Fecal Excretion Of Radioactivity Research Articles

Intestinal Excretion is a Major Disposition Pathway of Lenacapavir in Rat and Dog

Lenacapavir (LEN), previously known as GS-6207 or GS-CA2, is a first-in-class HIV capsid inhibitor in clinical development as a long-acting agent. LEN displays three characteristics of an ideal long-acting agent: picomolar potency, low systemic clearance and a slow subcutaneous (SC) release. In Phase 1 clinical studies, a single SC administration of LEN was safe and well tolerated, showed sustained pharmacologically active plasma concentrations for > 6 months, and led to mean maximum reductions in HIV-1 RNA of 1.4-2.3 log10 over 9 days. Herein, we present the pharmacokinetics (PK) and mechanistic understanding of LEN disposition in rat and dog. PK was determined following intravenous (IV) administration of LEN alone or coadministration with either activated charcoal (AC) or elacridar, a Pgp inhibitor, in intact and bile-duct cannulated (BDC) rats or dogs. The disposition was assessed following a single IV administration of [14C]LEN to intact and BDC rats and dogs. LEN and [14C] concentrations were determined by LC-MS/MS and liquid scintillation counting, respectively. In vitro metabolic stability and metabolic profiles were assessed in hepatocytes using [3H]LEN and in Hµrel® hepatic co‑cultures using [14C]LEN. In intact rats, 94% of dose, including 64% unchanged LEN, was excreted in feces. In BDC rats, 42% and 35% of dose was excreted in bile and feces, respectively, with unchanged LEN accounting for 31% of dose in feces. In intact dogs, 86% of dose, including 65% unchanged LEN, was excreted in feces. In BDC dog, 32% and 63% of dose was excreted in bile and feces, respectively, with unchanged LEN accounting for 60% of dose in feces. Renal excretion was low (< 1% of dose) in both species. Almost all radioactivity was unchanged LEN in plasma. Metabolites were observed in excreta; these included conjugates formed with glutathione, pentose and glucuronic acid. LEN was stable in vitro; minor turnover was observed in Hµrel® hepatic co‑cultures, and the observed metabolites were consistent with those formed in vivo. Excretion of radioactivity in feces after IV administration in BDC rats and dogs confirmed significant intestinal excretion (IE) of parent LEN. Oral coadministration of AC had minimum effect on LEN systemic exposure and the amount excreted in feces following LEN IV administration in intact and BDC dogs. Oral coadministration of elacridar increased LEN systemic exposure, half-life and decreased LEN amount in feces following IV dosing in intact and BDC rats, but changes in clearance were less than 2-fold. IE was a major (>25% of dose and > 25% of LEN) disposition pathway for LEN in rat and dog in addition to biliary excretion. The lack of impact with AC coadministration was attributed to the lack of binding interactions and/or the poor permeability which limited charcoal's ability to “pull” intact LEN out of systemic circulation. Coadministration of a Pgp inhibitor resulted in a modest decrease in LEN clearance. Overall, LEN is mainly cleared intact via biliary and IE pathways; metabolic clearance played a lesser role. Few drugs have described clearance by IE and our studies highlight the importance of IE for highly metabolically stable compounds with slow elimination.

Absorption, Distribution, and Excretion of 14C-APX001 after Single-Dose Administration to Rats and Monkeys

BackgroundAPX001 is a small-molecule therapeutic agent in clinical development for the treatment of invasive fungal infections (IFI).MethodsThe absorption, distribution and excretion profiles of [14C]APX001-derived radioactivity were determined in rats (albino and pigmented) and monkeys. Rats (some implanted with bile duct cannulae) were administered a single 100 mg/kg oral dose or a 30 mg/kg intravenous (IV) dose. Monkeys were administered a single 6 mg/kg IV dose. Samples of blood, urine, feces and bile, as well as carcasses, were collected through 168 hours after dosing. Samples were analyzed for total radioactivity content by liquid scintillation counting, and carcasses were analyzed by quantitative whole-body autoradiography.Results[14C]APX001-derived radioactivity was rapidly and extensively absorbed and extensively distributed to most tissues for both routes of administration in both species. In rats, tissues with the highest radioactivity Cmax values included bile, abdominal fat, reproductive fat, subcutaneous fat, and liver, but radioactivity was also detected in tissues associated with IFI, including lung, brain and eye. In monkeys, the highest Cmax values were in bile, urine, uveal tract, bone marrow, abdominal fat, liver, and kidney cortex. Liver and kidney were the tissues with highest radioactivity, but as in the rat, radioactivity was also detected in lung, brain and eye tissues. In pigmented rats, radiocarbon was densely distributed into pigmented tissue and more slowly cleared than from other tissues.Mean recovery of radioactivity in rats was approximately 95–100%. In bile duct-intact rats, >90% of radioactivity was recovered in feces. In cannulated rats, biliary excretion of radioactivity was the major route of elimination and accounted for 88.8% of the dose, whereas urinary and fecal excretion of radioactivity was minor and accounted for 2.56% and 5.42% of the dose, respectively. In monkeys, the overall recovery of radioactivity was 87.6%, and was eliminated in feces (49.8% of dose) and to a lesser extent in urine (20.6% of dose).ConclusionTogether, the results indicate that APX001-related radioactivity is extensively distributed to major tissues (including tissues relevant to IFI) in both rats and monkeys and cleared primarily by biliary/fecal excretion.Disclosures R. Mansbach, Amplyx Pharmaceuticals Inc.: Consultant, Consulting fee; K. J. Shaw, Amplyx Pharmaceuticals Inc.: Employee, Salary; M. R. Hodges, Amplyx Pharmaceuticals: Employee, Salary; S. Coleman, Covance Laboratories: Employee, Salary; M. E. Fitzsimmons, Covance Laboratories: Employee, Salary

