Recovery Of Radioactivity In Urine Research Articles

Study of the mass balance, biotransformation and safety of [14C]SHR8554, a novel μ-opioid receptor injection, in healthy Chinese subjects.

Background: SHR8554 is a novel μ-opioid receptor-biased agonist. It has analgesic effects by selectively activating the G protein-coupled pathway. Additionally, it can weakly activate the ß-arrestin-2 pathway, resulting in a limited number of side effects, such as gastrointestinal inhibition. Previous studies have shown that SHR8554 has good analgesic effects, safety and tolerability, but the pharmacokinetic characteristics of SHR8554 in humans have not been reported. This study was designed to investigate the pharmacokinetics and safety of SHR8554 in healthy Chinese male subjects. Methods: A single 1mg/41.3μCi intravenous dose of [14C]SHR8554 was administered to six healthy male subjects. Blood, urine and faecal samples were collected at continuous time points to analyse SHR8554 parent drug levels and their metabolites. The total radioactivity in blood, plasma, urine and faeces was detected by using a liquid scintillation counter. The dynamic changes of SHR8554 and its metabolite concentration were by liquid chromatography-tandem mass spectrometry (LC/MS), and then pharmacokinetic analysis. The safety of the drug on the subjects was also observed after a single intravenous injection. Results: The total recovery of radioactivity in urine and faeces was 99.68% ± 0.79% in 216h, including 76.22% ± 1.12% in urine and 23.46% ± 1.36% in faeces. Seventeen major metabolites in blood, urine and faeces were analysed and identified. The main metabolic pathways of SHR8554 in the human body involve 1) N-dealkylation; 2) O-deethylation; 3) mono-oxidation; 4) glucuronidation, etc. The primary mechanism of SHR8554 clearance in the human body is through urinary excretion, primarily in its parent drug and metabolite forms. The drug has good safety, and no serious adverse effects were observed. Conclusion: SHR8554 showed favourable pharmacokinetic characteristics and safety profiles in this study. SHR8554 is extensively metabolized in human body. The main metabolic pathways include N-dealkylation and O-deethylation, as well as mono-oxidation and glucuronidation. The main excretion route of SHR8554 and its metabolites is through urine. Clinical Trial Registration: http://www.chinadrugtrials.org.cn/, identifier CTR20220450.

Pharmacokinetics and metabolism of mirogabalin, a novel α2δ ligand, in rats and monkeys

The purpose of this study was to investigate the pharmacokinetic behaviour of mirogabalin in rats and monkeys. Pharmacokinetic parameters of mirogabalin after its oral and intravenous administration were determined. Distribution study, mass balance study and metabolite identification were also conducted after the oral administration of [14C]mirogabalin. Plasma exposure (Cmax and AUCinf) increased dose-proportionally after the oral administration of mirogabalin at 1, 3 and 10 mg/kg to rats and monkeys. Mean total body clearance (CLtot) after intravenous administration at 3 mg/kg was 13.5 mL/min/kg in rats and 9.02 mL/min/kg in monkeys, and absolute bioavailability at 3 mg/kg was 97.6% in rats and 85.2% in monkeys. There was greater recovery of radioactivity in urine than that in faeces after the oral administration of [14C]mirogabalin. The main radioactive component in the plasma, urine and faeces was mirogabalin. A204-4455 (lactam form), an oxidised metabolite of mirogabalin, mirogabalin N-glucuronide and O-glucuronide of oxidised A204-4455 were detected as minor components in monkeys and rats. Mirogabalin administered orally was almost completely eliminated via urinary excretion. A small part of the orally administered dose of mirogabalin was metabolised via glucuronidation at the amine and carboxylic acid moiety and oxidation as the primary metabolic pathway.

731. Pharmacokinetics of Gepotidacin (GSK2140944) in Subjects with Hepatic Impairment

BackgroundGepotidacin (GEP), a first in class novel triazaacenaphthylene bacterial topoisomerase inhibitor, inhibits bacterial replication and has in vitro and in vivo efficacy activity against key pathogens, including drug-resistant strains, associated with a range of infections. In a previous absorption, distribution, metabolism, and excretion study for GEP, the mean recovery of radioactivity in urine and feces accounted for approximately 31.2% and 52.5%, respectively, of [14C]-GEP administered as a single oral dose. GEP was eliminated mainly as parent in urine, accounting for approximately 20% of the administered dose. Elimination via metabolism accounted for a total of 13% to 19% of the dose. Average total intravenous clearance of approximately 43 L/hour and renal clearance (CLr) of approximately 16 L/hour provides a hepatic clearance of 27 L/hour, suggesting that hepatic clearance is a major route of elimination of GEP.MethodsParticipants with normal and varying degrees of hepatic impairment (HI) received a single oral dose of GEP 1,500 mg. PK collections of blood, urine and saliva were performed.ResultsRelative to normal hepatic function, GEP Cmax and AUC(0-∞) in plasma were increased by 1.2-fold in subjects with moderate, and between 1.7-fold to 1.9-fold in severe HI. The fraction of dose excreted in urine increased with an increase in hepatic impairment. GEP urine concentrations remained high over a 12-hour period. Saliva concentrations displayed a linear relationship with plasma (both total and unbound) concentrations (R2 = 0.76). The geometric mean ratio of saliva AUC to unbound plasma AUC values ranged from 0.746 to 0.839 across all groups. Administration of 1,500 mg oral GEP was generally tolerated.ConclusionAn increase in the dosing interval or dose reduction may be required in patients with severe hepatic impairment. Disclosures All authors: No reported disclosures.

