Structural identification of bitespiramycin metabolites in rat: a single oral dose study

Bitespiramycin is a macrolide antibiotic consisting of a mixture of some nine spiramycin ester derivatives. It has a similar spectrum of antibiotic activity to that of spiramycin but has superior pharmacokinetic properties. In this study, a rapid and facile LC/ESI-MSn method was applied to study the metabolism of bitespiramycin in rat following a single oral dose (80 mg kg-1). Concentrations of parent drug constituents and metabolites were determined in plasma, urine, feces and bile. Concentrations of parent drug constituents and metabolites in plasma were very low. In urine, feces and bile, parent drug constituents and 38 metabolites were identified on the basis of their chromatographic and mass spectrometric properties. The identity of 17 metabolites was confirmed by comparison with reference substances. The principal metabolites were the corresponding spiramycins formed by hydrolysis of the 4'-(3-methylbutanoate) groups. Other important metabolic pathways were: hydrolytic loss of the forosamine and mycarose sugars; aldehyde reduction; cysteine conjugation of the aldehyde group; and hydrolysis of the lactone ring. Products formed by lactone ring opening were found only in urine, and those formed by aldehyde reduction were found only in feces. Aldehyde reduction and hydrolytic loss of forosamine represent novel biotransformation pathways for spiramycin derivatives.     

Identification of novel metabolites of pioglitazone in rat and dog

1. Four new metabolites of pioglitazone were identified by liquid chromatography-mass spectrometry (LC-MS/MS) as being formed by hydroxylation (M-VII and M-VIII), opening of the thiazolidinedione ring (M-X) and by desaturation of the terminal ethyl side chain or tether ethoxy moiety (M-IX), respectively. The structure of one of the hydroxylated metabolites (M-VII) was confirmed by chemical modification using the Jones reaction. 2. Oxidative cleavage of the thiazolidinedione ring is a novel pathway not previously reported for pioglitazone. 3. The hydroxylated M-VII was detected in incubations with rat, dog and human liver and kidney microsomes, and in plasma from rats and dogs dosed orally with [3 H]pioglitazone. 4. The carboxylic acid derivative of M-VII (M-V) and its taurine conjugate were the major radioactive components in dog bile.     

The pharmacokinetics of flutamide and its major metabolites after a single oral dose and during chronic treatment

Summary Flutamide is a nonsteroidal antiandrogen used in the treatment of prostatic carcinoma. We have investigated the disposition of flutamide and its two major metabolites in ten urological in-patients without significant liver or renal disease.After oral administration flutamide is absorbed from the gastrointestinal tract with a t_max of about 2 h.Flutamide undergoes extensive first-pass metabolism, and its major metabolites are 2-hydroxyflutamide and the hydrolysis product 3-trifluoromethyl-4-nitroaniline.After the oral administration of a single dose of 250 mg or 500 mg maximum flutamide plasma concentrations of 0.02 and 0.1 µg·ml^–1 respectively were observed. Maximum plasma concentrations of 2-hydroxylfutamide for the same flutamide doses were 1.3 and 2.4 µg·ml^–1 (mean ofn=2 orn=3).Steady-state concentrations of the biologically active metabolite 2-hydroxyflutamide (0.94±0.23 µg·ml^–1, mean±SD,n=5) were found at 2–4 days after the administration of 250 mg every 8 h.The area under the plasma concentration time curve for 2-hydroxyflutamide averaged 11.4 (10.6 and 12.1) and 24.3 (21.5–29.4,n=3) µg·ml^–1·h for 250 mg and 500 mg flutamide orally.2-Hydroxyflutamide and 3-trifluoromethyl-4-nitroaniline were eliminated monoexponentially with half-times of 4.3–21.9 and 4.3–17.2 h (n=5) respectively.     

