When is Protein Binding Important?*

Age-Related Changes in Vancomycin Protein Binding: Is It Time to Take It Seriously?

BACKGROUND

Vancomycin (VAN) protein binding in plasma is influenced by illness and age; hence, doses titrated according to total concentrations are fraught. In this study, model-estimated free VAN concentrations (EFVC) were compared with assumed free VAN concentrations (AFVC) in neonates, children, and adults in the intensive care unit and those on dialysis.

METHODS

Patient cohorts were identified from the hospital database. Demographics, clinical characteristics, total VAN concentrations, and laboratory variables were obtained from electronic health records. EFVC was derived from 6 models identified in the literature. For all models, total VAN concentration was the most important predictor; other predictors included albumin, total protein, and dialysis status. The AFVC was calculated as 50% of the total concentration (ie, assumption of 50% bound).

RESULTS

Differences between EFVC and AFVC in adults were insignificant; however, differences in pediatric intensive care unit patients, according to 2 different models, were significant: mean ± SD = 4.1 ± 1.58 mg/L and 4.7 ± 2.46 mg/L ( P < 0.001); the percentages within the free VAN trough range = 30.4% versus 55.1% and 30% versus 55.1%; and the supratherapeutic percentages = 65.2% versus 31.9% and 66.7% versus 31.9%, respectively. In neonates, the difference between EFVC and AFVC was mean ± SD = 6.9 ± 1.95 mg/L ( P < 0.001); the percentages within the free VAN trough range for continuous and intermediate dosing were 0% versus 81.3% and 14.3% versus 71.4%, and the supratherapeutic percentages were 100% versus 6.25% and 71.4% versus 0%, respectively.

CONCLUSIONS

The fraction of free unbound VAN is higher in sick children and neonates than in adults. Therefore, total VAN concentrations do not correlate with the pharmacologically active free VAN concentrations in the same manner as in adults. Adjusting VAN doses in neonates and children to target the same total VAN concentration as the recommended therapeutic range for adults may result in toxicfree concentrations.

Molecular docking of antidiabetic molecules of libas (Spondias pinnata) fruit and prediction of their pharmacokinetic properties

Diabetes mellitus is one of the chronic metabolic disorders that affects more than 16 million Filipinos. Proper education, medical intervention, and a good lifestyle can help individuals control and manage this disease. Spondias pinnata is one of the underutilized crops in the Philippines that is well-known for its satisfactory flavor and medicinal properties, including its antidiabetic activity. The quest for a natural and effective drug to manage diseases is a continuous work in progress. Drug discovery and design is a tedious and expensive process. Computer-aided drug design guides the design and makes the process more efficient and less costly. Molecular docking was used to determine the potential antidiabetic compounds from the 48 reported compounds found in S. pinnata fruit. Seven compounds namely squalene (-9.1 kcal/mol), rutin (-9 kcal/mol), catechin (-8.7 kcal/mol), quercetin (-8.5 kcal/mol), tocopherol (-8.4 kcal/mol), myricetin (-8.4 kcal/mol), and ellagic acid (-8.3 kcal/mol) showed binding affinities comparable to those of pioglitazone, a standard drug, with peroxisome proliferator-activated receptor gamma (PPARγ). Tocopherol and catechin showed good ADMET properties. Among the two compounds, catechin passed the four filters for drug-likeness. Thus, catechin could be a potential compound for the development of antidiabetic drugs.

Supplementary Information

The online version contains supplementary material available at 10.1007/s40203-024-00230-3.

Metabolites in the regulatory risk assessment of pesticides in the EU

A large majority of chemicals is converted into metabolites through xenobiotic-metabolising enzymes. Metabolites may present a spectrum of characteristics varying from similar to vastly different compared with the parent compound in terms of both toxicokinetics and toxicodynamics. In the pesticide arena, the role of metabolism and metabolites is increasingly recognised as a significant factor particularly for the design and interpretation of mammalian toxicological studies and in the toxicity assessment of pesticide/metabolite-associated issues for hazard characterization and risk assessment purposes, including the role of metabolites as parts in various residues in ecotoxicological adversities. This is of particular relevance to pesticide metabolites that are unique to humans in comparison with metabolites found in in vitro or in vivo animal studies, but also to disproportionate metabolites (quantitative differences) between humans and mammalian species. Presence of unique or disproportionate metabolites may underlie potential toxicological concerns. This review aims to present the current state-of-the-art of comparative metabolism and metabolites in pesticide research for hazard and risk assessment, including One Health perspectives, and future research needs based on the experiences gained at the European Food Safety Authority.

Plasma Protein Binding Determination for Unstable Ester Prodrugs: Remdesivir and Tenofovir Alafenamide

Remdesivir (RDV) and tenofovir alafenamide (TAF) are prodrugs designed to be converted to their respective active metabolites. Plasma protein binding (PPB) determination of these prodrugs is important for patients with possible alteration of free fraction of the drugs due to plasma protein changes in renal impairment, hepatic impairment, or pregnancy. However, the prodrugs' instability in human plasma presents a challenge for accurate PPB determination. In this research work, two approaches were used in the method development and qualification for PPB assessment of RDV and TAF. For RDV, dichlorvos was used to inhibit esterase activity to stabilize the prodrug in plasma during equilibrium dialysis (ED). The impact of dichlorvos on protein binding was evaluated and determined to be insignificant by comparing the unbound fraction (fu) determined by the ED method with dichlorvos present and the fu determined by an ultrafiltration method without dichlorvos. In contrast to RDV, TAF degradation in plasma is ∼3-fold slower, and TAF stability cannot be improved by dichlorvos. Fit-for-purpose acceptance criteria for the TAF PPB method were chosen, and an ED method was developed based on these criteria. These two methods were then qualified and applied for PPB determinations in clinical studies.

Antidiabetic Activity, Molecular Docking, and ADMET Properties of Compounds Isolated from Bioactive Ethyl Acetate Fraction of Ficus lutea Leaf Extract

Diabetes contributes to the rising global death rate. Despite scientific advancements in understanding and managing diabetes, no single therapeutic agent has been identified to effectively treat and prevent its progression. Consequently, the exploration for new antidiabetic therapeutics continues. This study aimed to investigate the antidiabetic bioactive ethyl acetate fraction of F. lutea at the molecular level to understand the molecular interactions and ligand-protein binding. To do this, the fraction underwent column chromatography fractionation to yield five compounds: lupeol, stigmasterol, α-amyrin acetate, epicatechin, and epiafzelechin. These compounds were evaluated in vitro through α-glucosidase inhibition and glucose utilization assays in C2C12 muscle and H-4-11-E liver cells using standard methods. In silico analysis was conducted using molecular docking and ADMET studies. Epicatechin exhibited the most potent α-glucosidase inhibition (IC50 = 5.72 ± 2.7 µg/mL), while epiafzelechin stimulated superior glucose utilization in C2C12 muscle cells (33.35 ± 1.8%) and H-4-11-E liver cells (46.7 ± 1.2%) at a concentration of 250 µg/mL. The binding energies of the isolated compounds for glycogen phosphorylase (1NOI) and α-amylase (1OSE) were stronger (<-8.1) than those of the positive controls. Overall, all tested compounds exhibited characteristics indicative of their potential as antidiabetic agents; however, toxicity profiling predicted epiafzelechin and epicatechin as better alternatives. The ethyl acetate fraction and its compounds, particularly epiafzelechin, showed promise as antidiabetic agents. However, further comprehensive studies are necessary to validate these findings.

