Search

Tolvaptan is a selective vasopressin V2 receptor antagonist, approved in several countries for the treatment of hyponatremia and autosomal dominant polycystic kidney disease (ADPKD). No liver injury has been observed with tolvaptan treatment in healthy subjects and in non-ADPKD indications, but ADPKD clinical trials showed evidence of drug-induced liver injury (DILI). Although all DILI events resolved, additional monitoring in tolvaptan-treated ADPKD patients is required. In vitro assays identified alterations in bile acid disposition and inhibition of mitochondrial respiration as potential mechanisms underlying tolvaptan hepatotoxicity. This report details the application of DILIsym software to determine whether these mechanisms could account for the liver safety profile of tolvaptan observed in ADPKD clinical trials. DILIsym simulations included physiologically based pharmacokinetic estimates of hepatic exposure for tolvaptan and2 metabolites, and their effects on hepatocyte bile acid transporters and mitochondrial respiration. The frequency of predicted alanine aminotransferase (ALT) elevations, following simulated 90/30 mg split daily dosing, was 7.9% compared with clinical observations of 4.4% in ADPKD trials. Toxicity was multifactorial as inhibition of bile acid transporters and mitochondrial respiration contributed to the simulated DILI. Furthermore, simulation analysis identified both pre-treatment risk factors and on-treatment biomarkers predictive of simulated DILI. The simulations demonstrated that in vivo hepatic exposure to tolvaptan and the DM-4103 metabolite, combined with these 2 mechanisms of toxicity, were sufficient to account for the initiation of tolvaptan-mediated DILI. Identification of putative risk-factors and potential novel biomarkers provided insight for the development of mechanism-based tolvaptan risk-mitigation strategies.

Host-gut microbial interactions contribute to human health and disease states and an important manifestation resulting from this co-metabolism is a vast diversity of bile acids (BAs). There is increasing interest in using BAs as biomarkers to assess the health status of individuals, and therefore, an increased need for their accurate separation and identification. In this study, the negative ion fragmentation behaviors of C24 BAs were investigated by UPLC-ESI-QTOF-MS. The step-by-step fragmentation analysis revealed a distinct fragmentation mechanism for the unconjugated BAs containing a 12-hydroxyl group. The unconjugated BAs lacking 12-hydroxylation fragmented via dehydration and dehydrogenation. In contrast, the 12-hydroxylated ones, such as deoxycholic acid (DCA) and cholic acid (CA), employed dissociation routes including dehydration, loss of carbon monoxide or carbon dioxide, and dehydrogenation. All fragmentations of the 12-hydroxylated unconjugated BAs, characterized by means of stable isotope labeled standards, were associated with the rotation of the carboxylate side-chain and the subsequent rearrangements accompanied with proton transfer between 12-hydroxyl and 24-carboxyl groups. Compared to DCA, CA underwent further cleavages of the steroid skeleton. Accordingly, the effects of stereochemistry on the fragmentation pattern of CA were investigated using its stereoisomers. Based on the knowledge gained from the fragmentation analysis, a novel BA, 3β, 7β, 12α-trihydroxy-5β-cholanic acid, was identified in the postprandial urine samples of patients with nonalcoholic steatohepatitis. The analyses used in this study may contribute to a better understanding of the chemical diversity of BAs and the molecular basis of human liver diseases that involve BA synthesis, transport, and metabolism.

Background Candida is a leading cause of infection in infants on extracorporeal membrane oxygenation (ECMO). Optimal micafungin dosing is unknown in this population because ECMO can alter drug pharmacokinetics (PK). Methods To characterize micafungin pharmacokinetics and safety in infants on ECMO, we conducted an open-label pharmacokinetics trial. Infants on ECMO either received intravenous micafungin 4 mg/kg every 24 h for invasive candidiasis prophylaxis or 8 mg/kg every 24 h when a fungal infection was suspected or confirmed. We collected plasma samples after single and multiple micafungin doses. We defined the therapeutic target as the adult exposure associated with efficacy in phase III trials and the prophylactic target as one-half of the therapeutic target. Results We enrolled 12 infants (124 samples) with a median age of 59 days. Using a 1-compartment model, median weight-normalized volume of distribution and clearance were 0.64 L/kg and 0.041 L/kg/h, respectively. Dose-exposure simulations revealed that doses of 2.5 and 5 mg/kg every 24 h matched exposure targets for prophylaxis and treatment of invasive candidiasis, respectively. We did not observe any drug-related adverse events. Conclusions In infants on ECMO, micafungin volume of distribution was higher and clearance was in the upper range of previously published values for infants not on ECMO. Based on these data, we recommend dosing of 2.5 and 5 mg/kg every 24 h for prophylaxis and treatment of invasive candidiasis, respectively, to match adult exposure proven effective against Candida spp.

