Investigation of the effects of axitinib on the pharmacokinetics of loperamide and its main metabolite N-demethylated loperamide in rats by UPLC-MS/MS.

The epidemic of loperamide abuse and misuse in the patients for the alternative to opioids has become an increasing worldwide concern and has led to considerations about the potential for drug-drug interactions between loperamide and other combined drugs, especially inhibitors of cytochrome P450 (CYP450) enzymes, such as axitinib. This study assessed the effects of axitinib on the metabolism of loperamide and its main metabolite N-demethylated loperamide in rats and in rat liver microsomes (RLM), human liver microsomes (HLM) and recombinant human CYP3A4*1. The concentrations of both compounds were determined by ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS). The exposures (AUC(0-t), AUC(0-∞) and Cmax) of loperamide and N-demethylated loperamide showed a conspicuous increase when loperamide was co-administered with axitinib. The Tmax of loperamide increased while CLz/F decreased under the influence of axitinib. In vitro, axitinib inhibited loperamide metabolism with the IC50 of 18.34 µM for RLM, 1.705 µM for HLM and 1.604 µM for CYP3A4*1, and it was confirmed as a non-competitive inhibitor in all enzymes. Taken together, the results indicated that axitinib had an obvious inhibitory impact on loperamide metabolism both in vivo and in vitro. Thus, more attention should be paid to the concurrent use of loperamide and axitinib to reduce the risk of unexpected clinical outcomes.

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.

Pharmacokinetics interaction between imatinib and genistein in rats.

The objective of this work was to investigate the effect of orally administered genistein on the pharmacokinetics of imatinib and N-desmethyl imatinib in rats. Twenty-five healthy male SD (Sprague-Dawley) rats were randomly divided into five groups: A group (control group), B group (multiple dose of 100 mg/kg genistein for consecutive 15 days), C group (multiple dose of 50 mg/kg genistein for consecutive 15 days), D group (a single dose of 100 mg/kg genistein), and E group (a single dose of 50 mg/kg genistein). A single dose of imatinib is administered orally 30 min after administration of genistein (100 mg/kg or 50 mg/kg). The pharmacokinetic parameters of imatinib and N-desmethyl imatinib were calculated by DAS 3.0 software. The multiple dose of 100 mg/kg or 50 mg/kg genistein significantly (P < 0.05) decreased the AUC0-t and C max of imatinib. AUC0-t and the C max of N-desmethyl imatinib were also increased, but without any significant difference. However, the single dose of 100 mg/kg or 50 mg/kg genistein has no effect on the pharmacokinetics of imatinib and N-desmethyl imatinib. Those results indicated that multiple dose of genistein (100 mg/kg or 50 mg/kg) induces the metabolism of imatinib, while single dose of genistein has no effect.

UPLC-MS/MS determination of voriconazole in human plasma and its application to a pharmacokinetic study.

A sensitive and rapid ultra performance liquid chromatography tandem mass spectrometry (UPLC-MS/MS) method was developed to determine voriconazole in human plasma. Sample preparation was accomplished through a simple one-step protein precipitation with methanol. Chromatographic separation was carried out on an Acquity UPLC BEH C18 column using an isocratic mobile phase system composed of acetonitrile and water containing 1% formic acid (45:55, v/v) at a flow rate of 0.50 mL/min. Mass spectrometric analysis was performed using a QTrap5500 mass spectrometer coupled with an electrospray ionization source in the positive ion mode. The multiple reaction monitoring transitions of m/z 351.0 → 281.5 and m/z 237.1 → 194.2 were used to quantify voriconazole and carbamazepine (internal standard), respectively. The linearity of this method was found to be within the concentration range of 2.0-1000 ng/mL with a lower limit of quantification of 2.0 ng/mL. Only 1.0 min was needed for an analytical run. This fully validated method was successfully applied to the pharmacokinetic study after oral administration of 200 mg voriconazole to 20 Chinese healthy male volunteers.

The effect of clopidogrel on pharmacokinetics of ivabradine and its metabolite in rats.

