Pharmacokinetic interference of doxorubicin with tolbutamide due to reduced metabolic clearance with increased serum unbound fraction in rats.

The study examined the effect of doxorubicin (DOX) on the hepatic expression of CYP2C and its activity for metabolizing tolbutamide (TB), a specific CYP2C substrate, in rats and whether the pharmacokinetics of tolbutamide were altered by doxorubicin exposure. The expression level of hepatic CYP2C11 was depressed 1 day after doxorubicin administration (day 1), and this effect on CYP2C11 was augmented on day 4. However, the expression level of hepatic CYP2C6 remained unchanged. The activity of tolbutamide 4-hydroxylation in hepatic microsomes was decreased with time following doxorubicin administration. Regarding the enzyme kinetic parameters for tolbutamide 4-hydroxylation on day 4, the maximum velocity (Vmax ) was significantly lower in the DOX group than that in the control group, while the Michaelis constant (Km ) was unaffected. On pharmacokinetic examination, the total clearance (CLtot ) of tolbutamide on day 4 was increased, despite the decreased metabolic capacity. On the other hand, the serum unbound fraction (fu ) of tolbutamide was elevated with a reduced serum albumin concentration in the DOX group. Contrary to CLtot , CLtot /fu , a parameter approximated to the hepatic intrinsic clearance of unbound tolbutamide, was estimated to be significantly reduced in the DOX group. These findings indicate that the metabolic capacity of CYP2C11 in the liver is depressed time-dependently by down-regulation after doxorubicin exposure in rats, and that the decreased enzyme activity of TB 4-hydroxylation in hepatic microsomes reflects the pharmacokinetic change of unbound tolbutamide, not total tolbutamide, in serum.

Effects of shuanghuanglian injection on the activities of CYP1A2, 2C11, 2D1 and 3A1/2 in rats in vivo and in vitro.

Shuanghuanglian Injection (SHLI), one of the most popular herbal prescription in China, has been commonly used to treat pneumonia, tonsillitis, and other respiratory diseases caused by bacterium and virus. This study is to investigate the effects of SHLI on the activities of Cytochrome P450 (CYP) 1A2, 2C11, 2D1 and 3A1/2 in rats. Sixteen rats were randomly divided into two groups (SHLI-treated and blank control). They were administered SHLI or physiological saline for consecutive seven days. On day eight, 16 animals were administrated cocktail drugs as probe substrates of the four CYP in vivo. In addition, other four probe drugs were added, respectively, into incubation systems of rat liver microsomes (RLM) to assess the effects of SHLI on the four CYP isoforms in vitro. SHLI exhibited an inductive effect on CYP2C11 in vivo by decreasing Cmax, t1/2 and AUC0-∞ of tolbutamide, while the main pharmacokinetic parameters of caffeine, metoprolol and dapsone have no significant changes. In vitro study, SHLI showed no significant effects on the activities of CYP1A2, 2D1 and 3A1/2, but increasing the metabolism of tolbutamide in RLM. SHLI induced the activities of CYP2C11, but had no significant effects on the activities of CYP1A2, CYP2D1 and CYP3A1/2 in rats.

Pharmacokinetics and metabolic elimination of tolbutamide in female rats: Comparison with male rats.

As there are to be known gender differences in the expression profiles of rat hepatic CYP2C, we examined the pharmacokinetic behavior of tolbutamide (TB), a typical probe for CYP2C, and hepatic enzyme activities for metabolizing TB in female rats to compare with male rats. On the pharmacokinetic analysis of TB after intravenous administration to female rats, the elimination rate constant at the terminal phase (ke ), total clearance (CLtot ) and the apparent volume of distribution at steady-state (Vdss ) were significantly lower than in male rats. The binding rates of TB to serum protein were similar in male and female rats, indicating that the change in unbound TB concentration in serum is not associated with the difference in the pharmacokinetic disposition of TB. On metabolic examination using hepatic microsomes, the maximum reaction velocity (Vmax ) of the metabolic conversion from TB to 4-hydroxytolbutamide (4-OH-TB) in female rats was lower than that in male rats, although there was no significant difference in the Michaelis constant (Km ) between genders. Consistent with this, the Vmax -to-Km ratio (Vmax /Km ) was significantly lower in female rats than in male rats. Therefore, the low in vitro CYP2C-dependent activity for hepatic TB removal in female rats provided a clear explanation for the lower in vivo elimination clearance of TB. Our findings strongly suggest that there is a gender difference in the metabolic capacity to eliminate drugs that serve as substrates of hepatic CYP2C enzymes in rats.

