Distribution and biomarker of carbon‐14 labeled fullerene C60 ([14C(U)]C60) in pregnant and lactating rats and their offspring after maternal intravenous exposure

A comprehensive distribution study was conducted in pregnant and lactating rats exposed to a suspension of uniformly carbon‐14 labeled C₆₀ ([¹⁴C(U)]C₆₀). Rats were administered [¹⁴C(U)]C₆₀ (~0.2 mg [¹⁴C(U)]C₆₀ kg^–1 body weight) or 5% polyvinylpyrrolidone (PVP)‐saline vehicle via a single tail vein injection. Pregnant rats were injected on gestation day (GD) 11 (terminated with fetuses after either 24 h or 8 days), GD15 (terminated after 24 h or 4 days), or GD18 (terminated after 24 h). Lactating rats were injected on postnatal day 8 and terminated after 24 h, 3 or 11 days. The distribution of radioactivity in pregnant dams was influenced by both the state of pregnancy and time of termination after exposure. The percentage of recovered radioactivity in pregnant and lactating rats was highest in the liver and lungs. Radioactivity was quantitated in over 20 tissues. Radioactivity was found in the placenta and in fetuses of pregnant dams, and in the milk of lactating rats and in pups. Elimination of radioactivity was < 2% in urine and feces at each time point. Radioactivity remained in blood circulation up to 11 days after [¹⁴C(U)]C₆₀ exposure. Biomarkers of inflammation, cardiovascular injury and oxidative stress were measured to study the biological impacts of [¹⁴C(U)]C₆₀ exposure. Oxidative stress was elevated in female pups of exposed dams. Metabolomics analysis of urine showed that [¹⁴C(U)]C₆₀ exposure to pregnant rats impacted the pathways of vitamin B, regulation of lipid and sugar metabolism and aminoacyl‐tRNA biosynthesis. This study demonstrated that [¹⁴C(U)]C₆₀ crosses the placenta at all stages of pregnancy examined, and is transferred to pups via milk. Copyright © 2015 John Wiley & Sons, Ltd.     

Transplacental and mammary passage of radioactivity in rats treated vaginally and orally with [14C]propranolol

The milk transfer, maternal-fetal distribution, and disposition of the antihypertensive/spermicidal agent propranolol were studied in pregnant and lactating rats. Single doses (10 mg/kg) of an aqueous solution of [14C]propranolol were administered either orally (po) or intravaginally (ivg) on gestational d 15, or on postpartum d 7-10. Upon ivg administration, [14C]propranolol was quickly transferred to systemic circulation and the mean blood [14C] concentrations were significantly greater during the first 0.25-2 h than in po dosed counterparts. About 98% of the ivg applied dose was absorbed after 6 h in gravid rats, and the combined 6-h excretions of radioactivity in the urine (ivg = 24.6%; po = 22.9%) and feces (ivg = 16.8%; po = 14.6%) were equivalent in both groups. At the end of 6 h, the levels of [14C] in the urinary bladder, adrenal, uterus, ovary, spleen, skeletal muscle, brain, heart, lung and fat were significantly higher in ivg treated rats than po dosed animals. Compared with the maternal plasma (ivg = 0.76; po = 0.88 microgram/ml), the mean concentrations of [14C] in the placentas were similar in both groups, while the amounts of [14C] were three to five times lower in the amniotic fluids and the fetuses of both po and ivg treated dams. In lactating rats, over 99% of the administered radioactivity was absorbed from the vagina within 6 h. The blood concentrations of [14C] were significantly elevated at 0.5 and 1 h in the per vaginam treated animals, and afterward the disappearance rate of [14C] followed a similar course in both groups. Following ivg application, the milk radioactivity peaked at 0.5 h and declined rapidly. However, the appearance of [14C] in milk was rather slow after oral dosing: the milk [14C] peaked between 2 and 3 h posttreatment and remained steady thereafter. The milk to blood (M/B) [14C] concentration ratios were markedly greater during 0.5 to 1 h in the ivg group than in their po dosed counterparts. At 6 h, the [14C] levels in the whole blood, plasma, milk, and mammary gland were virtually equivalent in the ivg and po treated females. Comparison of the areas under the milk [14C] concentration-time curves (AUCs) indicated that the milk availability of [14C] was about 31% more in dams dosed vaginally. These data suggest that route of administration alters the disposition and milk excretion of [14C]propranolol-derived radioactivity in pregnant and lactating rats.     

