Biomedical subjects

F S Abbott

Publications and source records attributed to F S Abbott.

At least 37 records · Page 2Linked to original sources

PubMed1996

Bioactivation of a toxic metabolite of valproic acid, (E)-2-propyl-2,4-pentadienoic acid, via glucuronidation. LC/MS/MS characterization of the GSH-glucuronide diconjugates.

The hepatotoxicity of the anticonvulsant drug valproic acid may be associated with the formation of potentially reactive metabolites, one of which is (E)-2-propyl-2,4-pentadienoic acid ((E)-2,4-diene VPA). This report describes the characterization of new GSH-related conjugates of this diene. Bile samples collected from male Sprague-Dawley rats dosed ip with (E)-2,4-diene VPA (100 mg/kg) were analyzed by LC/MS/MS. Initial Q1 parent in scanning indicated that the daughter ions m/z 162 and 123 could be derived from the ions at m/z 624 and 480, respectively. Subsequent collision-induced dissociation (CID) of these parent ions revealed a common neutral loss of 176 Da which is diagnostic for glucuronides. A similar neutral loss of 176 Da was observed in daughter ion spectra of the biliary metabolites arising from [2H7]-4-ene VPA dosed ip to rats, where the ion fragments containing the VPA portion were 7 amu higher than those derived from the unlabeled drug. CID of the ion at m/z 624 also gave fragments characteristics for GSH conjugates such as the loss of glycine and glutamate moieties. Based on the MS data, the metabolites were assigned the diconjugate structures 1-O-(2-propyl-5-(glutathion-S-yl)-3-pentenoyl)-beta-D-glucur onide (5-GS-3-ene VPA-glucuronide I, MH+, 624) and the corresponding 5-NAC-3-ene VPA-glucuronide (MH+, 480). Further proof of structural identity was obtained from 1H NMR of HPLC-purified metabolites. The amount of biliary 5-GS-3-ene VPA-glucuronide I was 7-fold greater than the corresponding 5-GS-3-ene VPA, the sum of the two metabolites accounting for 6.6% of the dose. Incubation of 1-O-(2-propyl-2,4-pentadienoyl)-beta-D-glucuronide (2,4-diene VPA-glucuronide) with GSH in the presence or absence of GST enzyme led to the formation of 5-GS-3-ene VPA-glucuronide I which was readily detected by LC/MS/MS, suggesting that in vivo the diconjugate may arise from the reaction of GSH with 2,4-diene VPA-glucuronide. To our knowledge, this is the first recorded instance in which glucuronide formation activates a drug to further conjugate with GSH via a Michael addition reaction.

Animals↗

PubMed1996

Comparative effects of carbamazepine and carbamazepine-10,11-epoxide on hepatic cytochromes P450 in the rat.

The effects of treatment with carbamazepine (CBZ), carbamazepine-10, 11-epoxide (CBZE), and phenobarbital (PB) on total hepatic cytochrome P450 and on cytochrome P450-mediated enzyme activity and protein levels were determined and compared in the present study. Adult male Long Evans rats were treated intraperitoneally with either CBZ (100 mg/kg) or CBZE (50 mg/kg) every 12 hr for 3, 7, 10, or 14 days, or PB (75 mg/kg/day) for 4 days. The dose of CBZE selected was half that of CBZ because serum levels of CBZE in patients on CBZ therapy are generally less than half those of the parent compound. The mean hepatic cytochrome P450 content for the CBZ treatment groups over the 14-day treatment period was 1.9-fold to 2.3-fold greater compared with the untreated group, whereas treatment with CBZE resulted in a more modest increase in total hepatic cytochrome P450. Pentoxyresorufin O-dealkylase and testosterone 2 beta-hydroxylase and 16 beta-hydroxylase activities, as well as androstenedione formation, were increased to a similar extent in CBZ-treated and PB-treated rats relative to the control groups. Immunoblot analysis indicated that hepatic levels of cytochromes P4502B1 and P4502B2 were highly induced, whereas cytochrome P4503A levels were increased slightly, by treatment with CBZ. In comparison, treatment with CBZE was approximately half as effective as CBZ for induction of pentoxyresorufin O-dealkylase activity, and for induction of cytochromes P4502B1/2B2 and cytochrome P4503A levels. In contrast, cytochrome P4501A1 and P4502E1 levels were not altered by treatment with CBZ, CBZE, or PB. The possibility that autoinduction of CBZ metabolism occurred was investigated, but urinary recoveries of CBZ, CBZE, and carbamazepine diol were too low to confirm this finding. In summary, the results demonstrated that cytochromes P4502B1 and P4502B2 are highly inducible by CBZ and CBZE. Maximal induction by CBZ occurred after 3 days of treatment at a dose of 100 mg/kg intraperitoneally every 12 hr and CBZ, when used at this dosage, was as effective as PB for inducing hepatic cytochrome P450. Maximal induction by CBZE also occurred after 3 days of treatment, but the extent of induction was less than that produced by CBZ, possibly because of the smaller dose used.

