Biotransformation and mass balance of faldaprevir,a hepatitis C NS3/NS4 protease inhibitor in rats

Abstract

1.?The metabolism, pharmacokinetics, excretion and tissue distribution of a hepatitis C NS3/NS4 protease inhibitor, faldaprevir, were studied in rats following a single 2?mg/kg intravenous or 10?mg/kg oral administration of [¹⁴C]-faldaprevir.

2.?Following intravenous dosing, the terminal elimination t_1/2 of plasma radioactivity was 1.75?h (males) and 1.74?h (females). Corresponding AUC_0–∞, CL and V_ss were 1920 and 1900?ngEq?·?h/mL, 18.3 and 17.7?mL/min/kg and 2.32 and 2.12?mL/kg for males and females, respectively.

3.?After oral dosing, t_1/2 and AUC_0–∞ for plasma radioactivity were 1.67 and 1.77?h and 11?300 and 17?900 ngEq?·?h/mL for males and females, respectively.

4.?In intact rats, ≥90.17% dose was recovered in feces and only ≤1.08% dose was recovered in urine for both iv and oral doses. In bile cannulated rats, 54.95, 34.32 and 0.27% dose was recovered in feces, bile and urine, respectively.

5.?Glucuronidation plays a major role in the metabolism of faldaprevir with minimal Phase I metabolism.

6.?Radioactivity was rapidly distributed into tissues after the oral dose with peak concentrations of radioactivity in most tissues at 6?h post-dose. The highest levels of radioactivity were observed in liver, lung, kidney, small intestine and adrenal gland.     

Metabolism,excretion and pharmacokinetics of [14C]glasdegib (PF-04449913) in healthy volunteers following oral administration

1.?The metabolism, excretion and pharmacokinetics of glasdegib (PF-04449913) were investigated following administration of a single oral dose of 100?mg/100 μCi [¹⁴C]glasdegib to six healthy male volunteers (NCT02110342).

2.?The peak concentrations of glasdegib (890.3?ng/mL) and total radioactivity (1043 ngEq/mL) occurred in plasma at 0.75?hours post-dose. The AUC_inf were 8469?ng.h/mL and 12,230 ngEq.h/mL respectively, for glasdegib and total radioactivity.

3.?Mean recovery of [¹⁴C]glasdegib-related radioactivity in excreta was 91% of the administered dose (49% in urine and 42% in feces). Glasdegib was the major circulating component accounting for 69% of the total radioactivity in plasma. An N-desmethyl metabolite and an N-glucuronide metabolite of glasdegib represented 8% and 7% of the circulating radioactivity, respectively. Glasdegib was the major excreted component in urine and feces, accounting for 17% and 20% of administered dose in the 0–120?hour pooled samples, respectively. Other metabolites with abundance <3% of the total circulating radioactivity or dose in plasma or excreta were hydroxyl metabolites, a desaturation metabolite, N-oxidation and O-glucuronide metabolites.

4.?Elimination of [¹⁴C]glasdegib-derived radioactivity was essentially complete, with similar contribution from urinary and fecal routes. Oxidative metabolism appears to play a significant role in the biotransformation of glasdegib.     

Clinical disposition,metabolism and in vitro drug–drug interaction properties of omadacycline

1.?Absorption, distribution, metabolism, transport and elimination properties of omadacycline, an aminomethylcycline antibiotic, were investigated in vitro and in a study in healthy male subjects.

2.?Omadacycline was metabolically stable in human liver microsomes and hepatocytes and did not inhibit or induce any of the nine cytochrome P450 or five transporters tested. Omadacycline was a substrate of P-glycoprotein, but not of the other transporters.