In vivo pharmacokinetic interaction by ethanolic extract of Gymnema sylvestre with CYP2C9 (Tolbutamide), CYP3A4 (Amlodipine) and CYP1A2 (Phenacetin) in rats.

Gymnema sylvestre (GS) is a medicinal herb used for diabetes mellitus (DM). Herbs are gaining popularity as medicines in DM for its safety purpose. The aim of the present study was to evaluate in vivo pharmacokinetic (PK) interaction between allopathic drugs tolbutamide (TOLBU), amlodipine (AMLO), and phenacetin (PHENA) at low (L) and high (H) doses with ethanolic extract (EL) from GS. EL was extracted and subjected to TLC, total triterpenoid content (19.76 ± 0.02 W/W) and sterol content (0.1837 ± 0.0046 W/W) estimation followed by identification of phytoconstituents using HRLC-MS and GC-MS. PK interaction study with CYP2C9, CYP3A4 and CYP1A2 enzymes were assessed using TOLBU, AMLO and PHENA respectively to index cytochrome (CYP) mediated interaction in rats after concomitant administration of EL extract (400 mg/kg) from GS for 7 days. The rats were divided into four groups for each PK study where, group I and II were positive control for low and high dose of test drugs (CYP substrates) while group II and IV were orally administered EL. The PK study result of PHENA indicated that area under the plasma concentration-time curve (AUC0-24) was significantly (P < 0.0001) increased by 1.4 (L) and 1.3-fold (H), plasma concentration (Cmax) was significantly (P < 0.001) increased by 1.6 (L) and 1.4-fold (H). Whereas for TOLBU; clearance rate (CL) was significantly (P < 0.0001) decreased by 2.4 (L) and 2.3-fold (H), Cmax, was significantly (P < 0.001) decreased by 26.5% (L) and 50.4% (H) and AUC0-24 was significantly (P < 0.0001) decreased by 59.8% (L) and 57.5% (H). Thus, EL is seen to be interacting with CYP1A2 by inhibiting its metabolic activity. HRLC-MS and GC-MS helped identify the presence of gymnemic acid (GA), triterpenoids and steroids in EL which could be the reason for PK interaction of CYP1A2 and CYP2C9. Also, in silico structure based site of metabolism study showed Fe accessibility and intrinsic activity for GA-IV, GA-VI, GA-VII and GA-X with CYP2C9. PK parameters of AMLO were not significantly affected by pre-treatment of EL. Thereby our findings indicate that co-administration of GS with drugs that are metabolized by CYP2C9 and CYP1A2 could lead to potential HDI.

The Effects of Formaldehyde on Cytochrome P450 Isoform Activity in Rats.

Formaldehyde (FA) is an occupational and indoor pollutant. Long-term exposure to FA can irritate the respiratory mucosa, with potential carcinogenic effects on the airways. The effects of acute FA poisoning on the activities of CYP450 isoforms CYP1A2, CYP2C11, CYP2E1, and CYP3A2 were assessed by determining changes in the pharmacokinetic parameters of the probe drugs phenacetin, tolbutamide, chlorzoxazone, and testosterone, respectively. Rats were randomly divided into three groups: control, low FA dose (exposure to 110 ppm for 2 h for 3 days), and high FA dose (exposure to 220 ppm for 2 h for 3 days). A mixture of the four probe drugs was injected into rats and blood samples were taken at a series of time points. Plasma concentrations of the probe drugs were measured by HPLC. The pharmacokinetic parameters t1/2, AUC(0-t), and Cmax of tolbutamide, chlorzoxazone, and testosterone increased significantly in the high dose versus control group (P < 0.05), whereas the CL of chlorzoxazone and testosterone decreased significantly (P < 0.05). However, t1/2, AUC(0-t), and Cmax of phenacetin decreased significantly (P < 0.05), whereas the CL of phenacetin increased significantly (P < 0.05) compared to controls. Thus, acute FA poisoning suppressed the activities of CYP2C11, CYP2E1, and CYP3A2 and induced the activity of CYP1A2 in rats. And the change of CYP450 activity caused by acute FA poisoning may be associated with FA potential carcinogenic effects on the airways.

