Development of an ion-pair to improve the colon permeability of a low permeability drug: Atenolol.

Abstract To ensure the optimal performance of oral controlled release formulations, drug colon permeability is one of the critical parameters. Consequently developing this kind of formulations for low permeability molecules requires strategies to increase their ability to cross the colonic membrane. The objective of this work is to show if an ion-pair formation can improve the colon permeability of atenolol as a low permeability drug model. Two counter ions have been tested: brilliant blue and bromophenol blue. The Distribution coefficients at pH 7.00 (DpH7) of atenolol, atenolol + brilliant blue and atenolol + bromophenol blue were experimentally determined in n-octanol. Moreover, the colo…

Exploring Bioequivalence of Dexketoprofen Trometamol Drug Products with the Gastrointestinal Simulator (GIS) and Precipitation Pathways Analyses

The present work aimed to explain the differences in oral performance in fasted humans who were categorized into groups based on the three different drug product formulations of dexketoprofen trometamol (DKT) salt&mdash

A topological substructural approach for the prediction of P-glycoprotein substrates

A topological substructural molecular design approach (TOPS-MODE) has been used to predict whether a given compound is a P-glycoprotein (P-gp) substrate or not. A linear discriminant model was developed to classify a data set of 163 compounds as substrates or nonsubstrates (91 substrates and 72 nonsubstrates). The final model fit the data with sensitivity of 82.42% and specificity of 79.17%, for a final accuracy of 80.98%. The model was validated through the use of an external validation set (40 compounds, 22 substrates and 18 nonsubstrates) with a 77.50% of prediction accuracy; fivefold full cross-validation (removing 40 compounds in each cycle, 80.50% of good prediction) and the predictio…

A promising camptothecin derivative: Semisynthesis, antitumor activity and intestinal permeability.

Oral administration of camptothecin (Cm) derivatives and other antitumoral agents is being actively developed in order to improve the quality of life of patients with cancer. Though several lipophilic derivatives of CPT have shown interesting oral bioavailability in preclinical and clinical studies, only Topotecan has been approved for this route of administration. Semisynthesis, antitumor activity, biological inhibition mechanism, and in situ intestinal permeability of 9, 10-[1,3]-Dioxinocamptothecin (CDiox), an unexplored CPT derivative, have been studied in this paper. The hexacyclic analog was as effective as Topotecan and CPT in different tumor cell lines, showing an expected similar a…

In vitro–in vivocorrelations: general concepts, methodologies and regulatory applications

The major objective of in vitro-in vivo correlations is to be able to use in vitro data to predict in vivo performance serving as a surrogate for an in vivo bioavailability test and to support biowaivers. Therefore, the aims of this review are: (i) to clarify the factors involved during bio-predictive dissolution method development; and (ii) the elements that may affect the mathematical analysis in order to exploit all information available. This article covers the basic aspects of dissolution media and apparatus used in the development of in vivo predictive dissolution methods, including the latest proposals in this field as well as the summary of the mathematical methods for establishing …

Global testing of a consensus solubility assessment to enhance robustness of the WHO biopharmaceutical classification system

The WHO Biopharmaceutical Classification System (BCS) is a practical tool to identify active pharmaceutical ingredients (APIs) that scientifically qualify for a waiver of in vivo bioequivalence studies. The focus of this study was to engage a global network of laboratories to experimentally quantify the pH-dependent solubility of the highest therapeutic dose of 16 APIs using a harmonized protocol. Intra-laboratory variability was ≤5 %, and no apparent association of inter-laboratory variability with API solubility was discovered. Final classification “low solubility” vs “high solubility” was consistent among laboratories. In comparison to the literature-based provisional 2006 WHO BCS classi…

Variability of permeability estimation from different protocols of subculture and transport experiments in cell monolayers.

Abstract Introduction In vitro models with high predictive ability have been revealed as strong tools for pharmaceutical industry. However, the variability in permeability estimations complicates the comparison and combination of data from different laboratories and it makes necessary the careful validation of the model and the continuous suitability demonstration. The adequate standardization of pre-experimental, experimental and post-experimental factors might help to reduce the inter- and intra-laboratory variability in permeability values. Methods The objective of this paper is the evaluation of the effect of passage number, experimental protocol, time after seeding and calculation meth…

Influence of polyunsaturated fatty acids on Cortisol transport through MDCK and MDCK-MDR1 cells as blood-brain barrier in vitro model.

Abstract Transport across the blood–brain barrier is a relevant factor in the pharmacological action of many drugs and endogenous substances whose action site is located in brain. An overactive P-gp has been suggested to be of relevance for the resistance of the HPA system to be suppressed by glucocorticoids, which is one of the best described biological abnormalities in certain types of depression. PUFA acids have shown clinical efficacy in depressed patients and the hypothesis is that these compounds are able to reduce HPA axis activity as this effect has been shown in animal models of depression. The objective of the present work was (1) to characterize Cortisol transport through MDCK an…

PAMPA—a drug absorption in vitro model

Parallel artificial membrane permeability assay (PAMPA) was used to measure the effective permeability, P(e), as a function of pH from 4 to 10, of 17 fluoroquinolones, including three congeneric series with systematically varied alkyl chain length at the 4'N-position of the piperazine residue. The permeability values spanned over three orders of magnitude. The intrinsic permeability, P(o), and the membrane permeability, P(m), were determined from the pH dependence of the effective permeability. The pK(a) values were determined potentiometrically. The PAMPA method employed stirring, adjusted such that the unstirred water layer (UWL) thickness matched the 30-100 microm range estimated to be i…

In Situ Perfusion Model in Rat Colon for Drug Absorption Studies: Comparison with Small Intestine and Caco-2 Cell Model.

