Disease-induced changes in the plasma binding of basic drugs

Species-Specific Unbound Fraction Differences in Highly Bound PFAS: A Comparative Study across Human, Rat, and Mouse Plasma and Albumin

Per- and polyfluoroalkyl substances (PFAS) are a diverse group of fluorinated compounds which have yet to undergo comprehensive investigation regarding potential adverse health effects and bioaccumulative properties. With long half-lives and accumulative properties, PFAS have been linked to several toxic effects in both non-clinical species such as rat and mouse as well as human. Although biological impacts and specific protein binding of PFAS have been examined, there is no study focusing on the species-specific fraction unbound (fu) in plasma and related toxicokinetics. Herein, a presaturation equilibrium dialysis method was used to measure and validate the binding of 14 individual PFAS with carbon chains containing 4 to 12 perfluorinated carbon atoms and several functional head-groups to albumin and plasma of mouse (C57BL/6 and CD-1), rat, and human. Equivalence testing between each species-matrix combination showed positive correlation between rat and human when comparing fu in plasma and binding to albumin. Similar trends in binding were also observed for mouse plasma and albumin. Relatively high Spearman correlations for all combinations indicate high concordance of PFAS binding regardless of matrix. Physiochemical properties of PFAS such as molecular weight, chain length, and lipophilicity were found to have important roles in plasma protein binding of PFAS.

Functionalisation of brush polyethylene glycol polymers with specific lipids extends their elimination half-life through association with natural lipid trafficking pathways

Polymeric prodrugs have been applied to control the delivery of various types of therapeutics. Similarly, conjugation of peptide therapeutics to lipids has been used to prolong systemic exposure. Here, we extend on these two approaches by conjugating brush polyethylene glycol (PEG) polymers with different lipid components including short-chain (1C2) or medium-chain (1C12) monoalkyl hydrocarbon tails, cholesterol (Cho), and diacylglycerols composed of two medium-chain (2C12) or long-chain (2C18) fatty acids. We uniquely evaluate the integration of these lipid-polymers into endogenous lipid trafficking pathways (albumin and lipoproteins) and the impact of lipid conjugation on plasma pharmacokinetics after intravenous (IV) and subcutaneous (SC) dosing to cannulated rats. The IV and SC elimination half-lives of Cho-PEG (13 and 22 h, respectively), 2C12-PEG (11 and 17 h, respectively) and 2C18-PEG (12 h for both) were prolonged compared to 1C2-PEG (3 h for both) and 1C12-PEG (4 h for both). Interestingly, 1C2-PEG and 1C12-PEG had higher SC bioavailability (40 % and 52 %, respectively) compared to Cho-PEG, 2C12-PEG and 2C18-PEG (25 %, 24 % and 23 %, respectively). These differences in pharmacokinetics may be explained by the different association patterns of the polymers with rat serum albumin (RSA), bovine serum albumin (BSA) and lipoproteins. For example, in pooled plasma (from IV pharmacokinetic studies), 2C18-PEG had the highest recovery in the high-density lipoprotein (HDL) fraction. In conclusion, the pharmacokinetics of brush PEG polymers can be tuned via conjugation with different lipids, which can be utilised to tune the elimination half-life, biodistribution and effect of therapeutics for a range of medical applications. STATEMENT OF SIGNIFICANCE: Lipidation of therapeutics such as peptides has been employed to extend their plasma half-life by promoting binding to serum albumin, providing protection against rapid clearance. Here we design and evaluate innovative biomaterials consisting of brush polyethylene glycol polymers conjugated with different lipids. Importantly, we show for the first time that lipidated polymeric materials associate with endogenous lipoprotein trafficking pathways and this, in addition to albumin binding, controls their plasma pharmacokinetics. We find that conjugation to dialkyl lipids and cholesterol leads to higher association with lipid trafficking pathways, and more sustained plasma exposure, compared to conjugation to short and monoalkyl lipids. Our lipidated polymers can thus be utilised as delivery platforms to tune the plasma half-life of various pharmaceuticals.

Pharmacokinetics and Safety of Glasdegib in Participants With Moderate/Severe Hepatic Impairment: A Phase I, Single-Dose, Matched Case-Control Study

This phase I open-label trial (NCT03627754) assessed glasdegib pharmacokinetics and safety in otherwise healthy participants with moderate (Child-Pugh B) or severe (Child-Pugh C) hepatic impairment. Participants with hepatic impairment and age/weight-matched controls with normal hepatic function received a single oral 100-mg glasdegib dose under fasted conditions. The primary end points were area under the plasma concentration-time curve from time zero to infinity (AUCinf ) and maximum plasma concentration (Cmax ). Twenty-four participants (8/cohort) were enrolled. Glasdegib plasma exposures in moderate hepatic impairment were similar to controls, with adjusted geometric mean ratios (GMRs) of 110.8% (90% confidence interval [CI], 78.0-157.3) for AUCinf and 94.8% (69.9-128.4) for Cmax versus controls. In severe hepatic impairment, glasdegib plasma exposures were lower than controls (AUCinf GMR, 75.7%; 90%CI, 51.5-111.0; Cmax GMR, 58.0%; 90%CI, 37.8-89.0). Unbound glasdegib exposures were similar to controls for moderate (AUCinf,u GMR, 118.1%; 90%CI, 88.7-157.2; Cmax,u GMR, 101.1%; 90%CI, 78.4-130.3) and severe hepatic impairment (AUCinf,u GMR, 116.3%; 90%CI 81.8-165.5; Cmax,u GMR, 89.2%, 90%CI, 60.2-132.3). No treatment-related adverse events or clinically significant changes in laboratory values, vital signs, or electrocardiograms were observed. Together with previous findings, this suggests glasdegib dose modifications are not required based on hepatic impairment.

Development and Evaluation of a Physiologically Based Pharmacokinetic Drug-Disease Model of Propranolol for Suggesting Model Informed Dosing in Liver Cirrhosis Patients

AIM

The study was aimed to understand the underlying causes for the differences in propranolol pharmacokinetics (PK) between healthy and cirrhosis populations by using a systematic whole-body physiologically based pharmacokinetic (PBPK) model-building approach for suggesting model informed propranolol dosing in liver cirrhosis patients with different stages of disease severity.

