Pre-clinical pharmacokinetics of the acridine antitumour candidate AC04 and its 1-oxo-metabolite plasma profile

1. This work aimed to investigate plasma pharmacokinetics and tissue distribution of a new acridine derivative 5-acridin-9-ylmethylene-3-(4-methyl-benzyl)-thiazolidine-2,4-dione (AC04) and its 1-oxo-AC04 metabolite disposition in Wistar rats.

2. After a single AC04 1.5?mg/kg intravenous (i.v.) bolus dose, blood samples were taken up to 120?h. Plasma samples were deproteinization, and AC04 and metabolite were quantified by validated liquid chromatography in tandem with mass spectrometry method. Protein binding was determined by ultrafiltration. AC04 tissue disposition was evaluated after i.v. bolus dose.

3. Individual AC04 concentration–time profiles were best fitted by a two-compartment model showing CL_tot of 3.4?±?3.4?L/h/kg, Vd_SS of 137.9?±?91.4?L/kg, AUC_0–∞ of 788?±?483 ng·h/mL and a t_1/2 of 45.5?±?31.5?h. Protein binding was 98.1?±?1.6%. AC04 showed higher penetration into the lung, spleen and liver, with AUC_0–96 of 798,443, 263,211 and 303,722 ng·h/mL, respectively. The 1-oxo-AC04 metabolite represented 10% of AC04 plasma concentration, showing a t_1/2 of 23.2?±?10.4?h.

4. These results suggest that, despite the small free plasma fraction, AC04 penetrates extensively reaching high concentrations in most tissues residing for a long time, which is important for its activity on solid tumours. All results combined indicate that AC04 is potentially a good antitumour candidate.

     

Effect of genistein on the activities of cytochrome P450 3A and P-glycoprotein in Chinese healthy participants

1. To determine the effect of genistein on cytochrome P450 3A (CYP3A) and P-glycoprotein (P-gp) function using the probe substrates midazolam and talinolol, respectively. Eighteen healthy adult male participants were enrolled in a two-phase randomized crossover design. In each phase, the participants received placebo or genistein for 14 days. On the 15th day, midazolam and talinolol were administered and blood samples were obtained. Midazolam and talinolol pharmacokinetic parameter values were calculated and compared before and after genistein administration.

2. Co-administration of genistein decreased the area under the concentration–time curve from 0 to 36?h (AUC 0-36) (143.65?±?55.40?ng h/mL versus 126.10?±?40.14?ng h/mL, p?<?0.05), and the area under the concentration–time curve from zero to infinity (AUC 0-∞) (209.18?±?56.61?ng h/mL versus 180.59?±?43.03?ng h/mL, p?<?0.05), and also maximum concentration (Cmax) of midazolam (48.86?±?20.21?ng/mL versus 36.25?±?14.35?ng/mL p?<?0.05). Similarly, AUC 0-36 (2490.282?±?668.79?ng h/mL versus 2114.46?±?861.11?ng h/mL, p?<?0.05), AUC 0-∞ (2980.45?±?921.09?ng h/mL versus 2626.92?±?1003.78?ng h/mL, p?<?0.05) and Cmax of talinolol (326.58?±?197.67?ng/mL versus 293.42?±?127.19?ng/mL, p?<?0.05) were reduced by genistein co-administration. The oral clearance of midazolam (1.68?±?0.85 h-1 versus 3.98?±?0.59 h-1, p?<?0.05) and talinolol (3.34?±?1.24 h-1 versus 3.79?±?1.55 h-1, p<0.05) were increased by genistien significantly.

3. Administration of genistein can result in a modest induction of CYP3A and possibly P-gp activity in healthy volunteers.

     

The impact of P-glycoprotein mediated efflux on absorption of 11 sedating and less-sedating antihistamines using Caco-2 monolayers

1. Caco-2 cells were used to compare P-gp mediated efflux and passive permeability using bidirectional transport of 11 antihistamines. An efflux ratio >2 indicated active efflux, with PSC833 and GF120918 used as functional P-gp inhibitors.