Our aim is to develop and to validate the in situ closed loop perfusion method in rat colon and to compare with small intestine and Caco-2 cell models. Correlations with human oral fraction absorbed (Fa) and human colon fraction absorbed (Fa_colon) were developed to check the applicability of the rat colon model for controlled release (CR) drug screening. Sixteen model drugs were selected and their permeabilities assessed in rat small intestine and colon, and in Caco-2 monolayers. Correlations between colon/intestine/Caco-2 permeabilities versus human Fa and human Fa_colon have been explored to check model predictability and to apply a BCS approach in order to propose a cut off value for CR…

Modified nonsink equation for permeability estimation in cell monolayers: comparison with standard methods.

Cell culture permeability experiments are valuable tools in drug development and candidate selection, but the monolayer preparation protocols and the calculations procedures can affect the permeability estimation. Hence, standardization and method suitability demonstration are necessary steps for using permeability data for regulatory and in vivo prediction purposes. Much attention is usually paid to experimental procedure validation and less to the mathematical analysis of the results although the standard equations used imply several assumptions that many times do not hold. The aim of this study was to use a simulation strategy to explore the performance of a new proposed modified nonsink…

TOPS-MODE approach for the prediction of blood-brain barrier permeation.

The blood-brain barrier permeation has been investigated by using a topological substructural molecular design approach (TOPS-MODE). A linear regression model was developed to predict the in vivo blood-brain partitioning coefficient on a data set of 119 compounds, treated as the logarithm of the blood-brain concentration ratio. The final model explained the 70% of the variance and it was validated through the use of an external validation set (33 compounds of the 119, MAE = 0.33), a leave-one-out crossvalidation (q(2) = 0.65, S(press) = 0.43), fivefold full crossvalidation (removing 28 compounds in each cycle, MAE = 33, RMSE = 0.43) and the prediction of +/- values for an external test set …

Compared effects of synthetic and natural bile acid surfactants on xenobiotic absorption I. Studies with polysorbate and taurocholate in rat colon

Some expected differences between synthetic and natural bile acid surfactants relative to their influences on xenobiotic absorption are briefly outlined on the basis of literature data. Then, experimental work is presented which shows that these differences exist and that they can be even more relevant than suspected. Absorption tests were developed in rat colon in situ with polysorbate (synthetic) and sodium taurocholate (natural) surfactants, using a homologous series of phenylalkylcarboxylic acids as test compounds. At the critical micelle concentration (CMC), the two previously reported actions of synthetic surfactants on xenobiotic absorption (i.e. the increase in absorbing membrane po…

Pharmacokinetics in Drug Discovery

The aim of this current review is to summarize the present status of pharmacokinetics in Drug Discovery. The review is structured into four sections. The first section is a general overview of what we understand by pharmacokinetics and the different LADMET aspects: Liberation, Absorption, Distribution, Metabolism, Excretion, and Toxicity. The second section highlights the different computational or in silico approaches to estimate/predict one or several aspects of the pharmacokinetic profile of a discovery lead compound. The third section discusses the most commonly used in vitro methodologies. The fourth and last section examines the various approaches employed towards the pharmacokinetic …

Usefulness of Caco-2/HT29-MTX and Caco-2/HT29-MTX/Raji B Coculture Models To Predict Intestinal and Colonic Permeability Compared to Caco-2 Monoculture

The Caco-2 cellular monolayer is a widely accepted in vitro model to predict human permeability but suffering from several and critical limitations. Therefore, some alternative cell cultures to mimic the human intestinal epithelium, as closely as possible, have been developed to achieve more physiological conditions, as the Caco-2/HT29-MTX coculture and the triple Caco-2/HT29-MTX/Raji B models. In this work the permeability of 12 model drugs of different Biopharmaceutical Classification System (BCS) characteristics, in the coculture and triple coculture models was assessed. Additionally, the utility of both models to classify compounds according to the BCS criteria was scrutinized. The obta…

A novel approach to determining physicochemical and absorption properties of 6-fluoroquinolone derivatives: experimental assessment

The ToSS MoDe approach is used to estimate the n-octanol/buffer partition coefficient, the apparent intestinal absorption rate constant and intestinal permeability from a 6-fluoroquinolone data set. Improved in silico methods for predicting a drug's ability to be transported across biological membranes and other biopharmaceutical properties is highly desirable to optimize new drug development. The physicochemical property (Log P) of 26 6-fluoroquinolone derivatives and the absorption properties (Log K(a) and Log P(eff)) of 21 derivatives were well described by the present approach. The models obtained confirm the important role of lipophilicity in the absorption process and its relation wit…

Unique pharmacology of KAR-2, a potential anti-cancer agent: absorption modelling and selective mitotic spindle targeting.