Abstract CT159: Investigation of the absorption, metabolism, excretion, and mass balance of [14C]-pacritinib in healthy subjects: a phase I study

Abstract Introduction: Dysregulation in tyrosine kinase signaling has been implicated in development of hematologic malignancies including myelofibrosis and lymphomas. Pacritinib is an oral kinase inhibitor with specificity for JAK2, FLT3, CSF1R, and IRAK1. In mouse distribution studies of radiolabeled pacritinib, ∼91% of administered dose was recovered in the feces, suggesting an important role for biliary elimination in clearance of pacritinib. This phase 1 trial investigated clearance pathways, excretion, pharmacokinetics, and recovery of pacritinib, its major metabolites, and total radioactivity in healthy volunteers. Methods: Healthy male volunteers aged 18-55 y were eligible for inclusion. Study volunteers received a single 400 mg dose of pacritinib capsules plus a single dose of [14C]-pacritinib (100 μCi radioactivity per <1 mg of pacritinib as a 30 mL suspension). Blood, urine, and feces were sampled predose and up to 42 days postdose. Pacritinib and metabolites were identified using HPLC-MS/MS/radio flow-through detector (RFD), high resolution mass spectrometry, and authentic metabolite standards. Results: Six subjects were enrolled and received [14C]-pacritinib. Peak radioactivity in plasma was reached approximately 2 h following administration. Mean apparent volume of distribution and apparent clearance in plasma were 137 L and 1.73 L/h, respectively. Elimination half-life for total radioactivity in plasma was 55.1 h. Twelve pacritinib metabolites were identified: M1, M2, M3, M5, M6, M7, M8, M9, M12, M13, M14, and M14a and reflected metabolic pathways including oxidation, N-dealkylation, O-dealkylation, hydrolysis, and dehydrogenation. Pacritinib was the predominant radioactive component (72%) recovered in plasma from 0.5-120 h with mean maximum concentration (Cmax) of 4117.2 ng/mL. Mean Cmax for M2, M1, M3, and M8 were 887.0, 854.5, 292.3, and 148.6 ng/mL respectively. Mean metabolite exposure ratios for major metabolites, M1 and M2, in plasma relative to pacritinib were 0.0963 and 0.105, respectively. Mean recovery of radioactivity in urine (0-48 h) was 3.22% of administered dose; M7, a glucuronidated metabolite, was the predominant radioactive component (3.03% of administered dose). Pacritinib recovered in urine accounted for 0.12% of administered dose. From 0-240 h postdose, mean recovery of radioactivity in feces was 85.5% of administered dose. Pacritinib was detected by MS in fecal samples, but not by RFD. Metabolite M2 was the predominant radioactive fecal component, (24.1% of administered dose). Five individuals (83.3%) reported 9 total adverse events (AEs); all AEs were grade 1 and included diarrhea (5 events in 4 individuals) and nausea (1 event in 1 individual). There were no clinically significant abnormalities in vital signs, ECG, or by physical examination. Conclusions: Following oral administration, pacritinib was the predominant moiety recovered in plasma. Pacritinib was extensively metabolized; major metabolites (M1, oxidation; M2, dealkylation) have relatively low pharmacological potency and are unlikely to substantially contribute to the activity of pacritinib. Intact pacritinib was minimally excreted in urine and feces. Most radioactivity was recovered as metabolites in feces, suggesting extensive biliary clearance and hepatic metabolism of pacritinib. Citation Format: Suliman Al-Fayoumi, Sherri Amberg, Huafeng Zhou, Lindsey Millard, Jack W. Singer, James P. Dean. Investigation of the absorption, metabolism, excretion, and mass balance of [14C]-pacritinib in healthy subjects: a phase I study. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr CT159.

Absorption, distribution, metabolism, and excretion (ADME) of 14C-sonidegib (LDE225) in healthy volunteers