METHODS

A whole-body PBPK model was developed by using population simulator PK-Sim® by using reported physicochemical and clinical data for propranolol in healthy and liver cirrhosis populations. The model evaluation was done by visual verification and comparison of PK parameters using their observed/predicted ratios (Robs/pred).

RESULTS

The developed model has effectively described the disposition of propranolol after intravenous and oral application in healthy and liver cirrhosis populations. All the model predictions were comparable to the observed clinical data and the Robs/pred for all the PK parameters were within a 2-fold range. A significant increase in plasma concentration of propranolol and decrease in drug clearance was observed in progressive stages of liver cirrhosis. The developed model after evaluation with the reported clinical PK data was used for suggesting model informed propranolol dosing in different stages of liver cirrhosis based on systemic unbound drug concentration.

CONCLUSION

The developed PBPK model has successfully described propranolol PK in healthy and cirrhosis populations after IV and oral administration. The evaluated PBPK propranolol-cirrhosis model can have many implications in predicting propranolol dosing in liver cirrhosis patients with different stages of disease severity.

Identification of candidate proteomic markers in the serum of medication overuse headache patients: An exploratory study

PURPOSE OF THE STUDY

The pathophysiological mechanism of medication overuse headache is uncertain; no distinctive markers have been described right now. The aim of this study was to conduct proteomic analyses on serum samples from patients with medication overuse headache and healthy individuals. Specifically, mono- (SDS-PAGE) and two-dimensional gel electrophoresis (2-DE) followed by liquid chromatography tandem mass spectrometry (LC-MS/MS) were used to evaluate changes in serum proteins.

MAIN FINDINGS

By SDS-PAGE, four over-expressed bands were revealed in patients, compared to controls. 2-DE combined with LC-MS/MS analysis allowed confirmation of some proteins preliminarily detected by SDS-PAGE: Hemopexin, alpha-1-acid glycoprotein 1, apolipoprotein A4 and haptoglobin. Moreover, other differential proteins were isolated, mostly increased in MOH patients: Alpha-1-antitrypsin, immunoglobulin heavy constant alpha 1, retinol binding protein and transthyretin. Only one protein, immunoglobulin kappa constant, was decreased in the patients' group.

CONCLUSIONS

The investigation of the serum proteome can offer a better understanding about biological mechanisms underlying medication overuse headache. Specifically, medication overuse headache shares some serum biochemical markers with chronic pain conditions. Further studies might uncover the relevance of these proteins in medication overuse headache.

An overview of albumin and alpha-1-acid glycoprotein main characteristics: highlighting the roles of amino acids in binding kinetics and molecular interactions

Although Albumin (ALB) and alpha-1-acid glycoprotein (AGP) have distinctive structural and functional characteristics, they both play a key role in binding a large variety of endogenous and exogenous ligands. An extensive binding to these plasma proteins could have a potential impact on drugs disposition (e.g. bioavailability, distribution and clearance), on their innocuity and their efficacy. This review summarizes the common knowledge about the structural and molecular characteristics of both ALB and AGP in humans, and about the most involved amino acids in their high-affinity binding pockets. However, the variability in residues found in binding pockets, for the same species, allows each plasma protein to interact differently with the ligands. The protein-ligand interaction influences differently the disposition of drugs that bind to either of these plasma proteins. The content of this review is useful for the design of new drug entities with high-binding characteristics, in qualitative and quantitative modelling (e.g. in vitro-in vivo extrapolations, 3D molecular docking, interspecies extrapolations), and for other interdisciplinary research.

Steady-state population pharmacokinetics of terizidone and its metabolite cycloserine in patients with drug-resistant tuberculosis

AIMS

Despite terizidone being part of the second-line recommended drugs for treatment of drug-resistant tuberculosis (DR-TB), information on its pharmacokinetics is scarce. The aim of this study was to describe the steady-state population pharmacokinetics (PPK) of terizidone and its primary metabolite cycloserine in patients with DR-TB and determine the effect of patient characteristics.

METHODS

This clinical study involved 39 adult DR-TB patients admitted to Brewelskloof Hospital in Cape Town, South Africa for intensive treatment phase. Blood samples were collected at predose and 0.5, 1, 2, 3, 3.5, 4, 8, 16 and 24 hours after drug administration. The estimation of PPK parameters was performed using nonlinear mixed-effects modelling software Monolix 2018R1. Free-fat mass was used to perform allometric scaling on disposition parameters.

RESULTS

A 1-compartment model best described the pharmacokinetics of terizidone and cycloserine. A modified transit compartment model described the absorption of terizidone. The parameters of terizidone model were mean transit time (1.7 h), absorption rate constant (2.97 h^-1 ), apparent volume of distribution (Vp/F: 13.4 L) and apparent total clearance (0.51 L h^-1 ). In the joint model, apparent fraction of terizidone converted to cycloserine was 0.29 while apparent clearance of terizidone via other routes and apparent cycloserine clearance was 0.1 L h^-1 and 2.94 L h^-1 , respectively. Serum albumin had significant effect on Vp/F.

CONCLUSIONS

The developed PPK model described well the concentration-time profile for terizidone and cycloserine in DR-TB patients. High albumin concentration was associated with low Vp/F.

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.

Antipsychotic-Induced Dopamine Supersensitivity Psychosis: Pharmacology, Criteria, and Therapy

The first-line treatment for psychotic disorders remains antipsychotic drugs with receptor antagonist properties at D2-like dopamine receptors. However, long-term administration of antipsychotics can upregulate D2 receptors and produce receptor supersensitivity manifested by behavioral supersensitivity to dopamine stimulation in animals, and movement disorders and supersensitivity psychosis (SP) in patients. Antipsychotic-induced SP was first described as the emergence of psychotic symptoms with tardive dyskinesia (TD) and a fall in prolactin levels following drug discontinuation. In the era of first-generation antipsychotics, 4 clinical features characterized drug-induced SP: rapid relapse after drug discontinuation/dose reduction/switch of antipsychotics, tolerance to previously observed therapeutic effects, co-occurring TD, and psychotic exacerbation by life stressors. We review 3 recent studies on the prevalence rates of SP, and the link to treatment resistance and psychotic relapse in the era of second-generation antipsychotics (risperidone, paliperidone, perospirone, and long-acting injectable risperidone, olanzapine, quetiapine, and aripiprazole). These studies show that the prevalence rates of SP remain high in schizophrenia (30%) and higher (70%) in treatment-resistant schizophrenia. We then present neurobehavioral findings on antipsychotic-induced supersensitivity to dopamine from animal studies. Next, we propose criteria for SP, which describe psychotic symptoms and co-occurring movement disorders more precisely. Detection of mild/borderline drug-induced movement disorders permits early recognition of overblockade of D2 receptors, responsible for SP and TD. Finally, we describe 3 antipsychotic withdrawal syndromes, similar to those seen with other CNS drugs, and we propose approaches to treat, potentially prevent, or temporarily manage SP.