Animals↗

PubMed1996

Conjugation of glutathione with a toxic metabolite of valproic acid, (E)-2-propyl-2,4-pentadienoic acid, catalyzed by rat hepatic glutathione-S-transferases.

The hepatotoxic metabolite of the anticonvulsant drug valproic acid (VPA), namely (E)-2-propyl-2,4-pentadienoic acid (E)-2,4-diene VPA), is known to react with glutathione (GSH) in vivo. Although glutathione-S-transferase (GST) was suspected of being the catalyst for this conjugation reaction, this was yet to be confirmed. In this study, GST activities were detected in the hepatic cytosolic and sonic-disrupted mitoplast fractions isolated from male Sprague-Dawley rats by using 1-chloro-2,4-dinitrobenzene as a substrate. An elevation of GST activities by 45 to 100% was observed after pretreatment of rats with phenobarbital (PB). Subsequently, these apparent GST activities were examined for their effects on the in vivo conjugation of GSH with N-acetyl-S-((E)-2-propyl-2,4-pentadienoyl)cysteamine (2,4-diene VPA-NACA), a structural mimic of (E)-2,4-diene VPA coenzyme A thioester. Reaction products were identified and quantitated by combined liquid chromatography-tandem mass spectrometry. The GST-mediated conjugation of GSH with 2,4-diene VPA-NACA produced two structural isomers via either 5,6- or 1,6-addition of GSH. Only the 1,6- addition product was found for the spontaneous conjugation reaction (control). Quantitatively, GSH conjugates formed in the cytosolic fraction were 23-fold that of control. An additional 1.5-fold enhancement was observed in the cytosolic fraction from PB-treated rats. The production of the GSH conjugates was increased by 2-fold for reactions involving the sonic-disrupted mitoplasts, either from untreated or PB-treated rats. Partially purified GST was found to catalyze the conjugation reactions in a fashion similar to that of the isolated subcellular fractions. No reaction with GSH could be detected for the free acid form of (E)-2,4-diene VPA. As was the case with the in vitro data, two structural isomers of GSH conjugates were detected in the bile of rats that received (E)-2,4-diene VPA. These results indicate that in vivo production of the GSH conjugates of (E)-2,4-diene VPA is most likely catalyzed by GST enzymes, with the esterified diene being essential for the conjugation reaction. In a separate experiment, 2,4-diene VPA-NACA was observed to alkylate reduced oxytocin through one or both cysteine residues. Thus, the toxicity of (E)-2,4-diene VPA might be produced via either GST-promoted depletion of cellular GSH, or a direct modification of key proteins, or both.

Animals↗

PubMed1995

Structure-activity relationships of unsaturated analogues of valproic acid.