The absorption, distribution, metabolism, and excretion of the hedgehog pathway inhibitor sonidegib (LDE225) were determined in healthy male subjects. Six subjects received a single oral dose of 800 mg ¹⁴C-sonidegib (74 kBq, 2.0 µCi) under fasting conditions. Blood, plasma, urine, and fecal samples were collected predose, postdose in-house (days 1-22), and during 24-h visits (weekly, days 29-43; biweekly, days 57-99). Radioactivity was determined in all samples using accelerator mass spectrometry (AMS). Liquid chromatography-tandem mass spectrometry (LC-MS/MS) was used to determine concentrations of sonidegib and its main circulating metabolite in plasma. Metabolite profiles and structures were determined in pooled plasma, urine, and fecal samples using high-performance LC-AMS and LC-MS/MS, respectively. A single dose of ¹⁴C-sonidegib was well tolerated in healthy subjects. Unchanged sonidegib and total radioactivity reached peak concentration in plasma by 2 and 3 h, respectively, and demonstrated similarly long half-lives of 319 and 331 h, respectively. Absorbed sonidegib (estimated 6-7 %) was extensively distributed, and the approximate terminal volume of distribution was 2,500 L. Unchanged sonidegib and a metabolite resulting from amide hydrolysis were the major circulating components (36.4 and 15.4 % of radioactivity area under the curve, respectively). Absorbed sonidegib was eliminated predominantly through oxidative metabolism of the morpholine part and amide hydrolysis. Unabsorbed sonidegib was excreted through the feces. Metabolites in excreta accounted for 4.49 % of the dose (1.20 % in urine, 3.29 % in feces). The recovery of radioactivity in urine and feces was essentially complete (95.3 ± 1.93 % of the dose in five subjects; 56.9 % of the dose in one subject with incomplete feces collection suspected). Sonidegib exhibited low absorption, was extensively distributed, and was slowly metabolized. Elimination of absorbed sonidegib occurred largely by oxidative and hydrolytic metabolism.

Absorption, metabolism and excretion of [14C]gemigliptin, a novel dipeptidyl peptidase 4 inhibitor, in humans

1. Gemigliptin (formerly known as LC15-0444) is a newly developed dipeptidyl peptidase 4 inhibitor for the treatment of type 2 diabetes. Following oral administration of 50 mg (5.4 MBq) [14C]gemigliptin to healthy male subjects, absorption, metabolism and excretion were investigated.2. A total of 90.5% of administered dose was recovered over 192 hr postdose, with 63.4% from urine and 27.1% from feces. Based on urinary recovery of radioactivity, a minimum 63.4% absorption from gastrointestinal tract could be confirmed.3. Twenty-three metabolites were identified in plasma, urine and feces. In plasma, gemigliptin was the most abundant component accounting for 67.2% ∼ 100% of plasma radioactivity. LC15-0636, a hydroxylated metabolite of gemigliptin, was the only human metabolite with systemic exposure more than 10% of total drug-related exposure. Unchanged gemigliptin accounted for 44.8% ∼ 67.2% of urinary radioactivity and 27.7% ∼ 51.8% of fecal radioactivity. The elimination of gemigliptin was balanced between metabolism and excretion through urine and feces. CYP3A4 was identified as the dominant CYP isozyme converting gemigliptin to LC15-0636 in recombinant CYP/FMO enzymes.

Abstract 3367: Massbalance, excretion and metabolism of [14C]-Pralatrexate (PDX) incancer patients in a phase I trial.

Abstract Background: PDX is a novel 10-deaza-aminopterin analogue of methotrex[[Unsupported Character - Codename ­]]ate consisting of a mixture of R- and S-diastereomeric folate derivatives. PDX inhibits folate metabolism by binding to and inhibiting the enzyme dihydrofolate reductase (DHFR). PDX is the first drug approved by the US Food and Drug Admin[[Unsupported Character - Codename ­]]istration (FDA) specifically for the treatment of patients with relapsed or refractory peripheral T-cell lymphoma. Mass balance studies in animals and humans with radiolabeled compounds represent a standard part of the development process for new drugs. Isotopically labeled analogs of a drug or its metabolites play an important role in understanding the absorption, distribution, metabolism and excretion profiles of a compound. The objectives of this study were to determine the pharmacokinetics (PK), metabolism and routes of excretion of [14C]-PDX and to characterize its metabolites in human plasma and urine. Methods: Four patients were administered intravenously with a mixture of 50 μCi of [14C]-PDX (0.5 mg) and 224.5 mg of non radioactive PDX over a 3-5 minute infusion. Serial blood and plasma samples were drawn at: 0 (before PDX infusion), and up to 144 h after the start of infusion. Urine and fecal samples were collected for up to 168 h after the start of infusion. Expired air samples were collected up to 24 hours after administration. The radioactivity measurement in biological fluids was performed using liquid scintillation counting. Results: Mass balance was achieved with a mean recovery radioactivity in excreta= 82.9 % ± 20.0 % for the four patients. The mean recovery of radioactivity in urine, feces, and expired air were 34.1%, 38.7% and 10.1%, respectively, indicating renal and fecal excretions were the major route of elimination of [14C]-PDX. A three-compartment open model adequately described [14C]-PDX time radioactivity-concentration courses. The AUC0-∞, and clearance values for total radioactivity in plasma were 18.1 nCi.h/mL, and 3.95 L/h, respectively. Metabolite profiling will be performed using HPLC with beta radiation detector. Conclusions: This study quantified the mass balance of PDX and defined its substantial excretion in both urine and feces after IV administration. The PK of [14C]-PDX was best described by a three compartment open model. The metabolite profiling of PDX is ongoing. Citation Format: Elodie Odore, Keyvan Rezaï, Olivier Madar, Sophie Weill, Ahmad Awada, Bert Pronk, Esteban Cvitkovic, Francois Lokiec. Massbalance, excretion and metabolism of [14C]-Pralatrexate (PDX) incancer patients in a phase I trial. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3367. doi:10.1158/1538-7445.AM2013-3367