With the advent of the direct-acting antiviral agents, significant drug-drug interaction (DDI) potential now exists for patients treated for chronic hepatitis C virus (HCV) infection. However, little is known about how often patients with HCV infection use medications that may interact with newer HCV treatments, especially those with cytochrome P450 3A (CYP3A) DDI potential.Using a large US commercial insurance database, medication use and comorbidity burden were examined among adult patients with a chronic HCV diagnosis from 2006 to 2010. Medications were examined in terms of total number of prescription claims, proportion of patients exposed, and DDI potential with the prototypical CYP3A direct-acting antiviral agents boceprevir and telaprevir, for which data were available.Patient comorbidity burden was high and increased over the study period. Medication use was investigated in 53 461 patients with chronic HCV. Twenty-one (53%) of the top 40 most utilized medications were classified as having interaction potential, with 62% of patients receiving at least one of the top 22 interacting medications by exposure. Of these, 59 and 41% were listed in a common DDI resource but not in medication-prescribing information, 77 and 77% had not been investigated in DDI studies, 41 and 36% did not have clear recommendations for DDI management, and only 14 and 23% carried a recommendation to avoid coadministration for boceprevir and telaprevir, respectively.Practitioners may expect a medication with CYP3A DDI potential in two-thirds of patients with HCV and may expect almost one-half of the most frequently used medications to have CYP3A DDI potential. However, DDI potential may not be reflected in prescribing information.

Azithromycin (AZI), a broad-spectrum antibiotic, accumulates in polymorphonuclear cells and peripheral blood mononuclear cells. The distribution of AZI in proinflammatory cells may be important to the anti-inflammatory properties. Previous studies have described plasma AZI pharmacokinetics. The objective of this study was to describe the pharmacokinetics of AZI in whole blood (concentration in whole blood [ C b ]) and plasma (concentration in plasma [ C p ]) of healthy subjects. In this study, 12 subjects received AZI (500 mg once a day for 3 days). AZI C b and C p were quantified in serial samples collected up to 3 weeks after the last dose and analyzed using noncompartmental and compartmental methods. After the last dose, C b was greater than C p . Importantly, C b , but not C p , was quantifiable in all but one subject at 3 weeks. The blood area under the curve during a 24-h dosing interval (AUC 24 ) was ∼2-fold greater than the plasma AUC 24 , but simulations suggested that C b was not at steady state by day 3. Upon exploration of numerous models, an empirical 3-compartment model adequately described C p and C b , but C p was somewhat underestimated. Intercompartmental clearance (CL; likely representing cells) was lower than apparent oral CL (18 versus 118 liters/h). Plasma, peripheral, and cell compartmental volumes were 439 liters, 2,980 liters, and 3,084 liters, respectively. Interindividual variability in CL was low (26.2%), while the volume of distribution variability was high (107%). This is the first report to describe AZI C b in healthy subjects, the distribution parameters between C p and C b , and AZI retention in blood for up to 3 weeks following 3 daily doses. The model can be used to predict C b from C p for AZI under various dosing regimens. (This study has been registered at ClinicalTrials.gov under registration no. NCT01026064.)

Inhibition of bile acid (BA) transport may contribute to the hepatotoxicity of troglitazone (TRO), a peroxisome proliferator-activated receptor gamma agonist. Typically, studies use taurocholic acid (TCA) as a model substrate to investigate effects of xenobiotics on BA disposition. However, TRO may differentially affect the transport of individual BAs, potentially causing hepatocyte accumulation of more cytotoxic BAs. The effects of TRO on the disposition of [(14)C]-labeled chenodeoxycholic acid ([(14)C]CDCA), an unconjugated cytotoxic BA, were determined in suspended hepatocytes and sandwich-cultured hepatocytes (SCH) from rats. (E)-3-[[[3-[2-(7-chloro-2-quinolinyl)ethenyl]phenyl][[3-(dimethylamino)-3-oxopropyl]thio]methyl]thio]-propanoic acid (MK571), a multidrug resistance-associated protein (MRP) inhibitor, was included to evaluate involvement of MRPs in CDCA disposition. Accumulation in cells + bile of total [(14)C]CDCA species in SCH was sixfold greater than [(3)H]TCA and unaffected by 1 and 10μM TRO; 100μM TRO and 50μM MK571 ablated biliary excretion and significantly increased intracellular accumulation of total [(14)C]CDCA species. Results were similar in Mrp2-deficient TR(-) rat hepatocytes. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis revealed that taurine- and glycine-conjugated CDCA, in addition to unconjugated CDCA, accumulated in hepatocytes during the 10-min incubation. In suspended rat hepatocytes, initial [(14)C]CDCA uptake was primarily Na(+)-independent, whereas initial [(3)H]TCA uptake was primarily Na(+)-dependent; TRO and MK571 decreased [(14)C]CDCA uptake to a lesser extent than [(3)H]TCA. Unexpectedly, MK571 inhibited Na(+)-taurocholate cotransporting polypeptide and bile salt export pump. Differential effects on uptake and efflux of individual BAs may contribute to TRO hepatotoxicity. Although TCA is the prototypic BA used to investigate the effects of xenobiotics on BA transport, it may not be reflective of other BAs.