Relationship between Protein Binding and Extravascular drug Concentrations of a Water-soluble Drug, Cytosine Arabinoside

The degree of binding of a drug to plasma proteins has a marked effect on its distribution, elimination, and pharmacological effect. Since only the unbound fraction is available for distribution into extravascular space, the ratio of drug in cerebrospinal fluid (CSF) or saliva to that in plasma is often regarded as a physiological measure of the free fraction of a drug. CSF: plasma and saliva: plasma ratios of cytosine arabinoside (araC) have been measured in patients with acute leukaemia and found to be 0.1–0.28, implying a binding of 72–90%.

The protein binding of araC was measured by equilibrium dialysis in the plasma of patients with acute leukaemia at presentation. The mean binding ratio was 2.3 ± 6.8, implying that there was little or no protein binding. There was no correlation between alpha — 1 acid glycoprotein (AAG) levels and protein binding.

The low CSF and saliva: plasma araC ratios found, suggest that drugs such as araC which have low lipid solubility do not pass freely into extravascular space. Thus the CSF or saliva: plasma ratio cannot be considered a good physiological measure of protein binding for drugs with poor lipid solubility.

Alpha-1-acidglycoprotein levels in infants during cardiopulmonary bypass and deep hypothermic circulatory arrest

Plasma levels of alpha-1-acidglycoprotein (AGP), the plasma protein primarily responsible for binding of a number of highly protein bound drugs (e.g. fentanyl, sufentanil, lidocaine, propranolol) that are frequently used during and/or immediately after cardiopulmonary bypass (CPB) with deep hypothermic circulatory arrest (DHCA), were investigated in six infants undergoing surgical repair of congenital heart disease. AGP levels dropped to 32% of control values (147mg/I ± 56 versus 458mg/l ± 83; p<0.0001 ) whereas albumin and total protein levels only decreased to 47% and 41 % of prebypass values respectively. This discrepancy could be explained by the addition of albumin containing solutions to the pump prime. Since protein binding of the above mentioned drugs will be significantly decreased, with a subsequent increase in the free pharmacologically active fraction of the drugs, caution is recommended when administering these drugs during or immediately after CPB/DHCA in order to avoid side effects and toxicity.

Glucose, sodium and plasma protein levels during deep hypothermic circulatory arrest using a low volume, minimal glucose priming solution based on washed packed red cells

The effect of a low volume, minimal glucose priming solution based on washed packed red cells on glucose, sodium and plasma protein levels during deep hypothermic circulatory arrest (DHCA) was studied in six patients of less than six months of age undergoing repair of congenital heart disease. Glucose levels during DHCA were not significantly different from prebypass values (6.2mmol/l±2.7 vs 7.1 mmol/l±2.8; p = 0.518), whereas plasma protein levels were significantly decreased (51.0g/l±0.7 vs 20.0g/l± 0.3; P = 0.0001) and sodium levels slightly but significantly increased (142mmol/l±3.8 vs 150mmol±3.8; p = 0.0026). In summary, the priming solution used in this study achieved good control of glucose levels during DHCA, although it needs some modification in regard to sodium and plasma protein content. A discussion of the choice of priming solution and a hypothesis for potential calcium-mediated reperfusion injury are also presented.

Derivatives of biarylalkyl carboxylic acid induce pleiotropic phenotypes in adult Schistosoma mansoni in vitro

Schistosomes and other parasitic platyhelminths cause infectious diseases of worldwide significance for humans and animals. Despite their medical and economic importance, vaccines are not available and the number of drugs is alarmingly limited. For most platyhelminths including schistosomes, Praziquantel (PZQ) is the commonly used drug. With respect to its regular application in mass treatment programs, however, there is increasing concern about resistance development.Previous studies demonstrated that inhibitors used to treat non-parasitic human diseases may be useful to be tested for their effects on parasites. To this end, we focused on biarylalkyl carboxylic acids (BACAs) as basis, which had been shown before to be interesting candidates in the context of finding alternative approaches to treat diabetes mellitus. We tested 32 chemically modified derivatives of these substances (biarylalkyl carboxylic acid derivatives (BACADs)) for their effects on adult Schistosoma mansoni in vitro. Treatment with 18 BACADs resulted in egg production-associated phenotypes and reduced pairing stability. In addition, 12 of these derivatives affected vitality and/or caused severe tegument damage, gut dilatation, or other forms of tissue disintegration which led to the death of worms. In most cases (10/12), one derivative caused more than one phenotype at a time. In vitro experiments in the presence of serum albumin (SA) and alpha-acidic glycoprotein (AGP) indicated a varying influence of these blood components on the effects of two selected derivatives. The variety of observed phenotypes suggested that different targets were hit. The results demonstrated that BACADs are interesting substances with respect to their anti-schistosomal effects.

Pharmacokinetic considerations and recommendations in palliative care, with focus on morphine, midazolam and haloperidol

INTRODUCTION

A variety of medications are used for symptom control in palliative care, such as morphine, midazolam and haloperidol. The pharmacokinetics of these drugs may be altered in these patients as a result of physiological changes that occur at the end stage of life.

AREAS COVERED

This review gives an overview of how the pharmacokinetics in terminally ill patients may differ from the average population and discusses the effect of terminal illness on each of the four pharmacokinetic processes absorption, distribution, metabolism, and elimination. Specific considerations are also given for three commonly prescribed drugs in palliative care: morphine, midazolam and haloperidol).

EXPERT OPINION

The pharmacokinetics of drugs in terminally ill patients can be complex and limited evidence exists on guided drug use in this population. To improve the quality of life of these patients, more knowledge and more pharmacokinetic/pharmacodynamics studies in terminally ill patients are needed to develop individualised dosing guidelines. Until then knowledge of pharmacokinetics and the physiological changes that occur in the final days of life can provide a base for dosing adjustments that will improve the quality of life of terminally ill patients. As the interaction of drugs with the physiology of dying is complex, pharmacological treatment is probably best assessed in a multi-disciplinary setting and the advice of a pharmacist, or clinical pharmacologist, is highly recommended.

