Published papers

© 2019 Activated charcoal is known to decrease the intestinal absorption of co-administered drug by adsorption. The extent of this drug-drug interaction (DDI) is attenuated by food intake. The aim of this study was to quantitatively evaluate the effects of food type on the extent of DDI between phenobarbital and activated charcoal using a rat model. Phenobarbital was orally administered at a dose of 1.5 mg/kg with or without 33 mg/kg of activated charcoal under fasted or fed conditions, and the plasma concentration profile of phenobarbital was monitored. Several fed conditions, such as a standard breakfast, high-fat meal or enteral nutrient used in human studies, were examined. Under the fasted conditions, activated charcoal significantly decreased the area under the plasma concentration - time curve (AUC) of phenobarbital by 45.2%. When the standard breakfast or high-fat meal was fed, this DDI was reduced to 28.3 and 18.0%, respectively, as assessed by the reduction in the AUC. On the contrary, enteral nutrient did not significantly attenuate the DDI. In conclusion, the influence of food intake on the extent of DDI between phenobarbital and activated charcoal was found to differ among the types of food concomitantly ingested.

To estimate the influence of repeated administration of drug metabolism inhibitors on the extent of drug interaction, we investigated the ejects of single intravenous or repeated oral administration of itraconazole on the pharmacokinetics of midazolam in rats. In the single administration study, the plasma concentration of itraconazole was maintained by intravenous infusion, and midazolam was administered into the portal vein to investigate its kinetics. In the repeated administration study, the kinetics of midazolam was investigated after seven-day oral treatment with itraconazole. The in vitro metabolism of midazolam and the contents of cytochrome P450 were investigated using liver microsomes from the itraconazole-treated rats. © 2002, The Japanese Society for the Study of Xenobiotics. All rights reserved.

Purpose. The aim of this study is to investigate the effects of 50% ethyl acetate extracts of grapefruit juice (GFJ) and orange juice (OJ) on the transport activity of P-glycoprotein (P-gp) in the rat small intestine. Methods. The efflux of P-gp substrates from rat everted sac in the absence or presence of verapamil, GFJ, OJ or erythromycin was measured. Rhodamine123, fexofenadine and saquinavir were used as P-gp substrates. P-gp expression levels in the rat jejunum and ileum were determined by Western blot analysis. Results. The efflux of rhodamine123 from the everted sac increased from the apex of the jejunum to the low ileum and the expression of P-gp in the ileum was 2.31-fold higher than that in the jejunum. Verapamil and the 50% GFJ and OJ extracts inhibited the efflux from the intestine of all three drugs tested. Erythromycin decreased the efflux of rhodamine123 and fexofenadine, but did not affect the efflux of saquinavir in the intestine. Conclusions. GFJ and OJ extracts inhibited the efflux of P-gp substrates from the small intestine. Therefore, they may enhance the oral bioavailability of P-gp substrates by increasing absorption in the small intestine.

Domperidone (DOM), a peripheral dopamine D2 receptor antagonist, is a substrate of P-glycoprotein (P-gp). Therefore, the transport of DOM into the brain may be restricted by P-gp function at the blood-brain barrier, and when the function of P-gp is impaired by ATP depletion under conditions of brain ischaemia (e.g. cerebral thrombosis), side-effects may be induced as a result of increased distribution of DOM into the brain. In this study, we investigated the effects of brain ischaemia and verapamil, a P-gp inhibitor, on the permeability coefficient-surface area product (PS values) of DOM across the blood-brain barrier by using an in-situ rat brain perfusion technique. The PS values of DOM were increased 3.4- and 3.6-fold after brain ischaemia for 10 and 20 min, respectively. Furthermore, co-administration of verapamil significantly increased the PS values of DOM by 42.6- and 43.3-fold in the normal and ischaemia groups, respectively. Brain vascular volume was not affected by ischaemia or verapamil. These results show that the transport of DOM into the brain is restricted by P-gp and that the brain distribution of DOM can be increased by cerebral ischaemia or co-administration of a P-gp inhibitor.