Pharmacokinetics of terbinafine and of its five main metabolites in plasma and urine,following a single oral dose in healthy subjects

The plasma pharmacokinetics, and the urinary excretion, of terbinafine and its five main metabolites have been investigated after a single oral dose administration of 125 mg to 16 healthy subjects. In plasma, the highest concentrations are observed for the two carboxybutyl metabolites, with a predominance for the carboxybutylterbinafine. For this metabolite, as compared to terbinafine, the C_max and AUC are 2.4 and 13 times higher respectively. The demethylterbinafine presents a plasma profile close to that of terbinafine. The two hydroxy metabolites are only found as glucuronide and are of minor importance. The apparent terminal half-lives of terbinafine, demethylterbinafine, and the two carboxy metabolites appear to be similar (～ 25h). As compared to the plasma concentration of total radioactivity observed after a single oral administration of the same dose of ¹⁴C-terbinafine, the parent drug and these five metabolites, account for more than 80% of the total radioactivity in plasma over the 0–48 h interval following administration. In urine, the major metabolite is demethylcarboxybutylterbinafine, which amounted to about 10% of the administered dose. Terbinafine and demethylterbinafine are only excreted as trace amounts in urine. Carboxybutylterbinafine and the two hydroxy metabolites are excreted in the range of 0.5–2% either as glucuronides or free. Urinary excretion over the 0–48h interval of terbinafine and of the five metabolites amounted to about 14% of the administered dose. This is far below the level of total radioactivity measured in urine over the same interval (～ 57%), after administration of ¹⁴C-terbinafine. This shows in contrast to plasma, that numerous other metabolites are present in urine.     

Pharmacokinetics of dextromethorphan and its metabolites in horses following a single oral administration

Dextromethorphan is an N‐methyl‐D‐aspartate (NMDA) non‐competitive antagonist commonly used in human medicine as an antitussive. Dextromethorphan is metabolized in humans by cytochrome P450 2D6 into dextrorphan, which is reported to be more potent than the parent compound. The goal of this study is to describe the metabolism of and determine the pharmacokinetics of dextromethorphan and its major metabolites following oral administration to horses. A total of 23 horses received a single oral dose of 2 mg/kg. Blood samples were collected at time 0 and at various times up to 96 h post drug administration. Urine samples were collected from 12 horses up to 120 h post administration. Plasma and urine samples were analyzed using liquid chromatography‐mass spectrometry, and the resulting data analyzed using non‐compartmental analysis. The C_max, T_max, and the t_1/2 of dextromethorphan were 519.4 ng/mL, 0.55 h, and 12.4 h respectively. The area under the curve of dextromethorphan, free dextrorphan, and conjugated dextrorphan were 563.8, 2.19, and 6,691 h*ng/mL respectively. In addition to free and glucuronidated dextrorphan, several additional glucuronide metabolites were identified in plasma, including hydroxyl‐desmethyl dextrorphan, desmethyl dextrorphan, and three forms of hydroxylated dextrorphan. Dextromethorphan was found to be eliminated from the urine predominately as the O‐demethylated metabolite, dextrorphan. Several additional metabolites including several novel hydroxy‐dextrorphan metabolites were also detected in the urine in both free and glucuronidated forms. No significant undesirable behavioural effects were noted throughout the duration of the study. Copyright © 2016 John Wiley & Sons, Ltd.     

Metabolism of a tetraphenyltin compound in rats after a single oral dose

The metabolism of tetraphenyltin in rat liver and kidney has been examined. Tetraphenyltin and its metabolites in the tissue were determined periodically for 96 h after a single oral dose of 55.4 mg kg(-1) of tetraphenyltin by gas chromatography. The gas chromatographic method was able to determine simultaneously both inorganic tin and phenyltin compounds. Although initial (at 24 h) levels of tetraphenyltin in the liver approximated four times those in the kidneys, the levels of tetraphenyltin decreased more rapidly with time than those in the kidneys. These findings show that the tetraphenyltin accumulated more rapidly and highly in the liver, but was metabolized faster than that in the kidney. The levels of total tin in the liver 24 h after treatment were distinctly lower than those of di- or triphenyltin treatments in our previous studies and none of the animals showed characteristic symptoms. The toxic potencies of organotins generally correlate with accumulation of the chemicals. These results imply that the slight toxicities of tetraphenyltin might be due to the relatively low uptake of tin compounds after ingestion. The highest tin concentration among the metabolites of tetraphenyltin in the tissue, especially in liver, was observed as diphenyltin throughout the time period studied. These results suggest that part of the administered tetraphenyltin may cause some harmful effects as diphenyltin in rats, and this must be taken into consideration in toxicological research on tetraphenyltin.     