Absorption, Distribution, Metabolism, and Excretion of the Androgen Receptor Inhibitor Enzalutamide in Rats and Dogs.

Enzalutamide is an androgen receptor inhibitor that has been approved in several countries. Absorption, distribution, metabolism, and excretion (ADME) data in animals would facilitate understanding of the efficacy and safety profiles of enzalutamide, but little information has been reported in public. The purpose of this study was to clarify the missing ADME profile in animals. ADME of 14C-enzalutamide after oral administration as Labrasol solution were investigated in non-fasted male Sprague-Dawley rats and beagle dogs. Plasma concentrations of 14C-enzalutamide peaked in rats and dogs at 6-8h after a single oral administration. In most tissues, radioactivity concentration peaked at 4h after administration. Excluding the gastrointestinal tract, tissues with the highest concentration of radioactivity were liver, fat, and adrenal glands. The tissue concentrations of radioactivity declined below the limit of quantitation or <0.89% of maximum concentration by 168h post-dose. Two known metabolites (M1 and M2) and at least 15 novel possible metabolites were detected in this study. M1 was the most abundant metabolite in both rats and dogs. Unchanged drug was a minor component in excreta. In intact rats, the mean urinary and fecal excretion of radioactivity accounted for 44.20 and 49.80% of administered radioactivity, respectively. In intact dogs, mean urinary and fecal excretion was 62.00 and 22.30% of the administered radioactivity, respectively. Rapid oral absorption was observed in rats and dogs when 14C-enzalutamide was administered as Labrasol solution. Tissue distribution in rats was clarified. The elimination of enzalutamide is mediated primarily by metabolism. Species differences were observed in excretion route.

Metabolic disposition and excretion of quinocetone in rats, pigs, broilers, and carp

Excretion, disposition, and metabolism of [3H]-quinocetone in rats, pigs, broilers, and carp following oral administration were investigated. After a single p.o. dose, total radioactivity was rapidly excreted, with ⩾94% in all species within 14days. Fecal excretion of radioactivity was 68% and 65% of the administered dose in rats and pigs, respectively, with the remainder excreted in the urine. Six hours after the last of seven daily oral administrations of 3H-labeled QCT, radioactivity was found to be distributed throughout all tissues, with the majority of radioactivity cleared within 7days, and elimination was the slowest from the liver and kidney. QCT was extensively metabolized in all of the species, and the primary changes included N–O group reduction, carbonyl group reduction, double bond reduction, and hydroxylation. The major tissue metabolites of QCT were Q2, Q4, Q5, Q8, and Q9 in rats; Q1, Q2, Q3, Q4, and Q5 in pigs; Q1, Q2, Q3, Q4, and Q7 in broilers; and Q1, Q2 in carp. This confirmed the potential link between QCT metabolism through N–O group reduction and its organ toxicity. The results of the present study provide important data that could help understand the relationship between the toxicities and metabolic disposition of QCT.

Initial Human PET Studies of Metabotropic Glutamate Receptor Type 1 Ligand 11C-ITMM