Estimation of Interindividual Variability of Pharmacokinetics of CYP2C9 Substrates in Humans.

The activity of metabolic enzymes varies across individuals and populations. Activity varies even among individuals sharing the same genotype. Genetic polymorphisms in CYP2C9 cause significant interindividual variability in the metabolism of its substrates. However, the variability of CYP2C9 intrinsic hepatic clearance (CLint,h,CYP2C9) among subjects of the same genotype has not been reported. In this study, we estimated the coefficient of variation (CV) for the intrinsic hepatic clearance of tolbutamide by CYP2C9 for each CYP2C9 genotype using previously reported area under the blood concentration curve (AUC) and oral clearance (CLoral) values in a Monte Carlo simulation with a dispersion model. The CVs for tolbutamide CLint,h,CYP2C9 were estimated to be 18.1%, 23.9%, 25.4%, 22.3%, 13.0%, and 19.8% for CYP2C9*1/*1, *1/*2, *1/*3, *2/*2, *2/*3, and *3/*3, respectively. These values are smaller than those previously reported for CYP2D6*1/*1 (43%), CYP2C19*1/*1 (66%), and CYP3A4 (33%). These CV values were used to predict AUC and CLoral variability of other CYP2C9 substrates, which are also substrates of other CYP isoforms. Then, the estimated CVs were consistent with those reported in previous studies of genotyped and ungenotyped subjects. Our estimates of CLint,h,CYP2C9 variability together with the variabilities of other isoforms are useful for predicting the AUC variability of CYP2C9 substrates.

Effect of Evodiamine on CYP Enzymes in Rats by a Cocktail Method.

The aim of this study was to assess the influence of evodiamine on the activities of the drug-metabolizing enzymes cytochrome P450 (CYP) 1A2, CYP2C9, CYP2C19, CYP2D6 and CYP3A4 in rats. The activities of CYP1A2, CYP2C9, CYP2C19, CYP2D6 and CYP3A4 were measured using specific probe drugs. After pretreatment for 1 week with evodiamine or physiological saline (control group) by oral administration, probe drugs phenacetin (5.0 mg/kg; CYP1A2 activity), tolbutamide (1.0 mg/kg; CYP2C9 activity), omeprazole (10 mg/kg; CYP2C19 activity), metoprolol (20 mg/kg; CYP2D6 activity) and midazolam (10 mg/kg; CYP3A4 activity) were administered to rats by oral administration. The blood was then collected at different times for ultra-performance liquid chromatography-tandem mass spectrometry analysis. The data showed that evodiamine exhibits an inhibitory effect on CYP1A2, CYP2C9 and CYP2D6 by increasing t(1/2), Cmax and AUC(0-∞), and decreasing CL/F compared with those of the control group. However, no significant changes in CYP2C19 and CYP3A4 activities were observed. In conclusion, the results indicated that evodiamine could inhibit CYP1A2, CYP2C9 and CYP2D6, which may affect the disposition of medicines primarily dependent on these pathways. Our work may be the basis of related herb-drug interactions in the clinic.

Therapeutic drug monitoring in dried blood spots using liquid microjunction surface sampling and high resolution mass spectrometry.