Characterization of the Phase II metabolites of rutaecarpine in rat by liquid chromatography-electrospray ionization-tandem mass spectrometry

From the authors’ previous studies on the Phase I metabolism of rutaecarpine, nine metabolites formed were identified as products of hydroxylation on the aromatic rings in rat liver microsomes. In order to determine the possible metabolic fate of rutaecarpine, the Phase II metabolites of rutaecarpine were characterized in the present study by using liquid chromatography/electrospray ionization-tandem mass spectrometry (LC/ESI-MS). When male Sprague–Dawley rats were treated intravenously with 4?mg?kg^?1 rutaecarpine, 16 different Phase I and II metabolites were identified in urine including four sulfate and four glucuronide conjugates. Phase I metabolites of rutaecarpine were identified as four mono-hydroxylated metabolites (M2–5) and four isobaric di-hydroxylated metabolites (M6–9). These metabolites were identical to the in vitro metabolites except one, which was hydroxylated in the aliphatic moiety. In addition, Phase II metabolites were identified as conjugated with sulfate (S1–4) and glucuronide (G1–4). In faeces, 11 different metabolites were identified. The metabolites M8 and glucuronide conjugated (G1–4) were not detected. Structures of all metabolites were confirmed with CID fragmentation spectra of MS², MS³ and retention times by LC/ESI-MS.     

In vitro identification of metabolites of verapamil in rat liver microsomes

AIM: To investigate the metabolism of verapamil at low concentrations in rat liver microsomes. METHODS: Liver microsomes of Wistar rats were prepared using ultracentrifuge method. The in vitro metabolism of verapamil was studied with the rat liver microsomal incubation at concentration of 1.0 μmol/L and 5.0 μmol/L. The metabolites were separated and assayed by liquid chromatography-ion trap mass spectrometry (LC/MS^n), and further identified by comparison of their mass spectra and chromatographic behaviors with reference substances. RESULTS: Eightmetabolites, including two novel metabolites (M4 and MS), were found in rat liver microsomal incubates. They were identified as O-demethyl-verapamil isomers (M1 - M4), N-dealkylated derivatives of verapamil (MS-MT), and N, O-didemethyl-verapamil (MS). CONCLUSION: O-Demethylation and N-dealkylation were the main metabolic pathways of verapamil at low concentrations in rat liver microsomes, and the relative proportion of them in verapamil metabolism changed with different substrate concentrations.     

Pharmacokinetics of metamizol metabolites in healthy subjects after a single oral dose of metamizol sodium

Summary The linearity of the pharmacokinetics of the metamizol metabolites 4-methyl-amino-antipyrine (4-MAA), 4-amino-antipyrine (4-AA), 4-formyl-aminoantipyrine (4-FAA), and 4-acetyl-amino-antipyrine (4-AcAA) has been studied after administration to 15 healthy male volunteers of single oral doses of 750, 1500, and 3000 mg metamizol. The trial was open, randomized, and cross-over, with a one-week interval between dosing days. Metabolite concentrations in serum and urine were measured using reverse-phase HPLC.The mean C_max of 4-MAA increased linearly with dose whereas its AUC was not proportional to dose after administration of 1500 and 3000 mg.With 4-AA, the increase in mean C_max was linear, but the increase in AUC was not.The increases in mean C_max and AUC for 4-FAA after doses of 1500 and 3000 mg were not proportional to the dose.The increases in mean C_max and AUC for 4-AcAA were roughly proportional to the increase in dose.There were no significant differences in renal clearance between doses for any of the four metabolites.The observed non-linearities reflect the saturability of metabolic pathways. However, although they were statistically significant, the deviations from linearity were marginal and should not be of clinical relevance to the analgesic efficacy of metamizol in the dose range tested.     

