Proton pump inhibitors, such as omeprazole (OPZ), lansoprazole and rabeprazole (RPZ), have been widely used as acid inhibitory agents for the treatment of upper gastrointestinal diseases. 1 OPZ is a substituted benzimidazole, which effectively inhibits gastric acid secretion by irreversibly binding to the proton pump (H + ,K + -ATPase) in gastric parietal cells, 2, 3 and is mainly metabolized by a genetically determined enzyme, S-mephenytoin-4¢-hydroxylase (CYP2C19), in the liver to hydroxyomeprazole (OH-OPZ). 4±8 OPZ is partially metabolized by CYP3A4 to omeprazole sulphone (OPZ-SFN), which is then metabolized to hydroxyomeprazole sulphone (OH-OPZ-SFN) by CYP2C19. 9 In individuals with a poor metabolizer (PM) phenotype or genotype of CYP2C19, the SUMMARY Background: Omeprazole is mainly metabolized in the liver by CYP2C19, a genetically determined enzyme, whereas rabeprazole is mainly reduced non-enzymatically and partially metabolized by CYP2C19. The therapeutic effects of rabeprazole are therefore assumed to be less affected by an individual's CYP2C19 status. Aim: To investigate the acid inhibitory effects and plasma levels of omeprazole and rabeprazole with reference to different CYP2C19 genotypes. Methods: Fifteen healthy volunteers took a daily dose of 20 mg of omeprazole or rabeprazole for 8 days. On postdose days 1 and 8, 24-h pro®les of intragastric pH were recorded and plasma concentrations of omeprazole, rabeprazole and their metabolites were determined.

Atorvastatin (ATV) is primarily metabolized by CYP3A in the liver to form two active hydroxy metabolites. Therefore, the sequential transport system governed by hepatic uptake and efflux transporters is important for the drug disposition and metabolism. Here, we assessed the interaction of ATV with hepatic uptake transporter organic anion transporting polypeptide (Oatp) and efflux transporter multidrug resistance associated protein 2 (MRP2/Mrp2) in vitro and ex situ using the isolated perfused rat liver (IPRL). Rifampicin (RIF) was chosen as an inhibitor for Oatp in both uptake and IPRL studies. Its inhibitory effects on MRP2 and metabolism were also tested using MRP2-overexpressing cells and rat microsomes, respectively. Our results indicate that RIF effectively inhibits the Oatp-mediated uptake of ATV and its metabolites. Inhibition on MRP2-mediated efflux of ATV was also observed at a high RIF concentration. Compared with ATV alone in the IPRL, the area under the curve(s) (AUC) of ATV was significantly increased by RIF, whereas the AUC of both metabolites were also increased in a concentration-dependent manner. However, the extent of metabolism was significantly reduced, as reflected by the reduced amounts of metabolites detected in RIF-treated livers. In conclusion, inhibition of Oatp-mediated uptake seems to be the major determinant for interaction between ATV and RIF. Metabolites of ATV were subject to Oatp-mediated uptake as well, suggesting that they undergo a similar disposition pathway as the parent drug. These data emphasize the relevance of uptake transporter as being one of the major players in hepatic drug elimination, even for substrates that undergo metabolism.Atorvastatin (ATV), a member of the class of 3-hydroxy-3-methylglutaryl-CoA reductase inhibitors, also known as statins, is one of the most potent drugs for treatment of hypercholesterolemia (Nawrocki et al., 1995). ATV undergoes extensive metabolism primarily by cytochrome P450 3A (CYP3A) in the liver to form two active metabolites, orthohydroxy atorvastatin and para-hydroxy atorvastatin (Jacobsen et al., 2000). Black et al. (1999) demonstrated that ATV undergoes a similar metabolic pathway in rats, where both parent and metabolite compounds were exclusively excreted in the bile, indicating that hepatic metabolism and biliary excretion are the major routes of elimination.Drug-drug interactions of ATV are often reported at the level of hepatic phase I or phase II enzymes (Kantola et al., 1998;Lennernas, 2003). Coadministration of ATV and an inhibitor for CYP3A or UDP-glucuronosyltransferase may increase ATV blood concentrations and the risk of rhabdomyolysis (Jacobson, 2004). However, interactions can also occur by inhibition of the relevant hepatic transporters that are located both upstream and downstream of hepatic enzymes. Our group has demonstrated previously, using digoxin and erythromycin as examples, that the ratio of intracellular drug concentrations of parent to metabolite may change when hepatic transporters (both uptake ...