Absorption, Metabolism, and Excretion of Quizartinib (AC220), a FLT3 Tyrosine Kinase Inhibitor for Treatment of Acute Myeloid Leukemia, in Healthy Male Volunteers

AbstractAbstract 4327Quizartinib (AC220) is an oral tyrosine kinase inhibitor that has shown promising activity in refractory/relapsed acute myeloid leukemia patients in a Phase 1 and a Phase 2 study. The absorption, metabolism, and excretion of quizartinib were characterized in healthy volunteers in a Phase 1 mass balance study. Six healthy males (mean ± SD age 29 ± 8.4 years) received a single oral dose of 60 mg quizartinib as a solution; approximately 1.6% of the total dose was labeled with 14C (approximately 100 μCi). Blood, plasma, urine, and feces were collected for 14 days (336 h) after dosing.Maximum mean ± SD blood radioactivity concentrations, reached 4 h after dosing, were 296 ± 67.4 ng equivalents/g. Maximum blood radioactivity concentrations in individual subjects occurred 4 h after dosing and ranged from 228 to 397 ng equivalents/g.Excretion of radioactivity was relatively consistent throughout the study. The maximum mean ± SD urinary concentration of radioactivity was 112 ± 52.3 ng equivalents/g at 8 to 24 hours after dosing, and the maximum mean ± SD fecal concentration of radioactivity was 51,100 ± 21,300 ng equivalents/g at 24 to 48 h after dosing. A mean ± SD of 1.64 ± 0.482% of the dose was recovered in urine, and 76.3 ± 6.23% was recovered in feces. The overall mean ± SD recovery of radioactivity in urine and feces was 78.0 ± 6.24% over the course of the study, with recovery from individual subjects ranging from 72.4% to 88.3%. Excretion of radioactivity was still ongoing at study completion (336 h). Recovery of <90% was not unexpected given the long half-life (approximately 3.5 days) of quizartinib.The major radiolabeled components of plasma were unchanged quizartinib and the oxidative metabolite AC886. Five additional metabolites in plasma were identified by LC-MS but could not be identified by measurement of radioactivity, because of low levels. Eighteen radioactive peaks in urine were detected, representing less than 0.09% of the administered dose, but their putative structures could not be identified because of low levels.Quizartinib was extensively metabolized, with the metabolites excreted primarily in feces, suggesting hepatobiliary excretion of radioactivity, non-biliary excretion into the gastrointestinal tract, or metabolism within the gastrointestinal tract. Forty-two radioactive peaks were detected in fecal extracts, of which unchanged quizartinib was a significant radioactive component (mean of 4.0% of the administered radioactive dose), and 15 metabolites, each representing a mean of 1.0% to 3.5% of the administered radioactive dose, were identified.Quizartinib was predominantly metabolized by phase I biotransformations, as was evident by the absence of any conjugates of quizartinib or of oxidative metabolites under the analytical conditions used to profile plasma, urine, and feces. Quizartinib was metabolized by multiple biotransformation pathways, including oxidation, reduction, dealkylation, deamination, and hydrolysis, and by combinations of these pathways.Quizartinib was well tolerated as a single 60 mg dose in this study. There were no clinically significant changes in vital signs, ECGs, or laboratory test results. Two subjects experienced adverse events. Grade 1 dry skin in 1 subject was considered to be unrelated to study treatment, and Grade 1 diarrhea in 1 subject was considered to be possibly related to treatment.The results of this study indicated that, in humans, quizartinib was orally available and predominantly eliminated in feces, with renal clearance as a minor elimination route, and that AC886 was the only major metabolite in the circulation. Disclosures:Li:Ambit Biosciences: Employment. Bresnahan:Ambit Biosciences: Employment. Gammon:Ambit Biosciences: Employment. Sanga:Covance Laboratories, Inc.: Employment. Hale:Covance, Inc.: Employment. Hashimoto:Astellas Pharma, Inc.: Employment. Gill:Astellas Pharma, Inc.: Employment. James:Ambit Biosciences: Employment.

Absorption, Distribution, Metabolism and Excretion of [14C]Dexlansoprazole in Healthy Male Subjects

