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Despite the liver being the primary site for clearance of xenobiotics utilizing a myriad of mechanisms ranging from cytochrome P450 enzyme pathways, glucuronidation, and biliary excretion, there is a dearth of information available as to how the severity of hepatic impairment (HI) can alter drug absorption and disposition (i.e., pharmacokinetics [PK]) as well as their efficacy and safety or pharmacodynamics (PD). In general, regulatory agencies recommend conducting PK studies in subjects with HI when hepatic metabolism/excretion accounts for more than 20% of drug elimination or if the drug has a narrow therapeutic range. In this tutorial, we provide an overview of the global regulatory landscape, clinical measures for hepatic function assessment, methods to stage HI severity, and consequently the impact on labeling. In addition, we provide an in-depth practical guidance for designing and conducting clinical trials for patients with HI and on the application of modeling and simulation strategies in lieu of dedicated trials for dosing recommendations in patients with HI.

Characterizing interactions between new molecular entities (NMEs) and drug transporters is a critical element of drug development that helps in assessing potential transporter-based drug-drug interactions (DDIs). However, not all NME new drug applications (NDAs) include a full characterization of NMEs transporter-based DDIs, which necessitates the issuance of post-marketing requirement (PMR)/post-marketing commitment (PMC) by the US Food and Drug Administration (FDA) to characterize these potential interactions. The objective of this analysis is to identify trends in transporter-based PMRs/PMCs issued by the FDA between 2012 and 2021. A decrease in the number of transporter-based PMRs/PMCs was observed from 2012 to 2016 and an increasing trend in the number of PMRs/PMCs was observed after 2017. The majority of these transporter-based PMRs/PMCs requested clinical evaluation (48%), some requested in vitro assessment (38%), and 2.5% requested modeling and simulation assessment. Most of the PMRs/PMCs requested evaluation of NMEs as perpetrator with the efflux transporters, P-gp and/or BCRP (53%). Forty-eight percent of the PMRs/PMCs were fulfilled with 67% resulted in labeling updates. On average, 2.5 years were needed for the information related to PMRs/PMCs to show in NMEs labeling. In conclusion, this analysis highlights the increased emphasis from the FDA on proper characterization of transporter-based DDI and call for the need of early characterization of NMEs-transporters interaction before initial NDA approval.

There are more than 7000 rare diseases affecting approximately 30 million people in the United States. More than 90% of these diseases lack approved therapies. Several challenges face the development of "orphan drugs", such as the small populations of patients, high development costs, and long development timelines. This study evaluates clinical pharmacology assessments conducted during the development of drugs to treat rare diseases approved by the United States Food and Drug Administration in 2020 and 2021. Thirty-nine new drug applications (NDAs) have been identified and the associated regulatory reviews, approved labels, and approval letters were reviewed. Approximately, 95%, 74%, and 77% of these submissions contained at least one type of drug-drug interaction, the effect of organ impairment (hepatic and renal) on drug exposure, and QT liability assessment, respectively. Modeling and simulation approaches were utilized to address many clinical pharmacology questions, with population pharmacokinetic analyses used extensively in the evaluation of the effect of organ impairment on drug exposure and with physiologically based pharmacokinetic analyses used mainly in assessing drug interaction risks. In general, the clinical pharmacology packages in the NDAs of orphan drugs are not optimal and more work is needed to obtain a complete clinical pharmacology package at the time of initial approval to ensure the safe and effective use of these drugs across the spectrum of the target patient population. This study provides insights into the clinical pharmacology studies needed for drugs to treat rare diseases and would help both the regulators and drug developers to identify challenges and opportunities in conducting clinical pharmacology assessments for drugs developed to treat rare diseases.

The efficacy of drugs targeting the CNS is influenced by their limited brain access, which can lead to complete pharmacoresistance. Recently a tissue-specific and selective upregulation of the multidrug efflux transporter ABCB1 or P-glycoprotein (P-gp) in the spinal cord of both patients and the mutant SOD1-G93A mouse model of amyotrophic lateral sclerosis (ALS), a fatal neurodegenerative disease that prevalently kills motor neurons has been reported. Here, we extended the analysis of P-gp expression in the SOD1-G93A ALS mouse model and found that P-gp upregulation was restricted to endothelial cells of the capillaries, while P-gp expression was not detected in other cells of the spinal cord parenchyma such as astrocytes, oligodendrocytes, and neurons. Using both in vitro human and mouse models of the blood-brain barrier (BBB), we found that mutant SOD1 astrocytes were driving P-gp upregulation in endothelial cells. In addition, a significant increase in reactive oxygen species production, Nrf2 and NFκB activation in endothelial cells exposed to mutant SOD1 astrocytes in both human and murine BBB models were observed. Most interestingly, astrocytes expressing FUS-H517Q, a different familial ALS-linked mutated gene, also drove NFκB-dependent upregulation of P-gp. However, the pathway was not dependent on oxidative stress but rather involved TNF-α release. Overall, these findings indicated that nuclear translocation of NFκB was a converging mechanism used by endothelial cells of the BBB to upregulate P-gp expression in mutant SOD1-linked ALS and possibly other forms of familial ALS. GLIA 2016 GLIA 2016;64:1298-1313.

The aim of this work was to compare the intestinal absorption kinetics and the bioavailability of γ-tocotrienol (γ-T3) and α-tocopherol (α-Tph) administered separately as oil solutions to rats in vivo. Also, to explain the significant difference in the oral bioavailability of the compounds: (1) the release profiles using the dynamic in vitro lipolysis model, (2) the intestinal permeability and (3) carrier-mediated uptake by Niemann-Pick C1-like 1 (NPC1L1) transporter were examined. Absolute bioavailability studies were conducted after oral administration of γ-T3 or α-Tph prepared in corn oil to rats. In situ rat intestinal perfusion with ezetimibe (a NPC1L1 inhibitor) was performed to compare intestinal permeability. The in vitro interaction kinetics with NPC1L1 was examined in NPC1L1 transfected cells. While the in vitro release studies demonstrated a significantly higher release rate of γ-T3 in the aqueous phase, the oral bioavailability of α-Tph (36%) was significantly higher than γ-T3 (9%). Consequent in situ studies revealed significantly higher intestinal permeability for α-Tph compared with γ-T3 in rats. Moreover, the NPC1L1 kinetic studies demonstrated higher Vmax and Km values for α-Tph compared with γ-T3. Collectively, these results indicate that intestinal permeability is the main contributing factor for the higher bioavailability of α-Tph. Also, these results emphasize the potentially important role of intestinal permeability in the bioavailability of γ-T3, suggesting that enhancing its permeability would increase its oral bioavailability. Copyright © 2012 John Wiley & Sons, Ltd.