The principal metabolite of valproic acid (VPA), 2-ene VPA, appears to share most of VPA's pharmacological and therapeutic properties while lacking its hepatotoxicity and teratogenicity, thus making it a useful lead compound for the development of safer antiepileptic drugs. Analogues of 2-ene VPA were evaluated for anticonvulsant activity in mice using the subcutaneous pentylenetetrazole test. Cyclooctylideneacetic acid exhibited a potency markedly exceeding that of VPA itself with only modest levels of sedation. Potency, as either ED50 or brain concentration, was highly correlated (r > 0.85) with volume and lipophilicity rather than with one of the shape parameters calculated by molecular modeling techniques, arguing against the existence of a specific receptor site. Instead, a role for the plasma membrane in mediating the anticonvulsant effect is suggested.

Animals↗

PubMed1995

Determination of valproic acid and its metabolites using gas chromatography with mass-selective detection: application to serum and urine samples from sheep.

An improved method for the quantitative determination of valproic acid (VPA) and sixteen of its metabolites has been developed using gas chromatography-mass spectrometry with selected-ion monitoring. The method is applicable to serum or urine and all metabolites are measured in a single chromatographic run of 29.5 min. Ions selected for quantitative purposes were the characteristic [M-57]+ ions of the tert.-butyldimethylsilyl (tBDMS) derivatives. The method utilizes heptadeuterated VPA as well as six heptadeuterated metabolites as internal standards [i.e. 2-[2H7]propyl-2-pentenoic acid (2-ene[2H7]VPA), 2-[2H7]propyl-4-pentenoic acid (4-ene[2H7]VPA), 2-[2H7]propyl-3-oxopentanoic acid (3-keto[2H7]VPA), 2-[2H7]propyl-4-oxopentanoic acid (4-keto[2H7]VPA), 2-[2H7]propyl-3-hydroxypentanoic acid (3-OH[2H7]VPA), 2-[2H7]propyl-5-hydroxypentanoic acid (5-OH[2H7]VPA)]. The method demonstrates very good accuracy and precision over a large range of concentrations for VPA and all metabolites measured in both human and sheep biological fluids. The assay was applied to the analysis of VPA and metabolites in serum and urine samples collected from three non-pregnant ewes following intravenous bolus administration of a mixture of VPA and [13C4]VPA. Sheep were observed to produce measurable quantities of the majority of metabolites found in humans, with the notable exception of the di-unsaturated compounds (i.e. 2,3'-diene VPA and 2,4-diene VPA). The pharmacokinetics and metabolism of VPA and [13C4]VPA appear to be equivalent in the sheep model. The elimination half-life of VPA and [13C4]VPA in the ewe were estimated to be approximately 3.5 +/- 0.4 and 3.2 +/- 0.4 h, respectively.

Animals↗

PubMed1995

Simultaneous analysis of diphenylmethoxyacetic acid, a metabolite of diphenhydramine, and its deuterium-labeled stable isotope analog in ovine plasma and urine.

Diphenylmethoxyacetic acid (DPMA) is a major metabolite of diphenhydramine in monkeys, dogs, and humans. The metabolic fate of diphenhydramine (DPHM) in sheep is not yet well understood; however, preliminary studies have demonstrated the presence of DPMA in the plasma and urine of sheep following an intravenous bolus of DPHM. Our current studies employ the simultaneous intravenous co-administration of DPHM and the stable isotope analog of DPHM to investigate the pharmacokinetics of DPHM in sheep. In these studies, in order to investigate the pharmacokinetics of the DPMA metabolite, measurement of both unlabeled and stable-isotope labeled DPMA is required. Thus, a stable isotope analog of DPMA ([2H10]DPMA) was synthesized, characterized, and purified for use as an analytical standard. The quantitative method for the gas chromatography-electron-impact mass spectrometry (GC-EI-MS) analysis of DPMA and [2H10]DPMA used a single step liquid-liquid extraction procedure using toluene for sample cleanup. The samples were derivatized with N-methyl-N-(tert.-butyldimethylsilyl) trifluoroacetamide. A 1.0-microliter aliquot of the prepared sample was injected into the GC-MS system and quantitated using selected-ion monitoring (SIM). One ion was monitored for each compound, namely, m/z 165 for the internal standard diphenylacetic acid, m/z 183 for DPMA, and m/z 177 for [2H10]DPMA. The ion chromatograms were free from chromatographic peaks co-eluting with the compound of interest. The calibration curve was linear from 2.5 ng/ml (limit of quantitation) to 250.0 ng/ml in both urine and plasma. The intra-day and inter-day variabilities of this assay method were within acceptable limits (below 20% at the limit of quantitation and below 10% at all other concentrations). This method was used to measure the concentration of DPMA and [2H10]DPMA in plasma and urine samples from a ewe in which equimolar amounts of DPHM and [2H10]DPHM were administered by an intravenous bolus dose via the femoral vein. DPMA appeared to persist longer in the plasma and the urine as compared to DPHM. This method is robust and reliable for the quantitation of DPMA and [2H10]DPMA in biological samples obtained from sheep (e.g. plasma and urine).