3.?Omadacycline metabolic stability was confirmed in six healthy male subjects who received a single 300?mg oral dose of [¹⁴C]-omadacycline (36.6 μCi). Absorption was rapid with peak radioactivity (～610 ngEq/mL) between 1–4?h in plasma or blood. The AUC_last of plasma radioactivity (only quantifiable to 8?h due to low radioactivity) was 3096 ngEq?h/mL and apparent terminal half-life was 11.1?h. Unchanged omadacycline reached peak plasma concentrations (～563?ng/mL) between 1–4?h. Apparent plasma half-life was 17.6?h with biphasic elimination. Plasma exposure (AUC_inf) averaged 9418?ng?h/mL, with high clearance (CL/F, 32.8?L/h) and volume of distribution (Vz/F 828?L). No plasma metabolites were observed.

4.?Radioactivity recovery of the administered dose in excreta was complete (>95%); renal and fecal elimination were 14.4% and 81.1%, respectively. No metabolites were observed in urine or feces, only the omadacycline C4-epimer.     

Lumiracoxib metabolism in male C57bl/6J mice: characterisation of novel in vivo metabolites

1.?The pharmacokinetics and metabolism of lumiracoxib in male C57bl/6J mice were investigated following a single oral dose of 10?mg/kg.

2.?Lumiracoxib achieved peak observed concentrations in the blood of 1.26?+?0.51?μg/mL 0.5?h (0.5–1.0) post-dose with an AUC_inf of 3.48?+?1.09?μg?h/mL. Concentrations of lumiracoxib then declined with a terminal half-life of 1.54?+?0.31?h.

3.?Metabolic profiling showed only the presence of unchanged lumiracoxib in blood by 24?h, while urine, bile and faecal extracts contained, in addition to the unchanged parent drug, large amounts of hydroxylated and conjugated metabolites.

4.?No evidence was obtained in the mouse for the production of the downstream products of glutathione conjugation such as mercapturates, suggesting that the metabolism of the drug via quinone–imine generating pathways is not a major route of biotransformation in this species. Acyl glucuronidation appeared absent or a very minor route.

5.?While there was significant overlap with reported human metabolites, a number of unique mouse metabolites were detected, particularly taurine conjugates of lumiracoxib and its oxidative metabolites.     

The metabolism and pharmacokinetics of [14C]-S-777469, a new cannabinoid receptor 2 selective agonist,in healthy human subjects

Abstract

1.?The metabolism and pharmacokinetics of S-777469 were investigated after a single oral administration of [¹⁴C]-S-777469 to healthy human subjects.

2.?Total radioactivity was rapidly and well absorbed in humans, with C_max of 11?308?ng eq. of S-777469/ml at 4.0?h. The AUC_inf ratio of unchanged S-777469 to total radioactivity was approximately 30%, indicating that S-777469 was extensively metabolized in humans.

3.?The metabolite profiling in human plasma showed that S-777469 5-carboxymethyl (5-CA) and S-777469 5-hydroxymethyl (5-HM) were the main circulating metabolites, and the AUC_inf ratio of 5-CA and 5-HM to total radioactivity were 24 and 9.1%, respectively. These data suggest that S-777469 was subsequently metabolized to 5-CA in humans although the production amount of 5-CA was extremely low in human hepatocytes.

4.?Total radioactivity was mainly excreted via the feces, with 5-CA and 5-HM being the main excretory metabolites in feces and urine. Urinary excretion of 5-CA was comparable with that of 5-HM, whereas fecal excretion of 5-CA was lower than that of 5-HM.

5.?In conclusion, the current mass balance study revealed the metabolic and pharmacokinetic properties of S-777469 in humans. These data should be useful to judge whether or not the safety testing of metabolite of S-777469 is necessary.     