N-[4-[6-(isopropylamino)pyrimidin-4-yl]-1,3-thiazol-2-yl]-4-(11)C-methoxy-N-methylbenzamide ((11)C-ITMM) is a potential radioligand for mapping metabotropic glutamate receptor type 1 (mGluR1) in the brain by PET. The present study was performed to determine the safety, distribution, radiation dosimetry, and initial brain imaging of (11)C-ITMM in healthy human subjects. The multiorgan biodistribution and radiation dosimetry of (11)C-ITMM were assessed in 3 healthy human subjects, who underwent 2-h whole-body PET scans. Radiation dosimetry was estimated from the normalized number of disintegrations of source organs using the OLINDA/EXM program. Five healthy human subjects underwent 90-min dynamic (11)C-ITMM scans of brain regions with arterial blood sampling. For anatomic coregistration, T1-weighted MR imaging was performed. Metabolites in plasma and urine samples were analyzed by high-performance liquid chromatography. (11)C-ITMM uptake was assessed quantitatively using a 2-tissue-compartment model. There were no serious adverse events in any of the subjects throughout the study period. (11)C-ITMM PET demonstrated high uptake in the urinary bladder and gallbladder, indicating both urinary and fecal excretion of radioactivity. The absorbed dose (μGy/MBq) was highest in the urinary bladder wall (13.2 ± 3.5), small intestine (9.8 ± 1.7), and liver (9.1 ± 2.0). The estimated effective dose for (11)C-ITMM was 4.6 ± 0.3 μSv/MBq. (11)C-ITMM showed a gradual increase of radioactivity in the cerebellar cortex. The total distribution volume in the brain regions ranged from 2.61 ± 0.30 (cerebellar cortex) to 0.52 ± 0.17 (pons), and the rank order of the corresponding total distribution volume of (11)C-ITMM was cerebellar cortex > thalamus > frontal cortex > striatum ≈ pons, which was consistent with the known distribution of mGluR1 in the primate brain. The rate of (11)C-ITMM metabolism in plasma was moderate: at 60 min after injection, 62.2% ± 8.2% of the radioactivity in plasma was intact parent compound. The initial findings of the present study indicated that (11)C-ITMM PET is feasible for imaging of mGluR1 in the brain. The low effective dose will permit serial examinations in the same subjects.

Absorption, Distribution and Excretion of Radioactivity by Male Rats after a Single Intravenous or Subcutaneous Dose of 14C-azacitidine

The absorption, distribution and excretion of radioactivity were investigated in male Sprague-Dawley rats after a single intravenous or subcutaneous dose of 14C-azacitidine. After subcutaneous administration, 14C-azacitidine was rapidly absorbed and the radioactivity was distributed to the tissues. The absorption of radioactivity after subcutaneous administration was 76.6% of that observed after intravenous administration. There were no marked differences in the tissue distribution of the radioactivity between administration routes. The concentrations of radioactivity in most tissues, including the spleen and bone marrow, which are sites of action of azacitidine, were higher than those in the plasma. Particularly high concentrations of radioactivity were detected in the spleen, kidney and liver. The accumulation of radioactivity in blood cells increased from 0.5 to 48 h. The binding of azacitidine to serum protein was low at <9%, and the cumulative urinary and fecal excretion of radioactivity for 168 h after intravenous or subcutaneous administration was >95% of the administered dose, indicating that radioactivity did not accumulate in the tissues. The radioactivity was mainly excreted in the urine.

Metabolism and disposition of the oral absorption enhancer 14C-radiolabeled 8-(N-2-hydroxy-5-chlorobenzoyl)-amino-caprylic acid (5-CNAC) in healthy postmenopausal women and supplementary investigations in vitro

8-(N-2-hydroxy-5-chlorobenzoyl)-amino-caprylic acid (5-CNAC), a compound lacking pharmacological activity enhances the absorption of salmon calcitonin, when co-administered. Disposition and biotransformation of 5-CNAC was studied in six healthy postmenopausal women following a single oral dose of 200mg 14C-radiolabeled 5-CNAC (as disodium monohydrate salt).Blood, plasma, urine and feces collected over 7days were analyzed for radioactivity. Metabolite profiles were determined in plasma and excreta and metabolite structures were elucidated by LC–MS/MS, LC–1H NMR, enzymatic methods and by comparison with reference compounds.Oral 5-CNAC was safe and well tolerated in this study population. 5-CNAC absorption was rapid (tmax=0.5h; Cmax=9.00±2.74μM (mean±SD, n=6) and almost complete. The elimination half-life (t½) was 1.5±1.1h. The radioactive dose was excreted mainly in urine (⩾90%) in form of metabolites and 0.071% as intact 5-CNAC. Excretion of radioactivity in feces was minor and mostly as metabolites (<3%). Radioactivity in plasma reached Cmax (35.4±7.9μM) at 0.75h and declined with a half-life of 13.9±4.3h. 5-CNAC accounted for 5.8% of the plasma radioactivity AUC0–24h.5-CNAC was rapidly cleared from the systemic circulation, primarily by metabolism. Biotransformation of 5-CNAC involved: (a) stepwise degradation of the octanoic acid side chain and (b) conjugation of 5-CNAC and metabolites with glucuronic acid at the 2-phenolic hydroxyl group. The metabolism of 5-CNAC in vivo could be reproduced in vitro in human hepatocytes. No metabolism of 5-CNAC was observed in human liver microsomes.