Acetates↗

PubMed1995

Characterization of novel isocyanate-derived metabolites of the formamide N-formylamphetamine with the combined use of electrospray mass spectrometry and stable isotope methodology.

Bioactivation of the formamide N-formylamphetamine (NFA) to 1-methyl-2-phenylethyl isocyanate (MPIC) was investigated in rats by screening bile and urine for conjugates subsequent to the phase I event. NFA was administered to rats as a mixture of protio- and pentadeuteriophenyl analogues to gain insight into the carbamoylating activity of MPIC when traced by electrospray liquid chromatography/mass spectrometry (LC/MS). An LC/MS contour generated by recording the summed mass spectrum as a function of chromatographic retention time allowed four biliary metabolites to be identified from four sets of doublets, with the peak of each doublet offset by 5 amu and ca. 0.07 min. Tandem mass spectrometry experiments allowed these metabolites to be attributed structurally to the glutathione, cysteinylglycine, cysteine, and N-acetylcysteine conjugates of the isocyanate MPIC. These assignments were subsequently validated by comparison of the LC/MS properties of the metabolites to synthetic reference compounds. Only the carbamoylated N-acetylcysteine conjugate was detected in urine. The observed excretion in bile of all metabolites of the mercapturate pathway is novel for formamide metabolism. NFA can thus be added to the short list of compounds that are eliminated in this fashion. Factors envisioned as contributory to this metabolic profile in bile include hepatorenal, enterohepatic, and biliary-hepatic cycling, in addition to possible equilibrium exchange of the isocyanate from thiocarbamate conjugates to endogenous free thiols during the course of biliary transit.

Amphetamines↗

PubMed1995

New approaches for drug and kinetic analysis in the maternal-fetal unit.

The development of more sensitive and selective analytical techniques has greatly improved scientists' ability to study the PK, PD, and metabolism of drugs in pregnancy. This chapter has chronicled the evolution of the study of drug disposition in pregnant sheep in the laboratory. With the advent of more sensitive and selective analytical techniques, researchers have been able to progress significantly beyond measuring the extent of fetal drug exposure by a single-point determination. A number of interesting and significant advances have been made using highly selective and specific analytical techniques (i.e., gas chromatography-electron-capture detection, gas chromatography-nitrogen phosphoros-specific detection, and gas chromatography-mass spectroscopy). Researchers have characterized drug kinetics in multiple fluids from the pregnant sheep (amniotic fluid, fetal and maternal plasma and urine, and fetal tracheal fluid) and have demonstrated extensive accumulation of several basic drugs in the fluid produced by the fetal lung. With the simultaneous administration of labeled and unlabeled drug to the ewe and fetus researchers have, for the first time, examined the assumption that the clearance parameters determined from the model developed by Szeto and coworkers (1982) are not affected by the time interval between maternal and fetal infusions given on separate days. Also using SIL drug, researchers have characterized fetal hepatic first-pass drug clearance in a chronic preparation. With the establishment of a stereoselective assay for labetalol, scientists have begun to examine the fetal exposure to the individual enantiomers of racemic drugs in pregnancy. The availability of newer analytical tools and techniques (i.e., HPLC interfaced with tandem mass spectrometers) will further expand the study of drugs in pregnancy and challenge the creativity of future investigators in this field.