Identification of turkey biliary metabolites of ractopamine hydrochloride and the metabolism and distribution of synthetic [14C]ractopamine glucuronides in the turkey

1. The bile duct cannulated turkey poult (n = 3) dosed orally with [¹⁴C]ractopamine HCl {(1R*,3R*),(1R*,3S*)-4-hydroxy-α-[[[3-(4-hydroxy[¹⁴C]phenyl)-1-methylpropyl]-amino]methyl]-benzenemethanol hydrochloride; 19.9 mg; 9.28 μCi] excreted 37.46 12.1% (mean ± SD) of the administered radioactivity in bile by 24 h post-dosing. 2. A mono-glucuronide, conjugated at C-10 (the methylpropylamino phenol) of ractopamine, accounted for 76.6% of biliary radioactivity. 3. Urine collected from the colostomized turkey poult (n = 3) orally dosed with synthetic [¹⁴C]ractopamine-glucuronides (10.1 mg; 3.6 μCi) contained 11.96 1.0% (mean ± SD) of the administered radioactivity 24 h after dosing, indicating that some absorption of radioactivity occurred. Faeces contained 60.6% of the administered radioactivity and carcasses (with gastrointestinal tracts) contained 23.3% of the starting radioactivity. 4. Five colostomized poults were fitted with bile duct cannulas and were dosed intraduodenally with 10.2?mg (3.6 μCi) synthetic [¹⁴C]ractopamine-glucuronides. Urine and bile contained 15.5 ± 2.2 and 16.8 ± 2.1% respectively of the administered radiocarbon by 24 h post-dosing. Faeces contained 54.3% of the administered radioactivity. Total absorption of the dosed radioactivity averaged 33.4%. 5. Bile and urine collected from the colostomized, bile-duct cannulated bird contained mainly ractopamine glucuronides. Indirect evidence suggests that the dosed ractopamine glucuronides were not absorbed intact.     

Demonstration of 3,4-dihydroxy(14C)benzoic acid and (14C)vanillic acid after administration of (14C)noradrenaline in the rat

Rats were injected with 40 μCi (±)-[1-³H]noradrenaline and 10 μCi ±-[1-¹⁴C]noradrenaline. Three fractions with a decreased ³H:¹⁴C ratio were isolated from the urine by a combined alumina adsorption-ethyl acetate extraction procedure. Two of the fractions were identified as [¹⁴C]vanillic acid and 3,4-dihydroxy[¹⁴C]benzoic acid, respectively. Vanillic acid represented between 1.5 and 3.0% of the total [¹⁴C]activity excreted within 24 h and the contribution of dihydroxybenzoic acid was 0·2-0·5%. The third fraction with a decreased ³H: ¹⁴C ratio has not been identified and represented about 2% of the total [¹⁴C]activity excreted within 24 h. After monoamine oxidase blockade with 100 mg/kg of iproniazid, the excretion of vanillic acid, 3,4-dihydroxybenzoic acid and the unknown fraction was greatly diminished. The probability that these three substances represent those metabolites arising simultaneously with the formation of tritium water from (±)-[1-³H]noradrenaline is discussed.     

Distribution and biomarkers of carbon‐14‐labeled fullerene C60 ([14C(U)]C60) in female rats and mice for up to 30 days after intravenous exposure