Population pharmacokinetic/pharmacogenetic model of lopinavir/ritonavir in HIV-infected patients

AIM

This study aims to develop a population pharmacokinetic/pharmacogenetic model for lopinavir/ritonavir (LPV/r) in European HIV-infected patients.

MATERIALS & METHODS

A total of 693 LPV/r plasma concentrations were assessed and 15 single-nucleotide polymorphisms were genotyped. The population pharmacokinetic/pharmacogenetic model was created using a nonlinear mixed-effect approach (NONMEM^® v.7.2.0., ICON Development Solutions, Dublin, Ireland).

RESULTS

Covariates significantly related to LPV/r apparent clearance (CL/F) were ritonavir trough concentration (RTC), BMI, high-density lipoprotein cholesterol (HDL-C) and certain single-nucleotide polymorphisms in genes encoding for metabolizing enzymes, which are representable as follows: CL/F = (0.216BMI + 0.0125HDL-C) × 0.713^RTC × 1.26^{rs28371764[C/T]} × 0.528^{rs6945984[C/C]} × 0.302 ^{CYP3A4[1461insA/del]} Conclusion: The LPV/r standard dose appears to be appropriate for the rs28371764[C/T] genotype. However, lower doses should be recommended for the rs6945984[C/C] and CYP3A4[1461insA/del] genotypes and even for those patients without any of these variants, as the standard dose seems to be higher than that which is required in order to achieve therapeutic levels.

Serum albumin and α-1 acid glycoprotein impede the killing of Schistosoma mansoni by the tyrosine kinase inhibitor Imatinib

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The Abl tyrosine-kinase inhibitor Imatinib is toxic to S. mansoni in vitro but not in vivo in rodents.

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Blood components like serum albumin and alpha-1 acid glycoprotein (AGP) negated Imatinib’s toxicity in vitro.

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Erythromycin partially restored the toxicity of Imatinib in vitro.

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High levels of AGP upon infection make rodents poor models for examining some small molecule inhibitors.

In the search for new drugs and drug targets to treat the flatworm disease schistosomiasis, protein kinases (PKs) have come under particular scrutiny because of their essential roles in developmental and physiological processes in schistosome parasites. In this context the application of the anti-cancer Abl tyrosine kinase (TK) inhibitor Imatinib (Gleevec/Glivec; STI-571) to adult Schistosoma mansoni in vitro has indicated negative effects on diverse physiological processes including survival.

Motivated by these in vitro findings, we performed in vivo experiments in rodent models of S. mansoni infection. Unexpectedly, Imatinib had no effect on worm burden or egg-production. We found that the blood components serum albumin (SA) and alpha-1 acid glycoprotein (AGP or orosomucoid) negated Imatinib’s deleterious effects on adult S. mansoni and schistosomula (post-infective larvae) in vitro. This negative effect was partially reversed by erythromycin. AGP synthesis can increase as a consequence of inflammatory processes or infection; in addition upon infection AGP levels are 6–8 times higher in mice compared to humans. Therefore, mice and probably other rodents are poor infection models for measuring the effects of Imatinib in vivo. Accordingly, we suggest the routine evaluation of the ability of AGP and SA to block in vitro anti-schistosomal effects of small molecules like Imatinib prior to laborious and expensive animal experiments.

Toxicogenetics of lopinavir/ritonavir in HIV-infected European patients

AIMS

We present a genetic association study in 106 European HIV-infected individuals aimed at identifying and confirming polymorphisms that have a significant influence on toxicity derived from treatment with lopinavir/ritonavir (LPV/r).

PATIENTS & METHODS

Genotyping was performed by matrix-assisted laser desorption/ionization-time of flight and KASPar^® (KBiosciences, Hoddesdon, UK); LPV/r plasma concentrations were quantified using HPLC with an UV detection system and the pharmacokinetic parameters were estimated using Bayesian algorithms. Genetic association analysis was performed with PASW Statistics 18 (SPSS Inc., IL, USA) and R for Windows (Microsoft, WA, USA).

RESULTS

Suggestive relationships have been established between lipid plasma levels and total bilirubin and SNPs in CETP, MCP1, ABCC2, LEP and SLCO1B3 genes and between diarrhea and SNPs in IL6 gene.

CONCLUSION

Replication analysis should confirm the novel results obtained in this study prior to its application in the clinical practice to achieve a safer LPV/r-based combined antiretroviral therapy.

Protein-bound molecules: a large family with a bad character

Many small solutes excreted by the kidney are bound to plasma proteins, chiefly albumin, in the circulation. The combination of protein binding and tubular secretion allows the kidney to reduce the free, unbound concentrations of such solutes to lower levels than could be obtained by tubular secretion alone. Protein-bound solutes accumulate in the plasma when the kidneys fail, and the free, unbound levels of these solutes increase more than their total plasma levels owing to competition for binding sites on plasma proteins. Given the efficiency by which the kidney can clear protein-bound solutes, it is tempting to speculate that some compounds in this class are important uremic toxins. Studies to date have focused largely on two specific protein-bound solutes: indoxyl sulfate and p-cresyl sulfate. The largest body of evidence suggests that both of these compounds contribute to cardiovascular disease, and that indoxyl sulfate contributes to the progression of chronic kidney disease. Other protein-bound solutes have been investigated to a much lesser extent, and could in the future prove to be even more important uremic toxins.

Accuracy of the analysis of free vancomycin concentration by ultrafiltration in various disease states

The different ultrafiltrate volume results in different unbound vancomycin fractions as determined by centrifugal ultrafiltration and hollow fiber centrifugal ultrafiltration.