2. Antihistamines were measured directly by HPLC or LC/MS.

3. Fexofenadine had an efflux ratio of 37, yet had negligible passive permeability, even in the presence of a pH gradient (0.1?×?10^?6 cm/sec). Its precursor, terfenadine, had an efflux ratio of 2.5, while cetirizine, desloratadine and hydroxyzine were 4, 7 and 14, respectively. After incubation with P-gp inhibitors, these ratios dropped significantly. Loratadine, by contrast, had equivalent transport in both directions and passive permeability was high (24?×?10^?6 cm/sec). Dimenhydrinate was the only other sedating antihistamine to exhibit efflux, with a ratio of 10.

4. Gradient conditions of pH (6/7.4) increased efflux of terfenadine and desloratadine to over 31 and 38 fold respectively, yet this increased efflux was not associated with P-gp.

5. Altering functional P-gp in the gut is likely to influence absorption of some sedating antihistamines such as dimenhydrinate and hydroxyzine and most less-sedating antihistamines except loratadine. In addition, desloratadine exhibits pH dependent efflux which could further induce variable absorption of this antihistamine.

     

Pharmacokinetics of fexofenadine following LPS administration to rats

1. The function and expression of drug transporters, including P-glycoprotein (P-gp) and organic-anion transporting polypeptides (Oatps), have been investigated but it is not well established how variables such as disease processes affect them. Fexofenadine is a substrate of these transporters and it was previously shown that its clearance is reduced in the rat isolated perfused liver following treatment with E.coli lipopolysaccharide (LPS). However, whether this translates to altered fexofenadine pharmacokinetics in vivo is yet to be established.

2. E.coli LPS at 5?mg/kg or sterile saline (control) was injected intraperitoneally in rats. Oral or intravenous (IV) fexofenadine (10?mg/kg) was administered 24?h later and plasma and urine samples collected for pharmacokinetic analysis.

3. LPS treatment did not significantly change the pharmacokinetics of IV fexofenadine, although there was a good correlation between weight loss and clearance suggesting reduced clearance in more severely affected animals. However, AUC_0–∞ of oral fexofenadine was a significantly higher in LPS-treated animals (13.9?±?9.76 min·µg/ml) compared to controls (5.53?±?1.12 min·µg/ml).

4. In conclusion, LPS treatment increased the bioavailability of fexofenadine but did not affect other pharmacokinetic parameters. This is consistent with a reduction in hepatic Oatp and/or P-gp for a high extraction ratio drug such as fexofenadine.

     

Pharmacokinetics of antofloxacin hydrochloride,a novel fluoroquinolone,after single-dose intravenous administration in healthy Chinese male volunteers

1. The purpose of the study was to evaluate the pharmacokinetic characteristics of a single, intravenous dose of antofloxacin hydrochloride in healthy Chinese male volunteers.

2. Twelve subjects were randomly assigned to groups that received a single, intravenous dose of 200, 300, or 400?mg antofloxacin hydrochloride in a three-way crossover design study. The serum and urine concentrations of antofloxacin were then assayed with high-performance liquid chromatography (HPLC). Major pharmacokinetic parameters and urine excretion were obtained up to 96?h after administration.

3. All three dosages were well tolerated. No clinically adverse reactions or abnormal laboratory results were detected.

4. After single-dose intravenous administration, antofloxacin hydrochloride exhibited linear pharmacokinetic characteristics with increasing dosages. The C_max for groups treated with 200, 300, or 400?mg dosages were 2.05?±?0.38, 3.01?±?0.60, and 3.80?±?0.78?mg l^?1, respectively; the areas under the curve from zero to infinity (AUC_0–∞) were 25.14?±?2.95, 37.63?±?5.42, and 53.87?±?9.48?mg l^?1·h, respectively. The t_1/2β was around 20?h; and the urinary excretion was measured as being from 58% to 60% within 96?h.

5. Based on these results, 300?mg of antofloxacin hydrochloride administered once daily is the dose suggested for further investigation in multiple-dose administration studies.