A comprehensive distribution study was conducted in female rats and mice exposed to a suspension of uniformly carbon‐14‐labeled C₆₀ ([¹⁴C(U)]C₆₀). Rodents were administered [¹⁴C(U)]C₆₀ (~0.9 mg kg^?1 body weight) or 5% polyvinylpyrrolidone‐saline vehicle alone via a single tail vein injection. Tissues were collected at 1 h and 1, 7, 14 and 30 days after administration. A separate group of rodents received five daily injections of suspensions of either [¹⁴C(U)]C₆₀ or vehicle with tissue collection 14 days post exposure. Radioactivity was detected in over 20 tissues at all time points. The highest concentration of radioactivity in rodents at each time point was in liver, lungs and spleen. Elimination of [¹⁴C(U)]C₆₀ was < 2% in urine and feces at any 24 h time points. [¹⁴C(U)]C₆₀ and [¹⁴C(U)]C₆₀‐retinol were detected in liver of rats and together accounted for ~99% and ~56% of the total recovered at 1 and 30 days postexposure, respectively. The blood radioactivity at 1 h after [¹⁴C(U)]C₆₀ exposure was fourfold higher in rats than in mice; blood radioactivity was still in circulation at 30 days post [¹⁴C(U)]C₆₀ exposure in both species (<1%). Levels of oxidative stress markers increased by 5 days after exposure and remained elevated, while levels of inflammation markers initially increased and then returned to control values. The level of cardiovascular marker von Willebrand factor, increased in rats, but remained at control levels in mice. This study demonstrates that [¹⁴C(U)]C₆₀ is retained in female rodents with little elimination by 30 days after i.v. exposure, and leads to systemic oxidative stress. Copyright © 2015 John Wiley & Sons, Ltd.     

The Fate of [14C]Saccharin in Man,Rat and Rabbit and of 2-Sulphamoyl[14C]benzoic Acid in the Rat

1. [¹⁴C]Saccharin administered orally was excreted entirely unchanged by rats on a normal diet and by rats on a 1% and 5% saccharin diet for up to 12 months. Some 90% dose was excreted in 24?h, about 70–80% in urine and 10–20% in faeces. No metabolite was detected in the excreta by chromatography or reverse isotope dilution. No ¹⁴CO₂ was found in the expired air and no ¹⁴CO₃^2- or 2-sulphamoylbenzoic acid in the urine.

2. When [¹⁴C]saccharin was injected into bile-duct cannulated rats kept on a normal diet or on a 1% saccharin diet for 19 and 23 months, 0.1–0.3% dose appeared in the bile in 3?h and no more at 24?h after dosing. Most of the saccharin was excreted in the urine, 0.6% appearing in the faeces.

3. [¹⁴C]Saccharin given orally to rabbits kept on untreated water and on water containing 1% saccharin for 6 months was excreted unchanged, 60–80% in 24?h, with 70% in urine and 3–11% in faeces.

4. [3-¹⁴C]Saccharin taken orally was excreted unchanged mainly in urine (85–92% in 24?h) by 3 adult humans both before and after taking 1 g of saccharin daily for 21 days. No metabolite of saccharin was found.

5. When [¹⁴C]saccharin was administered orally to pregnant rats on the 21st day of gestation only at most 0.6% of dose entered the foetuses. The ¹⁴C cleared more slowly from the urinary bladder than from other maternal or foetal tissues.

6. Saccharin was not metabolized in vitro by liver microsomal preparations or faecal homogenates from rats kept on a normal diet or on a 1% saccharin diet for two years.

7. 2-Sulphamoyl[¹⁴C]benzoic acid given orally to rats was excreted unchanged more slowly than saccharin. It was not cyclized to saccharin in vivo.     

Placental transfer,excretion, and disposition of [14C]Zectran and [14C]Mesurol in maternal and fetal rat tissues

