/(R) concentration ratios of the (R)- and (S)-enantiomers were compared. In rats, the mean plasma ratio of (S)-venlafaxine to that of (R)-venlafaxine over 0.5 to 6.0 h varied from 2.97 to 8.50 with a mean value of 5.51 +/- 2.45. The Cmax, AUC0-infinity, and t 1/2 values of the (R)- and (S)-enantiomers in dogs were not significantly different from one another (P greater than 0.1). The mean ratios [(S)/(R)] of enantiomers of venlafaxine in human over a 2 to 6 h interval ranged from 1.33 to 1.35 with an overall ratio of 1.34 +/- 0.26 (n = 12). These ratios of the enantiomers [(S)/(R)] were not statistically different from unity (P greater than 0.1) indicating that the disposition of venlafaxine enantiomers in humans is not stereoselective and is more similar to that in dogs than that in rats.

Isolation and identification of bromfenac glucoside from rat bile.

Bromfenac (Duract(R)), a drug approved for pain, was expected to be metabolized by the rat to an acyl glucuronide, a metabolite formed with most compounds of similar structure. During the investigation of metabolite profiles in rat bile following administration of 1 mg/kg iv doses of 14C-bromfenac, an acid-labile metabolite was found that degraded to form 14C-bromfenac. Isolation and characterization of this metabolite indicated that it is an unusual conjugate, bromfenac N-glucoside.

Pharmacokinetics of venlafaxine and O-desmethylvenlafaxine in laboratory animals.

1. The pharmacokinetics of venlafaxine have been evaluated in mouse, rat, dog and rhesus monkey after i.v. and/or i.g. doses of venlafaxine from 2 to 120 mg/kg either as single or repeated doses. 2. In rat, dog and monkey, venlafaxine is a high clearance compound with a large volume of distribution after i.v. administration. 3. Absolute bioavailability was low in rat and rhesus monkey (12.6 and 6.5%, respectively) and moderate in dog (59.8%). Other species differences were seen, including an elimination half-life of venlafaxine that was longer in dog and rhesus monkey (2-4 h) than in rodent (around 1 h). 4. In mouse, rat and dog, exposure to venlafaxine increased more than proportionally with dose, suggesting saturation of elimination. Exposure of venlafaxine decreased with repeated dosing in mouse and rat, but was unchanged in dog. 5. Exposure of animals to the bioactive metabolite, O-desmethylvenlafaxine (ODV), was less than that of venlafaxine itself. ODV was not detected in dog and not measurable in rhesus monkey receiving venlafaxine.

Metabolic disposition of enciprazine, a non-benzodiazepine anxiolytic drug, in rat, dog and man.

1. The excretion and metabolism of enciprazine, an anxiolytic drug, was examined in rat, dog and man. 2. In rats and dogs that received 14C-enciprazine dihydrochloride orally and by i.v. injection, the drug was well absorbed. Radioactivity was excreted predominantly in the faeces of rats, equally in urine and faeces of dogs, and to a major extent in human urine. 3. Metabolic profiles, which were evaluated in urine and in rat bile, were similar following oral and i.v. dosing to rats and dogs. 4. Unchanged drug was not detected in rat, dog or human excreta. Glucuronide conjugates of 4-hydroxyenciprazine, m-desmethylenciprazine, p-desmethylenciprazine and enciprazine were detected in the excreta of all three species. A glycol metabolite was present only in rat bile and human urine. A metabolite desmethylated in the phenyl ring of the phenylpiperazine moiety also appeared to be present only in human urine. 5. Structural confirmation of the major metabolites in human urine and rat bile was accomplished by h.p.l.c.-mass spectrometry.

Determination of 17 alpha-dihydroequilenin in rat, rabbit and monkey plasma by high-performance liquid chromatography with fluorimetric detection.

A high-performance liquid chromatographic (HPLC) method with fluorescence detection for the determination of total (unconjugated and conjugated) 17 alpha-dihydroequilenin in male and female rat, female rabbit and male and female rhesus monkey plasma is described here. Plasma sample preparation involved hydrolysis with enzyme (Glusulase), addition of internal standard (14 beta-equilenin) and solvent extraction. The extracts were chromatographed on a C6, 5-microns reversed-phase HPLC column and detection was accomplished with a fluorescence detector operated at an excitation wavelength of 210 nm and an emission wavelength of 370 nm. The assay was linear over a range of 2.5 to 100 ng/ml in male and female rat plasma, and 5 to 500 ng/ml in female rabbit and male and female monkey plasma. The method was specific, accurate and reproducible (percent differences < 14.5; coefficients of variation < 9.5%) in all matrices examined. The applicability of this method was successfully tested by quantifying total plasma concentrations of 17 alpha-dihydroequilenin in ovariectomized female rats, ovariectomized female rabbits and a normal female rhesus monkey receiving 2.0, 8.3 and 0.1 mg/kg, respectively, of 17 alpha-dihydroequilenin sulfate intragastrically.

Simultaneous screen for microsomal stability and metabolite profile by direct injection turbulent-laminar flow LC-LC and automated tandem mass spectrometry.

A LC-LC/MS/MS method has been developed that significantly increases the throughput in metabolism screening of drug candidates during lead optimization in discovery. This was accomplished by the reduction of sample preparation time through an on-line extraction of a drug and its metabolites from microsomal proteins using turbulent flow chromatography. Following its injection onto a column at turbulent flow, the drug and its metabolites are backwashed onto a reverse-phase column via on-line column switching and resolved chromatographically at a laminar flow of 2 mL/min. This tandem turbulent-laminar flow chromatographic system in a total cycle time of 8 min can achieve adequate separation of isomeric metabolites of venlafaxine, haloperidol, or adatanserin. Further improvement in throughput can be achieved by multiplexing both microsomal stability assessment and metabolite profiling into a single analysis. This is made possible by the ability of the ion-trap mass spectrometer to perform simultaneously multiple-reaction monitoring for microsomal stability and data-dependent multiple-stage mass spectrometric analysis for metabolite profiling within a single LC analysis. Such a LC-LC/MS/MS approach can dramatically shorten the time for providing metabolism feedback to the drug discovery process.

Metabolic disposition of 14C-venlafaxine in mouse, rat, dog, rhesus monkey and man.

1. The metabolic disposition of venlafaxine has been studied in mouse, rat, dog, rhesus monkey and man after oral doses (22, 22, 2, and 10 mg/kg, and 50 mg, respectively) of 14C-venlafaxine as the hydrochloride. 2. In all species, over 85% of the administered radioactivity was recovered in the urine within 72 h, indicating extensive absorption from the GI tract and renal excretion. 3. Venlafaxine was extensively metabolized, with only 13.0, 1.8, 7.9, 0.3 and 4.7% dose appearing as parent compound in urine of mouse, rat, dog, monkey and man, respectively. The metabolite profile varied significantly among species, but primary metabolic reactions were demethylations and the conjugation of phase I metabolites. Hydroxylation of the cyclohexyl ring also occurred in mouse, rat and monkey, and a cyclic product was formed in rat and monkey. Glucuronidation was the primary conjugation reaction, although sulphate conjugates were also detected in mouse urine. 4. While no metabolite constituted more than 20% dose in any species except man, the major urinary metabolites were: mouse, N,O-didesmethyl-venlafaxine glucuronide; rat, cis-1,4-dihydroxy-venlafaxine; dog, O-desmethyl-venlafaxine glucuronide; monkey, N,N,O-tridesmethyl-venlafaxine; and man, O-desmethyl-venlafaxine.