Reduced variability in tacrolimus pharmacokinetics following intramuscular injection compared to oral administration in cynomolgus monkeys: Investigating optimal dosing regimens

Tacrolimus is one of the most commonly used immunosuppressive agents in animal models of transplantation. However, in these models, oral administration is often problematic due to the lowered compliance associated with highly invasive surgery and due to malabsorption in the intestinal tract. Therefore, we carried out a study to determine the pharmacokinetics of tacrolimus after intramuscular (IM) injection and to determine the optimal IM dosing regimens in primate models. Six male cynomolgus monkeys (Macaca fascicularis) were used in the study. Doses of 0.1 mg/kg and 5 mg were administered via IM injection and oral administration, respectively, once to determine single-dose pharmacokinetics and once daily for 5 days to determine multiple-dose pharmacokinetics. According to pharmacokinetic model estimates, the inter- and intra-individual variabilities in bioavailability following IM injection were remarkably reduced compared with those following oral administration. Monte Carlo simulations revealed that C_peak, C_trough and AUC would also have less variability following IM injection compared with oral administration. In this study, we found that the pharmacokinetic characteristics of tacrolimus were more constant following IM injection compared with oral administration. These results suggest that IM injection can be an alternative route of administration fin non-human primate model studies.     

Time Interval of Two Injections and First-Dose Dependent of Accelerated Blood Clearance Phenomenon Induced by PEGylated Liposomal Gambogenic Acid: The Contribution of PEG-Specific IgM

Repeated injection of PEGylated liposomes can cause the disappearance of long circulating property because of the induction of anti-PEG IgM antibody referred to as “accelerated blood clearance (ABC) phenomenon.” Although ABC phenomenon typically occurs when entrapped drugs are chemotherapeutic agent with low cytotoxic, there is little evidence of accelerated blood clearance of PEGylated herbal-derived compound on repeated injection. Herein, we investigated the blood concentration of PEGylated liposomal gambogenic acid (PEG-GEA-L), a model PEGylated liposomal herbal extract, on its repeated injection to rats. We found time interval between injections had considerable impact on the magnitude of ABC phenomenon induced by PEG-GEA-L. When time interval was prolonged from 3 days to 7 days, ABC phenomenon could be attenuated. Furthermore, its magnitude was enhanced accompanied by a marked rise in the accumulation of PEG-GEA-L in the liver and spleen in a first-dose–dependent manner. Consistently, the level of anti-PEG IgM significantly increased with the first dose of PEG-GEA-L and decreased with the extended time interval between injections, which implies anti-PEG IgM is a major contributor to the ABC phenomenon. Notably, the increased expression of liver anti-PEG IgM was accompanied by an increased expression of efflux transporters in the induction process of the ABC phenomenon.     

Physiologically Based Pharmacokinetic Modeling in Regulatory Science: An Update From the U.S. Food and Drug Administration’s Office of Clinical Pharmacology

This commentary provides an update on the status of physiologically based pharmacokinetic modeling and simulation at the U.S. Food and Drug Administration's Office of Clinical Pharmacology. Limitations and knowledge gaps in integration of physiologically based pharmacokinetic approach to inform regulatory decision making, as well as the importance of scientific engagement with drug developers who intend to use this approach, are highlighted.     

In Vitro and In Vivo Correlation of Hepatic Fraction of Metabolism by P450 in Dogs

1-Aminobenzotriazole (ABT) has been widely used as a nonspecific mechanism-based inhibitor of cytochrome P450 (P450) enzymes. It is extensively used in preclinical studies to determine the relative contribution of oxidative metabolism mediated by P450 in vitro and in vivo. The aim of present study was to understand the translation of fraction metabolized by P450 in dog hepatocytes to in vivo using ABT, for canagliflozin, known to be cleared by P450-mediated oxidation and UDP-glucuronosyltransferases–mediated glucuronidation, and 3 drug discovery project compounds mainly cleared by hepatic metabolism. In a dog hepatocyte, intrinsic clearance assay with and without preincubation of ABT, 3 Lilly compounds exhibited a wide range of fraction metabolized by P450. Subsequent metabolite profiling in dog hepatocytes demonstrated a combination of metabolism by P450 and UDP-glucuronosyltransferases. In vivo, dogs were pretreated with 50 mg/kg ABT or vehicle at 2 h before intravenous administration of canagliflozin and Lilly compounds. The areas under the concentration-time curve (AUC) were compared for the ABT-pretreated and vehicle-pretreated groups. The measured AUC_ABT/AUC_veh ratios were correlated to fraction of metabolism by P450 in dog hepatocytes, suggesting that in vitro ABT inhibition in hepatocytes is useful to rank order compounds for in vivo fraction of metabolism assessment.     

