Population Pharmacokinetics of Metoclopramide in Infants, Children, and Adolescents.

Metoclopramide is commonly used for gastroesophageal reflux. The aims of the present study were to develop a pediatric population pharmacokinetic (PopPK) model, which was applied to simulate the metoclopramide exposure following dosing used in clinical practice. Opportunistic pharmacokinetic data were collected from pediatric patients receiving enteral or parenteral metoclopramide per standard of care and these data were simultaneously fitted using NONMEM. Allometric scaling with body weight was included a priori in the model. Using the final model, the steady-state maximum concentrations (Css,max ) and the area under the metoclopramide plasma concentration-time curve at steady state from 0 to 6 hours (AUCss,0-6h ) were simulated following 0.1 or 0.15 mg/kg orally every 6 hours in virtual patients, and compared with previously reported ranges associated with toxicity or the efficacy for gastroesophageal reflux in infants. A two-compartment model with first-order absorption best characterized 87 concentration measurements from 50 patients (median [range] postnatal age of 8.89 years [0.01-19.13]). There were 20 infants (≤ 2 years), 9 children (2 years to age ≤ 12 years), and 21 adolescents (> 12 years). Body weight was the only covariate included in the final model. For > 75% of virtual patients, simulated Css,max and AUCss,0-6h estimates were within the range associated with efficacy for gastroesophageal reflux in infants; however, slightly lower exposures were predicted in virtual patients < 2 years. Our study suggests that a metoclopramide enteral dose of 0.1 mg/kg every 6 hours, which was previously recommended for pediatric patients, results in simulated exposure generally within suggested ranges for the treatment of gastroesophageal reflux.

Population pharmacokinetics of sildenafil in extremely premature infants.

AIMS: To characterize the population pharmacokinetics (PK) of sildenafil and its active metabolite, N-desmethyl sildenafil (DMS), in premature infants. METHODS: We performed a multicentre, open-label trial to characterize the PK of sildenafil in infants ≤28 weeks gestation and < 365 postnatal days (cohort 1) or < 32 weeks gestation and 3-42 postnatal days (cohort 2). In cohort 1, we obtained PK samples from infants receiving sildenafil as ordered per the local standard of care (intravenous [IV] or enteral). In cohort 2, we administered a single IV dose of sildenafil and performed PK sampling. We performed a population PK analysis and dose-exposure simulations using the software NONMEM®. RESULTS: We enrolled 34 infants (cohort 1 n = 25; cohort 2 n = 9) and collected 109 plasma PK samples. Sildenafil was given enterally (0.42-2.09 mg/kg) in 24 infants in cohort 1 and via IV (0.125 or 0.25 mg/kg) in all infants in cohort 2. A 2-compartment PK model for sildenafil and 1-compartment model for DMS, with presystemic conversion of sildenafil to DMS, characterized the data well. Coadministration of fluconazole (n = 4), a CYP3A inhibitor, resulted in an estimated 59% decrease in sildenafil clearance. IV doses of 0.125, 0.5 and 1 mg/kg every 8 hours (in the absence of fluconazole) resulted in steady-state maximum sildenafil concentrations that were generally within the range of those reported to inhibit phosphodiesterase type 5 activity in vitro. CONCLUSIONS: We successfully characterized the PK of sildenafil and DMS in premature infants and applied the model to inform dosing for a follow-up, phase II study.

External Evaluation of a Gentamicin Infant Population Pharmacokinetic Model Using Data from a National Electronic Health Record Database.

Gentamicin is a common antibiotic used in neonates and infants. A recently published population pharmacokinetic (PK) model was developed using data from multiple studies, and the objective of our analyses was to evaluate the feasibility of using a national electronic health record (EHR) database for further external evaluation of this model. Our results suggest that, with proper data capture procedures, EHR data can serve as a potential data source for external evaluation of PK models.

Glucuronidation: driving factors and their impact on glucuronide disposition.

Glucuronidation is a well-recognized phase II metabolic pathway for a variety of chemicals including drugs and endogenous substances. Although it is usually the secondary metabolic pathway for a compound preceded by phase I hydroxylation, glucuronidation alone could serve as the dominant metabolic pathway for many compounds, including some with high aqueous solubility. Glucuronidation involves the metabolism of parent compound by UDP-glucuronosyltransferases (UGTs) into hydrophilic and negatively charged glucuronides that cannot exit the cell without the aid of efflux transporters. Therefore, elimination of parent compound via glucuronidation in a metabolic active cell is controlled by two driving forces: the formation of glucuronides by UGT enzymes and the (polarized) excretion of these glucuronides by efflux transporters located on the cell surfaces in various drug disposition organs. Contrary to the common assumption that the glucuronides reaching the systemic circulation were destined for urinary excretion, recent evidences suggest that hepatocytes are capable of highly efficient biliary clearance of the gut-generated glucuronides. Furthermore, the biliary- and enteric-eliminated glucuronides participate into recycling schemes involving intestinal microbes, which often prolong their local and systemic exposure, albeit at low systemic concentrations. Taken together, these recent research advances indicate that although UGT determines the rate and extent of glucuronide generation, the efflux and uptake transporters determine the distribution of these glucuronides into blood and then to various organs for elimination. Recycling schemes impact the apparent plasma half-life of parent compounds and their glucuronides that reach intestinal lumen, in addition to prolonging their gut and colon exposure.