Abstract Bis-indols are a large group of the anti-cancer agents, which effectively arrest the uncontrolled division of the cancerous cells. Their use in clinical chemotherapy is still limited because of: (i) the non-specific targeting of the mitotic cells; (ii) low bioavailability of the drugs. KAR-2 has been identified as a tubulin binding agent which displays significantly lower cytotoxicity but favourable anti-cancer potency than its mother molecule, vinblastine. The objective of this paper, on one hand, was to show that the human intestinal epithelial Caco-2 cells, used for pharmacokinetic studies display distinct sensitivity against KAR-2 and vinblastine due to their distinct targeting…

An exploratory study of two Caco-2 cell models for oral absorption: A report on their within-laboratory and between-laboratory variability, and their predictive capacity

In 2005, the European Centre for the Validation of Alternative Methods (ECVAM) sponsored a study aimed at evaluating the reproducibility (between-laboratory and within-laboratory variability) and the predictive capacity of two in vitro cellular systems — the Caco-2/ATCC parental cell line and the Caco-2/TC7 clone — for estimating the oral fraction absorbed (Fa) in humans. Two laboratories, both of which had experience with Caco-2 cultures, participated in the study. Ten test chemicals with documented in vivo oral absorption data were selected. Atenolol, cimetidine and propranolol were included as reference compounds for low, medium and high intestinal absorption, respectively. Transport ex…

Transintestinal secretion of ciprofloxacin, grepafloxacin and sparfloxacin: in vitro and in situ inhibition studies.

The influence of the secretion process on the absorption of ciprofloxacin, grepafloxacin and sparfloxacin has been evaluated by means of inhibition studies. Two well known P-glycoprotein inhibitors (cyclosporine, verapamil), a mixed inhibitor of P-glycoprotein and the organic cation transporter OCT1 (quinidine) and a well established MRP substrate (p-aminohipuric acid) have been selected in order to distinguish the possible carriers implicated. An in situ rat gut perfusion model and CACO-2 permeability studies are used. Both methods suggest the involvement of several types of efflux transporters for every fluoroquinolone. The relevance of the secretory pathway depends on the intrinsic perme…

Biowaiver Monographs for Immediate Release Solid Oral Dosage Forms: Aciclovir

Literature data relevant to the decision to allow a waiver of in vivo bioequivalence (BE) testing (biowaiver) for the approval of immediate release (IR) solid oral dosage forms containing aciclovir are reviewed. Aciclovir therapeutic use and therapeutic index, pharmacokinetic properties, data related to the possibility of excipient interactions and reported BE/bioavailability (BA) studies were also taken into consideration in order to ascertain whether a biowaiver can be recommended. According to the Biopharmaceutics Classification System (BCS) and considering tablet strengths up to 400 mg, aciclovir would be BCS Class III. However, in some countries also 800 mg tablets are available which …

Innovative in Vitro Method To Predict Rate and Extent of Drug Delivery to the Brain across the Blood–Brain Barrier

The relevant parameters for predicting rate and extent of access across the blood-brain barrier (BBB) are fu,plasma (unbound fraction in plasma), Vu,brain (distribution volume in brain) and Kp,uu,brain (ratio of free concentrations in plasma and brain). Their estimation still requires animal studies and in vitro low throughput experiments which make difficult the screening of new CNS candidates. The aim of the present work was to develop a new whole in vitro high throughput method to predict drug rate and extent of access across the BBB. The system permits estimation of fu,plasma, Vu,brain and Kp,uu,brain in a single experimental system, using in vitro cell monolayers in different condition…

Computer simulations for bioequivalence trials: Selection of analyte in BCS class II and IV drugs with first-pass metabolism, two metabolic pathways and intestinal efflux transporter.

A semi-physiological two compartment pharmacokinetic model with two active metabolites (primary (PM) and secondary metabolites (SM)) with saturable and non-saturable pre-systemic efflux transporter, intestinal and hepatic metabolism has been developed. The aim of this work is to explore in several scenarios which analyte (parent drug or any of the metabolites) is the most sensitive to changes in drug product performance (i.e. differences in in vivo dissolution) and to make recommendations based on the simulations outcome. A total of 128 scenarios (2 Biopharmaceutics Classification System (BCS) drug types, 2 levels of KM Pgp, in 4 metabolic scenarios at 2 dose levels in 4 quality levels of t…

In-situ intestinal rat perfusions for human Fabs prediction and BCS permeability class determination: Investigation of the single-pass vs. the Doluisio experimental approaches.

Intestinal drug permeability has been recognized as a critical determinant of the fraction dose absorbed, with direct influence on bioavailability, bioequivalence and biowaiver. The purpose of this research was to compare intestinal permeability values obtained by two different intestinal rat perfusion methods: the single-pass intestinal perfusion (SPIP) model and the Doluisio (closed-loop) rat perfusion method. A list of 15 model drugs with different permeability characteristics (low, moderate, and high, as well as passively and actively absorbed) was constructed. We assessed the rat intestinal permeability of these 15 model drugs in both SPIP and the Doluisio methods, and evaluated the co…

Formulation predictive dissolution (fPD) testing to advance oral drug product development: an introduction to the US FDA funded ‘21st Century BA/BE’ project

Over the past decade, formulation predictive dissolution (fPD) testing has gained increasing attention. Another mindset is pushed forward where scientists in our field are more confident to explore the in vivo behavior of an oral drug product by performing predictive in vitro dissolution studies. Similarly, there is an increasing interest in the application of modern computational fluid dynamics (CFD) frameworks and high-performance computing platforms to study the local processes underlying absorption within the gastrointestinal (GI) tract. In that way, CFD and computing platforms both can inform future PBPK-based in silico frameworks and determine the GI-motility-driven hydrodynamic impac…

PLGA nanoparticles are effective to control the colonic release and absorption on ibuprofen.