A physiologically based pharmacokinetic (PBPK) approach to evaluate pharmacokinetics in patients with cancer

Potential differences in pharmacokinetics (PK) between healthy subjects and patients with cancer were investigated using a physiologically based pharmacokinetic approach integrating demographic and physiological data from patients with cancer. Demographic data such as age, sex and body weight, and clinical laboratory measurements such as albumin, alpha-1 acid glycoprotein (AAG) and hematocrit were collected in ~2500 patients with cancer. A custom oncology population profile was built using the observed relationships among demographic variables and laboratory measurements in Simcyp® software, a population based ADME simulator. Patients with cancer were older compared with the age distribution in a built-in healthy volunteer profile in Simcyp. Hematocrit and albumin levels were lower and AAG levels were higher in patients with cancer. The custom population profile was used to investigate the disease effect on the pharmacokinetics of two probe substrates, saquinavir and midazolam. Higher saquinavir exposure was predicted in patients relative to healthy subjects, which was explained by the altered drug binding due to elevated AAG levels in patients with cancer. Consistent with historical clinical data, similar midazolam exposure was predicted in patients and healthy subjects, supporting the hypothesis that the CYP3A activity is not altered in patients with cancer. These results suggest that the custom oncology population profile is a promising tool for the prediction of PK in patients with cancer. Further evaluation and extension of this population profile with more compounds and more data will be needed.

A chemogenomic analysis of ionization constants--implications for drug discovery

Chemogenomics methods seek to characterize the interaction between drugs and biological systems and are an important guide for the selection of screening compounds. The acid/base character of drugs has a profound influence on their affinity for the receptor, on their absorption, distribution, metabolism, excretion and toxicity (ADMET) profile and the way the drug can be formulated. In particular, the charge state of a molecule greatly influences its lipophilicity and biopharmaceutical characteristics. This study investigates the acid/base profile of human small-molecule drugs, chemogenomics datasets and screening compounds including a natural products set. We estimate the acid-ionization constant (pK(a)) values of these compounds and determine the identity of the ionizable functional groups in each set. We find substantial differences in acid/base profiles of the chemogenomic classes. In many cases, these differences can be linked to the nature of the target binding site and the corresponding functional groups needed for recognition of the ligand. Clear differences are also observed between the acid/base characteristics of drugs and screening compounds. For example, the proportion of drugs containing a carboxylic acid was 20 %, in stark contrast to a value of 2.4 % for the screening set sample. The proportion of aliphatic amines was 27 % for drugs and only 3.4 % for screening compounds. This suggests that there is a mismatch between commercially available screening compounds and the compounds that are likely to interact with a given chemogenomic target family. Our analysis provides a guide for the selection of screening compounds to better target specific chemogenomic families with regard to the overall balance of acids, bases and pK(a) distributions.

Revolutionary impact of nanodrug delivery on neuroscience

Brain research is the most expanding interdisciplinary research that is using the state of the art techniques to overcome limitations in order to conduct more accurate and effective experiments. Drug delivery to the target site in the central nervous system (CNS) is one of the most difficult steps in neuroscience researches and therapies. Taking advantage of the nanoscale structure of neural cells (both neurons and glia); nanodrug delivery (second generation of biotechnological products) has a potential revolutionary impact into the basic understanding, visualization and therapeutic applications of neuroscience. Current review article firstly provides an overview of preparation and characterization, purification and separation, loading and delivering of nanodrugs. Different types of nanoparticle bioproducts and a number of methods for their fabrication and delivery systems including (carbon) nanotubes are explained. In the second part, neuroscience and nervous system drugs are deeply investigated. Different mechanisms in which nanoparticles enhance the uptake and clearance of molecules form cerebrospinal fluid (CSF) are discussed. The focus is on nanodrugs that are being used or have potential to improve neural researches, diagnosis and therapy of neurodegenerative disorders.

A fast, sensitive and simple method for mirtazapine quantification in human plasma by HPLC-ESI-MS/MS. Application to a comparative bioavailability study

In the present study a simple, fast, sensitive and robust method to quantify mirtazapine in human plasma using quetiapine as the internal standard (IS) is described. The analyte and the IS were extracted from human plasma by a simple protein precipitation with methanol and were analyzed by high-performance liquid chromatography coupled to an electrospray tandem triple quadrupole mass spectrometer (HPLC-ESI-MS/MS). Chromatography was performed isocratically on a C(18), 5 µm analytical column and the run time was 1.8 min. The lower limit of quantitation was 0.5 ng/mL and a linear calibration curve over the range 0.5-150 ng/mL was obtained, showing acceptable accuracy and precision. This analytical method was applied in a relative bioavailability study in order to compare a test mirtazapine 30 mg single-dose formulation vs a reference formulation in 31 volunteers of both sexes. The study was conducted in an open randomized two-period crossover design and with a 14 day washout period. Since the 90% confidence interval for C(max) , AUC(last) and AUC(0-inf) were within the 80-125% interval proposed by the Food and Drug Administration and ANVISA (Brazilian Health Surveillance Agency), it was concluded that mirtazapine 30 mg/dose is bioequivalent to the reference formulation, according to both the rate and extent of absorption.

Plasma Protein Binding of Quinine: Binding to Human Serum Albumin, α1-Acid Glycoprotein and Plasma from Patients with Malaria

The binding of quinine to human serum albumin (HSA), α1-acid glycoprotein (AAG) and plasma obtained from healthy subjects (10 Caucasians and 15 Thais) and from Thai patients with falciparum malaria (n = 20) has been investigated. In healthy volunteers, plasma protein binding expressed as the percentage of unbound quinine was 7·9–31·0% (69–92·1% bound). The mean percentage of unbound quinine found with essentially fatty acid-free HSA (40 g L−1) was 65·4±1 −5% (mean±s.d.) and was comparable with the value (66·3 ± 3·8%, mean ± s.d.) for Fraction V HSA (40 g L−1)- This suggests that fatty acids do not influence the plasma protein binding of quinine. Binding of quinine to 0·7 g L−1 AAG was high (mean unbound 61·0 ± 5·0%), indicating that quinine is bound primarily to AAG and albumin, although other plasma proteins such as lipoproteins may be involved. The mean percentage of unbound quinine was slightly less in Caucasians (14·8 ± 6·7% unbound), compared with healthy Thai subjects (17·0 ± 6·7% unbound). The higher binding of quinine in Caucasian subjects was associated with a higher plasma AAG concentration observed in Caucasians. Mean percentage of unbound quinine was significantly lower in Thai patients with malaria (10·9 ± 4·0%) than in the healthy Thai subjects. The increase in the extent of quinine binding corresponded with the increase in the acute-phase reactant protein, AAG in the patients with malaria. Overall, when the data were combined there was a significant correlation (r = 0·846, P &lt; 0·005) between the binding ratio (bound/unbound) of quinine and the plasma AAG concentration. This suggests that plasma AAG concentration may serve as a useful index to predict alterations in quinine binding. Although quinine is bound to albumin, it was not bound to either site I or site II on HSA as indicated from equilibrium dialysis and fluorescent probe displacement studies. Binding displacement studies revealed that there was no marked displacement of quinine by a variety of highly bound acidic and basic drugs, including other antimalarial drugs at their therapeutic concentrations.