Recent Advancements and Strategies for Overcoming the Blood-Brain Barrier Using Albumin-Based Drug Delivery Systems to Treat Brain Cancer, with a Focus on Glioblastoma

Glioblastoma multiforme (GBM) is a highly aggressive malignant tumor, and the most prevalent primary malignant tumor affecting the brain and central nervous system. Recent research indicates that the genetic profile of GBM makes it resistant to drugs and radiation. However, the main obstacle in treating GBM is transporting drugs through the blood-brain barrier (BBB). Albumin is a versatile biomaterial for the synthesis of nanoparticles. The efficiency of albumin-based delivery systems is determined by their ability to improve tumor targeting and accumulation. In this review, we will discuss the prevalence of human glioblastoma and the currently adopted treatment, as well as the structure and some essential functions of the BBB, to transport drugs through this barrier. We will also mention some aspects related to the blood-tumor brain barrier (BTBB) that lead to poor treatment efficacy. The properties and structure of serum albumin were highlighted, such as its role in targeting brain tumors, as well as the progress made until now regarding the techniques for obtaining albumin nanoparticles and their functionalization, in order to overcome the BBB and treat cancer, especially human glioblastoma. The albumin drug delivery nanosystems mentioned in this paper have improved properties and can overcome the BBB to target brain tumors.

Hypoalbuminemia and Pharmacokinetics: When the Misunderstanding of a Fundamental Concept Leads to Repeated Errors over Decades

Surprisingly, misinterpretation of the influence of hypoalbuminemia on pharmacokinetics and the clinical effects of drugs seems to be a current problem, even though hypoalbuminemia has no impact on the pharmacologically active exposure. Exceptions to this fact are highly protein-bound anaesthetics with high elimination capacity (i.e., <5 drugs on the market). To assess the frequency of misinterpretation of the influence of hypoalbuminemia on pharmacokinetics and the clinical effects of drugs between 1975 and 2021, a PubMed literature review was conducted. Each paragraph on albumin binding was classified as correct, ambiguous or incorrect, creating two acceptable categories: (1) content without any errors, and (2) content containing some incorrect and/or ambiguous statements. The analyses of these articles showed that fewer than 11% of articles contained no interpretation errors. In order to contain this misinterpretation, several measures are proposed: (1) Make the message accessible to a wide audience by offering a simplified and didactic video representation of the lack of impact of albumin binding to drugs. (2) Precise terminology (unbound/free form/concentration) should be used for highly bound drugs. (3) Unbound/free forms should be systematically quantified for highly plasma protein bound drugs for clinical trials as well as for therapeutic drug monitoring.

Therapeutic drug monitoring of phenytoin and valproic acid in critically ill patients at Windhoek Central Hospital, Namibia

Background

Phenytoin and valproic acid, anticonvulsants, have a low therapeutic index and are highly plasma protein bound, mainly to albumin. Hypoalbuminaemia is common in critically ill patients and increases the unbound drug concentration. Thus, monitoring unbound rather than total plasma drug concentrations is recommended to optimise the dosing of these drugs.

Objective

This retrospective study determined unbound plasma concentrations of phenytoin and valproic as a more accurate value of drug levels than total plasma drug concentrations.

Methods

Total plasma concentrations were retrieved for 56 Intensive Care Unit patients for phenytoin and 93 for valproic acid. Total drug concentrations were converted to unbound concentrations using a serum albumin-based normalising equation.

Results

Total phenytoin plasma concentration was below (41.1% of patients), within (46.4%) or above (12.5%) the therapeutic range (10 μg/mL – 20 μg/mL). However, the predicted unbound plasma concentration of phenytoin was above the therapeutic range (1 μg/mL – 2 μg/mL) in the majority of patients (57.1%). For valproic acid, the total plasma concentration of most patients (87.1%) was below the therapeutic range (50 μg/mL – 100 μg/mL); among remaining patients (12.9%), it was within the therapeutic range. In the majority of patients (91.4%), the predicted unbound plasma concentration of valproic acid was between 2.5 μg/mL and 20 μg/mL.

Conclusion

The usefulness of monitoring the total phenytoin or valproic acid levels for dose optimisation is limited as it is an inaccurate indicator of a patient’s drug therapeutic state. Thus, the unbound plasma drug concentrations should be quantified experimentally or predicted in resource-limited settings.

The Effect of Dynamic, In Vivo-like Oxaliplatin on HCT116 Spheroids in a Cancer-on-Chip Model Is Representative of the Response in Xenografts

The cancer xenograft model in which human cancer cells are implanted in a mouse is one of the most used preclinical models to test the efficacy of novel cancer drugs. However, the model is imperfect; animal models are ethically burdened, and the imperfect efficacy predictions contribute to high clinical attrition of novel drugs. If microfluidic cancer-on-chip models could recapitulate key elements of the xenograft model, then these models could substitute the xenograft model and subsequently surpass the xenograft model by reducing variation, increasing sensitivity and scale, and adding human factors. Here, we exposed HCT116 colorectal cancer spheroids to dynamic, in vivo-like, concentrations of oxaliplatin, including a 5 day drug-free period, on-chip. Growth inhibition on-chip was comparable to existing xenograft studies. Furthermore, immunohistochemistry showed a similar response in proliferation and apoptosis markers. While small volume changes in xenografts are hard to detect, in the chip-system, we could observe a temporary growth delay. Lastly, histopathology and a pharmacodynamic model showed that the cancer spheroid-on-chip was representative of the proliferating outer part of a HCT116 xenograft, thereby capturing the major driver of the drug response of the xenograft. Hence, the cancer-on-chip model recapitulated the response of HCT116 xenografts to oxaliplatin and provided additional drug efficacy information.

Drug Interaction between Dexamethasone and Ketoprofen with Thiopental in Male Dogs: Effect on the Recovery from Anesthesia and Pharmacokinetics Parameters

Drug-drug interactions (DDIs) are an important part of clinical veterinary pharmacology. Forty-two healthy mixed breed male dogs were randomly divided into three groups. The control group (C) received normal saline (1 mg/kg) 5 minutes before intravenous administration of thiopental (17 mg/kg), the T1 group received ketoprofen (2.2 mg/kg), and the T2 group received dexamethasone (0.2 mg/kg) 5 minutes before thiopental, respectively. Clinical parameters of anesthesia, heart rate, respiration rate, and electrocardiography were measured. Serum samples were also used to assay thiopental concentration using the high-performance liquid chromatography (HPLC) method, and then, thiopental pharmacokinetic parameters were calculated. Changes in the heart rate and respiration were significant intragroup differences 5 and 10 minutes after anesthesia, respectively. Recovery time parameters showed a significant increase between T1 and control groups (P < 0.05). Elimination rate and half-life of thiopental in the T1 group compared to the control and T2 groups showed a significant decrease and increase, respectively. In addition, the distribution of thiopental in T1 showed a significant increase compared to other groups. However, thiopental clearance in T1 and T2 groups had no significant difference with control (P > 0.05). It can be concluded that drug interaction between ketoprofen and thiopental causes to change in the pharmacokinetics parameters and recovery time from anesthesia in comparison with dexamethasone.