Dried blood spots (DBS) are a versatile and stable tool for direct clinical blood analysis. Ambient high-resolution mass spectrometry is emerging as a method of choice for their quantitative analysis, for instance in therapeutic drug monitoring. Here, we coupled liquid microjunction surface sampling technology, a so-called Flowprobe, with an Orbitrap mass spectrometer and demonstrated the utility of this set-up for direct quantification of multiple drugs in DBS on filter paper. A three-layer set-up that we had introduced earlier enabled introduction of internal standards into DBS. We furthermore took an established point-of-care test system a step further and analyzed disposable test fields for blood glucose monitoring also for Flowprobe-based acetaminophen screening without additional sample preparation. Using as little as 2 µL blood, the method had an LOD of 1 µg mL(-1) (coefficient of variation of ≤15%) and acetaminophen recoveries of 82 to 119% for blinded samples, as assessed by LC-MS/MS. Half an hour after ingestions of a single 1000 mg acetaminophen dose, indistinguishable drug levels were measured in three healthy volunteers by LC-MS/MS and Flowprobe-Orbitrap MS analysis of DBS. Flowprobe analysis of DBS was 6- to 100-times more sensitive than corresponding desorption electrospray ionization MS analysis for four drugs. For instance, the LOD for salicylic acid analysis was 0.07 ng mL(-1) with Flowprobe measurement. Furthermore, we showed that multi-component analysis of five different substances, which may mimic polypharmacy in diabetes patients, in one blood sample for screening purposes was feasible. Taken together, our study suggests that microjunction surface sampling of DBS on filter paper and disposable point-of-care test fields may be developed into routine methods for near-patient multi-compound therapeutic drug monitoring that may advance blood screening analysis for patients with polypharmacy.

A limited sampling strategy based on maximum a posteriori Bayesian estimation for a five-probe phenotyping cocktail.

PURPOSE: Cocktail approach using a combination of probes to phenotype several cytochromes P450 or transporters is of high interest in anticipating drug­drug interactions and personalized medicine. Its clinical use remains however limited by the intensive sampling scheme required to obtain phenotyping indexes (PI) which consists in calculating the area under the concentration­time curves. We proposed to use maximum a posteriori Bayesian estimation (MAPBE) that incorporates available information from the whole population to derive PI from a few individual observations. The performance of a limited sampling strategy (LSS) based on MAPBE was evaluated for a five-probe cocktail. METHODS: The studied cocktail included midazolam, tolbutamide, caffeine, dextromethorphan, omeprazole and their relevant metabolites. Prior information for MAPBE was obtained by nonlinear mixed-effect modelling of data from a pilot study. Sampling times were chosen based on optimal design theory using the Bayesian Fisher information matrix. Through a simulation study, we investigated the predicted PI in terms of bias and imprecision for varying number and timing of samples. RESULTS: Some three-point Bayesian designs gave mean prediction errors in [−5 %, 5 %], root mean square errors below 30 % for all probes, except dextromethorphan whose model should be consolidated further with additional data. This approach gave overall less outlier predicted values than single-point metrics and was more flexible to the timing of the latest sampling. CONCLUSIONS: MAPBE is accurate for predicting simultaneously several PI while being flexible in terms of integrating clinical constraints. Therefore, LSS based on MAPBE could help reduce the time of presence in hospital for individuals to be phenotyped.

Effects of suberoylanilide hydroxamic acid on rat cytochrome P450 enzyme activities.

Vorinostat (suberoylanilide hydroxamic acid, SAHA) is the first approved histone deacetylase (HDAC) inhibitor for the treatment of cutaneous T-cell lymphoma after progressive disease following two systemic therapies. The rats were randomly divided into SAHA groups (low, medium and high dosage) and control group. The SAHA group rats were given 12.3, 24.5, and 49 mg/kg SAHA, respectively, by continuous intragastric administration for 7 days. The influence of SAHA on the activities of CYP450 isoforms CYP2B6, CYP1A2, CYP2C19, CYP2D6 and CYP2C9 were evaluated by cocktail method, they were responsed by the changes of pharmacokinetic parameters of bupropion, phenacetin, tolbutamide, metroprolol and omeprazole. The five probe drugs were given to rats through intragastric administration, and the plasma concentration were determined by UPLC-MS/MS. The result of SAHA group compared to control group, there were statistical pharmacokinetics difference for bupropion, phenacetin, tolbutamide and metroprolol. Continuous intragastric administration for 7 days may induce the activities of CYP2C19 of rats, inhibit CYP1A2 and slightly inhibit CYP2B6 and CYP2D6 of rats. This may give advising for reasonable drug use after co-used with SAHA. The results indicated that drug co-administrated with SAHA may need dose adjustment. Furthermore, continuous intragastric administration of SAHA for 7 days, liver cell damaged, causing liver cell edema, in liver metabolism process.