The oral controlled release (CR) formulations have become more important in recent years. Among them, the polymeric nanoparticles have been thoroughly studied during the last decades, consequently they are extensively employed for a broad range of applications and drugs. The objective of this research was to develop polymeric nanoparticles (NPs) of ibuprofen with poly(lactic-co-glycolic) acid (PLGA) as polymer, and to test their applicability for oral CR formulations development. Different proportions of drug/polymer were employed to develop the ibuprofen NPs and their in vitro release profiles were analysed. The in situ segmental permeability of ibuprofen was tested in Wistar rat and demon…

Semi-physiologic model validation and bioequivalence trials simulation to select the best analyte for acetylsalicylic acid

Abstract The objective of this paper is to apply a previously developed semi-physiologic pharmacokinetic model implemented in NONMEM to simulate bioequivalence trials (BE) of acetyl salicylic acid (ASA) in order to validate the model performance against ASA human experimental data. ASA is a drug with first-pass hepatic and intestinal metabolism following Michaelis–Menten kinetics that leads to the formation of two main metabolites in two generations (first and second generation metabolites). The first aim was to adapt the semi-physiological model for ASA in NOMMEN using ASA pharmacokinetic parameters from literature, showing its sequential metabolism. The second aim was to validate this mod…

Effect of thickener on disintegration, dissolution and permeability of common drug products for elderly patients

Dysphagia is a very common problem suffered by elderly patients. The use of thickeners during administration in these patients helps to prevent difficulties with swallowing larger solid dosage forms. However, there are several indications when the thickeners may influence disintegration and dissolution processes of solid dosage forms, potentially affecting therapeutic efficacy. In this paper the effects of a commonly used thickener on tablet disintegration, dissolution and subsequent absorption of 6 formulated drugs frequently used in elderly patients (Aspirin, Atenolol, Acenocumarol, Candesartan, Ramipril and Valsartan) in two different administration conditions (intact tablet and crushed …

Mechanistic analysis and experimental verification of bicarbonate-controlled enteric coat dissolution: Potential in vivo implications

Enteric coatings have shown in vivo dissolution rates that are poorly predicted by traditional in vitro tests, with the in vivo dissolution being considerably slower than in vitro. To provide a more mechanistic understanding of this, the dependence of the release properties of various enteric-coated (EC) products on bulk pH and bicarbonate molarity was investigated. It was found that, at presumably in vivo-relevant values, the bicarbonate molarity is a more significant determinant of the dissolution profile than the bulk pH. The findings also indicate that this steep relationship between the dissolution of enteric coatings and bicarbonate molarity limits those coatings' performance in vivo.…

In Silico Prediction of Caco-2 Cell Permeability by a Classification QSAR Approach

In the present study, 21 validated QSAR models that discriminate compounds with high Caco-2 permeability (Papp ≥8×10(-6)  cm/s) from those with moderate-poor permeability (Papp <8×10(-6)  cm/s) were developed on a novel large dataset of 674 compounds. 20 DRAGON descriptor families were used. The global accuracies of obtained models were ranking between 78-82 %. A general model combining all types of molecular descriptors was developed and it classified correctly 81.56 % and 83.94 % for training and test sets, respectively. An external set of 10 compounds was predicted and 80 % was correctly assessed by in vitro Caco-2 assays. The potential use of the final model was evaluated by a virtual s…

Candesartan Cilexetil In Vitro-In Vivo Correlation: Predictive Dissolution as a Development Tool

[EN] The main objective of this investigation was to develop an in vitro-in vivo correlation (IVIVC) for immediate release candesartan cilexetil formulations by designing an in vitro dissolution test to be used as development tool. The IVIVC could be used to reduce failures in future bioequivalence studies. Data from two bioequivalence studies were scaled and combined to obtain the dataset for the IVIVC. Two-step and one-step approaches were used to develop the IVIVC. Experimental solubility and permeability data confirmed candesartan cilexetil. Biopharmaceutic Classification System (BCS) class II candesartan average plasma profiles were deconvoluted by the Loo-Riegelman method to obtain th…

Defining level A IVIVC dissolution specifications based on individual in vitro dissolution profiles of a controlled release formulation.

Regulatory guidelines recommend that, when a level A IVIVC is established, dissolution specification should be established using averaged data and the maximum difference between AUC and Cmax between the reference and test formulations cannot be greater than 20%. However, averaging data assumes a loss of information and may reflect a bias in the results. The objective of the current work is to present a new approach to establish dissolution specifications using a new methodology (individual approach) instead of average data (classical approach). Different scenarios were established based on the relationship between in vitro-in vivo dissolution rate coefficient using a level A IVIVC of a cont…

Ionic Hydrogel Based on Chitosan Cross-Linked with 6-Phosphogluconic Trisodium Salt as a Drug Delivery System.