Albumin in Tears Modulates Bacterial Susceptibility to Topical Antibiotics in Ophthalmology

Bacterial keratitis is a serious and vision-threatening condition in veterinary and human patients, one that often requires culture and susceptibility testing to adjust therapy and improve clinical outcomes. The present study challenges the antimicrobial susceptibility testing (AST) paradigm in ophthalmology, enabling more accurate in vitro-to-in vivo translation by incorporating factors normally present during host-pathogen interactions in clinical patients. Thirty bacteria (10 Staphylococcus pseudintermedius, 10 Streptococcus canis, 10 Pseudomonas aeruginosa) were isolated from canine patients with infectious keratitis. For each isolate, commercial plates (Sensititre™ JOEYE2) were used to assess the minimal inhibitory concentration (MIC) of 17 different antibiotics in the absence (0% albumin, control) or presence of canine albumin (0.01–2%). For Staphylococcus pseudintermedius, the experiment was repeated with actual tear fluid collected from canine eyes with ocular surface inflammation. Kruskal-Wallis, Wilcoxon signed rank test and Spearman's correlation tests were used for statistical analysis. Clinical outcomes were unfavorable in selected canine patients with bacterial keratitis (e.g., globe perforation, graft dehiscence) despite standard AST (i.e., 0% albumin in test medium) confirming that most corneal infections (93%) were susceptible to ≥1 topical antibiotics used at the initial visit. Albumin levels ≥0.05% increased MICs in a dose-dependent, bacteria-specific, and antibiotic-specific manner. No significant differences (P = 1.000) were noted in MICs of any antibiotic whether albumin or tear fluid was added to the Mueller-Hinton broth. Percent protein binding inherent to each antibiotic was associated with clinical interpretations (Spearman's rho = −0.53, P = 0.034) but not changes in MICs. Albumin in tears impacted the efficacy of selected ophthalmic antibiotics as only the unbound portion of an antibiotic is microbiologically active. The present findings could improve decision making of clinicians managing bacterial keratitis, reduce development of antimicrobial resistance, influence current guidelines set by the Clinical and Laboratory Standards Institute, and serve as a reference for bacteriological evaluations across medical fields and across species.

Serum Albumin Nanoparticles: Problems and Prospects

The present paper aims to summarize the results regarding serum albumin-based nanoparticles (NPs) for drug delivery purposes. In particular, it focuses on the relationship between their preparation techniques and synthesis parameters, as well as their successful clinical application. In spite of the huge amount of consumed material and immaterial sources and promising possibilities, products made from different types of albumin NPs, with the exception of a few, still have not been invented. In the present paper, promising applications of serum albumin nanoparticles (SANPs) for different biomedical purposes, such as carriers, delivery systems and contrast agents, are also discussed. The most frequent utilization of the NPs for certain diseases, i.e., cancer therapy, and future prospects are also detailed in this study.

Influence of Malnutrition on the Pharmacokinetics of Drugs Used in the Treatment of Poverty-Related Diseases: A Systematic Review

Background

Patients affected by poverty-related infectious diseases (PRDs) are disproportionally affected by malnutrition. To optimize treatment of patients affected by PRDs, we aimed to assess the influence of malnutrition associated with PRDs on drug pharmacokinetics, by way of a systematic review.

Methods

A systematic review was performed on the effects of malnourishment on the pharmacokinetics of drugs to treat PRDs, including HIV, tuberculosis, malaria, and neglected tropical diseases.

Results

In 21/29 PRD drugs included in this review, pharmacokinetics were affected by malnutrition. Effects were heterogeneous, but trends were observed for specific classes of drugs and different types and degrees of malnutrition. Bioavailability of lumefantrine, sulfadoxine, pyrimethamine, lopinavir, and efavirenz was decreased in severely malnourished patients, but increased for the P-glycoprotein substrates abacavir, saquinavir, nevirapine, and ivermectin. Distribution volume was decreased for the lipophilic drugs isoniazid, chloroquine, and nevirapine, and the α1-acid glycoprotein-bound drugs quinine, rifabutin, and saquinavir. Distribution volume was increased for the hydrophilic drug streptomycin and the albumin-bound drugs rifampicin, lopinavir, and efavirenz. Drug elimination was decreased for isoniazid, chloroquine, quinine, zidovudine, saquinavir, and streptomycin, but increased for the albumin-bound drugs quinine, chloroquine, rifampicin, lopinavir, efavirenz, and ethambutol. Clinically relevant effects were mainly observed in severely malnourished and kwashiorkor patients.

Conclusions

Malnutrition-related effects on pharmacokinetics potentially affect treatment response, particularly for severe malnutrition or kwashiorkor. However, pharmacokinetic knowledge is lacking for specific populations, especially patients with neglected tropical diseases and severe malnutrition. To optimize treatment in these neglected subpopulations, adequate pharmacokinetic studies are needed, including severely malnourished or kwashiorkor patients.

Supplementary Information

The online version contains supplementary material available at 10.1007/s40262-021-01031-z.

Meropenem use and therapeutic drug monitoring in clinical practice: a literature review

WHAT IS KNOWN AND OBJECTIVE

Meropenem, a carbapenem antibiotic, is widely prescribed for the treatment of life-threatening infections. The main parameter associated with its therapeutic success is the percentage of time that the levels remain above the minimum inhibitory concentration. Inadequate levels of meropenem can lead to therapeutic failure and increase the possibility of microbial resistance. The employment of strategies involving dose regimens and drug pharmacodynamics has become increasingly important to optimize therapies. In the present study, we conducted a review with the purpose of assembling information about the clinical use of meropenem and therapeutic drug monitoring.

METHODS

A literature review emphasizing the application of therapeutic drug monitoring (TDM) of meropenem in clinical practice has been done. To identify articles related to the topic, we performed a standardized search from January 21, 2020 to December 21, 2020, using specific descriptors in PubMed, Lilacs and Embase.

RESULTS AND DISCUSSION

In total, 35 studies were included in the review. The daily dose of meropenem commonly ranged from 3 to 6 g/day. Critically ill patients and those with impaired renal function appear to be the most suitable patients for the application of meropenem TDM, in order to guide therapy. We observed that most of the studies recommend TDM and that, in nine locations, the TDM of meropenem and of other beta-lactams is a routine practice. TDM data can help to maximize the clinical outcomes of the treatment with meropenem. It can also improve the patient care by providing suitable levels of meropenem, guiding the most appropriate dose regimens, which is the main parameter associated with therapeutic success.

WHAT IS NEW AND CONCLUSION

The findings from this review suggest that the therapeutic monitoring of meropenem can be beneficial, since it adjusts the treatment and aids clinical outcomes. It does so by indicating the appropriate dosage and preventing failure, toxicity and possible antimicrobial resistance. The multidisciplinary effort, basic knowledge and communication among the medical team are also essential.

Evaluation of Quantitative Structure Property Relationship Algorithms for Predicting Plasma Protein Binding in Humans

The extent of plasma protein binding is an important compound-specific property that influences a compound's pharmacokinetic behavior and is a critical input parameter for predicting exposure in physiologically based pharmacokinetic (PBPK) modeling. When experimentally determined fraction unbound in plasma (fup) data are not available, quantitative structure-property relationship (QSPR) models can be used for prediction. Because available QSPR models were developed based on training sets containing pharmaceutical-like compounds, we compared their prediction accuracy for environmentally relevant and pharmaceutical compounds. Fup values were calculated using Ingle et al., Watanabe et al. and ADMET Predictor (Simulation Plus). The test set included 818 pharmaceutical and environmentally relevant compounds with fup values ranging from 0.01 to 1. Overall, the three QSPR models resulted in over-prediction of fup for highly binding compounds and under-prediction for low or moderately binding compounds. For highly binding compounds (0.01≤ fup ≤ 0.25), Watanabe et al. performed better with a lower mean absolute error (MAE) of 6.7% and a lower mean absolute relative prediction error (RPE) of 171.7 % than other methods. For low to moderately binding compounds, both Ingle et al. and ADMET Predictor performed better than Watanabe et al. with superior MAE and RPE values. The positive polar surface area, the number of basic functional groups and lipophilicity were the most important chemical descriptors for predicting fup. This study demonstrated that the prediction of fup was the most uncertain for highly binding compounds. This suggested that QSPR-predicted fup values should be used with caution in PBPK modeling.