Effect of Dimethoate on the Activity of Hepatic CYP450 Based on Pharmacokinetics of Probe Drugs.

BACKGROUND: Dimethoate (DM), one of the most widely used systemic organophosphate insecticide, has been reported to exert toxic effects after long-time subchronic exposure. This study aims at investigating the toxic effect of DM on liver after repeated administration of low doses of DM in rats. METHODS: Twenty Sprague-Dawley rats were randomly divided into the control group (n = 10) and the DM group (n = 10). After 2 weeks' exposure to DM at low dosage (5 mg/kg), biochemical parameters of hepatic functions were measured, histology and CYP450 expressed in liver was detected. The activities of CYP1A2, CYP2C11, CYP2D1, and CYP3A2 were evaluated by the Cocktail method. RESULTS: The level of AChE (acetylcholinesterase) was significantly decreased, hepatic functions were damaged and the mRNA level of CYP2D1 was significantly increased in the DM group (p < 0.05). The pharmacokinetics of probe drug revealed AUC(0-t), AUC(0-∞), t1/2 and Cmax of metoprolol was shorten in the DM group (p < 0.05). However, there were no statistical differences in MRT, t1/2, CL and Tmax for phenacetin, tolbutamide and midazolam. CONCLUSIONS: A low dosage of DM could induce the activity of CYP2D1 in liver and increase the metabolism of metoprolol when exposed for 2 weeks.

In vitro and in vivo characterization of 13 CYP2C9 allelic variants found in Chinese Han population.

Our previous study detected totally 35 CYP2C9 allelic variants in 2127 Chinese subjects, of whom 21 novel alleles were reported for the first time in Chinese populations. The aim of the present study was to characterize the 13 CYP2C9 allelic variants both in vitro and in vivo. Different types of CYP2C9 variants were highly expressed in COS-7 cells, and 50 µM tolbutamide was added as the probing substrate to evaluate their metabolic abilities in vitro. Subsequently, the concentrations of tolbutamide and its metabolite in the plasma and urine within individuals with different types of genotypes were determined by HPLC to evaluate the catalytic activity of the 13 mutant CYP2C9 proteins in vivo. Our results showed that compared with *1/*1 wild-type subjects, subjects with *1/*40 genotype showed increased oral clearance (CL/F), whereas individuals with *1/*3, *1/*13, *3/*3, *3/*13, *1/*16, *1/*19, *1/*34, *1/*42, *1/*45, *1/*46, and *1/*48 genotype exhibited significantly decreased CL/F, and those with *1/*27, *1/*29, *1/*40, and *1/*41 genotype presented similar CL/F value. When expressed in COS-7 cells, the CYP2C9 variants showed similar pattern to the results in clinical study. The study suggests that, besides two typical defective alleles, *3 and *13, seven CYP2C9 allelic variants (*16, *19, *34, *42, *45, *46, and *48) cause defective effects on the enzymatic activities both in vitro and in vivo. In clinic, patients with these defective alleles should be paid close attention to.

Simultaneous determination of bupropion, metroprolol, midazolam, phenacetin, omeprazole and tolbutamide in rat plasma by UPLC-MS/MS and its application to cytochrome P450 activity study in rats.

A specific ultra-performance liquid chromatography tandem mass spectrometry method is described for the simultaneous determination of bupropion, metroprolol, midazolam, phenacetin, omeprazole and tolbutamide in rat plasma with diazepam as internal standard, which are the six probe drugs of the six cytochrome P450 isoforms CYP2B6, CYP2D6, CYP3A4, CYP1A2, CYP2C19 and CYP2C9. Plasma samples were protein precipitated with acetonitrile. The chromatographic separation was achieved using a UPLC® BEH C18 column (2.1 × 100 mm, 1.7 µm). The mobile phase consisted of acetonitrile and water (containing 0.1% formic acid) with gradient elution. The triple quadrupole mass spectrometric detection was operated by multiple reaction monitoring in positive electrospray ionization. The precisions were <13%, and the accuracy ranged from 93.3 to 110.4%. The extraction efficiency was >90.5%, and the matrix effects ranged from 84.3 to 114.2%. The calibration curves in plasma were linear in the range of 2-2000 ng/mL, with correlation coefficient (r(2) ) >0.995. The method was successfully applied to pharmacokinetic studies of the six probe drugs of the six CYP450 isoforms and used to evaluate the effects of erlotinib on the activities of CYP2B6, CYP2D6, CYP3A4, CYP1A2, CYP2C19 and CYP2C9 in rats. Erlotinib may inhibit the activity of CYP2B6 and CYP3A4, and may induce CYP2C9 of rats.