The proton pump inhibitor dexlansoprazole is a modified-release formulation of dexlansoprazole, an enantiomer of lansoprazole, which employs a Dual Delayed Release™ (DDR) delivery system. This study was conducted in healthy subjects to assess the absorption, distribution, metabolism and excretion of a 60 mg dose of [14C]dexlansoprazole. After multiple daily doses of dexlansoprazole DDR for 4 days followed by a single dose of [14C]dexlansoprazole on day 5, absorption, distribution, metabolism and elimination of [14C]dexlansoprazole were assessed in six healthy male subjects whose CYP (cytochrome P450) 2C19 metabolizer status was also determined. Five subjects were phenotyped as extensive metabolizers (EMs) and one subject was a poor metabolizer (PM). Recovery of radioactivity in urine and faeces averaged 98% after 7 days (51% in urine and 48% in faeces) post-14C dosing. In plasma, dexlansoprazole was the largest component detected, with the main metabolites in the EM subjects being 5-glucuronyloxy dexlansoprazole and 5-hydroxy dexlansoprazole (CYP2C19 mediated), whereas the PM subject had greater amounts of dexlansoprazole sulfone (CYP3A mediated). Dexlansoprazole was not detected in urine; six metabolites were identified accounting for an average of 86% of the urinary radioactivity, with 5-glucuronyloxy dexlansoprazole, 5-glucuronyloxy dexlansoprazole sulfide, 2-S-N-acetylcysteinyl benzimidazole and 5-sulfonyloxy dexlansoprazole sulfide being the primary metabolites. In faeces, parent drug and six identified metabolites accounted for 23% and 72%, respectively, of the faecal radioactivity, with 5-hydroxy dexlansoprazole sulfide and dexlansoprazole sulfide being predominant. Overall, the results indicate that [14C]dexlansoprazole was well absorbed and extensively metabolized by oxidation, reduction and conjugation to 13 identified metabolites.

Abstract 751: Mass balance, excretion and metabolism of [14C] ASA404 in cancer patients in a phase I trial

Abstract Purpose: To determine the mass balance, excretion and metabolism of the small molecule flavonoid tumor vascular disrupting agent ASA404 in patients with advanced cancer. Methods: Seven cancer patients were given a single dose of 3000 mg [14C] ASA404 by intravenous infusion over 20 minutes prior to collection of samples of plasma, urine and faeces. Pharmacokinetic samples were analysed by HPLC, liquid scintillation counting, mass spectrometry, glusulase treatment and comparison to authentic standards. Descriptive pharmacokinetic parameters were generated by non-compartmental analysis. Results: Mass balance was achieved (mean recovery of radioactivity in excreta = 86.9% of the dose) with balanced excretion between urine (mean recovery of radioactivity in urine = 53.9% of dose) and faeces (mean recovery of radioactivity in faeces = 33.3% of dose). ASA404 was eliminated as parent drug, three known metabolites (6-hydroxy-ASA404, ASA404 acyl glucuronide and 6-hydroxy-ASA404 acyl glucuronide) and as two novel metabolites (an ASA404 dimer and an ASA404 dimer glucuronide conjugate). Unchanged ASA404 was the major radioactivity component detected in plasma within the first 24 hours after dosing. At later time-points, irreversibly protein bound ASA404 and all of the metabolites that had been detected in excreta, contributed to total plasma radioactivity. Conclusion: This study defined the substantial excretion of ASA404, mainly as metabolites, in both urine (over half of the dose) and faeces (about one third of the dose) after intravenous administration. Two novel metabolites were identified that were not reported by previous studies using nonradioactive techniques. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 751. doi:1538-7445.AM2012-751

Excretion mass balance and quantitative whole‐body autoradiography following a single oral (PO) administration of [14C]MSDC 0602, an mTOT‐modulating insulin sensitizer, in Sprague Dawley (SD) and Long‐Evans (LE) rats

The objectives of this study were to determine the mass balance excretion, plasma pharmacokinetics and tissue distribution of radioactivity following PO administration of [14C]MSDC‐0602 in rats. Five groups of male SD rats and 1 group of male LE rats (28 total rats) that weighed approximately 250 g were dosed. All rats were administered a single PO bolus of [14C]MSDC‐0602 as a suspension at a dose of 10 mg/kg (50 μCi/kg). Excretion of radioactivity was rapid, with the majority eliminated within 24 h post‐dose. Biliary excretion was the primary route of elimination in bile duct‐cannulated (BDC) rats. Total recovery in urine and bile in BDC rats suggested the extent of oral absorption was at least 60%. Urinary recovery of radioactivity from intact rats (22.4%) was higher than in BDC rats (12.3%), and total radioactivity recovered in feces (31.7%) and bile (48.1%) was higher in the BDC rats (79.8%) than in the feces of intact rats (67.0%), suggesting enterohepatic recirculation of radioactivity. Plasma radioactivity had a Tmax of 8 h and declined with a t1/2 of 14.6 h. [14C]MSDC‐0602‐derived radioactivity was widely distributed; tissues levels were lower than blood through 192 h post‐dose in LE rats.