     

Comparison of intrinsic metabolic clearance in fresh and cryopreserved human hepatocytes

1. We compared the intrinsic clearance (CL_int) of a number of substrates in suspensions of fresh and cryopreserved human hepatocytes from seven donors.

2. CL_int values for a cocktail incubation of phenacetin, diclofenac, diazepam, bufuralol, midazolam, and hydroxycoumarin were 4.9?±?3.4, 18?±?7.2, 5.1?±?4.9, 6.3?±?3.3, 9.8?±?5.8 and 22?±?14?μl min^?1/10⁶ cells, respectively, and they correlated well with corresponding CL_int values using cryopreserved hepatocytes from 25 different donors.

3. CL_int values of each cocktail substrate and 20 AstraZeneca new chemical entities were compared in fresh and cryopreserved hepatocytes from the same three donors. There was a statistically significant correlation between CL_int in fresh and cryopreserved hepatocytes for each of the three livers (p?int values was 1.03.

4. In conclusion, the results add further support to the use of cryopreserved human hepatocytes as a screening model for the intrinsic clearance of new chemical entities.

     

Testosterone hydroxylation in bovine liver: enzyme kinetic and inhibition study

1. In order to sort out the involvement of cytochrome P450 (CYP) 3A and possibly CYP2B in testosterone hydroxylation in cattle, enzyme kinetic and inhibition studies were performed.

2. Most relevant kinetic constants (Km and Vmax) for 6β-, 16β- and 2β-testosterone hydroxylase (OHT) activities were determined and accounted for 93.4?±?13.8, 36.4?±?6.1 and 110.8?±?15.2?μM, respectively, for Km and 0.558?±?0.03, 0.280?±?0.013, and 0.338?±?0.017?nmol min–1 mg–1 protein, respectively, for Vmax. Eadie–Hofstee plot analysis pointed out how these enzymatic activities in cattle follow a monophasic kinetic pattern.

3. Preliminary inhibition studies conducted with the CYP3A inhibitor ketoconazole and the CYP2B inhibitors orphenadrine and 9-ethynylphenanthrene seemed to suggest the major involvement of CYP3A in testosterone hydroxylation in cattle.

4. Immuno-inhibition studies with an anti-peptide antibody against bovine CYP3A4 confirmed the predominant role of CYP3A in testosterone hydroxylation in bovine liver, proving the usefulness of anti-peptide antibodies in defining the contribution of specific P450 isoforms in drug metabolism in veterinary species.

     

Disposition of GDC-0879, a B-RAF kinase inhibitor in preclinical species

1. The pharmacokinetics and disposition of GDC-0879, a small molecule B-RAF kinase inhibitor, was characterized in mouse, rat, dog, and monkey.

2. In mouse and monkey, clearance (CL) of GDC-0879 was moderate (18.7–24.3 and 14.5?±?2.1?ml min^?1 kg^?1, respectively), low in dog (5.84?±?1.06?ml min^?1 kg^?1) and high in rat (86.9?±?14.2?ml min^?1 kg^?1). The volume of distribution across species ranged from 0.49 to 1.9?l kg^?1. Mean terminal half-life values ranged from 0.28?h in rats to 2.97?h in dogs. Absolute oral bioavailability ranged from 18% in dog to 65% in mouse.

3. Plasma protein binding of GDC-0879 in mouse, rat, dog, monkey, and humans ranged from 68.8% to 81.9%.

4. In dog, the major ketone metabolite (G-030748) of GDC-0879 appeared to be formation rate-limited.

5. Based on assessment in dogs, the absorption of GDC-0879 appeared to be sensitive to changes in gut pH, food and salt form (solubililty), with approximately three- to four-fold change in areas under the curve (AUCs) observed.

     

Effects of verapamil on the pharmacokinetics of puerarin in rats

Abstract

1. The oral bioavailability of puerarin is poor which hindered its clinical performance.

2. This study investigates the effects of verapamil on the pharmacokinetics of puerarin in rats.

3. The pharmacokinetics of orally administered puerarin (50?mg/kg) with or without verapamil pretreatment (10?mg/kg/day for 7?days) were investigated. The plasma concentration of puerarin was determined using LC-MS/MS method, and the pharmacokinetics profiles were calculated and compared. Caco-2 cell transwell model was also used to investigate the effects of verapamil on the transport pf puerarin.