Absorption,distribution and excretion of the new thienopyridine agent prasugrel in rats

Prasugrel is converted to the pharmacologically active metabolite after oral dosing in vivo. In this study, ¹⁴C-prasugrel or prasugrel was administered to rats at a dose of 5?mg?kg^–1. After oral and intravenous dosing, the values of AUC_0–∞ of total radioactivity were 36.2 and 47.1?µg?eq.?h?ml^–1, respectively. Oral dosing of unlabeled prasugrel showed the second highest AUC_0–8 of the active metabolite of six metabolites analyzed. Quantitative whole body autoradiography showed high radioactivity concentrations in tissues for absorption and excretion at 1?h after oral administration, and were low at 72?h. The excretion of radioactivity in the urine and feces were 20.2% and 78.7%, respectively, after oral dosing. Most radioactivity after oral dosing was excreted in bile (90.1%), which was reabsorbed moderately (62.4%). The results showed that orally administered prasugrel was rapidly and fully absorbed and efficiently converted to the active metabolite with no marked distribution in a particular tissue.     

Mass balance and metabolism of Z-215, a novel proton pump inhibitor,in healthy volunteers

The human mass balance of [^14?C]Z-215, a novel proton pump inhibitor, was characterised in six healthy male volunteers following single oral administration of [^14?C]Z-215 (20?mg, 3.7 MBq) to determine the elimination pathway of Z-215 and the distribution of its metabolites in plasma, urine, and faeces (NCT02618629). [^14?C]Z-215 was rapidly absorbed, with a C_max of 434?ng/mL at 0.38?h for Z-215 and 732?ng eq./mL at 0.5?h for total radioactivity. Means of 59.61% and 31.36% of the administered radioactive dose were excreted in urine and faeces, respectively, within 168?h post-dose. The majority of the dose was recovered within 24?h in urine and 96?h in faeces. Unchanged Z-215 was excreted in urine at trace levels but was not detected in faeces. The main components in plasma were Z-215 and Z-215 sulphone, accounting for 29.8% and 13.3% of the total circulating radioactivity, respectively. Additionally, Z-215 was metabolised through oxidation, reduction and conjugation. Our in vitro Z-215 metabolism study showed that the major isozyme contributing to the oxidation of Z-215, including the formation of Z-215 sulphone, was CYP3A4. In conclusion, Z-215 is well absorbed in humans and primarily eliminated via metabolism, where CYP3A4 plays an important role.     

Pharmacokinetics,metabolism, and excretion of nefopam,a dual reuptake inhibitor in healthy male volunteers

1.?The disposition of nefopam, a serotonin–norepinephrine reuptake inhibitor, was characterized in eight healthy male volunteers following a single oral dose of 75?mg [¹⁴C]-nefopam (100 μCi). Blood, urine, and feces were sampled for 168 h post-dose.

2.?Mean (±?SD) maximum blood and plasma radioactivity concentrations were 359?±?34.2 and 638?±?64.7 ngEq free base/g, respectively, at 2 h post-dose. Recovery of radioactive dose was complete (mean 92.6%); a mean of 79.3% and 13.4% of the dose was recovered in urine and feces, respectively.

3.?Three main radioactive peaks were observed in plasma (metabolites M2 A-D, M61, and M63). Intact [¹⁴C]-nefopam was less than 5% of the total radioactivity in plasma. In urine, the major metabolites were M63, M2 A-D, and M51 which accounted for 22.9%, 9.8%, and 8.1% of the dose, respectively. An unknown entity, M55, was the major metabolite in feces (4.6% of dose). Excretion of unchanged [¹⁴C]-nefopam was minimal.     

Investigation on pharmacokinetics,tissue distribution and excretion of a novel platinum anticancer agent in rats by Inductively Coupled Plasma Mass Spectrometry (ICP-MS)

Abstract

1.?DN604 is a new platinum agent with encouraging anticancer activity. The present study was to explore the pharmacokinetic profiles, distribution and excretion of platinum in Sprague–Dawley rats after intravenous administration of DN604. A sensitive and selective inductively coupled plasma mass spectrometry (ICP-MS) method was established for determination of platinum in biological specimens. The pharmacokinetic parameters were calculated by a non-compartmental method.