Pregnant Sprague-Dawley rats were injected ip on the 18th and 19th days of gestation with a tracer dose of [¹⁴C]Zectran (Z) or [¹⁴C]Mesurol (M). The excretion and distribution of total ¹⁴C were examined in fetal and maternal tissues. The distribution of Zectran and Mesurol after an ip dose was characterized by rapid maternal distribution and placental transfer. A distribution and elimination phase was seen for 30–60 min postinjection. After 1 hr [¹⁴C]Zectran in the whole fetus fell very slowly (K_e = 0.086 hr). At 15 min 1.7 and 3.5% of an administered dose of Zectran and Mesurol, respectively, was recovered from the pooled rat fetuses of a dam. After 8 hr, 0.8 and 1.1%, respectively, of the administered ¹⁴C was still present in the pooled fetuses. Fetal kidney and heart contained the most ¹⁴C after both Zectran and Mesurol administration. Liver was the maternal tissue with highest ¹⁴C content. More radioactive ¹⁴CO₂ derived from [¹⁴C]Zectran and [¹⁴C]Mesurol was exhaled by the nonpregnant rat (Z = 82.6%; M = 76.7%) than by the pregnant rat (Z = 62.2%; M = 66.9%). There was no significant difference in urinary excretion of ¹⁴C by pregnant or nonpregnant rats with either Zectran or Mesurol administration. Based on total ¹⁴C activity recovered in the urine, feces, and exhaled air after 8 hr, the pregnant animal retained 10.4–23% more ¹⁴C than the nonpregnant rat treated with either Zectran or Mesurol.     

The fate of lysergic acid DI[14C]ethylamide ([14C]LSD) in the rat, guinea pig and rhesus monkey and of [14C]iso-LSD in rat.

The qualitative and quantitative aspects of the metabolism and elimination of [¹⁴C]LSD in the rat, guinea pig and rhesus monkey have been investigated. Rats given an i.p. dose (1 mg/kg) excreted 73% of the ¹⁴C in the faeces, 16% in the urine and 3.4% in the expired air as ¹⁴CO₂ in 96 hr. Guinea pigs similarly dosed, excreted 40% in the faeces, 28% (urine) and 18% (expired ¹⁴CO₂) in 96 hr. Rhesus monkeys (0.15 mg/kg i.m.) eliminated 39% of the ¹⁴C in the urine and 23% in the faeces in 96 hr.Extensive biliary excretion of [¹⁴C]LSD occurred in both the rat and guinea pig. Bile duct-cannulated rats excreted 68% of an i.v. dose (1.33 mg/kg) in the bile in 5 hr and the guinea pig 52% in 6 hr.[¹⁴C]LSD is almost completely metabolised by all three species and little unchanged drug is excreted. The metabolites identified were 13- and 14-hydroxy-LSD and their glucuronic acid conjugates. 2-oxo-LSD. de-ethyl LSD and a naphthostyril derivative. There occur, however, important species differences in the nature and amounts of the various metabolites. In the rat and guinea pig the major metabolites were the glucuronic acid conjugates of 13- and 14-hydroxy-LSD which were found in both urine and bile. The guinea pig excreted significant amounts of 2-oxo-LSD in urine and bile. De-ethyl LSD was a minor urinary metabolite in both species.The metabolism of LSD appeared to be more complicated in the rhesus monkey. The urine contained at least nine metabolites of which four were identified as follows: 13- and 14-hydroxy-LSD (as glucuronic acid conjugates) de-ethyl LSD and a naphthostyril derivative. Unlike the rat and guinea pig the glucuronic acid conjugates of 13- and 14-hydroxy-LSD were only present in small amounts. Of the remaining five unidentified metabolites, three were major.The biliary metabolites of [¹⁴C]iso-LSD in the rat have been studied and been shown to be similar to those produced from [¹⁴C]LSD, namely 13- and 14-hydroxy-iso-LSD and their glucuronic acid conjugates and 2-oxo-iso-LSD.     

UPLC-MS,HPLC-radiometric,and NMR-spectroscopic studies on the metabolic fate of 3-fluoro-[U-14C]-aniline in the bile-cannulated rat

1. A study of the rates and routes of excretion of 3-fluoro-[U-¹⁴C]aniline following intraperitoneal administration to male bile-cannulated rats by liquid scintillation counting (LSC) gave a total recovery of ～ 90% in the 48?h following dosing, with the majority of the dose being excreted in the urine during the first 24?h (～ 49%).

2. The total recovery as determined by ¹⁹F-nuclear magnetic resonance (¹⁹F-NMR) was ～ 49%, with the majority of the dose excreted in the first 24?h (～ 41%). The comparatively low recovery in comparison to that obtained from LSC was due to matrix effects in bile and a contribution from metabolic defluorination.