Simultaneous quantification of lenalidomide, ibrutinib and its active metabolite PCI-45227 in rat plasma by LC-MS/MS: application to a pharmacokinetic study.

Efficacy assessments using a combination of ibrutinib and lenalidomide necessitate the development of an analytical method for determination of both drugs in plasma with precision. A high performance liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed for the simultaneous determination of lenalidomide, ibrutinib, and its active metabolite PCI45227 in rat plasma. Extraction of lenalidomide, ibrutinib, PCI45227 and tolbutamide (internal standard; IS) from 50 µl rat plasma was carried out by liquid-liquid extraction with ethyl acetate:dichloromethane (90:10) ratio. Chromatographic separation of analytes was performed on YMC pack ODS AM (150 mm × 4.6 mm, 5 µm) column under gradient conditions with acetonitrile:0.1% formic acid buffer as the mobile phases at a flow rate of 1 ml/min. Precursor ion and product ion transition for analytes and IS were monitored on a triple quadrupole mass spectrometer, operated in the selective reaction monitoring with positive ionization mode. Method was validated over a concentration range of 0.72-183.20 ng/ml for ibrutinib, 0.76-194.33 ng/ml for PCI-45227 and 1.87-479.16 ng/ml for lenalidomide. Mean extraction recovery for ibrutinib, PCI-45227, lenalidomide and IS of 75.2%, 84.5%, 97.3% and 92.3% were consistent across low, medium, and high QC levels. Precision and accuracy at low, medium and high quality control levels were less than 15% across analytes. Bench top, wet, freeze-thaw and long term stability was evaluated for all the analytes. The analytical method was applied to support a pharmacokinetic study of simultaneous estimation of lenalidomide, ibrutinib, and its active metabolite PCI-45227 in Wistar rat. Assay reproducibility was demonstrated by re-analysis of 18 incurred samples.

Evaluation of the impact of Polygonum capitatum, a traditional Chinese herbal medicine, on rat hepatic cytochrome P450 enzymes by using a cocktail of probe drugs.

ETHNOPHARMACOLOGICAL RELEVANCE: Polygonum capitatum is a well-known Miao medicinal plant that has been used for many years for its unique therapeutic effects on various urological disorders, including urinary calculus and urinary tract infections. To investigate the effect of Polygonum capitatum on cytochrome P450 (CYP) isoforms (CYP1A2, CYP2C9, CYP2C19, CYP2E1, and CYP3A4) in vivo using a "cocktail" approach by administering five probe drugs to rats. This study assessed the potential of Polygonum capitatum to interact with co-administered drugs. MATERIALS AND METHODS: An aqueous extract of dried whole Polygonum capitatum was prepared and administered orally to rats at a dose of 0.58g/kg or 1.74g/kg twice daily for 7 or 14 consecutive days. A cocktail of caffeine (1.0mg/kg), tolbutamide (1.0mg/kg), omeprazole (2.0mg/kg), chlorzoxazone (4.0mg/kg) and midazolam (4.0mg/kg) was then administered on the eighth or fifteenth day to evaluate the effects of Polygonum capitatum on CYP1A2, 2C9, 2C19, 2E1, and 3A4, respectively. Blood samples were collected at a range of time-points and the plasma concentrations of the probe drugs were simultaneously quantified using ultra high-performance liquid chromatography-tandem mass spectrometry. Pharmacokinetic parameters were calculated to evaluate the effects of Polygonum capitatum on the activities of these CYP enzymes in rats. RESULTS: Polygonum capitatum pre-treatment had no significant effect on the pharmacokinetic parameters of caffeine, omeprazole or chlorzoxazone. However, the pharmacokinetics of tolbutamide and midazolam were affected significantly (P<0.05) by Polygonum capitatum, which induced more rapid metabolism of these probe compounds. CONCLUSIONS: These results suggested that Polygonum capitatum could induce CYP2C9 and CYP3A4, and did not influence CYP1A2, CYP2C19 or CYP2E1. Therefore, the clinical dose of drugs metabolized by human CYP2C9 or CYP3A4 may need to be adjusted in patients taking Polygonum capitatum, as this herbal medication may result in reduced effective concentrations of these drugs.