Pharmacokinetics of a single oral dose of hydroflumethiazide in health and in cardiac failure

Summary The pharmacokinetics of hydroflumethiazide (HFT) were investigated after single oral doses of 6 µmoles/ per kg body weight in five healthy subjects and in nine patients with moderate cardiac failure. HFT was excreted in urine together with 2,4-disulfamyl-5-trifluoromethylaniline (DTA), which was also present in the blood after administration of HFT. HFT and DTA were determined by TLC and spectrofluorodensitometry. Mean cumulative urinary excretion of HFT was 46.5 and 47.5 per cent of the dose both in healthy subjects and in patients. Distribution half-life (t1/2) was about 2 h in both groups of subjects, while biological half-life (t1/2) ranged from 12.4 to 26.9 h (mean 16.6) in healthy subjects, and from 6.3 to 13.7 h (mean 9.6) in patients. Mean renal clearance was 0.33 and 0.211 · h^–1 · kg^–1 in normal subjects and patients, respectively, and was almost equal to the total body clearance. HFT had a large apparent volume of distribution (V), with mean values of 6.4 and 3.11 · kg^–1 in normal subjects and patients. Mean cumulative urinary excretion of DTA was 1.8 and 1.9 per cent in healthy subjects and patients with cardiac failure. The apparent half-life of DTA, determined from urinary excretion rate in eleven subjects, ranged from 16 to 56 h but half-lives in three others were more than 100 h. The results indicate that HFT is partly metabolized in the body to DTA, and DTA and HFT are excreted in urine. The half-life of DTA was longer than that of the parent drug. The apparent volume of distribution, clearance and biological half-life of HFT were lower in patients with cardiac failure than in healthy subjects.     

Inter- and intra-individual variation in the metabolism of methaqualone in man after a single oral dose

Summary The urinary excretion of fiveC-monohydroxy metabolites and theN-oxide metabolite of methaqualone in the 24h period immediately after oral dosing with 250 mg methaqualone (Melsed) has been measured in nineteen healthy adults (13 male, 6 female) to assess interindividual variations and in five adults (3 male, 2 female) on five separate occasions to assess intraindividual variations. The overall importance of the six metabolites was 4-hydroxy > $$ " align="middle" border="0"> N-oxide > $$ " align="middle" border="0"> 2-hydroxymethyl > 3-hydroxy > 6-hydroxy = 2-hydroxymethyl. Variations in this order both within the 24h period and within each of the three eight-hour periods constituting the 24 hours were minor and variations in the absolute amount of each metabolite excreted ranged from two to three-fold. Intraindividual variations were generally smaller than interindividual variations and for each individual the pattern of metabolism was similar on the five occasions. There is evidence that theC-oxidation of methaqualone may be more sensitive to cyclical variations in hormone levels than isN-oxidation.     

Prediction of steady-state plasma levels of nortriptyline from single oral dose kinetics: A study in twins

Summary Five identical (monozygotic) and 6 fraternal (dizygotic) sets of healthy twins between 47 and 53 years of age were given a single oral dose of nortriptyline (NT) hydrochloride 1 mg/kg. The plasma half-life, the apparent volume of distribution, and the plasma clearance of NT were estimated for each subject as well as the urinary excretion rate of conjugated and unconjugated 10-hydroxynortriptyline (10-OH-NT). Steady-state plasma levels predicted from the reciprocal single dose plasma clearance rate of NT agreed well with those observed in a previous study of the same twins 2 years previously. In the present study, there was a 5-fold range of the plasma half-lives and 2-fold variation in the apparent volume of distribution of NT (assuming complete availability on oral administration). No correlation was found between the plasma half-life and the apparent volume of distribution. Analysis of variance showed that most of the variability between persons in plasma half-life, apparent volume of distribution and conjugation of 10-OH-NT was genetically determined. The plasma half-life and apparent volume of distribution may contribute independently to the total interindividual variability of the steady-state plasma level of NT.     