3. High-performance liquid chromatography with radiometric profiling of urine and bile revealed a complex pattern of metabolites with the bulk of the dose excreted as a single peak.

4. Ultra-performance liquid chromatography-orthogonal acceleration time of flight mass spectrometry profiling also showed a complex pattern of metabolites, detecting ～ 21 metabolites of 3-fluoroaniline (3-FA) with six of these detected only in urine and four solely in bile.

5. ¹⁹F-NMR revealed the presence of the parent compound and 15 metabolites in urine collected during the first 24?h after -dosing. The matrix effects of bile on ¹⁹F-NMR spectroscopy made metabolite profiling impractical for this biofluid.

6. The major metabolite of 3-FA was identified as 2-fluoro-4-acetamidophenol-sulfate.

     

Nadolol: placental transfer and excretion in the milk of rats.

The transfer of radioactivity from maternal blood to the fetuses of pregnant rats was studied after they had been dosed orally with 100 mg/kg of [¹⁴C]nadolol (2,3-cis-5-[3-[(1,1-dimethylethyl)amino]-2-hydroxypropoxy]-1,2,3,4-tetrahydro-2,3-naphthalenediol) on Days 12, 15, and 18 of gestation. On Day 12 of gestation, during the time of organogenesis, radioactivity crossed the placental barrier to the fetuses; however, the extent of this transfer was significantly reduced on Days 15 and 18 of gestation. The excretion of radioactivity was studied in the milk of lactating rats that had been given oral 100-mg/kg doses of [¹⁴C]nadolol. Twelve or 30 hr after the dams had been dosed, radioactivity was presentin greater concentrations in milk than it was in either blood or plasma. The amount of radioactivity found in the pups that had been allowed to suckle during the intervals of 0 to 6 and 12 to 24 hr after the dams had been dosed was, for both intervals, an average of 0.041% of the dose.     

Metabolic fate of [1-14C]isobutyric acid in the rat.

Isobutyric acid (IBA) has potential use as a fungistat for the storage of moist grain. Since a complete accounting of the fate of IBA has not been reported, the metabolic fate of [1-¹⁴C]IBA was investigated. [1-¹⁴C]IBA was administered by gavage to male Charles River CD rats at doses of 4, 40, and 400 mg/kg body weight and to female rats at 400 mg/kg. All rats showed a similar excretion pattern. [1-¹⁴C]IBA was eliminated rapidly in the breath as expired ¹⁴CO₂. At 4 hr, 75.4, 83.3, and 66.7% of the dose was eliminated in the breath by male rats dosed with 4, 40, or 400 mg/kg, respectively. At 48 hr, 85–90% of the dose was eliminated in the breath. Urinary radioactivity averaged 3.5% of the dose, with about $\text{2}\text{3}$ of the radioactivity present as urea. Fecal radioactivity was less than 1% of the dose. The excretion of radioactivity by female rats was similar to that of male rats dosed with [1-¹⁴C]IBA. Isobutyric acid disappeared rapidly from the plasma of rats dosed by gavage with 400 mg/kg. These studies show that IBA is rapidly metabolized to CO₂ and its use as a feed fungistat is unlikely to contribute to the endogenous levels of IBA in the flesh, eggs, or milk or grain-consuming animals.     

Biotransformation and disposition of the coumaphos metabolite 3-chloro-4-methyl-(4-14C)-7-hydroxycoumarin in rats

The biotransformation and disposition of 3-chloro-4-methyl-(4-¹⁴C)-7-hydroxycoumarin [(¹⁴C) chlorferron] were investigated in rats after single oral administration. Following administration of (¹⁴C) chlorferron at 0.5 and 20 mg/kg body weight to male rats, > 90% of the given dose was eliminated in the urine (77–84%) and faeces (7–15%) within 24 h. Low levels of (¹⁴C) chlorferron derived residues were detected in different organs of rats 7 days after dosing. Administration of (¹⁴C) chlorferron at 20 mg/kg allowed the isolation of three metabolites in the 24-h urine of male and female rats. Compounds tentatively identified were dechlorinated metabolites of chlorferron besides unchanged chlorferron. The majority of the metabolites were excreted in conjugated forms. The pattern of biotransformation of chlorferron was qualitatively similar in male and female rats. Comparative studies on the elimination and biodistribution of (¹⁴C) chlorferron and its parent compound (¹⁴C) coumaphos in male rats indicated rapid metabolism and faster elimination of chlorferron and its metabolites from the body than that of the parent compound.     