Hepatic transporter-mediated pharmacokinetic drug-drug interactions: Recent studies and regulatory recommendations

Transporter-mediated drug-drug interactions are one of the major mechanisms in pharmacokinetic-based drug interactions and correspondingly affecting drugs' safety and efficacy. Regulatory bodies underlined the importance of the evaluation of transporter-mediated interactions as a part of the drug development process. The liver is responsible for the elimination of a wide range of endogenous and exogenous compounds via metabolism and biliary excretion. Therefore, hepatic uptake transporters, expressed on the sinusoidal membranes of hepatocytes, and efflux transporters mediating the transport from hepatocytes to the bile are determinant factors for pharmacokinetics of drugs, and hence, drug-drug interactions. In parallel with the growing research interest in this area, regulatory guidances have been updated with detailed assay models and criteria. According to well-established preclinical results, observed or expected hepatic transporter-mediated drug-drug interactions can be taken into account for clinical studies. In this paper, various methods including in vitro, in situ, in vivo, in silico approaches, and combinational concepts and several clinical studies on the assessment of transporter-mediated drug-drug interactions were reviewed. Informative and effective evaluation by preclinical tools together with the integration of pharmacokinetic modeling and simulation can reduce unexpected clinical outcomes and enhance the success rate in drug development.

Enabling direct and definitive free fraction determination for highly-bound compounds in protein binding assay

Protein binding determination for highly-bound compounds using equilibrium dialysis remains a challenge in drug discovery. The reasons are mainly three-fold; 1. due to their slow diffusion rate, highly-bound compounds require a much longer incubation time to reach dialysis equilibrium than typically needed; 2. highly-bound compounds are often hydrophobic and prone to non-specific binding in dialysis; 3. free drug concentration in the post incubation dialysate is too low for reliable analytical quantification. Modified equilibrium dialysis approaches include using diluted plasma for dialysis, or pre-saturating the non-specific binding sites in the dialysis device with compounds of interest prior to dialysis. In this study, we developed a customized equilibrium dialysis assay with an extended incubation time of 24 h, followed by microflow (μF) LC-MS/MS for bioanalysis, for direct and definitive free fraction determination of highly protein-bound compounds. The extended incubation time ensured the dialysis to reach equilibrium and saturating the non-specific binding sites, while μFLC-MS/MS provided far better sensitivity than the conventional LC-MS/MS typically used for post incubation bioanalysis. For a group of commercially available, highly protein-bound compounds, the free fraction data generated by the developed assay correlated very well with the literature values generated with diluted plasma method or pre-saturation method. This novel assay approach has been successfully used to generate protein binding results for highly-bound compounds to support ongoing drug discovery research.

Evaluation of the In Vitro Stability of Stimuli-Sensitive Fatty Acid-Based Microparticles for the Treatment of Lung Cancer

The fatty acid-based microparticles containing iron oxide nanoparticles and paclitaxel (PAX) are a viable proposition for the treatment of lung cancer. The microparticles inhaled as a dry powder can be guided to selected locations using an external magnetic field, and when accumulated there, the active compound release can be triggered by local hyperthermia. However, this general strategy requires that the active compound is released from microparticles and can reach the targeted cells before microparticles are removed. Isothermal titration calorimetry was used to demonstrate that the components of microparticles were released and transferred to albumins and lipid bilayers. The morphology of the measured particulates was studied with scanning electron microscopy and dynamic light scattering. To determine the cytotoxicity of microparticles, cell culture studies were done. It has been shown that the transfer efficiency depends predominantly on the fatty acid composition of microparticles, which, together with the active ingredient, accumulate predominantly in membrane structures after being released from microparticles and before entering the cytoplasm. The release process is sufficient; hence, paclitaxel-loaded microparticles effectively suppressed the proliferation of A549 human lung epithelial cells of malignant origin (IC₅₀ values for both lauric acid-based and myristic/palmitic-based microparticles containing paclitaxel were below 0.375 μg/mL), while reference microparticles were noncytotoxic.

Clinical implications of trials investigating drug-drug interactions between cannabidiol and enzyme inducers or inhibitors or common antiseizure drugs

Highly purified cannabidiol (CBD) has demonstrated efficacy with an acceptable safety profile in patients with Lennox-Gastaut syndrome or Dravet syndrome in randomized, double-blind, add-on, controlled phase 3 trials. It is important to consider the possibility of drug-drug interactions (DDIs). Here, we review six trials of CBD (Epidiolex/Epidyolex; 100 mg/mL oral solution) in healthy volunteers or patients with epilepsy, which investigated potential interactions between CBD and enzymes involved in drug metabolism of common antiseizure drugs (ASDs). CBD did not affect CYP3A4 activity. Induction of CYP3A4 and CYP2C19 led to small reductions in exposure to CBD and its major metabolites. Inhibition of CYP3A4 activity did not affect CBD exposure and caused small increases in exposure to CBD metabolites. Inhibition of CYP2C19 activity led to a small increase in exposure to CBD and small decreases in exposure to CBD metabolites. One potentially clinically important DDI was identified: combination of CBD and clobazam (CLB) did not affect CBD or CLB exposure, but increased exposure to major metabolites of both compounds. Reduction of CLB dose may be considered if adverse reactions known to occur with CLB are experienced when it is coadministered with CBD. There was a small increase of exposure to stiripentol (STP) when coadministered with CBD. STP had no effect on CBD exposure but led to minor decreases in exposure to CBD metabolites. Combination of CBD and valproate (VPA) did not cause clinically important changes in the pharmacokinetics of either drug, or 2-propyl-4-pentenoic acid. Concomitant VPA caused small increases in exposure to CBD metabolites. Dose adjustments are not likely to be necessary when CBD is combined with STP or VPA. The safety results from these trials were consistent with the known safety profile of CBD. These trials indicate an overall low potential for DDIs between CBD and other ASDs, except for CLB.

Controlled pharmacokinetic anti-cancer drug concentration profiles lead to growth inhibition of colorectal cancer cells in a microfluidic device

We present a microfluidic device to expose cancer cells to a dynamic, in vivo-like concentration profile of a drug, and quantify efficacy on-chip. About 30% of cancer patients receive drug therapy. In conventional cell culture experiments drug efficacy is tested under static concentrations, e.g. 1 μM for 48 hours, whereas in vivo, drug concentration follows a pharmacokinetic profile with an initial peak and a decline over time. With the rise of microfluidic cell culture models, including organs-on-chips, there are opportunities to more realistically mimic in vivo-like concentrations. Our microfluidic device contains a cell culture chamber and a drug-dosing channel separated by a transparent membrane, to allow for shear stress-free drug exposure and label-free growth quantification. Dynamic drug concentration profiles in the cell culture chamber were controlled by continuously flowing controlled concentrations of drug in the dosing channel. The control over drug concentrations in the cell culture chambers was validated with fluorescence experiments and numerical simulations. Exposure of HCT116 colorectal cancer cells to static concentrations of the clinically used drug oxaliplatin resulted in a sensible dose-effect curve. Dynamic, in vivo-like drug exposure also led to statistically significant lower growth compared to untreated control. Continuous exposure to the average concentration of the in vivo-like exposure seems more effective than exposure to the peak concentration (Cmax) only. We expect that our microfluidic system will improve efficacy prediction of in vitro models, including organs-on-chips, and may lead to future clinical optimization of drug administration schedules.