Investigation of the Interaction Mode of Phenothiazine Neuroleptics with α1-Acid Glycoprotein

The interaction of phenothiazine neuroleptics with α1-acid glycoprotein (AGP) and desialylated AGP (asialoAGP) has been investigated by fluorescence, circular dichroism spectroscopy and by equilibrium dialysis. The binding parameters of phenothiazines obtained from fluorescence agreed closely with those obtained from circular dichroism and equilibrium dialysis. The binding affinities (nK) to AGP were slightly higher than binding affinities to asialoAGP. Attempts to correlate binding affinities with partition coefficients suggested that hydrophobic forces were mainly involved in the binding of phenothiazine neuroleptics to AGP and asialoAGP. However, electrostatic interaction was also found to be involved as suggested by experimental data obtained from the influence of oleic acid and caesium chloride on the drug binding to the two proteins.

Influence of changes in protein binding on the central activity of antidepressants

The central effect (expressed as analgesic response), protein binding and brain uptake of mianserin were measured in mice receiving drug intraperitoneally. A significant decrease of the central effect of mianserin (30 mg kg−1) was seen in mice with experimental inflammation when compared with control animals (reaction time (s)= 12·12 ± 1·22 vs 25·56 ± 2·92; P &lt; 0·001) and the dose-analgesia response curve (10−60 mg kg−1) was significantly shifted to the right in mice with inflammation. In serum of mice with inflammation, unbound concentration of mianserin was decreased from 19·37 ± 0·73 to 17·83 ± 0·30% (P &lt; 0·05) and seromucoid levels were significantly increased (P &lt; 0·001). Following the intraperitoneal administration of 30 mg kg−1 of mianserin, brain uptake decreased in diseased mice when compared with control animals (P &lt; 0·02), suggesting that the decrease in analgesia was secondary to a decrease in drug delivery to the brain because of increased protein binding.

Effects of a Perfluorochenical Emulsion on Propranolol Binding by Alpha-I-Acid Glycoprotein

The binding of propranolol by a perfluorochemical emulsion (PFCE), cXiacid glycoprotein (AGP), and their mixtures was examined by a dialysis exchange method at 37°C. A sedimentation method was used to verify propranolol binding by the PFCE. Binding of 100 and 500 ng/ml drug by 100, 75, 50 and 25% v/v concentrations of the PFCE or of 0.067% AGP was determined. Propranolol was highly bound by the PFCE with a percent free propranolol in undiluted PFCE of 13.1% at both 100 and 500 ng/ml propranolol. Propranolol was moderately bound by AGP. The percent free propranolol in 0.067% AGP was 31.4% and 32.4% for 100 and 500 ng/ml propranolol, respectively. The percent bound propranolol was not significantly different when the emulsion was diluted to 75 and 50% v/v with 0.067% AGP solution rather than buffer. When the PFCE was further diluted to 25% v/v with the 0.067% AGP solution the percent free propranolol was significantly lower than in the 25% v/v PFCE alone or 75% v/v protein solution alone. Thus, the PFCE has a relatively large affinity and capacity for propranolol. Propranolol did not partition from buffer to the PFC liquid. This indicates that propranolol bound by the PFCE is associated only with the emulsifiers.

Significance of protein binding in pharmacokinetics and pharmacodynamics

The significance of plasma protein binding on drug efficacy and, subsequently, the clinical relevance of changes in protein binding has been controversially discussed for decades. The uncertainty concerning the impact of plasma protein binding on a drug's pharmacological activity is, in part, related to the approach used when investigating and interpreting protein binding effects in vitro and in vivo. Frequently, a generalized one-size-fits-all approach, such as "protein binding does matter/does not matter," may not be applicable. An appropriate analysis requires careful consideration of both pharmacokinetic and pharmacodynamic processes, as they both contribute to the safety and efficacy of drugs. Therefore, the aim of this article is to provide a concise review of the theoretical concepts of protein binding, and to discuss relevant examples where applicable.

Evaluation of a hydrazide-linked alpha1-acid glycoprotein chiral stationary phase: separation of R- and S-propranolol

The binding and chiral separation of R- and S-propranolol was investigated on a new type of alpha1-acid glycoprotein (AGP) column. This column was prepared through the controlled and mild oxidation of AGP, followed by the immobilization of this protein to hydrazide-activated silica. The effects of temperature, pH, ionic strength, and organic modifiers on the retention and separation of R- and S-propranolol were investigated on this column. Both the association equilibrium constants and number of binding sites for R/S-propranolol on the AGP column were found to increase with temperature and affect the measured retention factors for these compounds. Regarding the other factors, a change in the organic modifier concentration was found to give the largest change in retention and separation. It was found through these studies that both coulombic and hydrophobic interactions played important roles in determining the retention of R- and S-propranolol on the AGP column. The efficiency and separation impedance of this system were also considered. Under the final optimum conditions identified in this study, it was possible to separate R- and S-propranolol with a resolution of greater than 1.38 in less than 5 min on a 4.1 mm I.D. x 5 cm column.

Reproducible and time-dependent modification of serum protein binding in Wistar Kyoto rats

INTRODUCTION

The theoretical basis of the influence of (alterations in) plasma protein binding on pharmacokinetics (PK) is well-established. In contrast, the impact of protein binding on pharmacodynamics has not been examined in a systematic manner. Here we present an experimental approach to modify serum protein levels and binding in the rat, in a robust, reproducible, and time-dependent manner.

METHOD

Male Wistar Kyoto rats were divided into three different groups. The control group (n=4) did not receive treatment. In the cannulation(-) group (n=6) the rats were instrumented with three permanent blood cannulas. The rats in the cannulation(+) group received in addition to the cannulation a subcutaneous injection of turpentine oil of 100 microl/100 g bodyweight. The effects were characterized in terms of 1) the time course of serum levels of albumin and alpha(1)-acid glycoprotein (AGP), and 2) the effect on the ex vivo serum protein binding of S(-)-propranolol.