4. The results showed that when the rats were pretreated with verapamil, the maximum concentration (C_max) of puerarin increased from 683.7?±?51.2 to 933.5?±?75.8?ng/mL (p?<?0.05), and the area under the concentration-time curve from zero to infinity (AUC_0-inf) also increased from 3687.3?±?444.6 to 5006.1?±?658.6?μg·h/L (p?<?0.05). The Caco-2 cell transwell experiments indicated that verapamil could decrease the efflux ratio of puerarin from 1.90 to 1.19 through inhibiting the activity of P-gp.

5. In conclusion, these results indicated that verapamil could affect the pharmacokinetics of puerarin, possibly by increasing the systemic exposure of puerarin by inhibiting the activity of P-gp.

     

In vitro metabolism and transport of the new dipeptidyl peptidase 4 inhibitors,KR66222 and KR66223

1. We investigated the in vitro metabolism and transport of KR66222 and KR66223, new inhibitors of dipeptidyl peptidase (DPP) 4, using human liver microsomes (HLMs) and a Caco-2 cell monolayer.

2. Human liver microsomal incubation of KR66222 in the presence of the NADPH-generating system resulted in the formation of two metabolites, identified as S-oxidation (KR68334) and hydrolysis (KR66223) products using liquid chromatography/tandem mass spectrometry. The formation of KR66223 via an esterase and the formation of KR68334 via CYP3A5 and CYP3A4 seem to be major factors in the in vitro metabolism of KR66222 using HLMs. Additionally, KR66222 had a significantly greater basal to apical transport rate (2.5-fold) than apical to basal transport in the Caco-2 cell monolayer, suggesting the involvement of an efflux transport system. Further studies using inhibitors of efflux transporters and P-glycoprotein (P-gp) overexpressed cells revealed that P-gp was involved in the basal to apical transport of KR66222. These findings suggest that KR66222 undergoes a significant first pass effect, which may serve to decrease the bioavailability of KR66222.

3. The active metabolite, KR66223, was stable for 1?h at 37°C in pooled HLMs (98.9?±?2.6% of control) and did not undergo P-gp-mediated efflux in Caco-2 cells. Apparent permeability of KR66223 (4.96?×?10^?6 cm/s) was comparable to that of KR66222 (4.08?×?10^?6 cm/s).

4. In conclusion, considering pharmacokinetic variability and the intestinal first-pass effect caused by the involvement of CYP3A and P-gp, KR66223 seems to have better in vitro metabolism and permeability characteristics than KR66222.

     

Pharmacokinetics of antofloxacin hydrochloride in healthy male subjects after multiple intravenous dose administration

1. The purpose of the study was to evaluate pharmacokinetic characteristics of antofloxacin hydrochloride, a new fluoroquinolone antibiotic, during a multiple, intravenous dosing regimen.

2. Twelve healthy, Chinese male volunteer subjects were each given 300?mg of antofloxacin by intravenous infusion once daily for 7 days. Blood and urine samples were taken at designated time points for analysis of antofloxacin concentration by high-performance liquid chromatography (HPLC). Safety and tolerability were assessed by evaluation of subject complaints, vital signs, electrocardiograms, electroencephalograms, clinical chemistry parameters, haematology and urinalysis and prothrombin time.

3. The serum steady concentration of antofloxacin was obtained in 96?h after the administration of a daily intravenous dose of 300?mg of the drug. In the present study, the following pharmacokinetic parameters after 7 days of treatment with antofloxacin were determined to be: C_max 3.81?±?0.66?mg/L, C_min 0.85?±?0.19?mg/L, AUC_0–24 60.51?±?8.30?mg/L·h, C_av 2.52?±?0.35?mg/L, PTF 87.45?±?3.37%, t_1/2β 20.34?±?1.88?h. The C_max and AUC_0–24 after 7-day treatment were both higher than after the first dose (by 43% and 110%, respectively). The cumulative urinary elimination of antofloxacin within 96?h after the last dose was about 56%.