Transport-Glucuronidation Classification System and PBPK Modeling: New Approach To Predict the Impact of Transporters on Disposition of Glucuronides.

Glucuronide metabolites require the action of efflux transporters to exit cells due to their hydrophilic properties. In this study, we proposed a transport-glucuronidation classification system and developed a PBPK model to predict the impact of BCRP on systemic exposure of glucuronides. The clearance by UGTs in S9 fractions and the efflux clearance of glucuronides by BCRP in human UGT1A9-overexpressing HeLa cells were incorporated in the classification system and PBPK model. Based on simulations for glucuronide AUC for theoretical compounds in the classification system, it was indicated that BCRP was more important for compounds with greater efflux clearance of their glucuronides by BCRP regardless of differences in clearance by UGTs. Pharmacokinetic studies were performed in WT and Bcrp1 (-/-) mice for 8 compounds to verify our predictions. Among eight compounds, the glucuronide AUC of daidzein and genistein increased significantly in Bcrp1 (-/-) mice, while only slight increases in systemic exposure were observed for other glucuronides. The results from pharmacokinetic studies were in agreement with the predictions except for resveratrol, which was effluxed predominantly by transporters other than BCRP. Therefore, for glucuronides that were predominantly mediated by BCRP, this study provided a useful approach in predicting the impact of BCRP on its disposition and the potential DDIs involving BCRP.

Disposition of flavonoids via recycling: Direct biliary excretion of enterically or extrahepatically derived flavonoid glucuronides.

SCOPE: Enterohepatic recycling is often thought to involve mostly phase II metabolites generated in the liver. This study aims to determine if direct biliary excretion of extrahepatically generated glucuronides would also enable recycling. METHODS AND RESULTS: Conventional and modified intestinal perfusion models along with intestinal and liver microsomes were used to determine the contribution of extrahepatically derived glucuronides. Glucuronidation of four flavonoids (genistein, biochanin A, apigenin, and chrysin at 2.5-20 µM) were generally more rapid in the hepatic than intestinal microsomes. Furthermore, when aglycones (at 10 µM each) were perfused, larger (1.7-9 fold) amounts of glucuronides were found in the bile than in the luminal perfusate. However, higher concentrations of glucuronides were not found in jugular vein than portal vein, and apigenin glucuronide actually displayed a significantly lower concentration in jugular vein (<1 nM) than portal vein (≈4 nM). A direct portal infusion of four flavonoid glucuronides (5.9-10.4 µM perfused at 2 mL/h) showed that the vast majority (>65%) of the glucuronides (except for biochanin A glucuronide) administered were efficiently excreted into the bile. CONCLUSION: Direct biliary excretion of extrahepatically generated flavonoid glucuronides is a highly efficient clearance mechanism, which should enable enterohepatic recycling of flavonoids without hepatic conjugating enzymes.

Establishment and use of new MDCK II cells overexpressing both UGT1A1 and MRP2 to characterize flavonoid metabolism via the glucuronidation pathway.

SCOPE: The purpose of this study is to characterize how overexpression of an efflux transporter and an UDP-glucuronosyltransferase (UGT) affects the cellular kinetics of glucuronidation processes. METHODS AND RESULTS: A new MDCK II cell line overexpressing both MRP2 and UGT1A1 (MDCKII-UGT1A1/MRP2 cells) was developed and used to determine how overexpression of an efflux transporter affects the kinetics of cellular flavonoid glucuronide production. The results showed that most model flavonoids (from a total of 13) were mainly metabolized into glucuronides in the MDCKII-UGT1A1/MRP2 cells and the glucuronides were rapidly excreted. Flavonoids with three or fewer hydroxyl group at 7, 3' or 6 hydroxyl group were also metabolized into sulfates. Mechanistic studies using 7-hydroxylflavone showed that its glucuronide was mainly (90%) effluxed by BCRP with a small (10%) but significant contribution from MRP2. Maximal velocity of glucuronide production MDCK-MRP2/UGT1A1 cells showed a fairly good correlation (R(2) >0.8) with those derived using UGT1A1 microsomes, but other kinetic parameters (e.g., Km ) did not correlate. CONCLUSION: Overexpression of a second efficient efflux transporter did not significantly change the fact that BCRP is the dominant transporter for flavonoid glucuronide nor did it diminish the influence of the efflux transporter as the "gate keeper" of glucuronidation process.

Curcumin Affects Phase II Disposition of Resveratrol Through Inhibiting Efflux Transporters MRP2 and BCRP.