2.?The area under concentration–time curve AUC_0?t and AUC_0?∞ for platinum originating from DN604 at 10?mg/kg were 25.15?±?1.29 and 28.72?±?1.04?μg/hml, respectively. The mean residence time MRT was 36.59?±?6.65?h. The volume of distribution V_z was 11.42?±?2.49?l/kg and clearance CL was 0.18?±?0.01?l/h/kg. In addition, the elimination half-life T_1/2z was 44.83?±?9.75?h. After intravenous administration of DN604, platinum was extensively distributed in most of tested tissues except brain. The majority of platinum excreted via urine, and its accumulative excretion ratio during the period of 120?h was 63.5%?±?7.7% for urine, but only 6.94%?±?0.11% for feces.

3.?The satisfactory half-life, wide distribution and high excretion made this novel platinum agent worthy of further research and development.     

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.     

Absorption,metabolism and excretion of [14C]omarigliptin,a once-weekly DPP-4 inhibitor,in humans

1.?Omarigliptin (MARIZEV®) is a once-weekly DPP-4 inhibitor approved in Japan for the treatment of type 2 diabetes. The objective of this study was to investigate the absorption, metabolism and excretion of omarigliptin in humans.

2.?Six healthy subjects received a single oral dose of 25?mg (2.1?μCi) [^14?C]omarigliptin. Blood, plasma, urine and fecal samples were collected at various intervals for up to 20?days post-dose. Radioactivity levels in excreta and plasma/blood samples were determined by accelerator mass spectrometry (AMS).

3.?[^14?C]Omarigliptin was rapidly absorbed, with peak plasma concentrations observed at 0.5–2?h post-dose. The majority of the radioactivity was recovered in urine (～74.4% of the dose), with less recovered in feces (～3.4%), suggesting the compound was well absorbed.

4.?Omarigliptin was the major component in urine (～89% of the urinary radioactivity), indicating renal excretion of the unchanged drug as the primary clearance mechanism. Omarigliptin accounted for almost all the circulating radioactivity in plasma, with no major metabolites detected.

5.?The predominantly renal elimination pathway, combined with the fact that omarigliptin is not a substrate of key drug transporters, suggest omarigliptin is unlikely to be subject to pharmacokinetic drug-drug interactions with other commonly prescribed agents.     

A conscious rat model involving bradycardia and hypotension after oral administration: a toxicokinetical study of aconitine

1.?A model of aconitine-induced bradycardia and hypotension, which is similar to aconitine poisoning in humans, was constructed in conscious rats by oral administration.

2.?Blood pressure (BP) and heart rate (HR) of Sprague-Dawley rats were measured using a volume pressure recording (VPR) system. The pharmacokinetics of toxic doses of aconitine and its metabolites were analyzed using UPLC-MS/MS.

3.?The HR was significantly decreased by 29% at 2?h after oral administration of 200?μg/kg aconitine. When the dose was increased to 400?μg/kg, systolic BP and diastolic BP were significantly decreased by 11% and 12% at 2?h after the administration, except when bradycardia occurred at 2?h and 4?h. The drug concentration-time curve showed a double-peak phenomenon in rats administered a 400?μg/kg dose. The AUC_0–12?h value in the 400?μg/kg group significantly increased 0.8-fold compared to the 200?μg/kg group. Moreover, a high plasma concentration of 16-O-demethyaconitine was found in the rats that received two toxic doses.

4.?In conclusion, bradycardia and hypotension are induced in conscious rats by a toxic dose of aconitine (400?μg/kg), and there was no significant difference in dose-normalized AUC_0–12?h values between oral administrations of 200?μg/kg and that of 400?μg/kg. However, the dose-normalized C_max and AUC_0–12?h values in 200?μg/kg and 400?μg/kg groups were significantly smaller than those in 100?μg/kg group. The metabolites of aconitine, 16-O-demethyaconitine, and benzoylaconitine may also contribute to the hypotensive response.     