Mass balance, excretion and metabolism of [14C] ASA404 in cancer patients in a phase I trial

To determine the mass balance, excretion and metabolism of the small molecule flavonoid tumour vascular disrupting agent ASA404 in patients with advanced cancer. Seven cancer patients were given a single dose of 3,000 mg [(14)C] ASA404 by intravenous infusion over 20 min prior to collection of samples of plasma, urine and faeces. Pharmacokinetic samples were analysed by HPLC, liquid scintillation counting, mass spectrometry, glusulase treatment and comparison to authentic standards. Descriptive pharmacokinetic parameters were generated by noncompartmental analysis. Mass balance was achieved (mean recovery of radioactivity in excreta = 86.9% of the dose) with balanced excretion between urine (mean recovery of radioactivity in urine = 53.9% of dose) and faeces (mean recovery of radioactivity in faeces = 33.3% of dose). ASA404 was eliminated as parent drug, three known metabolites (6-methylhydroxy-ASA404, ASA404 acyl glucuronide and 6-methylhydroxy-ASA404 acyl glucuronide) and two novel metabolites (an ASA404 dimer and an ASA404 dimer glucuronide conjugate). Unchanged ASA404 was the major radioactivity component detected in plasma within the first 24 h after dosing. At later time points, irreversibly protein bound ASA404 and all of the metabolites that had been detected in excreta contributed to total plasma radioactivity. This study defined the substantial excretion of ASA404, mainly as metabolites, in both urine (over half of the dose) and faeces (about one-third of the dose) after intravenous administration. Two novel metabolites were identified that were not reported by previous studies using nonradioactive techniques.

Absorption, Metabolism, and Excretion of Darunavir, a New Protease Inhibitor, Administered Alone and with Low-Dose Ritonavir in Healthy Subjects

Absorption, metabolism, and excretion of darunavir, an inhibitor of human immunodeficiency virus protease, was studied in eight healthy male subjects after a single oral dose of 400 mg of [(14)C]darunavir given alone (unboosted subjects) or with ritonavir [100 mg b.i.d. 2 days before and 7 days after darunavir administration (boosted subjects)]. Plasma exposure to darunavir was 11-fold higher in boosted subjects. Total recoveries of radioactivity in urine and feces were 93.9 and 93.5% of administered radioactivity in unboosted and boosted subjects, respectively. The most radioactivity was recovered in feces (81.7% in unboosted subjects and 79.5% in boosted subjects, compared with 12.2 and 13.9% recovered in urine, respectively). Darunavir was extensively metabolized in unboosted subjects, mainly by carbamate hydrolysis, isobutyl aliphatic hydroxylation, and aniline aromatic hydroxylation and to a lesser extent by benzylic aromatic hydroxylation and glucuronidation. Total excretion of unchanged darunavir accounted for 8.0% of the dose in unboosted subjects. Boosting with ritonavir resulted in significant inhibition of carbamate hydrolysis, isobutyl aliphatic hydroxylation, and aniline aromatic hydroxylation but had no effect on aromatic hydroxylation at the benzylic moiety, whereas excretion of glucuronide metabolites was markedly increased but still represented a minor pathway. Total excretion of unchanged darunavir accounted for 48.8% of the administered dose in boosted subjects as a result of the inhibition of darunavir metabolism by ritonavir. Unchanged darunavir in urine accounted for 1.2% of the administered dose in unboosted subjects and 7.7% in boosted subjects, indicating a low renal clearance. Darunavir administered alone or with ritonavir was well tolerated.

Absorption, metabolism, and excretion of 14C gimatecan (LBQ707) after oral administration in patients with advanced cancer

2564 Background: Gimatecan (Gim), a new potent oral topoisomerase I inhibitor is a lipophilic 7-oxyiminomethyl derivative of camptothecin. Its in vitro cytoxicity is more sustained than CPT-11 and topotecan, it has excellent anti-tumor activity in mouse xenografts, and shown good tolerability with Ph I activity. The study aim was to profile its disposition in cancer patients. Methods: 4 patients with advanced cancer received a single oral 1.5 mg dose of [14C] Gim (60 μCi) followed by standard Gim treatment on Day 15. Whole blood, plasma, urine, and feces were collected over 7 days with spot fecal collections up to Day 19. Total radioactivity was measured by liquid scintillation counting. Gim and metabolite concentrations in plasma and excreta were measured by LC- MS/MS and HPLC with radiometric detection. Results: Gim showed a rapid first-order absorption and a long elimination phase and was well tolerated. The median (range) Tmax for Gim was 1 h (0.5 to 3 h) and mean t1/2 and oral clearance values were 91 h and 0.6 L/h, respectively. Gim was the major moiety and its active metabolite LCF775 (t-butyl-mono-hydroxy Gim) was the main metabolite (albeit minor, 2–9%) in plasma. Trace glucuronide and sulfate metabolites were also detected in plasma. Mean recovery of radioactivity in urine (0-Day 7) and feces (0-Day 11) was 70.5 % (56.2–80.0%) of the dose. Incomplete recovery is attributed to opiates use in 2 patients and incomplete (sporadic) fecal sampling at later timepoints. Fecal excretion (0-Day 11) was prolonged and major in 3/4 patients (46- 73% of the dose, of which 14–23% is the unchanged Gim suggesting the drug is well absorbed). An additional 1.3–3.5% was recovered in spot collections (Days 14, 15 and 19). Urine excretion (0-Day 7) was 7.2–10.3% of the dose in 3 patients, one patient (cachectic, on opiates) excreted only 21% in feces and 46% in urine. Gim and several Gim metabolites (and glucuronide conjugates thereof) were the major components in excreta. Conclusions: Gim and its minor metabolite, LCF775 were the principal pharmacologically active components in plasma. Fecal excretion is the main elimination pathway in most patients. A long half-life (90hr) of Gim, uncomplicated metabolism, and good oral absorption make Gim an attractive candidate for Ph II development. [Table: see text]

