Determination of drug binding to plasma proteins using competitive equilibrium binding to dextran-coated charcoal

Esterase activity and interaction of human hemoglobin with diclofenac sodium: A spectroscopic and molecular docking study

To get an idea about the pharmacokinetics and pharmacodynamics, it is important to study the drug-protein interaction. Therefore, herein, we studied the interaction of diclofenac sodium (DIC) with human hemoglobin. The binding study of nonsteroidal antiinflammatory drug, DIC with human hemoglobin (HHB) was done by utilizing fluorescence, UV-visible, time-resolved fluorescence and far-UV circular dichroism spectroscopy (CD). Various thermodynamic parameters such as enthalpy change (ΔH), entropy change (ΔS), and Gibbs free energy change (ΔG) were also calculated. CD results showed that DIC induces secondary structure change in HHB. Fluorescence resonance energy transfer was also performed. Additionally, it was also observed that DIC inhibits the esterase-like enzymatic activity of HHB via competitive inhibition.

Physiologically-Based Pharmacokinetic Modeling for the Prediction of CYP2D6-Mediated Gene-Drug-Drug Interactions

The aim of this work was to predict the extent of Cytochrome P450 2D6 (CYP2D6)‐mediated drug–drug interactions (DDIs) in different CYP2D6 genotypes using physiologically‐based pharmacokinetic (PBPK) modeling. Following the development of a new duloxetine model and optimization of a paroxetine model, the effect of genetic polymorphisms on CYP2D6‐mediated intrinsic clearances of dextromethorphan, duloxetine, and paroxetine was estimated from rich pharmacokinetic profiles in activity score (AS)1 and AS2 subjects. We obtained good predictions for the dextromethorphan–duloxetine interaction (Ratio of predicted over observed area under the curve (AUC) ratio (R_pred/obs) 1.38–1.43). Similarly, the effect of genotype was well predicted, with an increase of area under the curve ratio of 28% in AS2 subjects when compared with AS1 (observed, 33%). Despite an approximately twofold underprediction of the dextromethorphan–paroxetine interaction, an R_pred/obs of 0.71 was obtained for the effect of genotype on the area under the curve ratio. Therefore, PBPK modeling can be successfully used to predict gene–drug–drug interactions (GDDIs). Based on these promising results, a workflow is suggested for the generic evaluation of GDDIs and DDIs that can be applied in other situations.

Duloxetine enters the brain - But why is it not found in the cerebrospinal fluid

BACKGROUND

Antidepressants enter the brain to reach their site of action in a different extent. However, there has been no study to date about duloxetine's ability to enter the brain and cerebrospinal fluid. Aim of this study was to measure blood and cerebrospinal fluid concentrations of duloxetine and to account for the distribution between the two compartments.

METHODS

Concentrations of duloxetine were measured in blood serum and cerebrospinal fluid of 19 patients treated with daily doses of 30-120mg. Daily doses were correlated with serum and cerebrospinal fluid concentrations and serum concentrations were correlated with concentrations in cerebrospinal fluid.

RESULTS

Serum concentrations of duloxetine showed a moderate but significant correlation with the applied daily dose, r=+0.473, p=0.04. Duloxetine concentrations in the cerebrospinal fluid above the designated limit of quantification of 2.0ng/mL were only found in three of the 19 patients.

CONCLUSIONS AND LIMITATIONS

Contrasting to own preceding studies on venlafaxine, mirtazapine and citalopram with comparably high concentrations in cerebrospinal fluid, the here presented findings indicate that duloxetine shows a very different distribution pattern. Very low concentrations in the cerebrospinal fluid may be due to the fact that the drug crosses the blood-cerebrospinal fluid barrier much worse than other antidepressants do, suggesting a low ability of duloxetine to enter the brain. Alternatively, low drug concentrations may be interpreted in a sense of a missing residence time in cerebrospinal fluid due to active transport mechanisms out of this environment either back into the bloodstream or into the brain.

Proposal of a pharmacokinetically optimized dosage regimen of antibiotics in patients receiving continuous hemodiafiltration

The aim of the study was to quantitatively predict the clearance of three antibiotics, amikacin, vancomycin, and teicoplanin, during continuous hemodiafiltration (CHDF) and to propose their optimal dosage in patients receiving CHDF. For this goal, in vitro CHDF experiments with a polyacrylonitrile (PAN) membrane were first performed using these antibiotics, and then the clearances were compared with in vivo CHDF situations determined in 16 critically ill patients. The in vitro CHDF clearances were described as the product of the outflow rate of a drain (Q(outflow)) and the drug unbound fraction in artificial plasma, indicating that drug adsorption to the PAN membrane has minor effect on drug clearance in our settings. The observed in vivo clearances also agreed very well with the predicted values, with a product of Q(outflow) and plasma unbound fraction, when residual creatinine clearance (CL(CR)) was taken into account (within a range of 0.67- to 1.5-fold for 15 of 16 patients). Based on these results, a nomogram of the optimized dosages of amikacin, vancomycin, and teicoplanin was proposed, and it was evident that Q(outflow) and residual CL(CR) are major determinants of the dosage and dosing interval for these antibiotics. Although the applicability needs to be confirmed with another type of membrane or higher Q(outflow), our nomogram can help determine the dosage setting in critically ill patients receiving CHDF.