Pharmacokinetics,metabolism and excretion of [14C]-lanicemine (AZD6765), a novel low-trapping N-methyl-d-aspartic acid receptor channel blocker,in healthy subjects

Abstract

1.?(1S)-1-phenyl-2-(pyridin-2-yl)ethanamine (lanicemine; AZD6765) is a low-trapping N-methyl-d-aspartate (NMDA) channel blocker that has been studied as an adjunctive treatment in major depressive disorder. The metabolism and disposition of lanicemine was determined in six healthy male subjects after a single intravenous infusion dose of 150?mg [¹⁴C]-lanicemine.

2.?Blood, urine and feces were collected from all subjects. The ratios of C_max and AUC_(0–∞) of lanicemine to plasma total radioactivity were 84 and 66%, respectively, indicating that lanicemine was the major circulating component with T_1/2 at 16?h. The plasma clearance of lanicemine was 8.3?L/h, revealing that lanicemine is a low-clearance compound. The mean recovery of radioactivity from urine was 93.8% of radioactive dose.

3.?In urine samples, 10 metabolites of lanicemine were identified. Among which, an O-glucuronide conjugate (M1) was the most abundant metabolite (～11% of the dose in excreta). In plasma, the circulatory metabolites were identified as a para-hydroxylated metabolite (M1), an O-glucuronide (M2), an N-carbamoyl glucuronide (M3) and an N-acetylated metabolite (M6). The average amount of each of metabolite was less than 4% of total radioactivity detected in plasma or urine.

4.?In conclusion, lanicemine is a low-clearance compound. The unchanged drug and metabolites are predominantly eliminated via urinary excretion.     

Pharmacokinetic characterization of hydroxylpropyl-β-cyclodextrin-included complex of cryptotanshinone,an investigational cardiovascular drug purified from Danshen (Salvia miltiorrhiza)

1.?The study aimed to investigate the pharmacokinetics of cryptotanshinone in a hydroxylpropyl-β-cyclodextrin-included complex in dogs and rats.

2.?Animals were administrated the inclusion complex of cryptotanshinone and the concentrations of cryptotanshinone and its major metabolite tanshinone IIA were determined by a liquid chromatography-tandem mass spectrometry (LC-MS/MS) method.

3.?Cryptotanshinone in inclusion complex was absorbed slowly after an oral dose, and the C_max and AUC_0–t were dose-proportional. The bioavailability of cryptotanshinone in rats was (6.9%?±?1.9%) at 60 mg kg^?1and (11.1%?±?1.8%) in dogs at 53.4 mg kg^?1. The t_1/2 of the compound in rats and dogs was 5.3–7.4 and 6.0–10.0 h, respectively. Cryptotanshinone showed a high accumulation in the intestine, lung and liver after oral administration, while the lung, liver and heart had the highest level following intravenous dose. Excretion data in rats showed that cryptotanshinone and its metabolites were mainly eliminated from faeces and bile, and the dose recovery rate was 0.02, 2.2, and 14.9% in urine, bile, and faeces, respectively.

4.?The disposition of cryptotanshinone in an inclusion complex was dose-independent and the bioavailability was increased compared with that without cyclodextrin used to formulate the drug. Cryptotanshinone was distributed extensively into different organs. Excretion of cryptotanshinone and its metabolites into urine was extremely low, and they were mainly excreted into faeces and bile.     

Metabolism,pharmacokinetics and excretion of a potent tachykinin NK1 receptor antagonist (CP-122,721) in rat: Characterization of a novel oxidative pathway