4. During the study, there were neither subject complaints nor significant adverse clinical findings.

5. Antofloxacin, administered intravenously as a single, daily 300?mg dose for 7 days, demonstrated favourable pharmacokinetic characteristics and tolerability. The results of this study indicate that antofloxacin hydrochloride is suitable for further clinical study.

     

Cysteine effects on the pharmacokinetics of etoposide in protein–calorie malnutrition rats: increased gastrointestinal absorption by cysteine

1. Protein–calorie malnutrition (PCM) occurs frequently in advanced cancer patients and has a profound impact on the toxicity of many drugs. Thus, the pharmacokinetics of etoposide were evaluated in control, control with cysteine (CC), PCM, and PCM with cysteine (PCMC) rats.

2. Etoposide was administered intravenously (2?mg/kg) or orally (10?mg/kg). Changes in hepatic and intestinal cytochrome P450s (CYPs) and effects of cysteine on intestinal P-glycoprotein (P-gp)-mediated efflux were also measured.

3. In PCM rats, the CL_NR (AUC_0–∞) of intravenous etoposide was significantly slower (greater) than that in controls, because of the significant decrease in the hepatic CYP3A subfamily and P-gp. In PCMC rats, the slowed CL_NR of etoposide in PCM rats was restored to the control level by cysteine treatment. PCMC rats showed a significantly greater AUC_{0–6 h} of oral etoposide than PCM rats, primarily because of the increased gastrointestinal absorption of etoposide as a result of the inhibition of intestinal P-gp by cysteine.

4. The gastrointestinal absorption of an oral anticancer drug, which is a substrate of P-gp, may be improved by co-administration of cysteine in advanced cancer patients if the present rat data can be extrapolated to patients.

     

Reactions of benzene oxide,a reactive metabolite of benzene,with model nucleophiles and DNA

1. Reactivity of benzene oxide (BO), a reactive metabolite of benzene, was studied in model reactions with biologically relevant S- and N-nucleophiles by LC-ESI-MS.

2. Reaction with N-acetylcysteine (NAC) in aqueous buffer solutions gave N-acetyl-S-(6-hydroxycyclohexa-2,4-dien-1-yl)cysteine (pre-phenylmercapturic acid, PPhMA), which was easily dehydrated in acidic solutions to phenylmercapturic acid (PhMA). The yield of PPhMA + PhMA increased exponentially with pH up to 11% in the pH range from 5.5 to 11.4.

3. Primary 6-hydroxycyclohexa-2,4-dien-1-yl (HC) adducts were detected also in reactions of purine nucleosides and nucleotides under physiological conditions. After a vigorous acidic hydrolysis, all HC adducts were converted to corresponding phenyl purines, which were identified as 7-phenylguanine (7-PhG), 3-phenyladenine (3-PhA) and N⁶-phenyladenine (6-PhA). The yield of 7-PhG amounted to 14?±?5 and 16?±?7?ppm for 2′-deoxyguanosine and 2′-deoxyguanosine-5′-monophosphate, respectively, that of 6-PhA was 500?±?70 and 455?±?75?ppm with 2′-deoxyadenosine and 2′-deoxyadenosine-5′-phosphate, respectively, with only traces of 3-PhA.

4. Reactions with the DNA followed by acidic hydrolysis yielded 26?±?11?ppm (mean ± SD; n?=?9) of 7-PhG as the sole adduct detected.

5. In contrast to the reactions with S-nucleophiles, the reactivity of BO with nucleophilic sites in the DNA is very low and can therefore hardly account for a significant DNA damage caused by benzene.

     

Modulation of transporter activity of OATP1B1 and OATP1B3 by the major active components of Radix Ophiopogonis

Abstract

1. Radix Ophiopogonis is often an integral part of many traditional Chinese formulas, such as Shenmai injection used to treat cardio-cerebrovascular diseases. This study aimed to investigate the influence of the four active components of Radix Ophiopogonis on the transport activity of OATP1B1 and OATP1B3.