[EN] In this work, 6-phosphogluconic trisodium salt (6-PG(-)Na(+)) is introduced as a new aqueous and nontoxic cross-linking agent to obtain ionic hydrogels. Here, it is shown the formation of hydrogels based on chitosan cross-linked with 6-PG(-)Na(+). This formulation is obtained by ionic interaction of cationic groups of polymer with anionic groups of the cross linker. These hydrogels are nontoxic, do not cause dermal irritation, are easy to extend, and have an adequate adhesion force to be applied as polymeric film over the skin. This AWN formulation exhibits a first order release kinetic and can be applied as drug vehicle for topical administration or as wound dressing for wound healing…

Correlation BetweenIn Vitro,In Situ, andIn Vivo Models

Mathematical modelling of in situ and in vitro efflux of ciprofloxacin and grepafloxacin

Abstract The efflux process due to p-glycoprotein-like mechanisms of ciprofloxacin (CIP) and grepafloxacin (GRX) has been studied “in situ” in rats and “in vitro” in Caco-2 cells. The results were modelled by a curve fitting procedure which allowed the characterization of the passive (Pd) and carrier mediated parameters (Vm and Km) from the raw data without initial velocities estimation. CIP absorption in rat was characterized as a passive diffusion at the assayed concentrations. Although the involvement of an efflux transporter cannot be ruled out, its relevance in the transport of the fluoroquinolone is negligible. In GRX absorption, an efflux process is implicated and it is detected in b…

Kinetic modelling of passive transport and active efflux of a fluoroquinolone across Caco-2 cells using a compartmental approach in NONMEM.

The purpose was to develop a general mathematical model for estimating passive permeability and efflux transport parameters from in vitro cell culture experiments. The procedure is applicable for linear and non-linear transport of drug with time,10 or10% of drug transport, negligible or relevant back flow, and would allow the adequate correction in the case of relevant mass balance problems. A compartmental kinetic approach was used and the transport barriers were described quantitatively in terms of apical and basolateral clearances. The method can be applied when sink conditions are not achieved and it allows the evaluation of the location of the transporter and its binding site. In this …

The Use of Rule-Based and QSPR Approaches in ADME Profiling: A Case Study on Caco-2 Permeability.

During the early ADME profiling the development of simple, interpretable and reliable in silico tools is very important. In this study, rule-based and QSPR approaches were investigated using a large Caco-2 permeability database. Three permeability classes were determined: high (H), moderate (M) and low (L). The main physicochemical properties related with permeability were ranked as follows: Polar Surface Area (PSA)>Lipophilicity (logP/logD)>Molecular Weight (MW)>number of Hydrogen Bond donors and acceptors>Ionization State>number of Rotatable Bonds>number of Rings. The best rule, based on the combination of PSA-MW-logD (3PRule), was able to identify the H, M and L classes with accuracy of …

Computer simulations for bioequivalence trials: selection of analyte in BCS drugs with first-pass metabolism and two metabolic pathways.

The objective of this work is to use a computer simulation approach to define the most sensitive analyte for in vivo bioequivalence studies of all types of Biopharmaceutics Classification System (BCS) drugs undergoing first-pass hepatic metabolism with two metabolic pathways. A semi-physiological model was developed in NONMEM VI to simulate bioequivalence trials. Four BCS classes (from Class I to IV) of drugs, with three possible saturation scenarios (non-saturation, saturation and saturation of only the major route of metabolism), two (high or low) dose schemes, and six types of pharmaceutical quality for the drug products were simulated. The number of investigated scenarios was 144 (4 × 3…

Mass Transport Analysis of the Enhanced Buffer Capacity of the Bicarbonate-CO2 Buffer in a Phase-Heterogenous System: Physiological and Pharmaceutical Significance

The bicarbonate buffer capacity is usually considered in a phase-homogeneous system, at equilibrium, with no CO2 transfer between the liquid buffer phase and another phase. However, typically, an in vitro bicarbonate buffer-based system is a phase-heterogeneous system, as it entails continuously sparging (bubbling) the dissolution medium with CO2 in a gas mixture, at constant ratio, to maintain a constant partial pressure of CO2 (g) and CO2(aq) molarity at a prescribed value, with CO2 diffusing freely between the gas and the aqueous phases. The human gastrointestinal tract is also a phase-heterogeneous system, with CO2 diffusing across the mucosal membrane into the mesenteric arterial blood…

New Insights of Oral Colonic Drug Delivery Systems for Inflammatory Bowel Disease Therapy

[EN] Colonic Drug Delivery Systems (CDDS) are especially advantageous for local treatment of inflammatory bowel diseases (IBD). Site-targeted drug release allows to obtain a high drug concentration in injured tissues and less systemic adverse effects, as consequence of less/null drug absorption in small intestine. This review focused on the reported contributions in the last four years to improve the effectiveness of treatments of inflammatory bowel diseases. The work concludes that there has been an increase in the development of CDDS in which pH, specific enzymes, reactive oxygen species (ROS), or a combination of all of these triggers the release. These delivery systems demonstrated a th…

A new mathematical approach for the estimation of the AUC and its variability under different experimental designs in preclinical studies

The aim of the present work was to develop a new mathematical method for estimating the area under the curve (AUC) and its variability that could be applied in different preclinical experimental designs and amenable to be implemented in standard calculation worksheets. In order to assess the usefulness of the new approach, different experimental scenarios were studied and the results were compared with those obtained with commonly used software: WinNonlin® and Phoenix WinNonlin®. The results do not show statistical differences among the AUC values obtained by both procedures, but the new method appears to be a better estimator of the AUC standard error, measured as the coverage of 95% confi…