The metabolism, pharmacokinetics and excretion of a potent and selective substance P receptor antagonist, (+)-(2S,3S)-3-(2-methoxy-5-trifluoromethoxybenzlamino)-2-phenylpiperidine, CP-122,721, have been studied in rat following oral administration of a single dose of [¹⁴C]CP-122,721. Total recovery of the administered dose was 84.1?±?1.1% for male rat and 80.9?±?2.7% for female rat. Approximately 81% of the administered radioactivity recovered in urine and faeces were excreted in the first 72?h. Absorption of CP-122,721 was rapid in both male and female rat, as indicated by the rapid appearance of radioactivity in plasma. The plasma concentrations of total radioactivity were always much greater than unchanged drug, indicating early formation of metabolites. CP-122,721 t_1/2 was 3.1 and 2.2?h for male and female rat, respectively. The plasma concentrations of CP-122,721 reached a peak of 941 and 476?ng?ml^?1 for male and female rat, respectively, at 0.5?h post-dose. Based on AUC_0–tlast, only 1.5% of the circulating radioactivity was attributable to unchanged drug (average of male and female rats) and the balance, approximately 98.5% of the plasma radioactivity was due to metabolites. The major metabolic pathways of CP-122,721 were due to O-demethylation, aromatic hydroxylation and indirect glucuronidation. The minor metabolic pathways included aliphatic oxidation at the piperidine moiety and aliphatic oxidation at the benzylic position of the trifluoromethoxy anisole moiety. In addition, a novel oxidative metabolite resulting from ipso substitution by the oxygen atom and trifluoromethoxy elimination followed by glucuronide conjugation was also identified.     

Distribution in female rats of an anaesthetic intravenous dose of 14C-propofol

1. Bolus i.v. doses of ¹⁴C-propofol (9?mg/kg) were administered to female rats for measurement of tissue levels of total ¹⁴C and propofol from 2?min to 24?h post-dose; whole-body autoradiography was studied at 6?min, 2h and 24?h post-dose, and also involved 15-day pregnant rats.

2. The blood propofol concentration-time profile was fitted by a tri-exponential function corresponding to a three-compartment open model. Data show rapid distribution during the mixing period into highly perfused tissues and muscle, comprising the central compartment, and slower uptake into less well-perfused skin and adipose tissues comprising the deeper compartments.

3. The initial decline in blood propofol concentration was associated with redistribution (t_1/2 4?min), the second decline (15–240?min post-dose) was associated with metabolism (t_1/2 33?min) and the third decline reflected slow depletion of drug from deep tissue compartments (t_1/2 6.4h).

4. Blood and brain propofol concentrations on waking (at 7?min post-dose) were 4 μg/ml and 9 μg/g respectively; the model shows that, at this time, 30% of the dose was lost from the central compartment by redistribution and a similar amount by metabolism.

5. Tissue profiles of total ¹⁴C and propofol diverged for highly perfused tissues (other than brain) because of slow clearance of metabolites, accentuated by enterohepatic recirculation.     

Absorption,distribution, metabolism and excretion of gemigliptin,a novel dipeptidyl peptidase IV inhibitor,in rats

Abstract

1.?The absorption, distribution, metabolism and excretion of a novel dipeptidyl peptidase IV inhibitor, gemigliptin, were examined following single oral administration of ¹⁴C-labeled gemigliptin to rats.

2.?The ¹⁴C-labeled gemigliptin was rapidly absorbed after oral administration, and its bioavailability was 95.2% (by total radioactivity). Distribution to specific tissues other than the digestive organs was not observed. Within 7 days after oral administration, 43.6% of the administered dose was excreted via urine and 41.2% was excreted via feces. Biliary excretion of the radioactivity was about 17.7% for the first 24?h. After oral administration of gemigliptin to rats, the in vivo metabolism of gemigliptin was investigated with bile, urine, feces, plasma and liver samples.

3.?The major metabolic pathway was hydroxylation, and the major circulating metabolites were a dehydrated metabolite (LC15-0516) and hydroxylated metabolites (LC15-0635 and LC15-0636).     

Absorption,distribution, metabolism and elimination of 14C-ETX0914, a novel inhibitor of bacterial type-II topoisomerases in rodents

1.?ETX0914 is a novel bacterial topoisomerase inhibitor that has a novel mode-of-inhibition and is in clinical development for the treatment of infections caused by Neisseria gonorrhoeae.

2.?The in vitro biotransformation studies of ETX0914 using mouse, rat, dog and human hepatocytes showed moderate intrinsic clearance in mouse and rat and low intrinsic clearance in dog and human.