2. The uptake of rosuvastatin in OATP1B1-HEK293T cells were stimulated by methylophiopogonanone A (MA) and ophiopogonin D′ (OPD′) with EC₅₀ calculated to be 11.33?±?2.78 and 4.62?±?0.64?μM, respectively. However, there were no remarkable influences on rosuvastatin uptake in the presence of methylophiopogonanone B (MB) or ophiopogonin D (OPD). The uptake of atorvastatin in OATP1B1-HEK293T cells can be increased by MA, MB, OPD and OPD′ with EC₅₀ calculated to be 6.00?±?1.60, 13.64?±?4.07, 10.41?±?1.28 and 3.68?±?0.85?μM, respectively.

3. The uptake of rosuvastatin in OATP1B3-HEK293T cells was scarcely influenced by MA, MB and OPD, but was considerably increased by OPD′ with an EC₅₀ of 14.95?±?1.62?μM. However, the uptake of telmisartan in OATP1B3-HEK293T cells was notably reduced by OPD′ with an IC₅₀ of 4.44?±?1.10?μM, and barely affected by MA, MB and OPD.

4. The four active components of Radix Ophiopogonis affect the transporting activitives of OATP1B1 and OATP1B3 in a substrate-dependent manner.

     

Pharmacokinetics,disposition and lipid-modulating activity of 5-{2-[4-(3,4-difluorophenoxy)-phenyl]-ethylsulfamoyl}-2-methyl-benzoic acid,a potent and subtype-selective peroxisome proliferator-activated receptor α agonist in preclinical species and human

1. 5-{2-[4-(3,4-Difluorophenoxy)-phenyl]-ethylsulfamoyl}-2-methyl-benzoic acid (1) is a novel, potent, and selective agonist of the peroxisome proliferator-activated receptor alpha (PPAR-α).

2. In preclinical species, compound 1 demonstrated generally favourable pharmacokinetic properties. Systemic plasma clearance (CL_p) after intravenous administration was low in Sprague–Dawley rats (3.2?±?1.4?ml min^?1 kg^?1) and cynomolgus monkeys (6.1?±?1.6?ml min^?1 kg^?1) resulting in plasma half-lives of 7.1?±?0.7?h and 9.4?±?0.8?h, respectively. Moderate bioavailability in rats (64%) and monkeys (55%) was observed after oral dosing. In rats, oral pharmacokinetics were dose-dependent over the dose range examined (10 and 50?mg kg^?1).

3. In vitro metabolism studies on 1 in cryopreserved rat, monkey, and human hepatocytes revealed that 1 was metabolized via oxidation and phase II glucuronidation pathways. In rats, a percentage of the dose (approximately 19%) was eliminated via biliary excretion in the unchanged form.

4. Studies using recombinant human CYP isozymes established that the rate-limiting step in the oxidative metabolism of 1 to the major primary alcohol metabolite M1 was catalysed by CYP3A4.

5. Compound 1 was greater than 99% bound to plasma proteins in rat, monkey, mouse, and human.

6. No competitive inhibition of the five major cytochrome P450 enzymes, namely CYP1A2, P4502C9, P4502C19, P4502D6 and P4503A4 (IC₅₀’s?>?30 μM) was discerned with 1.

7. Because of insignificant turnover of 1 in human liver microsomes and hepatocytes, human clearance was predicted using rat single-species allometric scaling from in vivo data. The steady-state volume was also scaled from rat volume after normalization for protein-binding differences. As such, these estimates were used to predict an efficacious human dose required for 30% lowering of triglycerides.

8. In order to aid human dose projections, pharmacokinetic/pharmacodynamic relationships for triglyceride lowering by 1 were first established in mice, which allowed an insight into the efficacious concentrations required for maximal triglyceride lowering. Assuming that the pharmacology translated in a quantitative fashion from mouse to human, dose projections were made for humans using mouse pharmacodynamic parameters and the predicted human pharmacokinetic estimates.