Segmental-dependent permeability throughout the small intestine following oral drug administration: Single-pass vs. Doluisio approach to in-situ rat perfusion

Abstract Intestinal drug permeability is position dependent and pertains to a specific point along the intestinal membrane, and the resulted segmental-dependent permeability phenomenon has been recognized as a critical factor in the overall absorption of drug following oral administration. The aim of this research was to compare segmental-dependent permeability data obtained from two different rat intestinal perfusion approaches: the single-pass intestinal perfusion (SPIP) model and the closed-loop (Doluisio) rat perfusion method. The rat intestinal permeability of 12 model drugs with different permeability characteristics (low, moderate, and high, as well as passively and actively absorbed…

Provisional Classification and in Silico Study of Biopharmaceutical System Based on Caco-2 Cell Permeability and Dose Number

Today, early characterization of drug properties by the Biopharmaceutics Classification System (BCS) has attracted significant attention in pharmaceutical discovery and development. In this direction, the present report provides a systematic study of the development of a BCS-based provisional classification (PBC) for a set of 322 oral drugs. This classification, based on the revised aqueous solubility and the apparent permeability across Caco-2 cell monolayers, displays a high correlation (overall 76%) with the provisional BCS classification published by World Health Organization (WHO). Current database contains 91 (28.3%) PBC class I drugs, 76 (23.6%) class II drugs, 97 (31.1%) class III d…

How and Where are Drugs Absorbed?

A drug must interact with its receptors at their action sites or therapeutic target to exert its pharmacological or toxic effects. Therefore, the absorption of drug is an essential step which determines pharmacologic effects of drug. This article focuses on the biological barriers that the drug must cross in order to enter the body, drug absorption mechanisms, and influence of physiological characteristics of the administration route on absorption rate and extent. Keywords: drugs; absorption mechanisms; administration routes; passive diffusion; endocytosis

Validation of a semi-physiological model for caffeine in healthy subjects and cirrhotic patients.

The objective of this paper was to validate a previously developed semi physiological model to simulate bioequivalence trials of drug products. The aim of the model was to ascertain whether the measurement of the metabolite concentration-time profiles would provide any additional information in bioequivalence studies (Fernandez-Teruel et al., 2009a,b; Navarro-Fontestad et al., 2010). The semi-physiological model implemented in NONMEM VI was used to simulate caffeine and its main metabolite plasma levels using caffeine parameters from bibliography. Data from 3 bioequivalence studies in healthy subjects at 3 different doses (100, 175 and 400mg of caffeine) and one study in cirrhotic patients …

Unraveling the behavior of oral drug products inside the human gastrointestinal tract using the aspiration technique: History, methodology and applications

Fluid sampling from the gastrointestinal (GI) tract has been applied as a valuable tool to gain more insight into the fluids present in the human GI tract and to explore the dynamic interplay of drug release, dissolution, precipitation and absorption after drug product administration to healthy subjects. In the last twenty years, collaborative initiatives have led to a plethora of clinical aspiration studies that aimed to unravel the luminal drug behavior of an orally administered drug product. The obtained drug concentration-time profiles from different segments in the GI tract were a valuable source of information to optimize and/or validate predictive in vitro and in silico tools, freque…

Validation of a biophysical drug absorption model by the PATQSAR system

Absorption rate constants (in situ rat gut technique) and in vitro antibacterial activities of twenty fluoroquinolones have been evaluated. A biophysical model that relates the absorption of the compounds with their lipophilicity was fitted. The model considers the absorption process from the intestinal lumen as the sum of two resistances in series: aqueous diffusional barrier and lipoidal membrane. Even if partitioning into the membrane and membrane diffusion are both enhanced for lipophilic compounds, the absorption rate constant is limited by the aqueous diffusion. To estimate the influence of structural modifications on each property and to establish the role of lipophilicity in control…

Comparison of segmental-dependent permeability in human and in situ perfusion model in rat.

Abstract Nowadays, alternative methods have been developed to predict intestinal permeability values in human as in vitro, in situ or ex vivo methods. They were developed by the necessity to avoid the problems of the human permeability experiments. However, determination of human permeability is needed to properly validate the alternative methods. For this reason, recently, Dahlgren et al. published an indirect method based on a deconvolution technique to estimate the human permeability in different gastrointestinal segments (jejunum, ileum and colon). Therefore, the objective of this research was to demonstrate that Doluisio technique is a useful method to predict the human permeability in…

Intrinsic Absolute Bioavailability Prediction in Rats Based on In Situ Absorption Rate Constants and/or In Vitro Partition Coefficients: 6‐Fluoroquinolones

A preliminary study attempting to predict the intrinsic absolute bioavailability of a group of antibacterial 6-fluoroquinolones-including true and imperfect homologues as well as heterologues-was carried out. The intrinsic absolute bioavailability of the test compounds, F, was assessed on permanently cannulated conscious rats by comparing the trapezoidal normalized areas under the plasma concentration-time curves obtained by intravenous and oral routes (n = 8-12). The high-performance liquid chromatography analytical methods used for plasma samples are described. Prediction of the absolute bioavailability of the compounds was based on their intrinsic rat gut in situ absorption rate constant…