Study of the absorption, metabolism, and excretion of (14C)-ramelteon (TAK-375)

This study investigated the pharmacokinetics, metabolism and excretion of ramelteon, a novel selective ML1 receptor agonist. Six healthy male subjects received a single oral dose of 16 mg (14C)-ramelteon. Ramelteon was rapidly absorbed (tmax of 0.3 hours) and eliminated (half-life of 1.2 hours). The metabolites MI, MI, MI11 and MIV were rapidly formed and eliminated (half-lives of 1 to 3 hours). Systemic exposure of metabolite M-II (major active metabolite) was 20- to 30-fold greater than that of ramelteon, while the exposures of M-I, M-III, and M-IV were one- to four-fold higher than that of ramelteon. Of total radioactivity administered, 84% was renally eliminated, and 4% was faecally eliminated, with metabolites of ramelteon accounting for the majority of the dose eliminated. High urinary recovery of radioactivity indicates that there was at least 84% oral absorption of ramelteon. Negligible urinary excretion of ramelteon and low serum concentrations of ramelteon (relative to metabolites) indicate that ramelteon undergoes extensive first-pass metabolism. Ramelteon was metabolized primarily via oxidation to hydroxyl and carbonyl groups, with secondary metabolism to form glucuronide conjugates. Clinical Pharmacology & Therapeutics (2004) 75, P22–P22; doi: 10.1016/j.clpt.2003.11.084

The in vivo human metabolism of tibolone.

In vivo metabolism of tibolone was studied in three healthy postmenopausal volunteers after daily oral administration of 2.5 mg of tibolone for 5 days and a single dose of 2.5 mg approximately equal 555 kBq of [(14)C]tibolone on day 6. The 0- to 192-h recovery of radioactivity in urine and feces was 31.2 +/- 10.5 and 53.7 +/- 5.1%, respectively. Total 0- to 192-h recovery ranged from 78.5 to 94.2% of the dose and averaged 84.9%. Metabolites were putatively identified using high-pressure liquid chromatography in plasma, urine, and feces. The most important phase I metabolic reactions were reduction of the 3-keto group to 3alpha- and 3beta-hydroxy metabolites, a shift of the Delta(5(10))-double bond to a Delta(4(5))-double bond, a reduction of the Delta(4(5))-double bond to 5alpha,10-dihydro or 5beta,10-dihydro metabolites, and hydroxylation at C2 and C7. The most important phase II metabolic reaction is sulfation of the C17 hydroxy group of tibolone and sulfation of the C3 hydroxy groups. In the circulation, over 75% of tibolone and its metabolites are present in the sulfated form. Local metabolism and local sulfatases may contribute to the tissue-specific activity. Using human microsomes, tibolone, 3alpha-hydroxy tibolone, 3beta-hydroxy tibolone, and Delta(4)-tibolone appeared to be at least 50-fold less potent inhibitors of CYP1A2, CYP2C9, CYP2E1, and CYP3A4 compared with enzyme-selective inhibitors. Tibolone and its metabolites, therefore, are not likely to play a clinically significant role at the level of these cytochrome P450 enzymes with regard to the metabolism of coadministered drugs.

Evaluation of the excretion, and metabolism of the cardiotonic agent bemoradan in male rats and female beagle dogs

The excretion and metabolism of (+/-) [6-(3,4-dihydro-3-oxo-1,4[2H]-benzoxazine-yl)-2,3,4,5-tetrahydro-5-methylpyridazin-3-one] (bemoradan; RWJ-22867) have been investigated in male Long-Evans rats and female beagle dogs. Radiolabeled [14C] bemoradan was administered to rats as a singkle 1 mg/kg suspension dose while the dogs received 0.1 mg/kg suspension dose. Plasma (0-24 h; rat and dog), urine (0-72 h; rat and dog) and fecal (0-72 h; rat and dog) samples were collected and analyzed. The terminal half-life of the total radioactivity for rats from plasma was estimate to be 4.3 +/- 0.1 h while for dogs it was 7.5 +/- 1.3 h. Recoveries of total radioactivity in urine and feces for rats were 49.1 +/- 2.4% and 51.1 +/- 4.9% of th dose, respectively. Recoveries of total radioactivity in urine and feces for dogs were 56.2 +/- 12.0% and 42.7 V 9.9% of the dose, respectively. Bemoradan and a total of nine metabolites were isolated and tentatively identified in rat and dog plasma, urine, and fecal extracts. Unchanged bemoradan accounted for approimately < 2% of the dose in rat urine and 20% in rat feces. Unchanged bemoradan accounted for approximately 5% of the dose in urine and 16% in feces in dog. Six proposed pathways were used to describe the metabolites found in rats and dogs: pyridazinyl oxidations, methyl hydroxylation, hydration, N-oxidation, dehydration and phase II conjugations.