The present study aimed to investigate the effect of clopidogrel (CLO) on pharmacokinetics of ivabradine (IVA) and its metabolite in rats and develop a reliable method to determine IVA and its metabolite N-demethyl ivabradine in serum. Healthy male SD rats were randomized to be given 0.8 mg/kg IVA or IVA combined with 8 mg/kg CLO. Blood samples were collected at 0.083, 0.16, 0.25, 0.5, 1, 1.5, 2, 3, 4, 6, 8, 12, 24 h after administration. The serum concentrations of IVA and N-demethyl ivabradine were determined by ultra-performance liquid chromatography-mass spectrometry and pharmacokinetic parameters were calculated using DASver3.0 software. The parameters of AUC(0 - t), AUC(0 - ∞), and Cmax for IVA in the group of IVA + CLO were significantly higher than those in the group of IVA (p < 0.01); the half-time (t1/2) in the IVA + CLO group was extended compared to IVA (p < 0.01) and CL/F was dropped obviously (p < 0.01). The decreases in AUC(0 - t), AUC(0 - ∞), and Cmax for N-demethyl ivabradine in the group of IVA + CLO was significantly compared to the group of IVA (p < 0.01). CL/F was higher than IVA (p < 0.01) and the t1/2 was slightly increased. In this study, we find that CLO restrains the metabolism of IVA into N-demethyl ivabradine, which may be related to its competitive inhibition effect on cytochrome P450 isoform 3A4(CYP3A4).

Inhibitory effects of curcumin on activity of cytochrome P450 2C9 enzyme in human and 2C11 in rat liver microsomes.

Cytochrome P450 2C9 (CYP2C9), one of the most important phase I drug metabolizing enzymes, could catalyze the reactions that convert diclofenanc into diclofenac 4'-hydroxylation. Evaluation of the inhibitory effects of compounds on CYP2C9 is clinically important because inhibition of CYP2C9 could result in serious drug-drug interactions. The objective of this work was to investigate the effects of curcumin on CYP2C9 in human and cytochrome P450 2C11 (CYP2C11) in rat liver microsomes. The results showed that curcumin inhibited CYP2C9 activity (10 µmol L(-1) diclofenac) with half-maximal inhibition or a half-maximal inhibitory concentration (IC50) of 15.25 µmol L(-1) and Ki = 4.473 µmol L(-1) in human liver microsomes. Curcumin's mode of action on CYP2C9 activity was noncompetitive for the substrate diclofenanc and uncompetitive for the cofactor NADPH. In contrast to its potent inhibition of CYP2C9 in human, diclofenanc had lesser effects on CYP2C11 in rat, with an IC50 ≥100 µmol L(-1). The observations imply that curcumin has the inhibitory effects on CYP2C9 activity in human. These in vitro findings suggest that more attention should be paid to special clinical caution when intake of curcumin combined with other drugs in treatment.

UPLC-MS/MS determination of thiamphenicol in human plasma and its application to a pharmacokinetic study.

A sensitive and rapid ultra performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) method was developed to determine thiamphenicol (TAP) in human plasma using chlorzoxazone as the internal standard (IS). Sample preparation was accomplished through a liquid-liquid extraction procedure with ethyl acetate to precipitation of plasma protein, and to a 0.1 mL plasma sample. The analyte and IS were separated on an Acquity UPLC BEH C18 column (2.1 mm × 50 mm, 1.7 µm) with the mobile phase of acetonitrile and 1% formic acid in water with gradient elution at a flow rate of 0.40 mL/min. The detection was performed on a triple quadrupole tandem mass spectrometer equipped with electrospray ionization (ESI) by multiple reactions monitoring (MRM) of the transitions at m/z 354.3→185.1 for TAP and m/z 168.1→132.1 for IS. The linearity of this method was found to be within the concentration range of 10-8000 ng/mL with a lower limit of quantification of 10 ng/mL. Only 1.5 min was needed for an analytical run. The method herein described was superior to previous methods and was successfully applied to the pharmacokinetic study of TAP in healthy Chinese volunteers after oral administration.