Tissue dosimetry, metabolism and excretion of pentavalent and trivalent dimethylated arsenic in mice after oral administration

Dimethylarsinic acid (DMA(V)) is a rat bladder carcinogen and the major urinary metabolite of administered inorganic arsenic in most mammals. This study examined the disposition of pentavalent and trivalent dimethylated arsenic in mice after acute oral administration. Adult female mice were administered [ 14C]-DMA(V) (0.6 or 60 mg As/kg) and sacrificed serially over 24 h. Tissues and excreta were collected for analysis of radioactivity. Other mice were administered unlabeled DMA(V) (0.6 or 60 mg As/kg) or dimethylarsinous acid (DMA(III)) (0.6 mg As/kg) and sacrificed at 2 or 24 h. Tissues (2 h) and urine (24 h) were collected and analyzed for arsenicals. Absorption, distribution and excretion of [ 14C]-DMA(V) were rapid, as radioactivity was detected in tissues and urine at 0.25 h. For low dose DMA(V) mice, there was a greater fractional absorption of DMA(V) and significantly greater tissue concentrations of radioactivity at several time points. Radioactivity distributed greatest to the liver (1–2% of dose) and declined to less than 0.05% in all tissues examined at 24 h. Urinary excretion of radioactivity was significantly greater in the 0.6 mg As/kg DMA(V) group. Conversely, fecal excretion of radioactivity was significantly greater in the high dose group. Urinary metabolites of DMA(V) included DMA(III), trimethylarsine oxide (TMAO), dimethylthioarsinic acid and trimethylarsine sulfide. Urinary metabolites of DMA(III) included TMAO, dimethylthioarsinic acid and trimethylarsine sulfide. DMA(V) was also excreted by DMA(III)-treated mice, showing its sensitivity to oxidation. TMAO was detected in tissues of the high dose DMA(V) group. The low acute toxicity of DMA(V) in the mouse appears to be due in part to its minimal retention and rapid elimination.

Pharmacokinetics, Metabolism, and Routes of Excretion of Intravenous Irofulven in Patients with Advanced Solid Tumors

Irofulven is currently in Phase 2 clinical trials against a wide variety of solid tumors and has demonstrated activity in ovarian, prostate, gastrointestinal, and non-small cell lung cancer. The objectives of this study were to determine its pharmacokinetics and route of excretion and to characterize its metabolites in human plasma and urine samples after a 30-min i.v. infusion at a dose of 0.55 mg/kg in patients with advanced solid tumors. Three patients were administered i.v. 100 microCi of [14C]irofulven over a 30-min infusion on day 1 of cycle 1. Serial blood and plasma samples were drawn at 0 (before irofulven infusion) and up to 144 h after the start of infusion. Urine and fecal samples were collected for up to 144 h after the start of infusion. The mean urinary and fecal excretion of radioactivity up to 144 h were 71.2 and 2.9%, respectively, indicating renal excretion was the major route of elimination of [14C]irofulven. The C(max), AUC(0-infinity), and terminal half-life values for total radioactivity were 1130 ng-Eq/ml, 24,400 ng-Eq . h/ml, and 116.5 h, respectively, and the corresponding values for irofulven were 82.7 ng/ml, 65.5 ng . h/ml, and 0.3 h, respectively, suggesting that the total radioactivity in human plasma was a result of the metabolites. Twelve metabolites of irofulven were detected in human urine and plasma by electrospray ionization/tandem mass spectrometry. Among these metabolites, the cyclopropane ring-opened metabolite (M2) of irofulven was found, and seven others were proposed as glucuronide and glutathione conjugates.

Absorption, metabolism, and excretion of (H)-ospemifene following a single oral dose to post-menopausal women

Background/Aims Ospemifene is a novel selective oestrogen receptor modulator being developed for osteoporosis. The aims were: to evaluate the pharmacokinetics of total radioactivity, unchanged ospemifene, and the major metabolite 4-hydroxyospemifene; to obtain mass balance by quantifying the urinary and faecal excretion of radioactivity; to examine the pattern of metabolites in plasma, urine and faeces and the ex-vivo plasma protein binding of total radioactivity and ospemifene. Methods A single oral dose (60 mg) of ospemifene, containing 20.2 MBq (3H)-ospemifene, was administered orally to 6 healthy post-menopausal women. Blood, urine and faeces sampling was performed up to 240h post-dose. Results/Conclusions Ospemifene was rapidly absorbed (tmax 0.75–3 h) and steadily eliminated (t1/2 of 25–29 h). 4-hydroxyospemifene underwent formation rate-limited elimination with tmax similar to the parent drug. Radioactivity was mainly faecally eliminated, with 75% of the dose being recovered over 240h, with 7% eliminated in urine. Ospemifene and total drug-related material were extensively plasma protein bound (93–98%) with minimal binding to blood cells. Ospemifene metabolism was extensive with several radiolabelled metabolites in plasma, urine and faeces. Clinical Pharmacology & Therapeutics (2005) 77, P82–P82; doi: 10.1016/j.clpt.2004.12.205