A variety of water-soluble polymers, when attached to a liposome, substantially increase liposome circulation half-life in animals. However, in certain conditions, liposomes modified with the most widely used polymer, polyethylene glycol (PEG), induce an IgM response resulting in an accelerated blood clearance (ABC) of the liposome upon the second injection. Modification of liposomes with other water-soluble polymers: HPMA (poly[N-(2-hydroxypropyl) methacrylamide]), PVP (poly(vinylpyrrolidone)), PMOX (poly(2-methyl-2-oxazoline)), PDMA (poly(N,N-dimethyl acrylamide)), and PAcM (poly(N-acryloyl morpholine)), increase circulation times of liposomes; but a precise comparison of their ability to promote long circulation or induce the ABC effect has not been reported. To obtain a more nuanced understanding of the role of polymer structure/MW to promote long circulation, we synthesized a library of polymer diacyl chain lipids with low polydispersity (1.04–1.09), similar polymer molecular weights (2.1–2.5 kDa) and incorporated them into 100 nm liposomes of a narrow polydispersity (0.25–1.3) composed of polymer-lipid/hydrogenated soy phosphatidylcholine/cholesterol/diD: 5.0/54.5/40/0.5. We confirm that HPMA, PVP, PMOX, PDMA and PAcM modified liposome have increased circulation times in rodents and that PVP, PDMA, PAcM do not induce the ABC effect. We demonstrate for the first time, that HPMA does not cause an ABC effect whereas PMOX induces a pronounced ABC effect in rats. We find that a single dose of liposomes coated with PEG and PMOX generate an IgM response in rats towards the respective polymer. Finally, in this homologous polymer series, we observe a positive correlation (R = 0.84 in rats, R = 0.92 in mice) between the circulation time of polymer-modified liposomes and polymer viscosity; PEG and PMOX, the polymers that can initiate an ABC response were the two most viscous polymers. Our findings suggest that that polymers that do not cause an ABC effect such as, HPMA or PVP, deserve further consideration as polymer coatings to improve the circulation of liposomes and other nanoparticles.

The disposition of digoxin and the influence of the organic anion transporting polypeptide (Oatp)2 inhibitor rifampicin and the P-glycoprotein (P-gp) inhibitor quinidine on its hepatic disposition were examined in the isolated perfused rat liver. Livers from groups of rats were perfused in a recirculatory manner after a bolus dose of digoxin (10 g), a dual substrate for Oatp2 and P-gp as well as CYP3A. Perfusions of digoxin were also examined in groups of rats in the presence of the inhibitors: rifampicin (100 M) or quinidine (10 M). In all experiments, perfusate samples were collected for 60 min. Digoxin and its primary metabolite were determined in perfusate and liver by liquid chromatography/mass spectrometry. The area under the curve (AUC) from 0 to 60 min was determined. The AUC Ϯ S.D. of digoxin was increased from control (3880 Ϯ 210 nM⅐min) by rifampicin (5200 Ϯ 240 nM⅐min; p Ͻ 0.01) and decreased by quinidine (3220 Ϯ 340 nM⅐min; P Ͻ 0.05). It is concluded that rifampicin limits the hepatic entrance of digoxin and reduced the hepatic exposure of digoxin to CYP3A by inhibiting the basolateral Oatp2 uptake transport, whereas quinidine increased the hepatic exposure of digoxin to CYP3A by inhibiting the canalicular P-gp transport. These data emphasize the importance of uptake and efflux transporters on hepatic drug metabolism.

ABSTRACT:The effects of hepatic uptake and efflux transporters on erythromycin (ERY) disposition and metabolism were examined by comparing results from rat hepatic microsomes, freshly isolated hepatocytes, and in vivo studies. Uptake studies carried out in freshly isolated rat hepatocytes showed that ERY and its metabolite (Ndemethyl-ERY) are substrates of Oatp1a4 and Oatp1b2. Whereas rifampin and GG918 [GF120918: N-{4-[2-(1,2,3,4-tetrahydro-6,7-dimethoxy-2-isoquinolinyl)-ethyl]-phenyl}-9,10-dihydro-5-methoxy-9-oxo-4-acridine carboxamine] exerted minimal effects on metabolism in microsomes, rifampin (2.5 M) and GG918 (0.5 M) significantly decreased and increased ERY metabolism in hepatocytes, respectively. Concentration-time course studies further demonstrated that, compared with the intracellular N-demethyl-ERY control area under the curve (AUC) (0.795 ؎ 0.057 M ⅐ min), a decreased AUC (0.513 ؎ 0.028 M ⅐ min, p < 0.005) was observed when ERY was coincubated with rifampin, and an increased AUC (2.14 ؎ 0.21 M ⅐ min, p < 0.05) was found when GG918 was present. The results of the i.v. bolus studies showed that, compared with the ERY clearance of the controls (47.2 ؎ 12.5 ml/ min/kg for the rifampin group and 42.1 ؎ 5.7 for the GG918 group), a decreased blood clearance, 29.8 ؎ 6.1 ml/min/kg (p < 0.05) and 21.7 ؎ 9.0 ml/min/kg (p < 0.01), was observed when rifampin or GG918, respectively, was coadministered. When either inhibitor was codosed with ERY, volume of distribution at steady state was unchanged, but t 1/2 and mean residence time significantly increased compared with the controls. Hepatic uptake and efflux transporters modulate intracellular concentrations of ERY, thereby affecting metabolism. The interplay of transporters and enzymes must be considered in evaluating potential drug-drug interactions.