9. First-in-human clinical studies on 1 following oral administration suggested that the human pharmacokinetics/dose predictions were in the range that yielded a favourable pharmacodynamic response.

     

Metabolism,pharmacokinetics and excretion of the GABAA receptor partial agonist [14C]CP-409,092 in rats

1. The metabolism and excretion of a GABA_A partial agonist developed for the treatment of anxiety, CP-409,092; 4-oxo-4,5,6,7-tetrahydro-1H-indole-3-carboxylic acid (4-methylaminomethyl-phenyl)-amide, were studied in rats following intravenous and oral administration of a single doses of [¹⁴C]CP-409,092.

2. The pharmacokinetics of CP-409,092 following single intravenous and oral doses of 4 and 15?mg kg^?1, respectively, were characterized by high clearance of 169?±?18?ml min^?1 kg^?1, a volume of distribution of 8.99?±?1.46 l kg^?1, and an oral bioavailability of 2.9% ± 3%.

3. Following oral administration of 100?mg kg^?1 [¹⁴C]CP-409,092, the total recovery was 89.1% ± 3.2% for male rats and 89.3% ± 0.58% for female rats. Approximately 87% of the radioactivity recovered in urine and faeces were excreted in the first 48?h. A substantial portion of the radioactivity was measured in the faeces as unchanged drug, suggesting poor absorption and/or biliary excretion. There were no significant gender-related quantitative/qualitative differences in the excretion of metabolites in urine or faeces.

4. The major metabolic pathways of CP-409,092 were hydroxylation(s) at the oxo-tetrahydro-indole moiety and oxidative deamination to form an aldehyde intermediate and subsequent oxidation to form the benzoic acid. The minor metabolic pathways included N-demethylation and subsequent N-acetylation and oxidation.

5. The present work demonstrates that oxidative deamination at the benzylic amine of CP-409,092 and subsequent oxidation to form the acid metabolite seem to play an important role in the metabolism of the drug, and they contribute to its oral clearance and low exposure.

     

Inhibitory effects of commonly used herbal extracts on UGT1A1 enzyme activity

1. Commonly used herbal supplements were screened for their potential to inhibit UGT1A1 activity using human liver microsomes. Extracts screened included ginseng, echinacea, black cohosh, milk thistle, garlic, valerian, saw palmetto, and green tea epigallocatechin gallate (EGCG). Estradiol-3-O-glucuronide (E-3-G) formation was used as the index of UGT1A1 activity.

2. All herbal extracts except garlic showed inhibition of UGT1A1 activity at one or more of the three concentrations tested. A volume per dose index (VDI) was calculated to estimate the volume in which the daily dose should be diluted to obtain an IC₅₀-equivalent concentration. EGCG, echinacea, saw palmetto, and milk thistle had VDI values >2.0?L per dose unit, suggesting a higher potential for interaction.

3. Inhibition curves were constructed for EGCG, echinacea, saw palmetto, and milk thistle. IC₅₀ values were (mean ± SE) 7.8?±?0.9, 211.7?±?43.5, 55.2?±?9.2, and 30.4?±?6.9 µg/ml for EGCG, echinacea, saw palmetto, and milk thistle extracts, respectively.

4. Based on our findings, inhibition of UGT1A1 by milk thistle and EGCG and to a lesser extent by echinacea and saw palmetto is plausible, particularly in the intestine where higher extract concentrations are anticipated. Further clinical studies are warranted.

     

Measurements of caffeine and plasma metabolite/caffeine ratios as a test for hepatic drug-oxidizing capacity in goats

1. The aim of this investigation was to determine the pharmacokinetics and demethylation of caffeine (CF) and the metabolite/CF ratios that correlated best with CF clearance, which were used to evaluate hepatic drug-oxidizing capacity of CF after a single intravenous dose (5?mg/kg) in hair goats (n?=?9).