Evaluation of the absorption, excretion, and metabolism of the antihypertensive agent RWJ-26899 in male and female CR wistar rats and beagle dogs

The absorption, excretion and metabolism of N-(2, 6-dichlorophenyl)-beta-[[(1-methylcyclohexyl)methoxylmethyl]-N-(phenylmethyl)-1-pyrrolidineethanamine (RWJ-26899; McN-6497) has been investigated in male and female CR Wistar rats and beagle dogs. Radiolabeled [14C] RWJ-26899 was administered to rats as a single 24 mg/kg suspension dose while the dogs received 15 mg/kg capsules. Plasma (0-36 h; rat and 0-48 h; dog), urine (0-192 h; rat and dog) and fecal (0-192 h; rat and dog) samples were collected and analyzed. There were no significant gender differences observed in the data. The terminal half-life of the total radioactivity for rats from plasma was estimated to be 7.7 +/- 0.6 h while for dogs it was 22.9 +/- 4.4 h. Recoveries of total radioactivity in urine and feces for rats were 8.7 +/- 2.9% and 88.3 +/- 10.4% of the dose, respectively. Recoveries of total radioactivity in urine and feces for dogs were 4.1 +/- 1.4% and 90.0 +/- 4.7% of the dose, respectively. RWJ-26899 and a total of nine metabolites were isolated and tentatively identified in rat urine, and fecal extracts. Unchanged RWJ-26899 accounted for approximately 1% of the dose in rat urine and 8% in rat feces. RWJ-26899 and a total of four metabolites were isolated and identified in dog urine, and fecal extracts. Unchanged RWJ-26899 accounted for approximately 1% of the dose in urine and 63% in feces in dog. Five proposed pathways were used to describe the metabolites found in rats: N-oxidation, oxidative N-debenzylation, pyrrolidinyl ring hydroxylation, phenyl hydroxylation and methyl or cyclohexyl hydroxylation. Two biotransformation pathways in dogs are proposed: N-oxidation and methyl or cyclohexyl ring hydroxylation.

Evaluation of the absorption, excretion and metabolism of [14 C] etoperidone in man

1. The absorption, excretion and metabolism of 2-{3-[4-(3-chlorophenyl)-1-piperazinyl]propyl}-4,5-diethyl-2,4-dihydro-3H-1,2,4 hydrochloride (etoperidone HCl) was investigated in six healthy men. Subjects were fasted overnight before receiving a single oral dose of a 100mg solution [14C] etoperidone HCl. 2. Plasma (0-48h), urine (0-120h) and faecal (0-120h) samples were collected. The terminal half-life of the total radioactivity from plasma was 21.7 ± 2.8 h with an apparent clearance of 1.01 ± 0.08 ml min-1. Recoveries of total radioactivity in urine and faeces were 78.8 ± 3.6% and 9.6 ± 4.1% of the dose, respectively. 3. Etoperidone and 21 metabolites were isolated and identified in the plasma, urine and faecal extracts. Unchanged etoperidone accounted for <0.01% of the dose in all excreta samples. Nine metabolites were identified in the plasma extracts and 21 urinary metabolites were identified. Seven faecal metabolites were identified. 4. Five proposed pathways were used to describe the formation of the metabolites: alkyl oxidation, piperazinyl oxidation, N -dealkylation, phenyl hydroxylation and conjugation. Alkyl oxidation of etoperidone resulted in the formation of 2-{3-[4-(3- chlorophenyl)-1-piperazinyl]propyl}-4-ethyl-2,4-dihydro-5-(1-hydroxyethyl)-3H-1 triazole-3-one. Piperazinyl oxidation of this metabolite leads to the formation of its N -oxide. N -dealkylation of the piperazinyl group led to the formation of 1-(3-chlorophenyl) piperazine and triazole propionic acid. Phenyl hydroxylation led to three important metabolites in the urine and faeces.

Biotransformation of the antipsychotic agent, mazapertine, in dog-mass spectral characterization and identification of metabolites

1. Biotransformation of the antipsychotic agent, mazapertine, was studied after a single oral administration of 14C-mazapertine succinate (10 mg/kg, free base) to six beagle dogs (three male, three female). 2. Following oral administration of 14C-mazapertine, plasma (0-48 h), urine (0-7 days), and faeces (0-7 days) were collected. Recoveries of total radioactivity in urine and faeces were 26.9 and 62.0% of the dose, respectively. 3. Unchanged mazapertine plus 14 metabolites were isolated and identified, which accounted for >60% of the sample radioactivity in the plasma, 17% of the dose in urine and 28% of the dose in faecal extract. 4. Unchanged mazapertine accounted for <4% of the radioactive dose in excreta samples and <21% of the sample radioactivity present in plasma samples. 5. Seven metabolic pathways for the formation of metabolites were identified including: (1) phenyl hydroxylation, (2) piperidyl oxidation, (3) O-dealkylation, (4) Ndephenylation, (5) oxidative N-debenzylation, (6) depiperidylation and (7) conjugation. 6. Pathways 1, 2, 5 and 6 produced 4-OH-piperidyl, OH-phenyl-OH-piperidyl, carboxybenzoyl piperidine and depiperidyl analogues of mazapertine as major metabolites.