Intestinal absorption, intestinal distribution, and excretion of (14C) labelled hyoscine N-butylbromide (butylscopolamine) in the rat

Butylscopolamine was labelled with ¹⁴C and its gastrointestinal absorption, biliary and urinary excretion, enterohepatic circulation and gastrointestinal distribution were examined in anaesthetized rats. Biliary excretion was the main elimination route of intra-portally administered [¹⁴C]butylscopolamine, with 42% of the dose recovered in the bile during 12 h. About 6% of the radioactivity administered orally as [¹⁴C]butylscopolamine was excreted in the bile and 1.2 % in the urine during 24 h, which indicates poor gastrointestinal absorption of butylscopolamine in the rat. When collected radioactive bile was readministered intrajejunally, only about 7% of the radioactivity was recovered in bile and urine during 12 h, which suggests that only a small fraction of butylscopolamine and its metabolites engage in an enterohepatic circulation. After oral administration of [¹⁴C]butylscopolamine, radioactivity was found to accumulate in the wall of the distal small intestine, and about 20% of the dose was found in this tissue 24 h after drug administration. As a result, local anti-acetylcholine effects of butylscopolamine might be expected.     

Pharmacokinetics of nimodipine. I. Communication: absorption, concentration in plasma and excretion after single administration of [14C]nimodipine in rat, dog and monkey

Studies on absorption, plasma concentrations and excretion with (+/-)isopropyl-2-methoxyethyl-1,4-dihydro-2,6-dimethyl-4-(3-nitrophenyl) -3,5-pyridinedicarboxylate (nimodipine, Bay e 9736, Nimotop) have been conducted in rat, dog and monkey using the carbon-14-labelled substance and a wide range of doses (0.05-10 mg/kg) administered via different routes (intravenous, oral, intraduodenal). Nimodipine was well absorbed in all species. Peak plasma concentrations of radioactivity were determined 28-40 min (male rat), 60 min (female rat), about 3 h (dog) and 7 h (monkey) after administration. Dependent on the observation period (24-216 h) terminal half-lives for the elimination of radioactivity from plasma ranging between 4.6 h (female rat) and 157 h (dog) were observed. Comparing the AUC, the concentration of unchanged [14C]nimodipine in plasma represented only a small (maximally 37% in dogs after i.v. dose) to negligible (about 1%, monkey after oral dosing) part of the total radioactivity. Excretion of radioactivity via feces and urine was rapid in all species after both oral and intravenous dosing. Fecal (biliary) excretion was the major excretory route in rat and dog. The monkeys excreted about 40 to 50% via the urine. Residues in the body never exceeded 1.5% of the dose. [14C]nimodipine and/or its radiolabelled metabolites were secreted in milk of orally dosed lactating rats. Binding of [14C]nimodipine to plasma proteins of rat and dog was about 97%.     

Metabolism and disposition of ferbam in the rat.

Approximately 40–70% of an oral dose of ferric [³⁵S]dimethyldithiocarbamate ([³⁵S]ferbam) or ferric [¹⁴C]dimethyldithiocarbamate ([¹⁴C]ferbam) was absorbed through the gastrointestinal tract of the rat during a 24-hr period. In rats receiving [³⁵S]ferbam, 22.7, 18.1, and 1.0% of the radioactivity was found in urine, expired air, and bile, respectively. Only small amounts of ³⁵S were found in the various tissues, including blood, kidneys, muscle, and brain. In rats receiving [¹⁴C]ferbam 42.9 and 1.4% of the ¹⁴C was found in the urine and bile, respectively; whereas only 0.6% of the radioactivity was recovered in the expired air. The other tissues contained only small amounts of ¹⁴C. Analysis of expired air indicated that the only expired ferbam metabolite was carbon disulfide. Major metabolites in the urine included inorganic sulfate, a salt of dimethylamine and a glucuronide conjugate of dimethyldithiocarbamate. Unchanged ferbam was not excreted in the urine. In pregnant rats given [¹⁴C]ferbam a small but significant amount of radioactivity readily crossed the placenta into the fetus. In lactating rats given [¹⁴C]ferbam, radioactivity was secreted into milk, absorbed by the pups and excreted in the pups' urine.     