Canagliflozin,a sodium glucose co-transporter 2 inhibitor,reduces post-meal glucose excursion in patients with type 2 diabetes by a non-renal mechanism: results of a randomized trial

Objective

Canagliflozin is a sodium glucose co-transporter 2 inhibitor approved for treating patients with type 2 diabetes. This study evaluated renal and non-renal effects of canagliflozin on postprandial plasma glucose (PG) excursion in patients with type 2 diabetes inadequately controlled with metformin.

Materials/Methods

Patients (N = 37) were randomized to a four-period crossover study with 3-day inpatient stays in each period and 2-week wash-outs between periods. Patients received Treatments (A) placebo/placebo, (B) canagliflozin 300 mg/placebo, (C) canagliflozin 300 mg/canagliflozin 300 mg, or (D) canagliflozin 300 mg/canagliflozin 150 mg on Day 2/Day 3 in one of four treatment sequences (similar urinary glucose excretion [UGE] expected for Treatments B–D). A mixed-meal tolerance test (MMTT) was given 20 minutes post-dose on Day 3 of each period.

Results

A single dose of canagliflozin 300 mg reduced both fasting and postprandial PG compared with placebo, with generally similar effects on fasting PG and UGE observed for Treatments B–D. An additional dose of canagliflozin 300 mg (Treatment C), but not 150 mg (Treatment D), prior to the MMTT on Day 3 provided greater postprandial PG reduction versus placebo (difference in incremental glucose AUC_0–2h, − 7.5% for B vs A; − 18.5% for C vs A; − 12.0% [P = 0.012] for C vs B), leading to modestly greater reductions in total glucose AUC_0–2h with Treatment C versus Treatment B or D. Canagliflozin was generally well tolerated.

Conclusions

These findings suggest that a non-renal mechanism (ie, beyond UGE) contributes to glucose lowering for canagliflozin 300 mg, but not 150 mg.     

Proposal of a Parameter for OATP1B1 Inhibition Screening at the Early Drug Discovery Stage

It is known that potent inhibition of organic-anion-transporting polypeptide (OATP)1B1 increases exposure to statins, leading to severe adverse effects. The aim of this study was to propose a parameter and its criteria in OATP1B1 inhibition assay at the early drug discovery stage to avoid compounds with the risk of statin-related adverse effects. According to drug label information, most compounds classified as “contraindicated” or “should be avoided” when administered concomitantly with statins increased their AUCs more than 4-fold. Generally, R values where R = 1 + plasma unbound fraction (fu) × maximum inhibitor concentration at the inlet to the liver/IC₅₀ are used to evaluate the extent of clinical drug interaction. However, clinical doses and C_max cannot be determined at the screening stage. Therefore, we estimated the correlations between change in AUC of statins concomitantly administered with OATP1B1 inhibitors and various parameters including fu/IC₅₀. Cyclosporin A, rifampicin, and telaprevir increased the AUC of statins more than 4-fold and fu/IC₅₀ of these compounds was >0.1 L/μmol. On the other hand, fu/IC₅₀ of other compounds was ≤0.03 L/μmol. This study indicates that fu/IC₅₀ is a useful parameter to avoid compounds that seriously affect statin potency through interaction with OATP1B1 at the screening stage.     

Glucoregulatory function among African Americans and European Americans with normal or pre-diabetic hemoglobin A1c levels

Objective

A hemoglobin (Hb) A1c range of 5.7%–6.4% has been recommended for the diagnosis of prediabetes. To determine the significance of such “prediabetic” HbA1c levels, we compared glucoregulatory function in persons with HbA1c levels of 5.7%–6.4% and those with HbA1c < 5.7%.