Use of intrinsic clearance for prediction of human hepatic clearance

IMPORTANCE OF THE FIELD

The use of intrinsic metabolic stability/clearance and other in vitro pharmacokinetic data for the selection of drug candidates for clinical evaluation during discovery lead optimization has become one of the primary focuses of research organizations involved in new drug discovery. Using intrinsic clearance determined from human liver microsomal preparations and/or hepatocyte to predict human clearance has become more acceptable.

AREAS COVERED IN THIS REVIEW

This review focuses on the current methods for determining intrinsic clearance and scaling to predict human hepatic clearance, and novel physiologically-based models for improvement of human hepatic clearance prediction. Published microsomal metabolic stability data and in-house hepatocyte clearance data were compared with published in vivo human hepatic clearance data. Various scaling models and the effect of protein binding were examined.

WHAT THE READER WILL GAIN

Use of a novel microfluidic model and other physiologically-based models are presented. Microsomal metabolic clearance requires correction for protein binding and in vitro microsomal binding in order to better predict in vivo hepatic clearance of compounds that are mainly eliminated by hepatic metabolism.

TAKE HOME MESSAGE

Metabolic clearance obtained using hepatocytes may work well in combination with the well-stirred model. Novel models incorporating flow and protein binding in the system may be the most complete models for prediction of human in vivo metabolism.

Interaction of weakly bound antibiotics neomycin and lincomycin with bovine and human serum albumin: biophysical approach

The thermodynamics of interaction of neomycin and lincomycin with bovine serum albumin (BSA) and human serum albumin (HSA) has been studied using isothermal titration calorimetry (ITC), in combination with UV-visible, steady state and time resolved fluorescence spectroscopic measurements. Neomycin is observed to bind weakly to BSA and HSA whereas lincomycin did not show any evidence for binding with the native state of these proteins, rather it interacts in the presence of surfactants. The ITC results suggest 1 : 1 binding stoichiometry for neomycin in the studied temperature range. The values of the van't Hoff enthalpy do not agree with the calorimetric enthalpy in the case of neomycin, suggesting conformational changes in the protein upon ligand binding, as well as with the rise in the temperature. Experiments at different ionic strengths, and in the presence of tetrabutyl ammonium bromide and surfactants suggest the predominant involvement of electrostatic interactions in the complexation process of neomycin with BSA and HSA, and non-specific interaction behaviour of lincomycin with these proteins.

Evaluation of alternatives to warfarin as probes for Sudlow site I of human serum albumin: characterization by high-performance affinity chromatography

Warfarin is often used as a site-specific probe for examining the binding of drugs and other solutes to Sudlow site I of human serum albumin (HSA). However, warfarin has strong binding to HSA and the two chiral forms of warfarin have slightly different binding affinities for this protein. Warfarin also undergoes a slow change in structure when present in common buffers used for binding studies. This report examined the use of four related, achiral compounds (i.e., coumarin, 7-hydroxycoumarin, 7-hydroxy-4-methylcoumarin, and 4-hydroxycoumarin) as possible alternative probes for Sudlow site I in drug binding studies. High-performance affinity chromatography and immobilized HSA columns were used to compare and evaluate the binding properties of these probe candidates. Binding for each of the tested probe candidates to HSA was found to give a good fit to a two-site model. The first group of sites had moderate-to-high affinities for the probe candidates with association equilibrium constants that ranged from 6.4 x 10(3)M(-1) (coumarin) to 5.5 x 10(4)M(-1) (4-hydroxycoumarin) at pH 7.4 and 37 degrees C. The second group of weaker, and probably non-specific, binding regions, had association equilibrium constants that ranged from 3.8 x 10(1)M(-1) (7-hydroxy-4-methylcoumarin) to 7.3 x 10(2)M(-1) (coumarin). Competition experiments based on zonal elution indicated that all of these probe candidates competed with warfarin at their high affinity regions. Warfarin also showed competition with coumarin, 7-hydroxycoumarin and 7-hydroxy-4-methycoumarin for their weak affinity sites but appeared to not bind and/or compete for all of the weak sites of 4-hydroxycoumarin. It was found from this group that 4-hydroxycoumarin was the best alternative to warfarin for examining the interactions of drugs at Sudlow site I on HSA. These results also provided information on how the major structural components of warfarin contribute to the binding of this drug at Sudlow site I.

Inter-species differences in sensitivity to the calcemic activity of the novel 1,25-dihydroxyvitamin D3 analog BXL746

The activities of 1,25-dihydroxyvitamin D3 and its synthetic analogs have been extensively studied in humans as well as in preclinical species, and recent data show potential therapeutic utility in cancer treatment. However, their chronic administration leads to changes in blood mineral ion concentrations, and at high doses can result in symptomatic hypercalcemia limiting therapeutic applicability. To overcome this issue, a therapeutic approach based on administration of intermittent, high doses of 1,25(OH)2D3 has been explored in prostate cancer patients. Despite these and other investigations, limited information is available on the effects of acute systemic administration of high doses of 1,25(OH)2D3 or its analogs. Here, we report a comparative analysis of the pro-calcemic effects of the novel 1,25(OH)2D3 analog BXL746 following acute or chronic administration in animals and humans. While chronic administration of BXL746 to rats, dogs and humans leads to similar modulation of calcemia in these species, single dose administration reveals >1000-fold higher sensitivity of dog compared to rat and human in induction of hypercalcemia and consequent systemic toxicity. Our data indicate that the rat is a more relevant species than the dog for the prediction of human results when acute administration of a 1,25(OH)2D3 analog is envisaged.