Disposition of Posaconazole following Single-Dose Oral Administration in Healthy Subjects

Posaconazole is a potent, broad-spectrum triazole antifungal agent currently in clinical development for the treatment of refractory invasive fungal infections. Eight healthy male subjects received a single 399-mg (81.7 microCi) oral dose of [(14)C]posaconazole after consuming a high-fat breakfast. Urine, feces, and blood samples were collected for up to 336 h postdose and assayed for total radioactivity; plasma and urine samples were also assayed for parent drug. Posaconazole was orally bioavailable, with a median maximum posaconazole concentration in plasma achieved by 10 h postdose. Thereafter, posaconazole was slowly eliminated, with a mean half-life of 20 h. The greatest peak in the radioactivity profile of pooled plasma extracts was due to posaconazole, with smaller peaks due to a monoglucuronide, a diglucuronide, and a smaller fragment of the molecule. The mean total amount of radioactivity recovered was 91.1%; the cumulative excretion of radioactivity in feces and in urine was 76.9 and 14.0% of the dose, respectively. Most of the fecal radioactivity was associated with posaconazole, which accounted for 66.3% of the administered dose; however, urine contained only trace amounts of unchanged posaconazole. The radioactivity profile of pooled urine extracts included two monoglucuronide conjugates and a diglucuronide conjugate of posaconazole. These observations suggest that oxidative (phase 1) metabolism by cytochrome P450 isoforms represents only a minor route of elimination for posaconazole, and therefore cytochrome P450-mediated drug interactions should have a limited potential to impact posaconazole pharmacokinetics.

Metabolic distribution of radioactivity in Sprague–Dawley rats and B6C3F1 mice exposed to 1,3-[2,3- 14C]–butadiene by whole body exposure

The uptake of 1,3-[2,3- 14C]–butadiene and its disposition, measured as radioactivity in urine, faeces, exhaled volatiles and CO 2 during and following 6 h whole body exposure to 20 ppm butadiene has been investigated in male Sprague–Dawley rats and B6C3F1 mice. Whilst there were similarities between the two species, the uptake and metabolic distribution of butadiene were somewhat different for rats and mice. The major differences observed were in the urinary excretion of radioactivity and in the exhalation of 14C–CO 2. After 42 h from the start of exposure, 51.1% of radioactivity was eliminated in rat urine compared with 39.5% for mouse urine. 34.9% of the recovered radioactivity was exhaled by rats as 14C–CO 2, compared with 48.7% by mice. Excretion of radioactivity in faeces was similar for both species (3.8% for rats and 3.4% for mice). The tissue concentrations of 14C–butadiene equivalents measured in liver, testes, lung and blood of exposed mice were 0.493, 0460, 0.457, and 1.626 nmol/g tissue, respectively. The values for the corresponding rat tissues were 0.869, 0.329, 0.457, and 1.626 nmol butadiene equivalents/g tissue, respectively. For rats, 6.2% of recovered radioactivity (0.288 nmol butadiene equivalents/g tissue) was retained in carcasses whereas for mice the amount was 3.6% (0.334 nmol butadiene equivalents/g tissue). There were also some significant differences between the metabolic conversion of 1,3-[2,3- 14C]–butadiene and excretion by mice following the 20 ppm whole body exposure compared to previously reported data for nose-only exposure to 200 ppm butadiene [Richardson et al., Toxicol. Sci. 49 (1999) 186]. The main difference between the high- and low-exposure studies was in the exhalation of 14C–CO 2. At the 200 ppm exposure, 40% of the radioactivity was exhaled as 14C–CO 2 by rats whereas 6% was measured by this route for mice. The proportional conversion of butadiene to CO 2 by mice was significantly greater at the low exposure concentration compared with that reported for the higher concentration. This shift was not observed for rats. The difference between species could be caused by a saturation of metabolism in mice between 20 and 200 ppm for the pathways leading to CO 2. Restraint or error in collection of CO 2 in the 200 ppm study could also be factors.