Animals↗

PubMed1995

The pharmacokinetics of valproic acid in pregnant sheep after maternal and fetal intravenous bolus administration.

The pharmacokinetics and disposition of valproic acid (VPA) have been assessed in pregnant sheep after both maternal and fetal iv bolus administration. The time course of VPA and 16 of its metabolites was followed in maternal and fetal arterial blood, amniotic fluid, and fetal tracheal fluid for 48 hr after administration. Fetal blood gas, acid-base, metabolic, cardiovascular, and fetal breathing activity parameters were also monitored. The disposition of VPA in maternal serum is best described by a biexponential function with a terminal elimination half-life of 2.13 +/- 0.49 hr and volume of distribution of 0.242 +/- 0.036 liter/kg. VPA transfer to fetal serum and other fetal fluids was rapid after drug administration. There was significant fetal exposure to VPA after maternal dosing (mean AUCinfinityFA/AUCinfinityMA = 0.410 +/- 0.118). Similarly, the disposition of VPA in fetal serum after fetal dosing is best described by a biexponential decay with a terminal elimination half-life of 3.37 +/- 1.37 hr. Once again, VPA transfer to other fluids was rapid. However, unlike basic compounds studied previously, VPA did not accumulate extensively in either amniotic or fetal tracheal fluid. The following metabolites were detected after drug administration in these experiments: (E)- and (Z)-2-ene VPA, (E)- and (Z)-3-ene VPA, 4-ene VPA, 3-keto VPA, 4-keto VPA, 3-OH VPA, 4-OH VPA, 5-OH VPA, and 2-PGA. Both maternal and fetal bolus administration of VPA elicited a significant reduction in fetal breathing movements, which may be attributed to the drug's action on gamma-aminobutyric acid dynamics in the central nervous system (CNS). This suggests that the significant fetal exposure to VPA may produce further CNS-related effects in utero.

Amniotic Fluid↗

PubMed1994

Rapid assay for gamma-aminobutyric acid in mouse brain synaptosomes using gas chromatography-mass spectrometry.

A sensitive and efficient assay for gamma-aminobutyric acid (GABA) was applied to fresh mouse whole brain synaptosomes where the extracted GABA was analyzed as its di(tert.-butyl(dimethylsilyl)) derivative by gas chromatography-mass spectrometry (GC-MS) using GABA-d6 as an internal standard. Endogenous levels of 20.01 +/- 0.75 nmol GABA/mg protein were found. The method is characterized by a detection limit of about 10 fmol injected GABA derivative and coefficients of intra-day and inter-day variation of 0.95% and 7.7%, respectively. The rate of synaptosomal GABA synthesis was used to determine the activity of glutamate decarboxylase (GAD) as 314.9 +/- 9.0 nmol GABA/mg protein/h. Both GABA levels and GAD activity were significantly elevated by therapeutic doses of the antiepileptic drug valproic acid.

Acetamides↗

PubMed1994

Determination of metoclopramide and two of its metabolites using a sensitive and selective gas chromatographic-mass spectrometric assay.