© 2018 American Pharmacists Association® Fluoropyrimidines, including 5-fluororacil (5-FU), cause gastrointestinal damage in the clinical setting and might affect the gastrointestinal absorption of concomitantly administered drugs. We aimed to evaluate the effects of fluoropyrimidine-induced gastrointestinal damage on the pharmacokinetics and pharmacodynamics of dabigatran etexilate (DABE), an anticoagulant, in rats with gastrointestinal damage induced by the repeated oral administration of 5-FU. Rats were administered DABE orally or dabigatran (DAB), an active moiety of DABE, intravenously. The plasma DAB concentration was determined using liquid chromatography-tandem mass spectrometry. The activated partial thromboplastin time (APTT) was measured before and 30 min after the administration of each drug, and the APTT ratio was calculated. In 5-FU-treated rats, the maximum plasma concentration, the area under the concentration-time curve of DAB after the oral administration of DABE, and the oral bioavailability of DABE were significantly decreased to 18.3%, 22.9%, and 16.3% of the respective control values. The 5-FU-treated rats’ APTT ratio was also significantly lower than the control value. Fluoropyrimidine-induced gastrointestinal damage might reduce the plasma concentration of DAB by impairing DABE absorption and might attenuate the anticoagulant effects of DABE in the clinical setting.

5-Fluorouracil (5-FU), an anticancer drug, causes severe gastrointestinal damage, which may affect the absorption of orally administered drugs including the substrates of intestinal uptake and efflux transporters. This study aimed to investigate quantitatively the effect of 5-FU-induced intestinal damage on the expression of intestinal transporters: P-glycoprotein (P-gp), breast cancer resistance protein (BCRP) and peptide transporter 1 (PEPT1) in rats. The rats were treated with 5-FU (30 mg/kg/day, p.o.) for 5 days to induce intestinal damage, and then the upper, middle and lower intestinal segments were removed. The mRNA and protein expression levels of these transporters in each segment were determined using quantitative real-time PCR and Western blotting, respectively. In the 5-FU-treated rats, the protein levels of P-gp and Bcrp in the upper segment were significantly increased to 15- and 2.6-fold of the control, respectively, while those in other segments were unaffected. Pept1 expression was increased by 5-FU in almost all segments. A remarkable increase in P-gp expression was shown, the uptake of digoxin, a P-gp substrate, in each intestinal segment was measured using a rat everted sac. As a result, the uptake of digoxin in the upper segments of 5-FU-treated rats was decreased compared with that of the control. In conclusion, 5-FU-induced intestinal damage was shown to alter the expression of these transporters, especially in the upper intestinal segment, while the characteristics of the influence varied among the transporters. The 5-FU-induced intestinal damage may affect transporter-mediated drug absorption of orally administered drugs in the clinical setting.

© Organic anion-transporting polypeptides (OATPs) 1A2 and OATP2B1 are expressed in the small intestine and are involved in drug absorption. We identified narirutin, which is present in grapefruit juice, as a novel OATP inhibitor. The citrus fruit jabara also contains high levels of narirutin; therefore, we investigated the inhibitory potency of jabara juice against OATPs. The inhibitory effects of various related compounds on the transport activity of OATPs were evaluated using OATP-expressing HEK293 cells. The IC50 values of narirutin for OATP1A2- and OATP2B1-mediated transport were 22.6 and 18.2 μM, respectively. Other flavanone derivatives from grapefruit juice also inhibited OATP1A2/OATP2B1-mediated transport (order of inhibitory potency: naringenin > narirutin > naringin). Five percent jabara juice significantly inhibited OATP1A2- and OATP2B1-mediated transport by 67 ± 11 and 81 ± 5.5%, respectively (p < 0.05). Based on their inhibitory potency and levels in grapefruit juice, the inhibition of OATPs by grapefruit juice is attributable to both naringin and narirutin. Citrus × jabara, which contains narirutin, potently inhibits OATP-mediated transport.

The placental trophoblast is considered to act as a barrier between mother and fetus, mediating the exchange of various materials across the placenta. ATP-binding cassette (ABC) transporters such as P-glycoprotein (P-gp) and multidrug-resistance protein (MRP) are expressed in the placenta and function as efflux transport systems for xenobiotics. In the present study, we aimed to determine the localization of MRP1 in the human placenta in comparison with that of P-gp. Western blotting analysis with human placental membrane vesicles indicated that P-gp and MRP1 are localized on the brush-border membranes and basal membranes, respectively. Immunohistochemical analysis with human normal full-term placenta showed that anti-P-gp monoclonal antibody F4 stained the brush-border side of the trophoblast cells, whereas anti-MRP1 monoclonal antibody MRPr1 stained the basal side. These results confirm that P-gp and MRP1 are located on the brush-border membranes and basal membranes, respectively, of human full-term placental trophoblast. MRP1 was also detected on the abluminal side of blood vessels in the villi. Accordingly, MRP1 may play a role distinct from that of P-gp, which is considered to restrict the influx of xenobiotics into the fetus. © 2003 Elsevier Ltd. All rights reserved.