Characterization of plasma protein binding in two mouse models of humanized liver, PXB mouse and humanized TK-NOG mouse

The unbound fractions in plasma (f _up) in two mouse models of humanized liver mice, PXB and humanized TK-NOG mice, were compared with human f _up values using equilibrium dialysis method. A good relationship between f _up values obtained from PXB mice and humans was observed; the f _up of 34/39 compounds (87.2%) in PXB mice were within 3-fold of human f _up. In contrast, a weak correlation was observed between human and humanized TK-NOG mouse f _up values; the f _up of 15/24 compounds (62.5%) in humanized TK-NOG mice were within 3-fold of human f _up. As different profiles of plasma protein binding (PPB) profiles were observed between PXB and humanized TK-NOG mice, f _up evaluation is necessary in each mouse model to utilize these humanized liver mice for pharmacological, drug-drug interaction (DDI), and toxicity studies. The unbound fraction in the mixed plasma of human and SCID mouse plasma (85:15) was well correlated with f _up in PXB mice (38/39 compounds within a 3-fold). Thus, this artificial PXB mouse plasma could be used to evaluate PPB.

Canine orosomucoid (alpha-1 acid glycoprotein) variants and their influence on drug plasma protein binding

Orosomucoid polymorphisms influence plasma drug binding in humans; however, canine variants and their effect on drug plasma protein binding have not yet been reported. In this study, the orosomucoid gene (ORM1) was sequenced in 100 dogs to identify the most common variant and its allele frequency determined in 1,464 dogs (from 64 breeds and mixed-breed dogs). Plasma protein binding extent of amitriptyline, indinavir, verapamil, and lidocaine were evaluated by equilibrium dialysis using plasma from ORM1 genotyped dogs (n = 12). Free and total drug plasma concentrations were quantified by liquid chromatography-mass spectrometry. From the five polymorphisms identified in canine ORM1, two were nonsynonymous. The most common was c.70G>A (p.Ala24Thr) with an allele frequency of 11.2% (n = 1464). Variant allele frequencies varied by breed, reaching 74% in Shetland Sheepdogs (n = 21). Free drug fractions did not differ significantly (p > .05; Mann-Whitney U) between plasma collected from dogs with c.70AA (n = 4) and those with c.70GG (n = 8) genotypes. While c.70G>A did not affect the extent of plasma protein binding in our study, the potential biological and pharmacological implication of this newly discovered ORM1 variant in dogs should be further investigated.

The Impact of Infection and Inflammation on Drug Metabolism, Active Transport, and Systemic Drug Concentrations in Veterinary Species

Within human medicine, it is recognized that the pharmacokinetics (PK) of many compounds can be altered by the presence of inflammation or infection. Research into the reason for these changes has identified pathways that can influence drug absorption, clearance, and tissue distribution. In contrast, far less is known about these relationships within the framework of veterinary medicine. Rather, most of the PK data generated in veterinary species employs healthy subjects, raising the question of whether these studies are founded on an assumption that healthy animal PK reflect that of the diseased animal population. Accordingly, there is a need to explore the PK changes that might be overlooked in studies that recruit only healthy animals to assesses drug PK. To meet this objective, we surveyed the published literature for studies focusing on the impact of disease on the dose-exposure relationships in food-producing and companion animal species. We found that, consistent with humans and laboratory species, both up- and downregulation of the various cytochrome isoenzymes and/or transporters have occurred in response to an increase in inflammatory mediators. These findings suggest that, as observed in human medicine, the potential for differences in the drug PK in healthy versus animal patients points to a need for acquiring a greater understanding of these changes and how they may influence the dose-exposure-response relationships of veterinary pharmaceuticals. SIGNIFICANCE STATEMENT: This review delivers a much-needed summary of published information that provides insights into how disease and inflammation can influence the appropriateness of extrapolating laboratory-based dose-exposure-response relationships to what will occur in the actual veterinary patient. As part of this review, we also examine some of the method-associated issues to be considered when assessing the reported nature and magnitude of these changes.

A Fully Integrated Assay Panel for Early Drug Metabolism and Pharmacokinetics Profiling

Evaluation and optimization of physicochemical and metabolic properties of compounds are a crucial component of the drug development process. Continuous access to this information during the design-make-test-analysis cycle enables identification of chemical entities with suitable properties for efficient project progression. In this study, we describe an integrated and automated assay panel (DMPK Wave 1) that informs weekly on lipophilicity, solubility, human plasma protein binding, and metabolic stability in rat hepatocytes and human liver microsomes. All assays are running in 96-well format with ultraperformance liquid chromatography-mass spectrometry (MS)/MS as read-out. A streamlined overall workflow has been developed by optimizing all parts of the process, including shipping of compounds between sites, use of fit-for-purpose equipment and information systems, and technology for compound requesting, data analysis, and reporting. As a result, lead times can be achieved that well match project demands across sites independently of where compounds are synthesized. This robust screening strategy is run on a weekly basis and enables optimization of structure-activity relationships in parallel with DMPK properties to allow efficient and informed decision making.

Investigating the Role of Altered Systemic Albumin Concentration on the Disposition of Theophylline in Adult and Pediatric Patients with Asthma by Using the Physiologically Based Pharmacokinetic Approach

Theophylline is commonly used for the treatment of asthma and has a low hepatic clearance. The changes in plasma albumin concentration occurring in asthma may affect the exposure of theophylline. The aim of the presented work was to predict theophylline pharmacokinetics (PK) after incorporating the changes in plasma albumin concentration occurring in patients with asthma into a physiologically based pharmacokinetic (PBPK) model to see whether these changes can affect the systemic theophylline concentrations in asthma. The PBPK model was developed following a systematic model building approach using Simcyp. The predictions were performed initially in healthy adults after intravenous and oral drug administration. Only when the developed adult PBPK model had adequately predicted theophylline PK in healthy adults, the changes in plasma albumin concentrations were incorporated into the model for predicting drug exposure in patients with asthma. After evaluation of the developed model in the adult population, it was scaled to children on physiologic basis. The model evaluation was performed by using visual predictive checks and comparison of ratio of observed and predicted (R_obs/Pre) PK parameters along with their 2-fold error range. The developed PBPK model has effectively described theophylline PK in both healthy and diseased populations, as R_obs/Pre for all the PK parameters were within the 2-fold error limit. The predictions in patients with asthma showed that there were no significant changes in PK parameters after incorporating the changes in serum albumin concentration. The mechanistic nature of the developed asthma-PBPK model can facilitate its extension to other drugs. SIGNIFICANCE STATEMENT: Exposure of a low hepatic clearance drug like theophylline may be susceptible to plasma albumin concentration changes that occur in asthma. These changes in systemic albumin concentrations can be incorporated into a physiologically based pharmacokinetic model to predict theophylline pharmacokinetics in adult and pediatric asthma populations. The presented work is focused on predicting theophylline absorption, distribution, metabolism, and elimination in adult and pediatric asthma populations after incorporating reported changes in serum albumin concentrations to see their impact on the systemic theophylline concentrations.