A modified gas chromatographic-mass spectrometric (GC-MS) assay has been developed to quantitate metoclopramide (MCP) and two of its metabolites [monodeethylated-MCP (mdMCP), dideethylated-MCP (ddMCP)] in the plasma, bile and urine of sheep. The heptafluorobutyryl derivatives of the compounds were formed and quantitated using electron-impact ionization in the selected-ion monitoring mode (MCP, m/z 86, 380; mdMCP, m/z 380 and ddMCP, m/z 380). No interference was observed from endogenous compounds following the extraction of various biological fluids obtained from non-pregnant sheep. Sample preparation has been simplified and the method is more selective and sensitive (2 fold) than our previous assay using electron-capture detection. The limit of quantitation for MCP, mdMCP and ddMCP was 1 ng/ml in plasma, urine and bile, requiring 0.5 ml of sample. This represents 2.5 pg of the analytes at the detector. The standard curves were linear over a working range of 1-40 ng/ml. Absolute recoveries in plasma ranged from 76.5-94.7%, 79.2-96.8%, 80.3-102.2% for MCP, mdMCP and ddMCP, respectively. In urine, recoveries ranged from 56.5-87.8%, 61.5-87.5%, 62.6-90.2% for MCP, mdMCP and ddMCP, respectively. Recoveries in bile ranged from 83.5-100.9%, 78.5-90.5%, 66.9-79.2% for MCP, mdMCP and ddMCP, respectively. Overall intra-day precision ranged from 2.9% for MCP in plasma to 12.6% for mdMCP in bile. Overall inter-day precision ranged from 5.9% for MCP in urine to 14.9% for ddMCP in bile. Bias was the greatest at the 1 ng/ml concentration in all biological fluids ranging from a low of 2.4% for mdMCP in plasma to a high of 11.9% for ddMCP in urine. Applicability of the assay for pharmacokinetic studies of MCP, mdMCP and ddMCP in the plasma and urine of a non-pregnant ewe is demonstrated.

Animals↗

PubMed1993

Sensitive high-performance liquid chromatographic method for direct separation of labetalol stereoisomers in biological fluids using an alpha 1-acid glycoprotein stationary phase.

A chiral high-performance liquid chromatographic assay for the separation of the four stereoisomers of labetalol, an antihypertensive, in biological fluids has been developed. Baseline separation of the isomers was achieved using an alpha 1-acid glycoprotein stationary phase. No interference from endogenous substances was observed following extraction from various biological fluids obtained from pregnant (ewe and fetus) and non-pregnant sheep. The concentration of the individual isomers of labetalol was determined by first measuring the total concentration of racemic labetalol obtained from an achiral assay followed by reassay of each sample by the chiral method after which, by using the estimate of the percentage of each individual isomer, the individual concentration of each of the four isomers was determined. The mobile phase was 0.02 M phosphate buffer containing 0.015 M tetrabutylammonium phosphate. The pH of the mobile phase was adjusted to 7.10. The detector was set at an excitation wavelength of 230 nm and emission wavelength of 400 nm to monitor the nascent fluorescence intensity of the isomers of labetalol. The limit of detection of the individual isomers was 0.15 ng (0.6 ng of injected racemic labetalol). The assay was linear over the range 0.6-15.0 ng of labetalol (injected) with the intra- and inter-day mean coefficients of variation being less than 9.0 and 6.0%, respectively. Application of the assay in the study of pharmacokinetics of the stereoisomers of labetalol in sheep following administration of racemic labetalol has been demonstrated.

Animals↗

PubMed1993

Simultaneous analysis of diphenhydramine and a stable isotope analog (2H10)diphenhydramine using capillary gas chromatography with mass selective detection in biological fluids from chronically instrumented pregnant ewes.

This report describes both the synthesis of a stable isotope analog of the H1 receptor antagonist diphenhydramine (DPHM), and the simultaneous quantitation of DPHM and a deuterated stable isotope analog of DPHM, viz. (2H10)DPHM in biological fluids from the chronically instrumented pregnant ewe. (2H10)DPHM was synthesized and purified, and both its structure and purity were verified. Biological samples were prepared for analysis using liquid-liquid extraction prior to capillary gas chromatography/mass spectrometry. The method employed electron impact ionization with selective ion monitoring of ions with m/z 165 for DPHM and m/z 173 for (2H10)DPHM. The minimal quantifiable concentration of DPHM and (2H10)DPHM from a 1.0 ml sample was 2.0 ng ml-1 in fetal and maternal plasma, fetal tracheal fluid and amniotic fluid. The method was validated from 2.0 ng ml-1 to 200.0 ng ml-1 for both DPHM and (2H10)DPHM in plasma, fetal tracheal fluid and amniotic fluid. Differences in the disposition between DPHM and (2H10)DPHM were not apparent during a control experiment in which both labeled and unlabeled DPHM were administered to a chronically instrumented fetal lamb. This method provides the required sensitivity and selectivity for the simultaneous quantitation of unlabeled and labeled DPHM during pharmacokinetic experiments conducted in near-term pregnant sheep.