Some grapefruit juice (GFJ) ingredients and resveratrol, a fruit-derived phytoalexin, are known to inhibit cytochrome P450 (CYP) 2C9. However, their inhibition modes and detailed inhibition kinetics remain undetermined. This study aimed to investigate the inhibitory effects of two GFJ ingredients, bergamottin (BG) and dihydroxybergamottin (DHB), and resveratrol on CYP2C9 activity in vitro. DHB inhibited CYP2C9 activity, as assessed by warfarin 7-hydroxylation, in a preincubation time-dependent manner (i.e., mechanism-based inhibition; MBI), in the same manner as CYP2C19 and CYP3A4. The maximal inactivation rate (kinact,max) was 0.0638 min−1 and 0.12- and 0.26-fold of that for CYP2C19 and CYP3A4, respectively. BG showed both MBI and time-independent competitive inhibition. Resveratrol showed non-competitive inhibition with an inhibition constant (Ki) of 3.64 μM. Unlike the inhibition of CYP2C19 and CYP3A4, resveratrol did not induce MBI. These findings are important for estimating the risk of drug interactions between CYP2C9 substrates and some beverages. (146 words)

Purpose: We reported the first case of phenytoin intoxication due to the concomitant use of phenytoin and TS-1, together with a review of the literature regarding the occurrence of phenytoin intoxication due to the concomitant use of phenytoin and fluoropyrimidine antitumor drugs such as fluorouracil (5-FU) and tegafur (FT). Methods: We showed the clinical course of our patient. Reports of phenytoin intoxication due to the concomitant use of phenytoin and fluoropyrimidine antitumor drugs in the English and Japanese language literature up to 2007 were identified by searching Medline and ICHUSHI Web (Japana Centra Revuo Medicina). Results: A patient taking phenytoin and TS-1, a combination preparation of tegafur, gimeracil, and oteracil potassium, experienced lightheadedness and repeated falls associated with an increase in serum phenytoin concentration (32.8 μg/ml) at 1 month after the start of TS-1 treatment. The time lag between initiation of combined treatment and onset of adverse symptoms suggests the presence of an indirect mechanism, rather than direct inhibition of drug-metabolizing enzymes by drugs in TS-1 or their active metabolites. Conclusions: Plasma phenytoin concentration should be closely monitored in patients receiving TS-1 and phenytoin concomitantly. © 2007 Springer-Verlag.

In a previous study, it was shown that the novel canine single nucleotide polymorphism (SNP) CYP1A2 1117C>T yields an inactive enzyme. In this study, the effect that this SNP has on the pharmacokinetics of 4-cyclohexyl-1-ethyl-7- methylpyrido[2,3-d]pyrimidine-2-(1H)-one (YM-64227) was investigated. Plasma concentrations of the unchanged drug and five of its metabolites (MM-1 to MM-5) were determined after either intravenous or oral administration of YM-64227 to genotyped dogs (C/C, C/T, and T/T groups). Liver microsomes were prepared from these dogs to determine the in vitro metabolic clearance of YM-64227. After a single oral administration, the maximum plasma concentration and absolute bioavailability of YM-64227 in the T/T group were 17.1 times and 27.2 times higher than those in the C/C group, respectively, whereas the pharmacokinetics of YM-64227 after intravenous administration were not affected by genotype. The metabolic profiles in the T/T group were quite distinct from the others; i.e., the main metabolite was MM-2 in the C/C group, whereas MM-1 and MM-5 were the main metabolites in the T/T group. The formation clearances of MM-2 and MM-3 in the microsomes derived from T/T type dogs were significantly lower, whereas those of MM-1, MM-4, and MM-5 were not affected. A statistically significant correlation was observed between the in vivo and in vitro metabolic intrinsic clearances (r = 0.82, p < 0.001). The canine CYP1A2 1117C>T SNP proved to be responsible for a substantial portion of the interindividual variability in the pharmacokinetics of YM-64227. Copyright © 2006 by The American Society for Pharmacology and Experimental Therapeutics.