This study characterized 99mTc-Mebrofenin (MEB) and 99mTc-Sestamibi (MIBI) hepatic transport and preferential efflux routes (canalicular vs. basolateral) in rat and human sandwich-cultured hepatocytes (SCH).99mTc-MEB and 99mTc-MIBI disposition was determined in suspended hepatocytes and in SCH in the presence and absence of inhibitors and genetic knockdown of breast cancer resistance protein (Bcrp).The general organic anion transporting polypeptide (Oatp/OATP) inhibitor rifamycin SV reduced initial 99mTc-MEB uptake in rat and human suspended hepatocytes. Initial 99mTc-MIBI uptake in suspended rat hepatocytes was not Na+-dependent or influenced by inhibitors. Multidrug resistance-associated protein (Mrp2/MRP2) inhibitors decreased 99mTc-MEB canalicular efflux in rat and human SCH. 99mTc-MEB efflux in human SCH was predominantly canalicular (45.8 +/- 8.6%) and approximately 3-fold greater than in rat SCH. 99mTc-MIBI canalicular efflux was similar in human and rat SCH; basolateral efflux was 37% greater in human than rat SCH. 99mTc-MIBI cellular accumulation, biliary excretion index and in vitro biliary clearance in rat SCH were unaffected by Bcrp knockdown.99mTc-MEB hepatic uptake is predominantly Oatp-mediated with biliary excretion by Mrp2. 99mTc-MIBI appears to passively diffuse into hepatocytes; biliary excretion is mediated by P-gp. The SCH model is useful to investigate factors that may alter the route and/or extent of hepatic basolateral and canalicular efflux of substrates.

Trabectedin is a promising anticancer agent, but dose-limiting hepatotoxicity was observed during phase I/II clinical trials. Dexamethasone (DEX) has been shown to significantly reduce trabectedin-mediated hepatotoxicity. The current study was designed to assess the capability of sandwich-cultured primary rat hepatocytes (SCRH) to predict the hepato-protective effect of DEX against trabectedin-mediated cytotoxicity. The role of multidrug resistance-associated protein 2 (Mrp2; Abcc2) in trabectedin hepatic disposition also was examined. In SCRH from wild-type Wistar rats, cytotoxicity was observed after 24-h continuous exposure to trabectedin. SCRH pretreated with additional DEX (1 microM) exhibited a 2- to 3-fold decrease in toxicity at 100 nM and 1000 nM trabectedin. Unexpectedly, toxicity in SCRH from Mrp2-deficient (TR(-)) compared to wild-type Wistar rats was markedly reduced. Depletion of glutathione from SCRH using buthionine sulfoximine (BSO) mitigated trabectedin toxicity associated with 100 nM and 1000 nM trabectedin. Western blot analysis demonstrated increased levels of CYP3A1/2 and Mrp2 in SCRH pretreated with DEX; interestingly, Mrp4 expression was increased in SCRH after BSO exposure. Trabectedin biliary recovery in isolated perfused livers from TR(-) rats was decreased by approximately 75% compared to wild-type livers. In conclusion, SCRH represent a useful in vitro model to predict the hepatotoxicity of trabectedin observed in vivo. The protection by DEX against trabectedin-mediated cytotoxicity may be attributed, in part, to enhanced Mrp2 biliary excretion and increased metabolism by CYP3A1/2. Decreased trabectedin toxicity in SCRH from TR(-) rats, and in SCRH pretreated with BSO, may be due to increased basolateral excretion of trabectedin by Mrp3 and/or Mrp4.