Amniotic Fluid↗

PubMed1993

Transplacental and nonplacental clearances, metabolism and pharmacodynamics of labetalol in the fetal lamb after direct intravenous administration.

Labetalol has been previously shown to cause significant maternal and fetal metabolic effects in pregnant sheep after maternal administration. To investigate these observations further, the present study describes the pharmacokinetics, metabolism and pharmacodynamics of labetalol in the fetal lamb after direct fetal i.v. bolus (4 mg) administration. The fetal total body clearance of labetalol (50.45 +/- 1.37 ml m-1 kg-1), which was significantly higher than that previously determined in the ewe, was composed of transplacental and nonplacental CLs of 23.4 +/- 8.99 ml m-1 kg-1 and 27.05 +/- 10.36 ml m-1 kg-1, respectively. The maternal to fetal plasma labetalol area under the curve ratio was 0.031 +/- 0.002 and the CLmp and CLmn were 7.27 +/- 2.11 ml m-1 kg-1 and 30.5 +/- 5.94 ml m-1 kg-1, respectively. Labetalol concentrations in fetal tracheal fluid were consistently higher than that in fetal plasma. The glucuronide conjugate of labetalol was found in the amniotic fluid at up to 20 times the free drug concentration but the oxidative metabolite, 3-amino-1-phenyl-butane, was not detected in plasma or amniotic fluid samples. The fetal effect of labetalol was characterized by an acute lactic acidosis. The calculated hind limb arteriovenous lactate flux showed a net output of lactic acid equal to 3.85 +/- 2.05 g from the hind limb over 24 h after labetalol administration. Although the fetal exposure to labetalol in this study was roughly 4 times that after a 100-mg maternal bolus administration, the magnitude of fetal lactic acidosis was not significantly different in these studies. The clinical implications of the observations made in this study remain to be investigated.

Animals↗

PubMed1992

Identification and quantitation of an oxidative metabolite of labetalol in sheep: pharmacokinetic and metabolic implications.

A sensitive and selective assay has been developed for the identification and quantitation of 3-amino-1-phenyl butane (3-APB), a metabolite of labetalol, in biological fluids using electron impact gas chromatography/mass-selective detection. Samples were extracted with n-hexane, derivatized with heptafluorobutyric anhydride and chromatographed on a cross-linked fused-silica capillary column. A positive EI spectrum was obtained using a mass-selective detector. Identification of the metabolite was accomplished using an authentic standard; quantitation was performed in the selected ion monitoring mode using ions m/z 345 (M+) and 132. The assay was linear over the calibration range of 0.5-1000 ng of the analyte and the intra-sample coefficients of variation were less than 12% in all cases. The absolute recovery of 3-APB following extraction from urine and bile was found to be 102.9 +/- 4.9% and 98.3 +/- 1.45% (mean +/- SEM) respectively. The minimum quantitation limit of the assay was 0.5 ng ml-1 (approximately 2 pg injected). Application of the assay in a pharmacokinetic-pharmacodynamic study of labetalol in sheep is demonstrated. The metabolite was detected in urine and bile samples obtained from adult non-pregnant sheep following labetalol administration. The cumulative amount of 3-APB excreted in urine over 24 h was found to be 71.55 micrograms in one animal following a 100 mg dose of labetalol. Evidence for biliary excretion, glucuronidation and sulfation of 3-APB was also found.