Biological barriers, and the influence of protein binding on the passage of drugs across them

Drug-protein binding plays a key role in determining the pharmacokinetics of a drug. The distribution and protein binding ability of a drug changes over a lifetime, and are important considerations during pregnancy and lactation. Although proteins are a significant fraction in plasma composition, they also exist beyond the bloodstream and bind with drugs in the skin, tissues or organs. Protein binding influences the bioavailability and distribution of active compounds, and is a limiting factor in the passage of drugs across biological membranes and barriers: drugs are often unable to cross membranes mainly due to the high molecular mass of the drug-protein complex, thus resulting in the accumulation of the active compounds and a significant reduction of their pharmacological activity. This review describes the consequences of drug-protein binding on drug transport across physiological barriers, whose role is to allow the passage of essential substances-such as nutrients or oxygen, but not of xenobiotics. The placental barrier regulates passage of xenobiotics into a fetus and protects the unborn organism. The blood-brain barrier is the most important barrier in the entire organism and the skin separates the human body from the environment.

Application and Impact of Human Dose Projection from Discovery to Early Drug Development

The application and impact of human dose projection (HDP) has been well recognized in the late drug development phase, with increasing appreciation earlier during discovery and early development. This commentary describes the perspective of pharmaceutical scientists on the evolving application and impact of HDP at various phases from discovery to early development, including lead generation, lead optimization, lead up to candidate nomination, and early drug development. The underlying fundamental concepts and key input parameters for HDP are briefly discussed. A broad overview of phase-specific tools and approaches commonly utilized for human dose projection in the pharmaceutical industry is provided. A discussion of phase-appropriate implementation strategies, associated limitations/assumptions and continuous refinement for HDP from discovery to early development is presented. The authors describe the phase-specific applications of human dose projection to facilitate key assessments and relative impact on decision points.

A Phase II Randomized Trial to Explore the Potential for Pharmacokinetic Drug-Drug Interactions with Stiripentol or Valproate when Combined with Cannabidiol in Patients with Epilepsy

BACKGROUND

In recent randomized, placebo-controlled, phase III trials, highly purified cannabidiol demonstrated efficacy with an acceptable safety profile in patients with Lennox-Gastaut syndrome or Dravet syndrome. It is anticipated that antiepileptic drugs such as stiripentol and valproate will be administered concomitantly with cannabidiol.

OBJECTIVES

This trial evaluated the effect of cannabidiol on steady-state pharmacokinetics of stiripentol or valproate in patients with epilepsy, and the safety and tolerability of cannabidiol.

METHODS

This phase II, two-arm, parallel-group, double-blind, randomized, placebo-controlled trial recruited male and female patients with epilepsy aged 16-55 years. Patients receiving a stable dose of stiripentol or valproate were randomized 4:1 to receive concomitant double-blind cannabidiol or placebo. Patients received plant-derived, highly purified cannabidiol medicine (Epidiolex^® in the USA; Epidyolex^® in the EU; 100 mg/mL oral solution) at a dose of 20 mg/kg/day from day 12 to 26, following a 10-day dose-escalation period. Blood samples for pharmacokinetic evaluations were collected on days 1 and 26 before stiripentol/valproate dosing and up to 12 h postdose. Treatment-emergent adverse events (AEs) were recorded.

RESULTS

In total, 35 patients were recruited to the stiripentol arm (n = 14) or the valproate arm (n = 21). Both the safety and the pharmacokinetic populations of the stiripentol arm comprised 14 patients (2 placebo; 12 cannabidiol). The safety population of the valproate arm comprised 20 patients (4 placebo; 16 cannabidiol; one withdrew before receiving treatment); the pharmacokinetic population comprised 15 patients (3 placebo; 12 cannabidiol). Concomitant cannabidiol led to a small increase in stiripentol exposure (17% increase in maximum observed plasma concentration [C_max]; 30% increase in area under the concentration-time curve over the dosing interval [AUC_tau]). Concomitant cannabidiol also had little effect on valproate exposure (13% decrease in C_max; 17% decrease in AUC_tau) or its metabolite, 2-propyl-4-pentenoic acid (4-ene-VPA) (23% decrease in C_max; 30% decrease in AUC_tau). All changes in exposure are expressed as the dose-normalized geometric mean (CV%) day 26 to day 1 ratio. The most common AE was diarrhea; most AEs were mild. Two patients discontinued cannabidiol because of serious AEs (rash [n = 1] in the stiripentol arm; hypertransaminasemia [n = 1] in the valproate arm). A separate in vitro study investigated the bidirectional effect of cannabidiol, or its metabolite 7-carboxy-cannabidiol, on valproate plasma protein binding; no change in plasma protein binding was observed for either compound.

CONCLUSIONS

The clinical relevance of the increase in stiripentol exposure is unknown; patients receiving cannabidiol and stiripentol concomitantly should be monitored for adverse reactions as individual patient responses may vary. Coadministration of cannabidiol did not affect the pharmacokinetics of valproate or its metabolite, 4-ene-VPA, in adult patients with epilepsy. Safety results were consistent with the known safety profile of cannabidiol at a dose of 20 mg/kg/day. Clinicaltrials.gov: NCT02607891.

Pharmacokinetics and pharmacodynamics of inhaled corticosteroids for asthma treatment

The differences in the pharmacokinetic (PK) characteristics of inhaled corticosteroids (ICSs) critically influence the profile of each of them, but also the significant differences in glucocorticoid receptor selectivity, potency, and physicochemical properties are critical in defining the pharmacodynamic (PD) profile of an ICS. The PK and PD properties of ICSs used in asthma and the importance of their interrelationship have been reviewed. The differences among the ICSs in PK and PD must be considered when an ICS should be prescribed to an asthmatic patient because a better understanding of the PK/PD interrelationship of ICSs could be important to better fit with the between-patient variability and within-patient repeatability in the response to ICSs that often complicate the therapeutic approach to the asthmatic patient. The role of the device in influencing the PK profile of an ICS must be always considered because it is crucial. Also patient-related factors and disease severity affect pulmonary deposition of ICS.

Predicting Drug Binding to Human Serum Albumin and Alpha One Acid Glycoprotein in Diseased and Age Patient Populations

Plasma protein binding, namely the fraction unbound (f_u), can be an important determinant of the disposition and response of drugs. The primary objective of this study was to predict f_u values of 183 drugs utilizing either a single binding protein model, where the predominant binding protein had been established, or a multiple binding protein model (MBPM), where the relative binding contribution of human serum albumin (HSA) or alpha 1 acid glycoprotein (AAG) is known. Mean protein concentrations, dependent on disease or age, were used to account for changes in f_u. A simple scaling approach for binding protein concentration was employed to account for quantitative changes in molar concentrations of either HSA or AAG in their respective conditions. The MBPM predictive model works best if the relative binding contribution of HSA and AAG is known, and a scaler for the change in protein concentration can be adjusted accordingly. The value of MBPM was most evident when considering reported changes in lidocaine binding because of increasing AAG concentration in response to trauma. The present approach enhances the ability to predict f_u in diseased and age populations because of quantitative changes in major binding proteins.

Pharmacokinetic and pharmacodynamic interactions in anaesthesia. A review of current knowledge and how it can be used to optimize anaesthetic drug administration

This review describes the basics of pharmacokinetic and pharmacodynamic drug interactions and methodological points of particular interest when designing drug interaction studies. It also provides an overview of the available literature concerning interactions, with emphasis on graphic representation of interactions using isoboles and response surface models. It gives examples on how to transform this knowledge into clinically and educationally applicable (bedside) tools.