Disposition of a synthetic analogue of lipid A (E5564) in rats

1. E5564, a lipid A analogue that potently antagonises lipopolysaccharide, is being developed to treat sepsis caused by Gram-negative bacterial infections. The pharmacokinetic profile of E5564 is independent of dose between 0.1 and 1 mg kg − 1. The distribution volume of E5564 is slightly larger than the total plasma volume, and the terminal elimination half-life is about 5 h. 2. Following 14 C-E5564 administration (0.5 mg kg − 1), radioactivity rapidly accumulates in the liver and spleen. The half-life of E5564 in the liver is 5.1 h, which is similar to that in the plasma. At 48 weeks after dosing, 35.27% of the administered radioactivity was still present in the liver. Cumulative urinary and faecal excretion of radioactivity for up to 48 weeks after administration were 3.86 and 67.17% of the dose, respectively. 3. The results of mass spectroscopy and nuclear magnetic resonance analysis reveal that the main hepatic metabolite is di-dephosphorylated E5564. The half-life of di-dephosphorylated E5564 in the liver is 87.4 days, which is similar to that for the hepatic radioactivity. 4. The results indicate that E5564 is rapidly taken up by the liver, is metabolized via dephosphorylation pathways to form dephosphorylated E5564 and is mainly excreted in the faeces.

Characterization of urinary and fecal metabolites of testosterone and their measurement for assessing gonadal endocrine function in male nonhuman primates

The aims of the present study were (i) to provide basic comparative data on the time course, route, and characteristics of excreted [ 14C]testosterone (T) metabolites in three nonhuman primates: the common marmoset ( Callithrix jacchus), the long-tailed macaque ( Macaca fascicularis) and the chimpanzee ( Pan troglodytes) and (ii) to use this information to help validate the measurement of urinary and fecal testosterone metabolites for assessing androgen status in Anthropoid primates. Radiolabeled 14C-T (10–30 μCi) was injected intravenously into one adult male of each species and the excreta collected over the next 5 days. Peak radioactivity in urine was detected within 2 h and accounted for 67% (Mf), 80% (Cj) and 91% (Pt) of the total radioactivity recovered. The time course of excretion of radioactivity in feces showed a higher variation between species (4–26 h to peak values). In all three species, the majority (>90%) of urinary metabolites were excreted as conjugates whereas the proportion of conjugated metabolites in feces was substantially lower and more variable. High pressure liquid chromatography (HPLC) analysis of urinary and fecal extracts revealed multiple peaks of radioactivity in all three individuals, but each with a distinctive pattern. Native T was excreted in only small amounts into the urine, whereas it was virtually absent in the feces of all three individuals. Three C17 group-specific enzymeimmunoassays using antisera against testosterone, 5α-androstane-17α-ol-3-one and androsterone were evaluated for their ability to discriminate immunoreactive androgen levels between intact males, castrated males and females based on measurements in urine and feces. In the marmoset, all assays (except for T in feces) clearly discriminated between test groups; in the chimpanzee significantly higher levels of androgen immunoreactivity in intact versus castrated males were measured in urine, but not feces. In the macaque, only the 5α-androstanolone measurement in feces discriminated between groups. Data on the results of a radiometabolism study using 3H-DHEA (a weak adrenal androgen) in a long-tailed macaque suggested that co-measurement of metabolites derived from T and DHEA in the assays tested might explain the difficulties in discriminating gonadal status in the two Old World primate species. Collectively, the data show that T metabolism in primates is highly complex and that no single method for noninvasive assessment of androgen status can be used for application across species. The importance of a proper validation of the methodology for each species is emphasised.

Disposition of a low dose of bisphenol a in male and female cynomolgus monkeys.

Bisphenol A (BPA) is a weak estrogenic compound mass-produced with potential human exposure. Following a single oral or intravenous (iv) dose of 100 microg/kg [ring-14C(U)] radiolabeled bisphenol A (14C-BPA) to male and female cynomolgus monkeys, 79-86% of the administered radioactivity was excreted in urine over 7 days, and most of the urinary excretion was recovered by 24 h after dosing, a large part of this occurring within 12 h. The fecal excretion of radioactivity over 7 days was minimal (1.8-3.1%). Toxicokinetic parameters obtained from plasma 14C-BPA-derived radioactivity during 48 h were C(max) = 104-107 ng-eq/ml between 0.25 and 2 h, and AUC(oral) = 244-265 ng-eq*h/ml after oral dosing. In the case of the iv dose, AUC(iv) was 377-382 ng-eq*h/ml, and the bioavailability was 0.66-0.70. The terminal elimination half-life was larger post-iv dose (t(1/2iv) = 13.5-14.7 h) than post-oral dose (t(1/2oral) = 9.63-9.80 h). After iv dose, the fast-phase half-life (t(1/2f)) of total radioactivity was 0.61-0.67 h. The t(1/2f) of unchanged 14C-BPA for females (0.39 h) was smaller than that for males (0.57 h). These results suggested the distribution of lipophilic 14C-BPA in adipose tissue after iv dose, in contrast to first pass metabolism after oral dose. 14C-BPA-derived radioactivity was strongly bound to plasma protein (f(p) = 0.055). Radio-HPLC analysis suggested the predominant plasma and urinary metabolites were mono- and diglucuronide of 14C-BPA and unchanged 14C-BPA was very low (< or =1.5%) after oral dose. These results indicate that the intestinal absorption and metabolism of BPA was rapid and extensive, and the major metabolites, glucuronide conjugates of 14C-BPA, were rapidly excreted into urine in monkeys.