The disposition of [14C]metronidazole in rats following vaginal and oral administration

The absorption, tissue distribution and excretion of [¹⁴C]metronidazole (¹⁴C-MTZ) were compared during the first 4 h after administration of 10 mg kg^?1 of ¹⁴C-MTZ either orally or intravaginally (i.v.g.) to rats. Peak ¹⁴C blood concentrations were reached at 1 h in both groups. Blood samples collected at 0·5, 3 and 4 h had a higher ¹⁴C concentration in orally dosed rats (P <0·05) than in i.v.g.-treated animals. About 3% of the i.v.g. applied dose remained in the vagina at 4 h. After 4 h, the plasma, liver, kidney, brain, lung and uterus concentrations of ¹⁴C were similar in both groups, whereas the blood, skeletal muscle and fat ¹⁴C values were significantly greater in the orally dosed rats. The total recoveries of ¹⁴C in the urine and faeces did not differ (ca 38% over 4 h) between the two groups. These results suggest that the kinetics of metronidazole are similar after the administration of equal amounts of this drug by either route.     

A double-tracer technique to characterize absorption,distribution, metabolism and excretion (ADME) of [14C]-basimglurant and absolute bioavailability after oral administration and concomitant intravenous microdose administration of [13C6]-labeled basimglurant in humans

1.?The emerging technique of employing intravenous microdose administration of an isotope tracer concomitantly with an [¹⁴C]-labeled oral dose was used to characterize the disposition and absolute bioavailability of a novel metabotropic glutamate 5 (mGlu5) receptor antagonist under clinical development for major depressive disorder (MDD).

2. Six healthy volunteers received a single 1?mg [¹²C/¹⁴C]-basimglurant (2.22 MBq) oral dose and a concomitant i.v. tracer dose of 100?μg of [¹³C₆]-basimglurant. Concentrations of [¹²C]-basimglurant and the stable isotope [¹³C₆]-basimglurant were determined in plasma by a specific LC/MS-MS method. Total [¹⁴C] radioactivity was determined in whole blood, plasma, urine and feces by liquid scintillation counting. Metabolic profiling was conducted in plasma, urine, blood cell pellet and feces samples.

3. The mean absolute bioavailability after oral administration (F) of basimglurant was ～67% (range 45.7–77.7%). The major route of [¹⁴C]-radioactivity excretion, primarily in form of metabolites, was in urine (mean recovery 73.4%), with the remainder excreted in feces (mean recovery 26.5%). The median t_max for [¹²C]-basimglurant after the oral administration was 0.71?h (range 0.58–1.00) and the mean terminal half-life was 77.2?±?38.5?h. Terminal half-life for the [¹⁴C]-basimglurant was 178?h indicating presence of metabolites with a longer terminal half-life. Five metabolites were identified with M1-Glucuronide as major and the others in trace amounts. There was minimal binding of drug to RBCs. IV pharmacokinetics was characterized with a mean?±?SD CL of 11.8?±?7.4?mL/h and a Vss of 677?±?229?L.

4. The double-tracer technique used in this study allowed to simultaneously characterize the absolute bioavailability and disposition characteristics of the new oral molecular entity in a single study.     

Metabolism of o-[methyl-14C]toluidine in the F344 rat

1. Following a single dose (400?mg/kg s.c.) of o-[methyl-¹⁴C]toluidine to male F344 rats, 56% of the ¹⁴C was recovered in the 24?h urine, 2–3% in the faeces and 1% as exhaled ¹⁴CO₂. After 48h, 83.9% of the ¹⁴C appeared in the urine, 3.3% in the faeces and 1.4% was exhaled.