Pralmorelin hydrochloride (pralmorelin), consisting of six amino acid residues, is a growth hormone-releasing peptide. The aim of this study is to analyze the pharmacokinetics of pralmorelin after intravenous bolus administration to rats, and to develop a physiologically based pharmacokinetic (PB-PK) model to describe and predict the concentrations of pralmorelin in blood and tissues. Pralmorelin (3 mg/kg) was administered intravenously to 24 Sprague-Dawley rats. Groups of three rats were sacrificed by decapitation at each designated time point (up to 4 h), and plasma and tissues (brain, lung, heart, liver, kidney, small intestine, muscle, adipose, and skin) were collected. Bile was also pooled until decapitation. The concentration of pralmorelin in samples was determined by liquid chromatography-tandem mass spectrometry. Plasma concentrations of pralmorelin declined rapidly in a biexponential manner. Biliary excretion of pralmorelin was so rapid that 80% of the dose was recovered unchanged in the bile within 1 h after administration. The distribution parameters in each tissue were obtained by using a hybrid model and an integration plot. They revealed that the distribution of pralmorelin into liver was blood flow-limited, and its distribution was permeability-limited in all other tissues. The PB-PK model developed in this study well described the time courses of pralmorelin concentration in the blood and tissues of rats. Copyright © 2005 by The American Society for Pharmacology and Experimental Therapeutics.

Objective: Itraconazole is a potent inhibitor of cytochrome P450 (CYP) 3A with an elimination half-life of more than 30 hours. Therefore, itraconazole may cause persistent CYP3A inhibition. Triazolam is primarily metabolized by CYP3A and its plasma concentration is increased remarkably by itraconazole. Although separating their dosages by 24 hours has been shown to reduce the interaction, an appropriate dosage interval remains to be determined. The aim of this study was to identify an appropriate dosage schedule to avoid their interaction. Materials and methods: We developed a pharmacokinetic model based on the assumption that both itraconazole and hydroxyitraconazole competitively and reversibly inhibit the first-pass metabolism and systemic elimination of triazolam. The developed model was simultaneously fitted to the plasma concentration profiles of triazolam, taken fromthe literature, by using the plasma concentration-time profiles of itraconazole and hydroxyitraconazole as input functions to estimate their in vivo Ki values. Subsequently, we simulated the plasma concentration profiles of triazolam administered after itraconazole therapy with various dosing intervals. Results: The model could explain and simulate the interaction between itraconazole-triazolam using a variety of dosage intervals between the administrations. Conclusions: The developed model may provide useful information with regard to the appropriate interval for triazolam administration during itraconazole therapy. ©2010 Dustri-Verlag Dr. K. Feistle.

CYP2D6の代謝活性に対するテルビナフィン(TER)の阻害に関して、時間依存性の有無を明らかにするとともに、その阻害特性に対するCYP2D6遺伝子変異の影響を解析した。TERの競合阻害実験において、全てのCYP2D6変異型分子の代謝活性は、TERの濃度依存的に低下した。一方、CYP2D6の各変異型分子に対するTERの時間依存的な酵素活性阻害作用は認められなかった。CYP2D6に対するTERの阻害メカニズムは、競合阻害作用のみが関与していることが示唆された。TERが示す長時間持続阻害作用は、時間依存性ではなく、TER自身の消失の遅さに起因すると考えられた。また、TERによる阻害に対するCYP2D6の感受性は各変異型分子間で大きく異なっていたことから、TERによるCYP2D6の阻害を介した薬物相互作用を考慮する際には、CYP2D6の遺伝子型を考慮する必要があると考えられた。

Aim: To evaluate quantitatively the influence of bioavailability and plasma unbound fraction (fu) on the extent of interaction between grapefruit juice (GFJ) and calcium antagonists. Methods: The extent of drug-GFJ interaction was evaluated from reported clinical interaction studies of 11 calcium antagonists. The relationship between extent of interaction and bioavailability or fu was analysed. Results: The following significant hyperbolic relationships were observed: [Extent] = 12.2/[bioavailability] + 1 and [Extent] = 0.718/[fu ] + 1. Conclusions: Bioavailability and fu are major determinant factors of calcium antagonist-GFJ interaction: a drug with smaller bioavailability or lower fu is likely to exhibit a more potent interaction, and vice versa. © 2006 Blackwell Publishing Ltd.