ABSTRACT:Pharmacokinetic coadministration experiments with atorvastatin (ATV) and rifampicin (RIF) in rats were performed to investigate the potential involvement of hepatic uptake transporters, Oatps (organic anion-transporting polypeptides), during hepatic drug elimination, as an in vivo extension of our recently published cellular and isolated perfused liver studies. ATV was administered orally (10 mg/kg) and intravenously (2 mg/kg) to rats in the absence and presence of a single intravenous dose of RIF (20 mg/kg), and pharmacokinetic parameters were compared between control and RIF-treatment groups. RIF markedly increased the plasma concentrations of ATV and its metabolites when ATV was administered orally. The area under the plasma concentration-time curve (AUC 0-ؕ ) for ATV also increased significantly after intravenous dosing of ATV with RIF, but the extent was much less than that observed for oral ATV dosing. Significant increases in plasma levels were observed for both metabolites as well. The 7-fold higher AUC ratio of metabolites to parent drug following oral versus intravenous ATV dosing suggests that ATV undergoes extensive gut metabolism. Both hepatic and intestinal metabolism contribute to the low oral bioavailability of ATV in rats. In the presence of RIF, the liver metabolic extraction was significantly reduced, most likely because of RIF's inhibition on Oatp-mediated uptake, which leads to reduced hepatic amounts of parent drug for subsequent metabolism. Gut extraction was also significantly reduced, but we were unable to elucidate the mechanism of this effect because intravenous RIF caused gut changes in availability. These studies reinforce our hypothesis that hepatic uptake is a major contributor to the elimination of ATV and its metabolites in vivo.Bioavailability of orally administered drugs is often limited by first-pass effects because of metabolism and transporter-mediated processes. In clinical studies, significant interactions between the cholesterol-lowering agent, atorvastatin (ATV), and cytochrome P450 3A (CYP3A) inhibitors such as itraconazole (Kantola et al., 1998) and erythromycin (Siedlik et al., 1999) were observed, with increased area under the plasma concentration-time curve (AUC) of ATV and reduction in the AUC values of its active metabolites ortho-or 2-hydroxy atorvastatin (2-OH ATV) and para-or 4-hydroxy atorvastatin (4-OH ATV). These results suggest extensive contribution of CYP3A toward ATV metabolism in vivo, even though other isoforms such as CYP2C8 have also been shown to metabolize ATV at a slower rate (Jacobsen et al., 2000). In humans, the absolute bioavailability of ATV is only 12% (Gibson et al., 1997), possibly as a result of substantial metabolism in both gut and liver by CYP3A4, the most abundant P450 enzyme expressed in both tissues. Our laboratory has noted that the two major active oxidative metabolites of ATV were formed during incubation with both human intestinal and hepatic microsomes Jacobsen et al., 2000).Various cell-based studies have suggested th...

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Objective: HIV prevention and treatment studies demonstrate that pharmacologic adherence metrics are more accurate than self-report. Currently available metrics use liquid-chromatography/tandem-mass-spectrometry (LC-MS/MS), which is expensive and laboratory-based. We developed a specific and sensitive antibody against tenofovir, the backbone of treatment and prevention, but conversion to a lateral flow assay (LFA) – analogous to a urine pregnancy test – is required for point-of-care testing. We describe the development of the first LFA to measure antiretroviral adherence in real-time. Methods: Previous work in a directly observed therapy study of providing tenofovir disoproxil fumarate (TDF) to HIV-noninfected volunteers at various simulated adherence patterns defined the appropriate cut-off for the LFA (1500 ng tenofovir/ml urine). We developed the LFA using a sample pad for urine; a conjugate pad coated with TFV-specific antibodies conjugated to colloidal gold nanoparticles; a nitrocellulose membrane striped with tenofovir-antigen (test line) and a control line; with an absorbent pad to draw urine across the reaction membrane. Results: We tested 300 urine samples collected from the directly observed therapy study by this LFA and the gold-standard method of LC-MS/MS. The LFA demonstrated 97% specificity (95% CI 93–99%) and 99% sensitivity (94–100%) compared with LC-MS/MS. The LFA accurately classified 98% of patients who took a dose within 24 h as adherent. Conclusion: We describe the development and validation of the first point-of-care assay to measure short-term adherence to HIV prevention and treatment in routine settings. The assay is low-cost, easy-to-perform and measures the breakdown product (tenofovir) of both TDF and tenofovir alafenamide (TAF). This assay has the potential to improve HIV and PrEP outcomes worldwide by triggering differentiated service delivery with further study merited.