Absorption, distribution and excretion of 3H-labeled cephaeline- and emetine-spiked ipecac syrup in rats.

The maximum plasma radioactivity levels of tritium (3H)-labeled cephaeline, (24.3, 28.7 and 40.6 ng eq./mL) were reached at 2.00-3.33 hours following oral dosing of ipecac syrup. The maximum plasma radioactivity levels of 3H-emetine (2.71, 6.47 and 9.62 ng eq./mL) were reached at 1.08-2.33 hours following ipecac syrup administration. The Cmax values of 3H-cephaeline were followed by a biexponential decrease with half-lives t 1/2(lambda z) of 3.45-9.40 hours. On the other hand, the t 1/2 (lambda z)of 3H-emetine were 65.4-163 hours, which revealed a biexponential decrease. The radioactivity of both tritium-labeled compounds was distrbuted maximally in most tissues at 24 hours. For 3H-cephaeline, the maximum radioactivity levels in tissues were approximately 100-150 times greater than in plasma. For 3H-emetine, the radioactivity levels in tissues were approximately 1000-3000 times greater than in plasma. Tissue radioactivity levels decreased at a substantially slower rate than that observed in plasma. Tissue radioactivity of 3H-emetine decreased more slowly than that of 3H-cephaeline. For 3H-cephaeline, the cumulative biliary excretion of radioactivity was 57.5% at 48 hours. The cumulative urinary and fecal excretion of radioactivity in these rats was 16.5% and 29.1%, respectively, of the dose at 48 hours following dosing. For 3H-emetine, the cumulative biliary excretion of radioactivity was 12.5% at 48 hours. The cumulative urinary and fecal excretion of radioactivity was 9.4% and 34.1%, respectively, of the administered dose at 48 hours. The radioactivity level of 3H-emetine remaining in the carcasses at 48 hours was equivalent to approximately 50% of the dose. A portion of each tritium-labeled compound was subjected to entero-hepatic circulation. Thus, the absorption rate of 3H-cephaeline and 3H-emetine was estimated to be approximately 70% on the basis of the data obtained from excretion studies. There was no difference in the absorption process between these two compounds. However, the difference was admitted in the biliary clearance, which is the main excretion route of both compounds. Delayed excretion of 3H-emetine may be primarily due to its resorption as related to entero-hepatic circulation and tissue retention. This study has determined the absorption, distribution and excretion of 3H-cephaeline and 3H-emetine in rats.

Studies on the Metabolic Fate of M17055, a Novel Diuretic. (3): Plasma Concentration, Distribution and Excretion of Radioactivity in Male Rats after Repeated Daily Intravenous Administration of [14C]M17055.

The plasma levels, tissue distribution and excretion of radioactivity were studied following repeated daily intravenous administration of [14C]M17055 to male rats at a dose of 0.3 mg/kg/day. 1. The plasma levels of radioactivity at 24 hours after each of 21 day-period of repeated administration to male rats were reached the steady state (6.90-8.87 ng eq./mL) by the 8th dosing. The calculated pharmacokinetic parameters were similar as those after the single administration. 2. Although the levels of radioactivity in all tissues at 24 hours after repeated administration to male rats rose according to the times of dosing, the rising rate was slow except for blood, lung, skin, digestive organs and their contents. At 1 hour after the 21st dosing, the radioactivity distributed highly to the liver and kidney as observed after the single administration. At 168 hours after the 21st dosing, the radioactivity tended to remain in highly perfused tissues, such as liver, kidney, spleen and lung. No tissue was identified in which the radioactivity retained for long period on the whole body autoradiograms. 3. Cumulative urinary and fecal excretions of radioactivity after 21 day repeated administration accounted for 58.17 and 37.35% of the total dose, respectively. The excretion rate in urine and feces well agreed to that after the single administration. The total excretion of radioactivity, including that present in the cage washing, accounted for 97.28% of the total dose.

Studies on the Metabolic Fate of M17055, a Novel Diuretic. (1): Plasma Concentration and Excretion of Radioactivity in Rat and Dog after a Single Intravenous Administration of [14C]M17055.