大鼠一次性灌服酸枣仁提取物后棘苷的药代动力学研究

目的用反相高效液相色谱法,以磺胺甲唑为内标,对一次性ig酸枣仁提取物后的大鼠血浆中棘苷进行药代动力学研究。方法血浆样品经乙腈沉淀蛋白后,于50 ℃氮气流下吹干,残渣用流动相溶解后进行分析。色谱条件为色谱柱:Hypersil C₁₈柱,200 mm×4.6 mm ID,5 μm;流动相:乙腈-水-冰醋酸(15∶85∶1);流速:0.7 mL·min^-1;检测波长:334 nm;柱温:35 ℃。结果血浆中棘苷在18.1～903.5 μg·L^-1成良好线性关系(R²≥0.995)。平均回收率为94.5%,日内、日间精密度RSD均小于9.0%。该法定量限为18.1 μg·L^-1,血浆样品在-20 ℃可稳定保存。结论该法简便、灵敏、准确,可用于大鼠一次性灌服酸枣仁提取物后血浆中棘苷的浓度测定及其药代动力学研究。     

Excretion of digoxin and its metabolites in urine after a single oral dose in healthy subjects

The 3-day urinary excretion of digoxin, its conjugated and unconjugated hydrolytic metabolites and dihydrodigoxin, was studied in 8 healthy men after oral administration of tritiated digoxin. Analysis was performed by high pressure liquid chromatography (HPLC). The total radioactivity corresponded to 45.4±2.0 per cent (mean ± S.E.M.) of the dose. By HPLC 424 ± 2.7 per cent was recovered before and 44.0 ± 2.7 per cent after deconjugation of the samples. Digoxin and dihydrodigoxin constituted 40.3 ± 2.9 per cent; of this 0.7 ± 0.4 per cent was dihydrodigoxin. The sum of the hydrolytic metabolites was 2.1 ± 0.3 per cent before and 3.4± 0.5 per cent after deconjugation. No correlation was found between gastric pH and the production of hydrolytic metabolites. The relative amount of these metabolites was maximal (mean 13.4 per cent of the excretion) in the 4.8 h sampling period. During the first 8 h an average of 8.6 per cent of the radioactivity was not recovered by HPLC. The metabolism of digoxin as judged by urinary excretion was limited and showed great variation during the early hours after treatment. The excretion of unchanged digoxin in some individuals constituted as little as 60 per cent over the first 12 h after dosing.     

Effect of a single oral dose of ddt on lipid metabolism in rat

A single oral dose of 1,1,1-trichloro-2,2-bis-(p-chlorophenyl)ethane (DDT) (600 $\text{mg}\text{kg}$ body weight) was given to rats and the levels of various lipids in adipose tissue, liver and plasma were studied. No alteration was observed in the levels of various lipid classes in these tissues except for a decrease in the phospholipid and triglyceride fractions of liver. Lipoprotein lipase activity of post-heparin plasma (protamine-sensitive and -resistant) was significantly decreased, whereas in liver and adipose tissue, the activity of this enzyme remained unchanged.     

Pharmacokinetics of chloroquine and some of its metabolites in healthy volunteers: a single dose study

Eight healthy volunteers who had not taken chloroquine 2 to 12 months previously participated in a single dose study designed to evaluate the pharmacokinetics of chloroquine and some of its metabolites. Each subject received two tablets of chloroquine sulfate (300 mg base) only. Blood and urine samples were collected just before and periodically after chloroquine administration. These samples were assayed for chloroquine and its N-dealkylated metabolites (monodesethylchloroquine, didesethylchloroquine, 7-chloro-4-aminoquinoline), chloroquine side chain N-oxide and chloroquine di-N-oxide using a high performance liquid chromatographic method. Residual levels of chloroquine and its N-oxidation metabolites were found in all subjects. 7-chloro-4-aminoquinoline was eliminated more slowly (t1/2z = 126.48 +/- 20.13 h) than the other metabolites and the unchanged drug (t1/2z = 106.43 +/- 10.13 h). Also, 7-chloro-4-aminoquinoline had a significantly faster (Student's t-test, P less than 0.05) formation clearance when compared with the other metabolites. The plasma concentration of 7-chloro-4-aminoquinoline was about twice that of the unchanged drug while the plasma concentration of monodesethylchloroquine was about 46% that of the unchanged drug. In order to investigate whether the metabolites were produced from the same binding sites or closely related sites on the cytochrome P-450 system, their formation clearances were correlated. The best correlation (r2 = 0.83) was observed for didesethylchloroquine and monodesethylchloroquine, and a fair correlation (r2 = 0.59) was observed for monodesethylchloroquine and 7-chloro-4-aminoquinoline. Formation clearances of the other metabolites were poorly correlated.(ABSTRACT TRUNCATED AT 250 WORDS)     