Compared effects of synthetic and natural bile acid surfactant on xenobiotic absorption. II. Studies with sodium glycocholate to confirm a hypothesis

Abstract The effects of sodium glycocholate (SGC) on the intestinal absorption of drug-related xeriobiotics are investigated, on the basis of previously established absorption/partition relationships. Six phenylalkylcarboxylic acids, closely related to nonsteroid anti-inflammatory drugs in structure and constituting a true homologous series, were used as test compounds through an in situ rat gut technique, using the whole colon as nonspecialized absorption membrane model. Whereas the synthetic surfactants (i.e., polysorbates and laurylsulphates) at the critical micelle concentration have been shown to disrupt the aqueous boundary layer adjacent to the membrane, SGC does not; in contrast, it…

Pharmacokinetics, bioavailability and absorption of flumequine in the rat.

Abstract The study demonstrates that the oral extent of bioavailability of flumequine in the rat, relative to the intravenous injection, is complete (0.94±0.04) and not significantly different from that found by the intraduodenal route (0.95±0.04). The rate of oral bioavailability, however, is slow ( k a =1.20±0.07 h −1 ; T max =2.0 h), but enough to maintain plasma levels above the minimal inhibitory concentration of the most common pathogens for an extended period of time (about 10 h). The reason for the oral absorption slowness could be a slow gastric emptying, an adsorption to the gastric mucosae, a precipitation in the gastric medium or any other feature concerning the stomach as the i…

In situ kinetic modelling of intestinal efflux in rats: functional characterization of segmental differences and correlation with in vitro results.

The objective was to devise and apply a novel modelling approach to combine segmental in situ rat perfusion data and in vitro cell culture data, in order to elucidate the contribution of efflux in drug absorption kinetics. The fluoroquinolone CNV97100 was used as a model P-gp substrate. In situ intestinal perfusion was performed in rat duodenum, jejunum, ileum and colon to measure the influence of P-gp expression on efflux. Inhibition studies of CNV97100 were performed in the presence of verapamil, quinidine, cyclosporin A and p-aminohippuric acid. Absorption/efflux parameters were modelled simultaneously, using data from both in situ studies as well as in vitro studies. The maximal efflux …

Semi-mechanistic Pharmacokinetic/Pharmacodynamic model of three pegylated rHuEPO and ior®EPOCIM in New Zealand rabbits.

Abstract Marketed formulations of erythropoietin (EPO) ior®EPOCIM, MIRCERA® and two newly developed pegylated-EPO analogues (PEG-EPO 32 and 40 kDa) formulations were intravenously administered to New Zealand rabbits. A semi-mechanistic Pharmacokinetic/Pharmacodynamic (PK/PD) model describing in a simultaneous and integrated form the time course of reticulocytes, red blood cells and hemoglobin was built to account for the time course of hematopoiesis stimulation after erythropoietin administration. Data analysis was performed based on the population approach with the software NONMEM version 7.3. Erythropoietin disposition of each of the administered formulations was best described with a two…

Population pharmacokinetic model of lithium and drug compliance assessment.

Population pharmacokinetic analysis of lithium during therapeutic drug monitoring and drug compliance assessment was performed in 54 patients and 246 plasma concentrations levels were included in this study. Patients received several treatment cycles (1-9) and one plasma concentration measurement for each patient was obtained always before starting next cycle (pre-dose) at steady state. Data were analysed using the population approach with NONMEM version 7.2. Lithium measurements were described using a two-compartment model (CL/F=0.41Lh-1, V1/F=15.3L, Q/F=0.61Lh-1, and V2/F = 15.8L) and the most significant covariate on lithium CL was found to be creatinine clearance (reference model). Lith…

Preclinical models for colonic absorption, application to controlled release formulation development.

Oral controlled release (CR) formulations have many benefits and have become a valuable resource for the local and systemic administration of drugs. The most important characteristic of these pharmaceutical products is that drug absorption occurs mainly in the colon. Therefore, this review analyses the physiological and physicochemical features that may affect an orally administered CR product, as well as the different strategies to develop a CR dosage form and the methods used to evaluate the formulation efficacy. The models available to study the intestinal permeability and their applicability to colonic permeability determinations are also discussed.

Investigating drug absorption from the colon: Single-pass vs. Doluisio approaches to in-situ rat large-intestinal perfusion

Traditionally, the colon is considered a secondary intestinal segment in the drug absorption process. However, in many cases the role of colonic drug permeability cannot be overlooked. The purpose of this research was to compare colon permeability data obtained using two different rat perfusion methods the single-pass intestinal perfusion (SPIP) approach and the closed-loop (Doluisio) perfusion model. A list of 14 structurally diverse model drugs was constructed, and their rat colon permeability was studied using the two methods. The two sets of results were compared to each other, and were evaluated vs. in-vitro, ex-vivo, and in-vivo literature values. The SPIP and the Doluisio results exh…

Progress in the development of early diagnosis and a drug with unique pharmacology to improve cancer therapy