Animals↗

PubMed1991

Determination of ritodrine in biological fluids of the pregnant sheep by fused-silica capillary gas chromatography using electron-capture detection.

A sensitive and selective gas chromatographic assay method employing splitless injection, fused-silica capillary columns and electron-capture detection is reported for the quantitation of the tocolytic drug, ritodrine, in a variety of biological fluids obtained from the pregnant ewe and fetus. This method has improved sensitivity and selectivity over previously published assay procedures. A 25 m x 0.31 mm I.D., cross-linked 5% phenylmethylsilicone, fused-silica capillary column was employed for all analyses. Linearity of response was observed over the range 2.5-75 ng of ritodrine base per 0.05-0.5 ml of biological fluid, representing approximately 1-75 pg at the detector. The coefficient of variation was less than 10% over the range 2.5-75 ng of added ritodrine. The minimum quantifiable amount is approximately 2.5 ng from a 0.5-ml biological fluid sample. Applicability of this method to biological fluids, obtained from ovine subjects, is demonstrated by the analysis of samples obtained during the course of ritodrine placental transfer studies.

Amniotic Fluid↗

PubMed1990

Pharmacokinetics and enterohepatic circulation of (E)-2-ene valproic acid in the rat.

A pharmacologically active monounsaturated metabolite of valproic acid (VPA), (E)-2-ene VPA, was administered by an intravenous bolus dose of 20 mg/kg to normal and bile-exteriorized rats. The total plasma clearance of (E)-2-ene VPA in normal rats was 4.9 ml/min/kg and in bile-exteriorized rats, 7.7 ml/min/kg. (E)-2-ene was recycled in the plasma of normal rats due to enterohepatic circulation. Approximately 32% of the dose was excreted in the urine of normal rats. Of the administered dose to bile exteriorized rats, approximately 27% was excreted in the urine and 38% in the bile. Administration of (E)-2-ene increased bile flow rate, and the induced choleresis lasted for 3-4 h. (E)-2-ene VPA was largely excreted in apparently conjugated form in the urine and bile. The pharmacokinetics of (E)-2-ene VPA were similar to that of the parent drug VPA.

Animals↗

PubMed1990

Identification of the biliary metabolites of (+/-)-3-dimethylamino-1,1-diphenylbutane HCl (recipavrin) in rats.

1. The in vivo biliary metabolites of (+/-)-3-dimethylamino-1,1-diphenylbutane hydrochloride (recipavrin) isolated from Wistar rats have been characterized by g.l.c.-mass spectrometry. 2. Non-conjugated metabolites include recipavrin (1), norrecipavrin (2), diphenylbutanone (3), diphenylbutanone oxime (4), diphenylbutanone phenol (12), diphenylbutanone oxime phenol (14), recipavrin phenol (19), diphenylbutanone O-methylcatechol (16) and diphenylbutanone oxime O-methylcatechol (18). 3. Following beta-glucuronidase hydrolysis and extraction from pH 10 solution, diphenylbutanone (3), diphenylbutanone oxime (4), an unidentified compound (6), primary amine (8), norrecipavrin (2), recipavrin (1), phenols (12, 14, 15), norrecipavrin phenol (13), O-methylcatechols (16, 18), diphenylbutanol O-methylcatechol (17), recipavrin O-methylcatechol (19) and a secondary formamide (5) were identified by g.l.c.-mass spectrometry. 4. Various extraction solvents were employed in sample workup. The formamide (5) was present regardless of solvent used, while the trace presence of secondary acetamide (7) may be associated with the use of ethyl acetate. 5. Metabolites isolated after beta-glucuronidase hydrolysis were characterized by g.l.c.-mass spectrometry of the underivatized form, and as the trimethylsilyl (TMS) derivatives, or following methylation with diazomethane or trimethylanilinium hydroxide (TMAH).

Animals↗