3.?Following intravenous administration of [¹⁴C]-ETX0914 in rats, the mean recovery of administered dose in urine, bile and feces was approximately 15%, 55% and 24%, respectively. Unchanged ETX0914 recovered in urine and bile was less than 5% of the dose, indicating that ETX0914 underwent extensive metabolism in rats. Metabolites M1, M2, M4, M6 and M12 detected in both rat and mouse urine samples were not detected in mouse urine when predosed with 1-aminobenzotriazole, indicating that these metabolites were cytochrome P450 mediated products. The major fecal metabolites observed in rats were not formed when ETX0914 was incubated with fresh feces from germ free rats under sterile condition or in incubations with rat intestinal microsome and cytosol, suggesting that most likely ETX0914 was directly excreted into gut lumen where metabolites were formed as intestinal microflora-mediated products. The major sites of metabolism by CYP enzymes were in the morpholine and oxazolidinone rings while it was benzisoxazole reduction with the gut microflora.     

Disposition of desloratadine in healthy volunteers

The absorption, metabolism and excretion of desloratadine (DL, Clarinex®) were characterized in six healthy male volunteers. Subjects received a single oral 10-mg dose of [¹⁴C]DL (～104?µCi). Blood, urine and feces were collected over 240?h. DL was well absorbed; drug-derived radioactivity was excreted in both urine (41%) and feces (47%). With the exception of a single subject, DL was extensively metabolized; the major biotransformation pathway consisted of hydroxylation at the 3 position of the pyridine ring and subsequent glucuronidation (3-OH-DL-glucuronide or M13). In five of the six subjects, DL was slowly eliminated (mean t_½?=?19.5?h) and persisted in the plasma for 48–120?h post-dose. This is in contrast to a t_½ of ～110?h and quantifiable plasma DL concentrations for the entire 240-h sampling period in one subject, who was identified phenotypically as a poor metabolizer of DL. This subject also exhibited correspondingly lower amounts of M13 in urine and 3-OH-DL (M40) in feces. Disposition of DL in this subject was characterized by slow absorption, slow metabolism and prolonged elimination. Further clinical studies confirmed the lack of safety issues associated with polymorphism of DL metabolism (Prenner et al. 2006, Expert Opinion on Drug Safety, 5: 211–223).     

LC-MS-MS analysis of 2-pyridylacetic acid,a major metabolite of betahistine: application to a pharmacokinetic study in healthy volunteers

1.?A sensitive liquid chromatographic-tandem mass spectrometric assay was developed and validated to determine the major metabolite of betahistine, 2-pyridylacetic acid, in human plasma.

2.?The analyte was extracted from plasma samples by liquid–liquid extraction and analysed using liquid chromatography-tandem mass spectrometry with an electrospray ionization interface. The method has a lower limit of quantitation of 1?ng?ml^?1 for a 0.5-ml plasma aliquot. The intra- and interday precision (relative standard deviation), calculated from quality control (QC) samples, was less than 10%. Accuracy as determined from QC samples was within ±7%.

3.?The validated method was successfully applied to a pharmacokinetic study of betahistine in healthy volunteers. After oral administration of a single dose of 24?mg betahistine mesylate to 20 healthy Chinese male volunteers, C_max was 339.4?ng?ml^?1 (range 77.3–776.4?ng?ml^?1). The t_1/2 was 5.2?h (range 2.0^?1?11.4?h). The AUC_0?t obtained was 1153.5?ng?ml^?1?h (range 278.5–3150.8?ng ml^?1?h). The disposition of the metabolite exhibited a marked interindividual variation.

4.?The plasma concentrations of the parent drug were less than 0.5?ng ml^?1, suggesting that it undergoes almost complete first-pass metabolism. The reported two active metabolites were not detected in the plasma of any volunteer. Although there is no evidence that the major metabolite has pharmacological activity, the clinical importance of 2-pyridylacetic acid in humans should be reinvestigated.