Vitamin A (retinol) status in the rat after a single oral dose of 2,3,7,8-tetrachlorodibenzo-p-dioxin

The effect of a single oral dose of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), 10 g · kg^–1, on the status of vitamin A (retinol) was studied in rats during an eight week period after administration. Retinol was determined spectrophotometrically after separation by means of high pressure liquid chromatography.In the liver of control animals the total storage and the concentration of retinol were found to increase linearly with time whilst in the TCDD-exposed animals both the concentration and total storage remained essentially unchanged. Differences in the storage levels were evident after 4 days, and after 8 weeks the treated animals had a total liver storage corresponding to about 30% of the controls. Retinol levels in serum were significantly higher in the treated animals after week 1 and 2.     

Urinary excretion of nortriptyline and five of its metabolites in man after single and multiple oral doses

Summary The urinary excretion of nortriptyline (NT) and five of its metabolites was studied by quantitative gas chromatography in 22 twins and 7 unrelated healthy subjects after single (1 mg/kg) and multiple oral doses (0.4 mg/kg t.i.d.) of NT hydrochloride. A mean recovery of 62% of the dose was found after both single and multiple doses. The metabolite pattern in the urine was qualitatively and quantitatively identical in the two regimes, but there were marked variations in the pattern of metabolites between individuals. The disappearance rate of NT from the plasma was mainly determined by the metabolism of NT to 10-hydroxynortriptyline, which varied considerably between individuals. The data suggest that in certain rapid NT metabolizers, the upper limit for the overall clearance of NT from the plasma (if extrahepatic metabolism is assumed to be negligible) might be set by the blood flow through the liver.     

Detection of the selective androgen receptor modulator GSK2881078 and metabolites in urine and hair after single oral administration

Hair and urine concentrations of the nonsteroidal selective androgen receptor modulator GSK2881078 were examined following single oral administration to investigate its hair incorporation and estimate the general suitability of hair testing for selected androgen receptor modulators. Hair segments were collected following a single dose of 1.5 mg GSK2881078 by repeated shaving of scalp hair at Week 0 (blank), Week 1 (representing the pre-application period), Week 3 (ideally focusing the time of incorporation), and Weeks 5 and 9 (post-administration period). The intact compound and various (at least 4) hydroxy-metabolites exhibited similar elimination profiles. The peak urinary concentration (approximately 920 pg/ml) was observed after 8 h and is reduced to the detection limit (2 pg/ml) on Day 42 following administration of 760 μg GSK2881078. Correspondingly, hair concentrations of GSK2881078 (intact compound only) following a single oral dose of 1.5 mg GSK2881078 reached a peak concentration of 1.7 pg/mg in the segments collected 3 weeks post administration, representing the time of ingestion. The concentration rapidly declined to trace amounts of 0.7 (Week 5) and 0.2 pg/mg (Week 9), respectively. In conclusion, measurement of the intact compound GSK2881078 is feasible for both urine and hair analysis. However, concentrations in hair after single oral administration are in the low pg/mg range and can only be detected, if the segments cover the administration period.     

吡喹酮在诱导和未诱导大鼠肝微粒体内的羟化代谢概貌及其羟化物的质谱鉴定

用细胞色素P450（P450）特异诱导剂研?究参与吡喹酮（PQT）代谢的P450同工酶，在未诱导肝微粒体内，PQT代谢仅生成其D环单羟化物. 在β-萘黄酮诱导肝微粒体内，PQT代谢后也生成其D环单羟化物. PQT在苯巴比妥诱导的肝微粒体内代谢生成D环，B环和A环三个单羟化物. 在地塞米松和红霉素诱导的肝微粒体内，PQT代谢生成七个代谢产物. 结果表明参与PQT分子羟化的P450同工酶至少包括CYP1A，CYP2B和CYP3A亚家族，每个亚家族代谢PQT的概貌各不相同，CYP3A优先羟化A环，CYP2B优先羟化D环和B环，CYP1A则几乎仅羟化D环.