Pharmacokinetic of four probe drugs in adriamycin-induced nephropathy rat.

BACKGROUND AND AIM: Probe drugs have been widely used to assess the activities of various CYP450 (cytochromes P450) isoenzymes in many fields of drug metabolism and pharmacogenetics. The nephrotic syndrome characterized by massive proteinuria and hypoproteinemia, whether that would influence the pharmacokinetics of probe drugs or not is still unclear. The purpose of the study was to investigate the pharmacokinetic of four probe drugs in adriamycin (ADR)-induced nephropathy rat. MATERIALS AND METHODS: The rats were randomly divided into Control-group (n = 10) and ADR-group (n = 10). Nephrotic syndrome was established by weekly injections of ADR for 2 weeks. After dynamic monitoring of 24-h total urinary protein for 4 weeks, we confirmed that nephrotic syndrome had developed. The rats were administered intragastrically with phenacetin, tolbutamide, omeprazole and bupropion (15, 5, 15, and 15 mg/kg, respectively). The blood samples were determined by LC-MS (Liquid Chromatography-Mass Spectrometry) method. RESULTS: The pharmacokinetics parameter of tolbutamide in ADR-group and Control-group were AUC(0-t) 15.371 ± 4.107, 6.901 ± 5.738 (mg/L*h), MRT(0-t) 8.751 ± 0.754, 6.032 ± 0.63 (h), t1/2 3.88 ± 0.423, 3.602 ± 0.693 (h), Tmax 6.2 ± 3.768, 1.95 ± 0.798 (h), CL/F 0.038 ± 0.005, 0.107 ± 0.037 (L/h/kg), V/F 0.212 ± 0.043, 0.567 ± 0.258 (L/kg), Cmax 1.853 ± 0.384, 1.422 ± 1.312 (mg/L). There was statistical difference in AUC, MRT, CL, V and Tmax of tolbutamide between two groups (p < 0.05), but no pharmacokinetics difference for phenacetin, bupropion and omeprazole. CONCLUSIONS: The pharmacokinetics of tolbutamide was changed in ADR-induced nephropathy rat. It is not suitable for tolbutamide to evaluate the activity of CYP450 in nephrotic syndrome.

Effects of peritoneal dialysis on pharmacotherapy: a deductive pharmacokinetic-model approach to predict drug concentration profiles in plasma and peritoneal fluid.

The aim of this study was to present a deductive compartment pharmacokinetic (PK) model to predict the concentration profiles of drugs in plasma and peritoneal fluid in peritoneal dialysis (PD) rats. PK parameters of model drugs in normal and experimentally induced acute renal failure (ARF) rats not undergoing PD were obtained inductively in a common regression manner with a two-compartment model. In PD normal and ARF rats, PK parameters relating to the transfer of drugs to the peritoneal dialysate and the progress of renal failure were deductively modified to simulate the drug concentration-time profiles in plasma and in the peritoneal fluid in PD rats. The deductively introduced modifiers were the volume of distribution in the peripheral compartment, plasma protein binding, and solvent movement factor to the peritoneal fluid. Predicted profiles of tolbutamide, propranolol and cefazolin in PD normal and ARF rats were compared with the corresponding observed data. This minimal deductive approach yielded satisfactory accuracy in the prediction of both the plasma and peritoneal fluid concentrations of tolbutamide and propranolol.

Effects of hydroxysafflor yellow A on the activity and mRNA expression of four CYP isozymes in rats.