Dynamic time-kill curve characterization of spectinamide antibiotics 1445 and 1599 for the treatment of tuberculosis

Spectinamides are a novel class of antibiotics under development for the treatment of MDR- and XDR-tuberculosis, with 1599 and 1445 as early lead candidates within this group. In order to evaluate and differentiate the pharmacological properties of these compounds and assist in candidate selection and design of optimal dosing regimens in animal models of Mtb infection, time kill curve assessments were performed in a previously established in vitro PK/PD model system. The performed studies and subsequent pharmacometric analysis indicate that the anti-mycobacterial activity of 1599 exhibits concentration-dependent killing whereas 1445 shows time-dependent killing. These findings are supported by the fact that the PKPD index that best describes bacterial killing is T > MIC for 1445, but fC_max/AUC for 1599. The differential killing behavior among the lead candidates can be rationalized by the differences in post-antibiotic effect: 15.7 h for 1445 compared the 133 h for 1599. Overall, the PK/PD based analysis of the in vitro pharmacologic killing profile of spectinamides 1599 and 1445 on mycobacteria provided valuable insights that contributed to lead candidate selection and preclinical development of these compounds.

An examination of protein binding and protein-facilitated uptake relating to in vitro-in vivo extrapolation

As explained by the free drug theory, the unbound fraction of drug has long been thought to drive the efficacy of a molecule. Thus, the fraction unbound term, or f_u, appears in equations for fundamental pharmacokinetic parameters such as clearance, and is used when attempting in vitro to in vivo extrapolation (IVIVE). In recent years though, it has been noted that IVIVE does not always yield accurate predictions, and that some highly protein bound ligands have more efficient uptake than can be explained by their unbound fractions. This review explores the evolution of f_u terms included when implementing IVIVE, the concept of protein-facilitated uptake, and the mechanisms that have been proposed to account for facilitated uptake.

Nonlinear Protein Binding: Not What You Think

Nonlinear protein binding is traditionally thought of as an increasing fraction unbound with increasing total drug concentration. In the past several years, research into the protein binding of several tetracyclines has shown that an unexpected and counterintuitive phenomenon has been observed, specifically that of decreasing unbound drug fraction with increasing total concentrations of drug over certain concentration ranges. Although several studies of tigecycline have shown the importance calcium and its chelation may play in the protein-drug interaction, the potential clinical implications and relevance have not been explored. Here, we define typical and atypical nonlinear protein binding, overview protein binding theory, and discuss theoretical implications on pharmacokinetics. Using tigecycline as an example, in silico simulations and calculations show how when atypical nonlinear protein binding is not accounted for free drug exposure, and drug tissue penetration may be overestimated. It is important to revisit the impacts of nonlinearity in protein binding on clinical pharmacokinetics and pharmacodynamics, and ultimately, clinical efficacy. Although this phenomenon could potentially warrant clinical dose adjustment for certain compounds, it also presents a potential opportunity to exploit underlying mechanisms to develop new therapies and better understand molecular interactions of xenobiotics within the physiological system.

Liquid chromatography-tandem mass spectrometry for the simultaneous quantitation of ceftriaxone, metronidazole and hydroxymetronidazole in plasma from seriously ill, severely malnourished children

We have developed and validated a novel, sensitive, selective and reproducible reversed-phase high-performance liquid chromatography method coupled with electrospray ionization mass spectrometry (HPLC-ESI-MS/MS) for the simultaneous quantitation of ceftriaxone (CEF), metronidazole (MET) and hydroxymetronidazole (MET-OH) from only 50 µL of human plasma, and unbound CEF from 25 µL plasma ultra-filtrate to evaluate the effect of protein binding. Cefuroxime axetil (CEFU) was used as an internal standard (IS). The analytes were extracted by a protein precipitation procedure with acetonitrile and separated on a reversed-phase Polaris 5 C18-Analytical column using a mobile phase composed of acetonitrile containing 0.1% (v/v) formic acid and 10 mM aqueous ammonium formate pH 2.5, delivered at a flow-rate of 300 µL/min. Multiple reaction monitoring was performed in the positive ion mode using the transitions m/z555.1→ m/z396.0 (CEF), m/z172.2→ m/z 128.2 (MET), m/z188.0→ m/z125.9 (MET-OH) and m/z528.1→ m/z 364.0 (CEFU) to quantify the drugs. Calibration curves in spiked plasma and ultra-filtrate were linear ( r ² ≥ 0.9948) from 0.4-300 µg/mL for CEF, 0.05-50 µg/mL for MET and 0.02 - 30 µg/mL for MET-OH. The intra- and inter- assay precisions were less than 9% and the mean extraction recoveries were 94.0% (CEF), 98.2% (MET), 99.6% (MET-OH) and 104.6% (CEF in ultra-filtrate); the recoveries for the IS were 93.8% (in plasma) and 97.6% (in ultra-filtrate). The validated method was successfully applied to a pharmacokinetic study of CEF, MET and MET-OH in hospitalized children with complicated severe acute malnutrition following an oral administration of MET and intravenous administration of CEF over the course of 72 hours.

Integration of a plasma protein binding factor to the Chemical-Specific Adjustment Factor (CSAF) for facilitating the estimation of uncertainties in interspecies extrapolations when deriving health-based exposure limits for active pharmaceutical ingredients: Investigation of recent drug datasets

The objective was to challenge cross-species extrapolation factors with which to scale animal doses to human by any route for non-carcinogenic endpoints. The conventional hypothesis of the toxicokinetics (TK)-toxicodynamics (TD) relationship was equal toxicity at equal plasma level of the total drug moiety in each species, but this should also follow the free drug assumption, which states that only the unbound drug moiety in plasma may elicit a TD effect in tissue. Therefore, a protein binding factor (PBF) was combined with the Chemical-Specific Adjustment Factor (CSAF) (i.e., CSAF x PBF). The value of PBF of each drug was set equal to the ratio between human and animals of the unbound fraction in plasma (fu_p). Recent drug datasets were investigated. Our results indicate that any CSAF value would be increased or decreased while PBF deviates to the unity, and this required more attention. Accordingly, further testing indicated that the CSAF values set equal to basic allometric uncertainty factors according to the conventional hypothesis (dog∼2, monkey∼3.1, rat∼7, mouse∼12) would increase by including PBF for 30% of the drugs tested that showed a superior fu_p value in human compared to animals. However, default uncertainty factors in the range of 10-100 were less frequently exceeded. Overall, PBF could be combined with any other uncertainty factor to get reliable estimate of CSAF for each bound drug in deriving health-based exposure limits.

Liquid chromatography-tandem mass spectrometry for the simultaneous quantitation of ceftriaxone, metronidazole and hydroxymetronidazole in plasma from seriously ill, severely malnourished children

We have developed and validated a novel, sensitive, selective and reproducible reversed-phase high-performance liquid chromatography method coupled with electrospray ionization mass spectrometry (HPLC-ESI-MS/MS) for the simultaneous quantitation of ceftriaxone (CEF), metronidazole (MET) and hydroxymetronidazole (MET-OH) from only 50 µL of human plasma, and unbound CEF from 25 µL plasma ultra-filtrate to evaluate the effect of protein binding. Cefuroxime axetil (CEFU) was used as an internal standard (IS). The analytes were extracted by a protein precipitation procedure with acetonitrile and separated on a reversed-phase Polaris 5 C18-Analytical column using a mobile phase composed of acetonitrile containing 0.1% (v/v) formic acid and 10 mM aqueous ammonium formate pH 2.5, delivered at a flow-rate of 300 µL/min. Multiple reaction monitoring was performed in the positive ion mode using the transitions m/z555.1→ m/z396.0 (CEF), m/z172.2→ m/z 128.2 (MET), m/z188.0→ m/z125.9 (MET-OH) and m/z528.1→ m/z 364.0 (CEFU) to quantify the drugs. Calibration curves in spiked plasma and ultra-filtrate were linear ( r 2 ≥ 0.9948) from 0.4-300 µg/mL for CEF, 0.05-50 µg/mL for MET and 0.02 - 30 µg/mL for MET-OH. The intra- and inter- assay precisions were less than 9% and the mean extraction recoveries were 94.0% (CEF), 98.2% (MET), 99.6% (MET-OH) and 104.6% (CEF in ultra-filtrate); the recoveries for the IS were 93.8% (in plasma) and 97.6% (in ultra-filtrate). The validated method was successfully applied to a pharmacokinetic study of CEF, MET and MET-OH in hospitalized children with complicated severe acute malnutrition following an oral administration of MET and intravenous administration of CEF over the course of 72 hours.