RESULTS

In control rats the AGP serum concentration was stable at a value of 169+/-16 microg/ml. In the cannulation(-) group a maximum ten- to fifteen-fold increase in serum AGP concentration was observed at 48 h post surgery, followed by a gradual return back to baseline within 1 week. In the cannulation(+) group a similar concentration-time profile for AGP was found, but without a complete return to baseline within 1 week and with a much higher variability. Ex vivo, an increase in AGP serum concentration from 55 to 675 microg/ml resulted in a profound decrease in the free fraction of S(-)-propranolol from 14+/-0.6 to 1.9+/-0.3%.

CONCLUSIONS

In conclusion, through cannulation alone the serum protein levels and binding were modified in a robust, reproducible and time-dependent manner. Therefore this experimental approach is suitable for the investigation of the influence of protein binding on both pharmacokinetics and pharmacodynamics.

Pharmacokinetics of Antiepileptic Drugs in Elderly Nursing Home Residents

With approximately 10% of elderly nursing home residents taking antiepileptic drugs (AEDs), it is critical to understand the pharmacokinetics, dosing, and possible adverse reactions of these AEDs. In this chapter, five AEDs commonly prescribed to nursing home residents will be discussed. Phenytoin (PHT), the most commonly used AED in this population, is extensively metabolized by the cytochrome P450 enzyme system, is highly protein bound, and interacts with many concomitant medications. Up to 45% of nursing home residents who receive PHT have concentrations below the range (subtherapeutic) used in adults (<65 years), while approximately 10% of residents have concentrations that are potentially toxic (>20 microg/ml). In addition, serum PHT concentrations can vary greatly within an individual resident and may be subtherapeutic one day and potentially toxic the next. Valproic acid is taken by approximately 9-17% of nursing home residents who are administered AEDs, with over half using it for nonseizure indications. Doses are approximately 16 mg/kg/day in elderly nursing home residents, but doses and serum concentrations are lower in the oldest age group (> or =85 years). A majority of residents are maintained at serum concentrations considered subtherapeutic for epilepsy, whereas relatively few (approximately 3%) are maintained at toxic levels. The average (+/-SD) carbamazepine (CBZ) dose is 8.8 +/- 4.7 mg/kg/day, yielding a mean serum concentration of 6.3 +/- 2.2 mg/liter. Subtherapeutic concentrations are found in up to 20% of serum measurements, while 2.5% of serum measurements are in the toxic range. CBZ is highly bound to serum albumin and alpha1-acid glycoprotein and is metabolized to carbamazepine-10,11-epoxide, an active metabolite thought to be responsible for some side effects. Phenobarbital (PB) is frequently combined with PHT. This combination can cause devastating side effects because both PB and PHT can produce cognitive side effects. Gabapentin is one of the newer AEDs frequently administered to nursing home residents. Its lack of both hepatic metabolism and protein binding potentially makes it a safer drug in this population.

Alfentanil-induced miosis clearance as a liver CYP3A4 and 3A5 activity measure in healthy volunteers: improvement of experimental conditions

The aims of this study were to demonstrate the correlation between alfentanil-induced miosis evaluation and alfentanil pharmacokinetics (PK) as a CYP3A4 and 3A5 activity probe in volunteers and to explain the variability in pupilar response and in alfentanil PK. In ambient light, the miosis kinetic parameters were significantly correlated with PK (CLs: r = 0.9, P = .00; AUCs: r = 0.8, P = .01). In dark, a similar correlation was observed between miosis and alfentanil clearances (r = 0.85, P = .03). In 6 volunteers, the sigmoid E(max) model was applicable (average E(max) = 2.5 +/- 0.7 mm, gamma = 2.5 +/- 1.6 and EC(50) = 76.8 +/- 22.3 ng/mL), and in 3, the simple E(max) model was applicable (average E(max) = 2.8 +/- 0.3 mm and EC(50) = 19.9 +/- 8.5 ng/mL). There was a large interindividual variability in PK parameters (coefficient of variation = 19.7%-31.2%). Free drug fraction concentrations were negatively correlated with plasma alpha(1)-AGP (r = -0.9, P = .04) and albumin levels (r = -0.94, P = .02). Alfentanil-induced miosis clearance as a noninvasive CYP3A4 and 3A5 activity measure can be done in both ambient and dark conditions. Drug free fraction may be responsible for large intersubject variability in alfentanil PK.

Opioids in pediatric anesthesia

Opioids are used widely in the practice of pediatric anesthesia and pediatric perioperative medicine. The benefits of opioids are well documented, and their pharmacology has been extensively studied. Nonetheless special care is important when using these agents in the pediatric population. This article addresses the developmental pharmacologic changes that occur with opioids as well as their most common clinical uses.

Development of a solid phase extraction for 13 'new' generation antidepressants and their active metabolites for gas chromatographic-mass spectrometric analysis

A solid phase extraction procedure (SPE) for 13 'new' antidepressants (venlafaxine, fluoxetine, viloxazine, fluvoxamine, mianserin, mirtazapine, melitracen, reboxetine, citalopram, maprotiline, sertraline, paroxetine and trazodone) together with eight of their metabolites (O-desmethylvenlafaxine, norfluoxetine, desmethylmianserine, desmethylmirtazapine, desmethylcitalopram, didesmethylcitalopram, desmethylsertraline and m-chlorophenylpiperazine) from plasma is optimized using HPLC-DAD as monitoring system. Special attention has been paid to the choice of washing and eluting solvent, resulting in a highly concentrated, clean and moisture free extract, also suitable for GC-MS. A total number of 10 sorbents (apolar, polymeric, ion-exchange and mixed mode) was evaluated. Based on recovery, reproducibility and absence of interfering substances the strong cation exchanger gave the best results. Recoveries were determined at low and high therapeutic and toxic levels and ranged between 70 and 109% for all compounds, except for trazodone (39%).

Role of biokinetics in risk assessment of drugs and chemicals in children

Whether children incur different risks from xenobiotics than adults will depend on the exposure, biokinetics, and dynamics of compound. In this paper, current knowledge on developmental physiology and possible effects on biokinetics are evaluated and the role of biokinetics in risk assessment both for drugs and chemicals is discussed. It is concluded that most dramatic age-related physiological changes that may affect biokinetics occur in the first 6-12 months of age. The difference in internal exposure between children and adults can generally be predicted from already known developmental physiological differences. However, for risk assessment it will also be necessary to determine whether internal exposure is within the drug's therapeutic window or if it will exceed the NOAEL of a chemical. Furthermore, the effects of internal exposure of potentially harmful compounds on developing organ systems is of utmost importance. However, knowledge on this aspect is very limited. Risk assessment in children could be improved by: (1) application of pediatric PBPK-models in order to gain insight into internal exposure in children, (2) studies in juvenile animals for studying effects on developing systems, and (3) extrapolation of knowledge on the relationship between internal exposure and dynamics for drugs to other chemicals.