ETHNOPHARMACOLOGICAL RELEVANCE: In traditional therapy with Chinese medicine, hydroxysafflor yellow A (HSYA), a main active component isolated from the dried flower of Carthamus tinctorius L., is the principal efficiency ingredient of Safflor Yellow Injection. Now HSYA has been demonstrated to have good pharmacological activities of antioxidation, myocardial and cerebral protective and neuroprotective effects. The purpose of this study was to find out whether HSYA influences the effect on rat cytochrome P450 (CYP) enzymes (CYP1A2, CYP2C11, CYP2D4 and CYP3A1) by using cocktail probe drugs in vivo; the influence on the levels of CYP mRNA was also studied. MATERIALS AND METHODS: A cocktail solution at a dose of 5 mL/kg, which contained phenacetin (20 mg/kg), tolbutamide (5 mg/kg), dextromethorphan (20 mg/kg) and midazolam (10 mg/kg), was given as oral administration to rats treated with short or long period of intravenous HSYA via the caudal vein. Blood samples were collected at a series of time-points and the concentrations of probe drugs in plasma were determined by HPLC-MS/MS. The corresponding pharmacokinetic parameters were calculated by the software of DAS 2.0. In addition, real-time RT-PCR was performed to determine the effect of HSYA on the mRNA expression of CYP1A2, CYP2C11, CYP2D4 and CYP3A1 in rat liver. RESULTS: HSYA had significant inhibition effects on CYP1A2 and CYP2C11 in rats as oriented from the pharmacokinetic profiles of the probe drugs. Furthermore, HSYA had no effects on rat CYP2D4. However, CYP3A1 enzyme activity was induced by HSYA. The mRNA expression results were in accordance with the pharmacokinetic results. CONCLUSIONS: HSYA can either inhibit or induce activities of CYP1A2, CYP2C11 and CYP3A1. Therefore, co-administration of some CYP substrates with HSYA may need dose adjustment to avoid an undesirable herb-drug interaction.

An ethinyl estradiol-levonorgestrel containing oral contraceptive does not alter cytochrome P4502C9 in vivo activity.

Oral contraceptives have been in wide use for more than 50 years. Levonorgestrel, a commonly employed progestin component of combined oral contraceptives, was implicated in drug-drug interactions mediated via CYP2C9. Although in vitro studies refuted this interaction, there are no confirmatory in vivo studies. In the current study, we examined the phenotypic status of CYP2C9 using low-dose (125 mg) tolbutamide before and after oral contraceptive use in reproductive age women. Blood was collected 24 hours after the tolbutamide oral dose was administered, plasma was isolated, and tolbutamide concentration (C24) was measured using liquid chromatography-mass spectrometry. The natural logarithm of tolbutamide C24, a metric for CYP2C9 phenotype, was found to be equivalent (within 80%-125% equivalency boundaries) before and after oral contraceptive use. In conclusion, levonorgestrel-containing oral contraceptives, the most commonly used form of oral contraception, do not affect the status of the CYP2C9 enzyme. This suggests that it is safe to co-administer levonorgestrel-containing oral contraceptives and CYP2C9 substrates, which include a wide array of drugs.

The effects of H2S on the activities of CYP2B6, CYP2D6, CYP3A4, CYP2C19 and CYP2C9 in vivo in rat.

Hydrogen sulfide (H2S) is a colorless, flammable, extremely hazardous gas with a "rotten egg" smell. The human body produces small amounts of H2S and uses it as a signaling molecule. The cocktail method was used to evaluate the influence of H2S on the activities of CYP450 in rats, which were reflected by the changes of pharmacokinetic parameters of five specific probe drugs: bupropion, metroprolol, midazolam, omeprazole and tolbutamide, respectively. The rats were randomly divided into two groups, control group and H2S group. The H2S group rats were given 5 mg/kg NaHS by oral administration once a day for seven days. The mixture of five probes was given to rats through oral administration and the blood samples were obtained at a series of time-points through the caudal vein. The concentrations of probe drugs in rat plasma were measured by LC-MS. In comparing the H2S group with the control group, there was a statistically pharmacokinetics difference for midazolam and tolbutamide; the area under the plasma concentration-time curve (AUC) was decreased for midazolam (p < 0.05) and increased for tolbutamide (p < 0.05); while there was no statistical pharmacokinetics difference for bupropion, metroprolol and omeprazole. H2S could not influence the activities of CYP2B6, CYP2D6 and CYP2C19 in rats, while H2S could induce the activity of CYP3A4 and inhibit the activity of CYP2C9 in rats.