Cancer continues to be one of the major health and socio-economic problems worldwide, despite considerable efforts to improve its early diagnosis and treatment. The identification of new constituents as biomarkers for early diagnosis of neoplastic cells and the discovery of new type of drugs with their mechanistic actions are crucial to improve cancer therapy. New drugs have entered the market, thanks to industrial and legislative efforts ensuring continuity of pharmaceutical development. New targets have been identified, but cancer therapy and the anti-cancer drug market still partly depend on anti-mitotic agents. The objective of this paper is to show the effects of KAR-2, a potent anti-m…

Mathematical modeling of oral absorption and bioavailability of a fluoroquinolone after its precipitation in the gastrointestinal tract

The objective was to characterize the in vivo absorption and bioavailability (BA) of a low solubility, high permeability fluoroquinolone (CNV97101) that precipitates in the gastrointestinal (GI) tract by mathematical modeling approach. In situ rat intestinal perfusion studies were performed to characterize the absorption mechanism. The oral fraction absorbed in vivo was lower than the predicted based on the in situ intestinal permeability. Two additional routes of administration, intraduodenal (ID) and intraperitoneal (IP) were investigated to explore if precipitation in stomach and subsequent partial re-dissolution were the causes of the lower in vivo BA. Ex vivo precipitation studies with…

Absorption-partition relationships for true homologous series of xenobiotics as a possible approach to study mechanisms of surfactants in absorption. IV. Phenylacetic acid derivatives and anionic surfactants

Abstract This paper — the latest in this series of reports — deals with the effects of the anionic surfactant sodium lauryl sulfate on the colonic absorption of acidic xenobiotics (phenylalkylcarboxylic acids), as compared with those exerted by the nonionic polysorbate 80. The effects of these surfactants are qualitatively identical but quantitatively different. Thus, the increase in polarity of the colonic absorbant membrane is greater with lauryl sulfate, whereas micellar solubilization is much higher with polysorbate. As for the rest (i.e. the elimination of the stagnant aqueous diffusion layer as a limiting step for absorption), the two surfactants behave in a similar way. The biopharma…

Computer simulations of bioequivalence trials: selection of design and analyte in BCS drugs with first-pass hepatic metabolism: linear kinetics (I).

Modeling and simulation approaches are useful tools to assess the potential outcome of different scenarios in bioequivalence studies. The aim of this study is to propose a new and improved semi-physiological model for bioequivalence trial simulations and apply it for all BCS (Biopharmaceutic Classification System) drug classes with non-saturated first-pass hepatic metabolism. The semi-physiological model was developed in NONMEM VI to simulate bioequivalence trials. Parent drug and metabolite levels for both reference and test were simulated. Eight types of drugs (with high or low permeability and high or low solubility (class I to IV) and high or low intrinsic clearance) were considered in …

Ion-pair approach coupled with nanoparticle formation to increase bioavailability of a low permeability charged drug.

Abstract Atenolol is a drug widely used for the treatment of hypertension. However, the great drawback it presents is a low bioavailability after oral administration. To obtain formulations that allow to improve the bioavailability of this drug is a challenge for the pharmaceutical technology. The objective of this work was to increase the rate and extent of intestinal absorption of atenolol as model of a low permeability drug, developing a double technology strategy. To increase atenolol permeability an ion pair with brilliant blue was designed and the sustained release achieved through encapsulation in polymeric nanoparticles (NPs). The in vitro release studies showed a pH-dependent relea…

Drug gastrointestinal absorption in rat: Strain and gender differences.

Predictive animal models of intestinal drug absorption are essential tools in drug development to identify compounds with promising biopharmaceutical properties. In situ perfusion absorption studies are routinely used in the preclinical setting to screen drug candidates. The objective of this work is to explore the differences in magnitude and variability on intestinal absorption associated with rat strain and gender. Metoprolol and Verapamil absorption rate coefficients were determined using the in situ closed loop perfusion model in four strains of rats and in both genders. Strains used were Sprague-Dawley, Wistar-Han, Wistar-Unilever, Long-Evans and CD∗IGS. In the case of Metoprolol only…

Kinetic modelling of the intestinal transport of sarafloxacin. Studiesin situin rat andin vitroin Caco-2 cells

The absorption kinetics of sarafloxacin, as a model of fluoroquinolone structure, were studied in the rat small intestine and in Caco-2 cells. The objective of the study was to investigate the mechanistic basis of the drug's intestinal transport in comparison with other members of the fluoroquinolone family and to apply a mathematical modelling approach to the transport process. In the rat small intestine, sarafloxacin showed dual mechanisms of intestinal absorption with a passive diffusional component and an absorptive carrier-mediated component. The characteristics of the animal study design made it suitable for population analysis, thus allowing the accurate estimation of transport param…

Computer Simulations as a Tool for Optimizing Bioequivalence Trials

Long-Circulating Hyaluronan-Based Nanohydrogels as Carriers of Hydrophobic Drugs

[EN] Nanohydrogels based on natural polymers, such as polysaccharides, are gaining interest as vehicles for therapeutic agents, as they can modify the pharmacokinetics and pharmacodynamics of the carried drugs. In this work, hyaluronan-riboflavin nanohydrogels were tested in vivo in healthy rats highlighting their lack of toxicity, even at high doses, and their different biodistribution with respect to that of native hyaluronan. They were also exploited as carriers of a hydrophobic model drug, the anti-inflammatory piroxicam, that was physically embedded within the nanohydrogels by an autoclave treatment. The nanoformulation was tested by intravenous administration showing an improvement of…