2. Ether-extractable urinary metabolites were separated by?h.p.l.c. and identified as: o-toluidine (5.1% dose); azoxytoluene (0.2%); o-nitrosotoluene (≤0.1%); N-acetyl-o-toluidine (0.2%); N-acetyl-o-aminobenzyl alcohol (0.3%); 4-amino-m-cresol (0.6%); N-acetyl-4-amino-m-cresol (0.3%); anthranilic acid (0.3%) and N-acetylanthranilic acid (0.3%).

3. Acid-conjugated urinary metabolites (51% of dose), separated by paper electrophoresis and by Sephadex LH-20 chromatography, were identified as sulphates of 4-amino-m-cresol (27.8% dose), N-acetyl-4-amino-m-cresol (8.5%), and 2-amino-m-cresol (2.1%), and glucuronides of 4-amino-m-cresol (2.6%), N-acetyl-4-amino-m-cresol (2.1%), and N-acetyl-o-aminobenzyl alcohol. Evidence for a double acid conjugate of 4-amino-m-cresol was also found.

4. These results show that N-acetylation and hydroxylation at the 4 position of o-toluidine are major metabolic pathways in the rat. Minor pathways include hydroxylation at the 6 position, oxidation of the methyl group and oxidation of the amino group. Sulphate conjugates predominate over glucuronides by a ratio of 6:1.     

Identification of turkey biliary metabolites of ractopamine hydrochloride and the metabolism and distribution of synthetic [14C]ractopamine glucuronides in the turkey

1. The bile duct cannulated turkey poult (n = 3) dosed orally with [14C]ractopamine HCl [(1R*,3R*),(1R*,3S*)-4-hydroxy-alpha-[[[3-(4-hydroxy[14C]phenyl)-1-methy lpropyl]amino]methyl]-benzenemethanol hydrochloride; 19.9 mg; 9.28 microCi] excreted 37.4 +/- 12.1% (mean +/- SD) of the administered radioactivity in bile by 24 h post-dosing. 2. A mono-glucuronide, conjugated at C-10 (the methylpropylamino phenol) of ractopamine, accounted for 76.6% of biliary radioactivity. 3. Urine collected from the colostomized turkey poult (n = 3) orally dosed with synthetic [14C]ractopamine-glucuronides (10.1 mg; 3.6 microCi) contained 11.9 +/- 1.0% (mean +/- SD) of the administered radioactivity 24 h after dosing, indicating that some absorption of radioactivity occurred. Faeces contained 60.6% of the administered radioactivity and carcasses (with gastrointestinal tracts) contained 23.3% of the starting radioactivity. 4. Five colostomized poults were fitted with bile duct cannulas and were dosed intraduodenally with 10.2 mg (3.6 microCi) synthetic [14C]ractopamine-glucuronides. Urine and bile contained 15.5 +/- 2.2 and 16.8 +/- 2.1% respectively of the administered radiocarbon by 24 h post-dosing. Faeces contained 54.3% of the administered radioactivity. Total absorption of the dosed radioactivity averaged 33.4%. 5. Bile and urine collected from the colostomized, bile-duct cannulated bird contained mainly ractopamine glucuronides. Indirect evidence suggests that the dosed ractopamine glucuronides were not absorbed intact.     

The biotransformation of [14C]minaprine in man and five animal species

1. [¹⁴C]Minaprine was administered as a single oral dose to five animal species and to a healthy and informed volunteer. Excretion of radioactivity was followed during 48?h in urine and faeces; biliary excretion was followed only in rat.

2. Urinary metabolites were isolated and identified by mass spectrometry.

3. A quantitative comparison of metabolites in different species was made. On the basis of these data it is concluded that the dog is not a suitable model for man for pharmacological or toxicological studies.

4. The major metabolic route is 4-hydroxylation of the aromatic ring. The only unexpected metabolic route found was the biotransformation of the morpholino ring, probably by reductive ring-cleavage.

5. About 50% of the ¹⁴C was excreted in 0-48?h urine. The other 50% was excreted in the 0-48?h faeces. In the rat, this was attributed entirely to biliary excretion. The drug is well absorbed after oral administration and is not accumulated in the body.