2. Pharmacokinetic parameters of CF and its metabolites, theobromine (TB), paraxanthine (PX) and theophylline (TP), were calculated. The plasma metabolic ratios TB/CF, PX/CF, TP/CF and TB+PX+TP/CF were determined at 6, 8 and 10?h after CF administration to evaluate their hepatic drug-oxidizing capacity.

3. The plasma concentration–time data of CF were fit to a two-compartment model in all animals. The clearance of CF was 0.08?±?0.02?L/h/kg, and the volume of distribution was 0.91?±?0.16?L/kg. The demethylation fractions of CF to TB, PX and TP were 0.24, 0.37 and 0.39, respectively.

4. Correlations between the metabolic ratios and CF clearance were quite high, except for the PX/CF ratio, particularly at 6?h (r?=?0.650–0.750, P?<?0.01, 0.05) and 10?h (r?=?0.650–0.767, P?<?0.01, 0.05).

5. Plasma metabolite/CF ratios, except for the PX/CF ratio, may be useful as an alternative to measurements of CF clearance for the determination of the hepatic drug-oxidizing capacity in goats.

     

Pharmacokinetics of the prodrug thiamphenicol glycinate and its active parent compound thiamphenicol in beagle dogs following intravenous administration

1. This study investigated the pharmacokinetics of thiamphenicol glycinate (TG) and thiamphenicol (TAP) in beagles (n?=?6) after intravenous administration of 50?mg/kg TG hydrochloride. Plasma concentrations of TG and TAP were measured by a HPLC-UV method.

2. Two-compartment model was selected to describe the pharmacokinetic characteristics of TG and TAP in vivo. Main parameters were as follows: AUC_0–∞ of TAP and TG were 16,328?±?1682 µg·min/mL and 3943?±?546 µg·min/mL, respectively. The total plasma clearance (CL) of TG and TAP were 12.7?±?2.0?mL/min/kg and 2.5?±?0.3?mL/min/kg, respectively. Mean residence time (MRT) of TG and TAP were 27.5?±?3.5 and 207.2?±?20.2?min, respectively. The transformative rate constant (k_1M) from TG to TAP was 0.0477?±?0.0028?min^?1. The elimination rate constant (k_M10) from TAP was 0.0238?±?0.0044?min^?1. Coefficients of variation (CV) between observed values and predicted ones were 5.9% and 18.2%, respectively. The volume of distribution of the central compartment for TG (V_C) and TAP (V_CM) were 0.264?±?0.022?L/kg and 0.127?±?0.023?L/kg, respectively.

3. Pharmacokinetic parameters suggested that TG was presumably cleaved quickly by tissue esterase to release TAP for effectiveness in beagles after administration.

     

Effect of continuous silymarin administration on oral talinolol pharmacokinetics in healthy volunteers

1. The objective of this study was to investigate the effect of concomitantly administered silymarin on the pharmacokinetics of talinolol, a typical substrate for P-glycoprotein (P-gp), in healthy Chinese volunteers and its association with a multidrug resistance 1 (MDR1) C3435T genetic polymorphism.

2. Eighteen healthy adult men (six MDR1 3435CC homozygotes, six MDR1 3435CT heterozygotes and six MDR1 3435TT homozygotes) were recruited in a two-phase, randomized, single-blind, crossover design. The pharmacokinetics of talinolol were measured after co-administration of placebo or 140?mg silymarin capsules three times daily for 14 days. Concentrations of talinolol in plasma were measured for up to 36?h after drug administration by liquid chromatography-mass spectrometry (HPLC-MS).

3. The peak plasma concentration (C_max) of talinolol was significantly higher after silymarin administration as compared with placebo (p?=?0.007). The area under the plasma concentration–time curve from zero to 36?h (AUC_0–36) and AUC_0–∞ of talinolol was increased by 36.2% ± 33.2% and 36.5% ± 37.9%, respectively, by silymarin co-administration. The oral clearance (CL/F) of talinolol was decreased by 23.1% ± 16.6% (p?t_max) and the blood elimination half-life (t_1/2) of talinolol was observed between the placebo- and silymarin-treated phases.

4. Co-administration of silymarin significantly increased the plasma concentration of talinolol in healthy volunteers.