The Binding of Selected Therapeutic Drugs to Human Serum α-1 Acid Glycoprotein and to Human Serum Albumin In Vitro

The binding of acetaminophen, lidocaine, phenobarbital, phenytoin, theophylline, and valproic acid to human serum alpha-1 acid glycoprotein (orosomucoid) and to human serum albumin separately in vitro was investigated using equilibrium dialysis of the unlabeled drugs. Each drug was studied at a therapeutic concentration. Alpha-1 acid glycoprotein was studied at one elevated and two physiological concentrations, whereas albumin was studied at one physiological and two low concentrations. The nonphysiological concentrations were consistent with those that might be seen in a variety of clinical conditions. Acetaminophen, phenobarbital, theophylline, and valproic acid showed negligible binding to alpha-1 acid glycoprotein. However, lidocaine and phenytoin demonstrated binding to this protein, and increases in the alpha-1 acid glycoprotein concentration produced decreases in the unbound (free) or "active" concentration of these two drugs. All drugs but acetaminophen bound to albumin, and decreases in the albumin concentration yielded increases in the unbound (free) or "active" concentration of the remaining 5 drugs. These findings are significant when lidocaine, phenytoin, phenobarbital, theophylline, or valproic acid are used in patients with clinical conditions that may affect the concentration of these two binding proteins.

Protein binding in antiretroviral therapies

There is marked variability in the extent to which the three classes of antiretroviral (ARV) drugs bind to plasma proteins (<5 to >99%). Protease inhibitors (PIs), with the exception of indinavir, are more than 90% protein bound, mainly to alpha1-acid glycoprotein (AAG). Efavirenz, a nonnucleoside reverse transcriptase inhibitor (NNRTI), is more than 99% bound, mainly to albumin. Nucleoside reverse transcriptase inhibitors (NRTIs) are not highly protein bound. The pharmacological activity of ARV drugs is dependent on unbound drug entering cells that harbor the human immunodeficiency virus (HIV). There has been concern that changes in protein binding could impact on antiviral activity and management. However, for PIs and NNRTIs, and for many drugs given orally, altered plasma binding would not be expected to influence the average exposure to unbound (active) drug after chronic oral dosing. Nevertheless, there will be a change in the relationship between total and unbound concentrations that will be important if, as part of therapeutic drug monitoring, the total rather than the unbound drug is measured. Measuring drug concentrations that are needed to inhibit different HIV strains (wild type and drug resistant) in vitro could also cause confusion because most methods employ bovine serum in the assay medium, and unbound concentrations are not directly measured. Estimating unbound drug concentrations in human plasma and in incubation media can be highly method dependent and thus may affect the calculated IC50 (the concentration of drug that results in 50% inhibition of viral replication). Because inhibitory quotients (IQs = C(trough)/IC50) are becoming part of pharmacokinetic/pharmacodynamic (PK/PD) analyses of clinical trial data, the strengths and weaknesses of the methods used for the determination of unbound drug concentration in plasma and in vitro systems--ultracentrifugation, ultrafiltration, and equilibrium dialysis--need to be understood. Consensus on standard procedures must be reached. In June 2002, a panel of experts assembled by the Forum for Collaborative HIV Research met in Washington, DC, to review the basic principles of protein binding of ARV drugs, and to discuss the impact that changes in plasma protein binding may have on the PKs and activity of ARV drugs as well as on therapeutic drug monitoring. The purpose of the meeting was to discuss the following topics: (1) basic principles of protein binding and how changes in binding can impact on drug PKs and drug exposure in vivo, (2) variability in plasma protein binding among patients taking ARV drugs, (3) the impact of HIV infection and concomitant diseases on the extent of plasma protein binding, (4) the likelihood of clinically relevant drug interactions at the level of plasma protein binding, (5) the evidence that measuring unbound concentrations of ARV drugs in the plasma of patients gives more meaningful information than total drug concentration and, therefore, should be considered in routine therapeutic drug monitoring of ARV agents, (6) optimal method(s) for measuring the unbound concentration of drugs in vitro (for IC50 determination) and in vivo, and (7) future studies that need to be considered to fully understand the importance of plasma protein binding in therapeutic drug monitoring. This report summarizes the topics discussed at this meeting. It guides the reader through the discussions that allowed the panel to formulate a series of statements regarding the significance of plasma protein binding of ARV drugs when studied in vitro and in vivo. The roundtable participants also identified research priorities that are important for understanding the sources of inter- and intraindividual variability in protein binding in patients. These include obtaining data on unbound as well as on total concentrations in PK studies; looking at variants of AAG and whether they differ in binding affinity; and emphasizing the importance of developing a standard procedure for drug susceptibility assays used to determine IC50 values.

Stereoselective protein binding of alprenolol in the renal diseased state

The investigation was undertaken to study the stereoselective protein binding of alprenolol in renal disease patient sera, compared to that in the sera of healthy volunteers. The in vitro stereoselective protein binding of beta-blockers was determined in undiluted serum and in isolated alpha(1)-acid glycoprotein (AGP) solutions by ultrafiltration. The stereoselctive serum protein binding of alprenolol, a beta-adrenergic blocking agent, in healthy volunteers was significantly altered in renal disease patients. We investigated the effects of AGP concentration and endogenous substances, including uremic toxins, on the stereoselective protein binding of alprenolol in renal disease patients. A good correlation between the unbound (R)/(S) ratio (F(R)/F(S) ratio), an apparent index of stereoselectivity in alprenolol serum binding and AGP concentration in serum, was found. However, stereoselective protein binding was not influenced by endogenous substances. This result can be explained by the difference in binding affinities of (R) and (S)-isomers of alprenolol to AGP. We conclude that the stereoselective protein binding of alprenolol in healthy volunteers and renal disease patients varies as a result of changes in AGP concentration. Accordingly, these findings might be useful in alprenolol therapy in renal disease patients.