Pharmacokinetics of the novel oral prostacyclin receptor agonist selexipag in subjects with hepatic or renal impairment

AIM

The aim of the present study was to explore the effect of hepatic or renal dysfunction on the pharmacokinetics (PK), tolerability and safety of selexipag, an orally active prostacyclin receptor agonist.

METHODS

Two prospective, open-label studies evaluated the PK of selexipag and its active metabolite ACT-333679 in healthy subjects and in subjects with mild, moderate and severe hepatic impairment or severe renal function impairment (SRFI). A single dose of 200 μg or 400 μg was administered. The PK parameters were derived from plasma concentration-time profiles.

RESULTS

Exposure increased with the severity of hepatic impairment. Geometric mean ratios and 90% confidence intervals of the area under the concentration-time curve from time zero to infinity (AUC0-∞ ) for selexipag and ACT-333679 increased 2.1-fold (1.7-2.6) and 1.2-fold (0.9-1.6) in subjects with mild hepatic impairment, and 4.5-fold (3.4-5.8) and 2.2-fold (1.7-2.8) in subjects with moderate hepatic impairment when compared with healthy subjects. The two subjects with severe hepatic impairment showed similar dose-normalized exposure to that of subjects with moderate hepatic impairment. A 1.7-fold increase in the AUC0-∞ of selexipag and ACT-333679 was observed with SRFI compared with healthy subjects. Although exposure to selexipag and/or ACT-333679 was higher in subjects with mild or moderate hepatic impairment or SRFI vs. healthy subjects, no safety concerns were raised in these groups.

CONCLUSIONS

Based on these observations, the PK data suggest that the clinically used starting dose needs no adjustments in patients with mild or moderate hepatic impairment or SRFI. However, doses should be up-titrated with caution in these patients. The small number of subjects limits the interpretation of selexipag PK in subjects with severe hepatic impairment.

Brief Report: Significant Decreases in Both Total and Unbound Lopinavir and Amprenavir Exposures During Coadministration: ACTG Protocol A5143/A5147s Results

This secondary analysis explored changes in protein-unbound concentrations of lopinavir and amprenavir when coadministered in HIV-infected subjects. Total and unbound pharmacokinetic parameters were calculated and compared between subjects receiving each agent alone and coadministration. When coadministered, unbound and total concentrations decrease. Coadministration significantly increased lopinavir unbound clearance, while significant changes in fraction unbound (fu) were not detected. For amprenavir, significant increases in fu and unbound clearance occurred with coadministration. This demonstrates the complex nature of drug-drug interactions between highly protein-bound, CYP-metabolized drugs, and the need to measure unbound concentrations in disease states such as hepatitis C, where such agents are coadministered.

The impact of the concentration of drug binding plasma proteins on drug distribution according to Øie-Tozer's model

1. New equations have been developed from an updated version of Øie-Tozer's model expressing how the free concentration and volume of distribution change in relation to changes in the concentration of drug binding plasma proteins. This updated model accommodates more than one drug binding plasma protein to contribute to the plasma protein binding. 2. Demonstrations of the model show that variability in the concentration of one plasma protein has considerably less impact on the free drug concentration and volume of distribution if other plasma proteins contribute to binding, than if they don't.

Discovery of Novel DNA Gyrase Inhibiting Spiropyrimidinetriones: Benzisoxazole Fusion with N-Linked Oxazolidinone Substituents Leading to a Clinical Candidate (ETX0914)

A novel class of bacterial type-II topoisomerase inhibitor displaying a spiropyrimidinetrione architecture fused to a benzisoxazole scaffold shows potent activity against Gram-positive and fastidious Gram-negative bacteria. Here, we describe a series of N-linked oxazolidinone substituents on the benzisoxazole that improve upon the antibacterial activity of initially described compounds of the class, show favorable PK properties, and demonstrate efficacy in an in vivo Staphylococcus aureus infection model. Inhibition of the topoisomerases DNA gyrase and topoisomerase IV from both Gram-positive and a Gram-negative organisms was demonstrated. Compounds showed a clean in vitro toxicity profile, including no genotoxicity and no bone marrow toxicity at the highest evaluated concentrations or other issues that have been problematic for some fluoroquinolones. Compound 1u was identified for advancement into human clinical trials for treatment of uncomplicated gonorrhea based on a variety of beneficial attributes including the potent activity and the favorable safety profile.

In vitro, in silico and integrated strategies for the estimation of plasma protein binding. A review

Plasma protein binding (PPB) strongly affects drug distribution and pharmacokinetic behavior with consequences in overall pharmacological action. Extended plasma protein binding may be associated with drug safety issues and several adverse effects, like low clearance, low brain penetration, drug-drug interactions, loss of efficacy, while influencing the fate of enantiomers and diastereoisomers by stereoselective binding within the body. Therefore in holistic drug design approaches, where ADME(T) properties are considered in parallel with target affinity, considerable efforts are focused in early estimation of PPB mainly in regard to human serum albumin (HSA), which is the most abundant and most important plasma protein. The second critical serum protein α1-acid glycoprotein (AGP), although often underscored, plays also an important and complicated role in clinical therapy and thus the last years it has been studied thoroughly too. In the present review, after an overview of the principles of HSA and AGP binding as well as the structure topology of the proteins, the current trends and perspectives in the field of PPB predictions are presented and discussed considering both HSA and AGP binding. Since however for the latter protein systematic studies have started only the last years, the review focuses mainly to HSA. One part of the review highlights the challenge to develop rapid techniques for HSA and AGP binding simulation and their performance in assessment of PPB. The second part focuses on in silico approaches to predict HSA and AGP binding, analyzing and evaluating structure-based and ligand-based methods, as well as combination of both methods in the aim to exploit the different information and overcome the limitations of each individual approach. Ligand-based methods use the Quantitative Structure-Activity Relationships (QSAR) methodology to establish quantitate models for the prediction of binding constants from molecular descriptors, while they provide only indirect information on binding mechanism. Efforts for the establishment of global models, automated workflows and web-based platforms for PPB predictions are presented and discussed. Structure-based methods relying on the crystal structures of drug-protein complexes provide detailed information on the underlying mechanism but are usually restricted to specific compounds. They are useful to identify the specific binding site while they may be important in investigating drug-drug interactions, related to PPB. Moreover, chemometrics or structure-based modeling may be supported by experimental data a promising integrated alternative strategy for ADME(T) properties optimization. In the case of PPB the use of molecular modeling combined with bioanalytical techniques is frequently used for the investigation of AGP binding.