Methods

We studied 280 nondiabetic adults (142 black, 138 white; mean (± SD) age 44.2 ± 10.6 years). Each subject underwent clinical assessment, blood sampling for HbA1c measurement, and a 75-g oral glucose tolerance test at baseline. Additional assessments during subsequent outpatient visits included insulin sensitivity, using homeostasis model assessment (HOMA)-IR and the hyperinsulinemic euglycemic clamp; insulin secretion, using HOMA-B and frequently samples intravenous glucose tolerance test (FSIVGTT) and disposition index (DI); and measurement of fat mass, using DXA.

Results

Compared to subjects with HbA1c < 5.7%, persons with HbA1c levels of 5.7%–6.4% were older, and had higher body mass index (BMI) and insulin secretion but similar insulin sensitivity. When the two groups were matched in age and BMI, persons with HbA1c 5.7%–6.4% were indistinguishable from those with HbA1c < 5.7% with regard to all measures of glycemia and glucoregulatory function.

Conclusions

Unlike glucose-defined prediabetes status, an HbA1c range of 5.7%–6.4% does not reliably identify individuals with impaired insulin action or secretion, the classical defects underlying the pathophysiology of prediabetes. Thus, HbA1c cannot validly replace blood glucose measurement in the diagnosis of prediabetes. If utilized as a screening test due to convenience, aberrant HbA1c values should be corroborated with blood glucose measurement before therapeutic intervention.     

An examination of sex and racial/ethnic differences in the metabolic syndrome among adults: A confirmatory factor analysis and a resulting continuous severity score

Objective

The metabolic syndrome (MetS) is typically diagnosed based on abnormalities in specific clustered clinical measures that are associated with increased risk for coronary heart disease (CHD) and Type 2 diabetes mellitus (T2DM). However, current MetS criteria result in racial/ethnic discrepancies. Our goals were to use confirmatory factor analysis (CFA) to delineate differential contributions to MetS by sub-group, and if contributions were discovered, develop sex and racial/ethnic-specific equations to calculate MetS severity.

Research Design and Methods

Using data on adults from the National Health and Nutrition Examination Survey 1999–2010, we performed a CFA of a single MetS factor that allowed differential loadings across groups, resulting in a sex and race/ethnicity-specific continuous MetS severity score.

Results

Loadings to the single MetS factor differed by sub-group for each MetS component (p < 0.001), with lower factor loadings among non-Hispanic-blacks for triglycerides and among Hispanics for waist circumference. Systolic blood pressure exhibited low factor loadings among all groups. MetS severity scores were correlated with biomarkers of future disease (high-sensitivity C-reactive-protein, uric acid, insulin resistance). Non-Hispanic-black-males with diabetics had a low prevalence of MetS but high MetS severity scores that were not significantly different from other racial/ethnic groups.

Conclusions

This analysis among adults uniquely demonstrated differences between sexes and racial/ethnic groups regarding contributions of traditional MetS components to an assumed single factor. The resulting equations provide a clinically-accessible and interpretable continuous measure of MetS for potential use in identifying adults at higher risk for MetS-related diseases and following changes within individuals over time. These equations hold potential to be a powerful new outcome for use in MetS-focused research and interventions.     

Sample size estimation for time‐dependent receiver operating characteristic

In contrast to the usual ROC analysis with a contemporaneous reference standard, the time‐dependent setting introduces the possibility that the reference standard refers to an event at a future time and may not be known for every patient due to censoring. The goal of this research is to determine the sample size required for a study design to address the question of the accuracy of a diagnostic test using the area under the curve in time‐dependent ROC analysis. We adapt a previously published estimator of the time‐dependent area under the ROC curve, which is a function of the expected conditional survival functions. This estimator accommodates censored data. The estimation of the required sample size is based on approximations of the expected conditional survival functions and their variances, derived under parametric assumptions of an exponential failure time and an exponential censoring time. We also consider different patient enrollment strategies. The proposed method can provide an adequate sample size to ensure that the test's accuracy is estimated to a prespecified precision. We present results of a simulation study to assess the accuracy of the method and its robustness to departures from the parametric assumptions. We apply the proposed method to design of a study of positron emission tomography as predictor of disease free survival in women undergoing therapy for cervical cancer. Copyright © 2013 John Wiley & Sons, Ltd.