PURPOSE: To evaluate the impact of curcumin on the disposition of resveratrol phase II metabolites in vivo, and explain the observations by performing in vitro studies in transporter-overexpressed cells. METHODS: Pharmacokinetic studies of resveratrol with and without the co-administration of curcumin were performed in both FVB wild-type and Bcrp1 (-/-) mice. Human UGT1A9-overexpressing HeLa cells and human MRP2-overexpressing MDCK II-UGT1A1 cells were used as in vitro tools to further determine the impact of curcumin as a transporter inhibitor on resveratrol metabolites. RESULTS: We observed higher exposure of resveratrol conjugates in Bcrp1 (-/-) mice compared to wild-type mice. In wild-type mice, curcumin increased the AUC of resveratrol glucuronide by 4-fold compared to the mice treated without curcumin. The plasma levels of resveratrol and its sulfate conjugate also increased moderately. In Bcrp1 (-/-) mice, there was a further increase (6-fold increase) in AUC of resveratrol glucuronide observed when curcumin was co-administered compared to AUC values obtained in wild-type mice without curcumin treatment. In the presence of 50 nM curcumin, the clearance of resveratrol-3-O-glucuronide and resveratrol-3-O-sulfate reduced in both MRP2-overexpressing MDCKII-UGT1A1 cells and Human UGT1A9-overexpressing HeLa cells. CONCLUSIONS: These results suggest that curcumin alters the phase II distribution of resveratrol through inhibiting efflux transporters including MRP2 and BCRP.

Challenges and Opportunities with Predicting in Vivo Phase II Metabolism via Glucuronidation from in Vitro Data.

Glucuronidation is the most important phase II metabolic pathway which is responsible for the clearance of many endogenous and exogenous compounds. To better understand the elimination process for compounds undergoing glucuronidation and identify compounds with desirable in vivo pharmacokinetic properties, many efforts have been made to predict in vivo glucuronidation using in vitro data. In this article, we reviewed typical approaches used in previous predictions. The problems and challenges in prediction of glucuronidation were discussed. Besides that different incubation conditions can affect the prediction accuracy, other factors including efflux / uptake transporters, enterohepatic recycling, and deglucuronidation reactions also contribute to the disposition of glucuronides and make the prediction more difficult. PBPK modeling, which can describe more complicated process in vivo, is a promising prediction strategy which may greatly improve the prediction of glucuronidation and potential DDIs involving glucuronidation. Based on previous studies, we proposed a transport-glucuronidation classification system, which was built based on the kinetics of both glucuronidation and transport of the glucuronide. This system could be a very useful tool to achieve better in vivo predictions.

Determination of pharmacokinetics of chrysin and its conjugates in wild-type FVB and Bcrp1 knockout mice using a validated LC-MS/MS method.

Chrysin, a flavone found in many plants, is also available as a dietary supplement because of its reported anticancer activities. However, its bioavailability is very poor due to extensive phase II metabolism. The purpose of this study was to develop an UPLC-MS/MS method to simultaneously quantify chrysin and its phase II metabolites, and to determine its pharmacokinetics in FVB wild-type and Bcrp knockout (Bcrp1 -/-) mice. In addition, the role of BCRP in chrysin phase II disposition was further investigated in Caco-2 cells. The results showed that our sensitive and reproducible UPLC-MS/MS method was successfully applied to the pharmacokinetic study of chrysin in wild-type and Bcrp1 (-/-) FVB mice after oral administration (20 mg/kg). Although there was no significant change in systemic exposure of chrysin and its metabolites, it was found that the Tmax for chrysin glucuronide was significantly shorter (p < 0.01) in Bcrp1-deficient mice. Furthermore, it was shown that inhibition of BCRP by Ko143 significantly reduced the efflux of chrysin sulfate in Caco-2 cells. In conclusion, BCRP had significant but less than expected impact on pharmacokinetics of chrysin and its conjugates, which were determined using a newly developed and validated LC-MS/MS method.

Validated LC-MS/MS method for the determination of 3-hydroxflavone and its glucuronide in blood and bioequivalent buffers: application to pharmacokinetic, absorption, and metabolism studies.

The purpose of this study is to develop an UPLC-MS/MS method to quantify 3-hydroxyflavone (3-HF) and its metabolite, 3-hydroxyflavone-glucuronide (3-HFG) from biological samples. A Waters BEH C8 column was used with acetonitrile/0.1% formic acid in water as mobile phases. The mass analysis was performed in an API 5500 Qtrap mass spectrometer via multiple reaction monitoring (MRM) with positive scan mood. The one-step protein precipitation by acetonitrile was used to extract the analytes from blood. The results showed that the linear response range was 0.61-2500.00 nM for 3-HF and 0.31-2500.00 nM for 3-HFG. The intra-day variance is less than 16.5% and accuracy is in 77.7-90.6% for 3-HF and variance less than 15.9%, accuracy in 85.1-114.7% for 3-HFG. The inter-day variance is less than 20.2%, accuracy is in 110.6-114.2% for 3-HF and variance less than 15.6%, accuracy in 83.0-89.4% for 3-HFG. The analysis was done within 4.0 min. Only 10 µl of blood is needed due to the high sensitivity of this method. The validated method was successfully used to pharmacokinetic study in A/J mouse, transport study in the Caco-2 cell culture model, and glucuronidation study using mice liver and intestine microsomes. The applications revealed that this method can be used for 3-HF and 3-HFG analysis in blood as well as in bioequivalent buffers such HBSS and KPI.