The plasma level and excretion of radioactivity were studied following a single intravenous administration of [14C]M17055 to male and female rats, and a female dog. 1. After a single intravenous administration to male and female rats at a dose of 0.3 mg/kg, plasma levels of radioactivity declined triphasically reaching at 48 hr the levels lower than 1/1000 of those observed at one minute after administration. Calculated CLtot, T1/2βand T1/2γ did not differ between male and female rats. But T1/2α of female rats showed lower value than that of male rats. 2. After a single intravenous administration to male rats at doses of 0.1, 1 and 3 mg/kg, plasma levels of radioactivity declined in similar manner with that at a dose of 0.3 mg/kg. Although calculated CLtot tends to decline at 1 and 3 mg/kg, the T1/2γ showed similar value at the dose range of 0.1-3 mg/kg. 3. Plasma level of radioactivity in a female dog declined triphasically reaching at 48 hr the levels 100 fold lower than those observed at 5 minutes after a single intravenous administration at a dose of 1 mg/kg. There-after, the level of radioactivity declined more slowly when compared with rats. 4. Cumulative urinary and fecal excretions of radioactivity within 168 ho urs after a single intravenous administration to male and female rats accounted for 94.10 and 97.61% of the dose, respectively. Over 90% of the dose was excreted within 48 hours after administration. Urinary excretion rate was higher in female rats than that in male rats, especially within 6 hours after administration. 5. Cumulative urinary and fecal excretions after a single intravenous administration to a female dog accounted for over 90% after administration. Total excretion of radioactivity within 168 hours accounted for 97.33% of the administered dose. 6. Biliary excretion of radioactivity after a single intravenous administration to bile-duct cannulated male rats accounted for 64.12% of the dose. About 67% of the excreted radioactivity in bile was re-absorbed in male rats. 7. The renal clearance of radioactivity after administration in male and female rats decreased and showed same level when treated with probenecid, which suggested that the sex difference of the urinary excretion may be caused by the active secretary mechanism.

Quantitative whole-body radioluminography-future strategy for balance and tissue distribution studies.

The present routine to conduct balance and/or tissue dissection distribution studies has now and then been questioned, because the way they are generally conducted does not produce information in proportion to the spending of animal and personnel resources. Usually only total radioactivity is measured and due considerations are not always taken to the metabolic fate of the label. In this study a different strategy is presented-integrating quantitative whole-body radioluminography and different chromatographic methods on extracts of tissue pieces punched from the whole-body sections. In addition to the saving in cost and time, the proposed integrated whole-body radioluminographic/metabolic profile protocol will provide (i) a detailed picture of the distribution of radioactivity at selected dose levels and time points in male, female, and pregnant animals; (ii) the time course of radioactivity in blood/plasma and tissues selected from the images (approximate half-life and AUC); (iii) accumulated urinary and fecal excretion of radioactivity and an estimate of the proportion of radioactive metabolites; (iv) tissue information about the proportion of parent drug versus metabolites of pieces punched from the whole-body sections; and (v) indications of possible tissue binding.

Absorption, Distribution and Excretion of 14C-labeled Tacrolimus(FK506) Ointment after a Single Dermal Application to the Rat.

The absorption, distribution, and excretion of radioactivity were studied in the male rat after a single dermal application of 14C-labeled FK506 ointment at an FK506 dose level of 1.6 mg/kg. The application period of the ointment was 24 hours. 1. Urinary and fecal excretion of radioactivity were 0.5 and 5.1% of the administered dose, respectively, over 168 hours after application to the intact skin under the non-occlusive dressing condition, 0.4 and 4.2% to the intact skin under the occlusive condition, and 2.4 and 53.8% to the damaged skin under the occlusive condition. Radioactivity remaining at the application site and in the animal body were respectively 14.6 and 0.3% at 168 hours after application to the intact skin under the non-occlusive condition, and were 4.7 and 0.4% after application to the damaged skin under the occlusive condition. 2. Radioactivity was not detected in the whole blood and plasma at any sampling points after ointment application to the intact dorsal skin under occlusive dressing condition. After application to the damaged dorsal skin under the occlusive condition, the pharmacokinetic parameters of radioactivity in the whole blood and plasma were respectively as follows: maximal concentration (Cmax), 42.7 and 37.9 ng eq./mL; time to reach Cmax, both 2 hours; area under the concentration-time curve, 559 and 457 ng eq.·h/mL; and half life, 9.0 and 9.3 hours. 3. After ointment application to the damaged dorsal skin under the occlusive dressing condition, rank order of radioactivity detected at 30 minutes after application was as follows: lung and adrenal gland>brown fat, heart, thyroid gland, kidney, liver and spleen>plasma, urinary bladder and eyeball>cerebrum and testis. The maximal level of radioactivity was observed between 1/2 and 2 hours after application in most tissues. The proportion of radioactivity at 72 hours after application of the maximal level was less than 0.1 in all tissues except the urinary bladder where the proportion was 0.94.