Recent advances and novel strategies in pre-clinical formulation development: An overview

Vehicle Effect on In-Vitro and In-Vivo Performance of Spray Dry Dispersions

In early drug development, amorphous spray-dried dispersions (SDDs) applied to enhance the bioavailability of poorly water-soluble compounds are typically administered to preclinical species via oral gavage in the form of suspensions. The liquid formulations are usually prepared on the same day of dosing to minimize the exposure of the amorphous material to the aqueous vehicle, thereby reducing the risk of crystallization. Dose-ability (e.g. syringeability) of the suspensions is also a critical factor for the administration, particularly when high doses, thus concentrations, are required for toxicology studies. As a result, it is standard practice during early formulation screening to assess the stability and the maximum feasible concentration of SDDs in various vehicles. In this study, we evaluated the impact of different vehicles on the performance of a model SDD in in-vitro and in-vivo settings, to mitigate the risks associated with its administration in liquid form. A poorly water-soluble compound (GEN-A) was selected to screen various SDDs and generate the SDD model at 30% drug load with HPMCAS-MF polymer carrier. The SDD was suspended in selected aqueous vehicles after a careful vehicle components screening, that included suspending agents (HPC-SL), solubilizers (PEG400, Propylene glycol), surfactants (Vitamin E TPGS, SLS, Tween 80, Poloxamer 188), and complexing agents (HP-ꞵ-CD, SBE-ꞵ-CD). The suspensions were characterized for stability, dose-ability and dissolution in biorelevant media, prior administration in pre-clinical species. The SDD dissolution profile revealed that the drug's supersaturation level was positively impacted by the presence of a surfactant (SLS) and a complexing agent (SBE-ꞵ-CD) with respect to a suspending agents (HPC-SL) in the vehicle. Similarly, the pharmacokinetics profiles of the drug following the administration of the SDD in a vehicle with a complexing agent (SBE-ꞵ-CD) achieved greater exposure compare to the SDD in a vehicle with a suspending agent (HPC-SL). These findings confirm a synergistic effect between the SDD and the vehicles, suggesting that this combination could be leveraged to maximize the advantages of the amorphous approach.

Relationship between Endotoxin Content in Vaccine Preclinical Formulations and Animal Welfare: An Extensive Study on Historical Data to Set an Informed Threshold

The most widely known pyrogen impurity in vaccines is the Gram-negative bacterial endotoxin lipopolysaccharide (LPS). When administered at toxic doses, endotoxin triggers inflammatory responses, which lead to endotoxic shock. The literature on endotoxic content (EC) for preclinical vaccines' formulations used in animal studies is very poor, and the recommended thresholds are solely based on commercial vaccine limits set for humans and are, therefore, not connected to the actual impact of EC on animal welfare for species used in preclinical research studies. An extensive study to evaluate the presence of a potential relationship between endotoxin content in formulations administered to mice (the most common species used in preclinical research studies) and their welfare was conducted to calculate an EC threshold for formulations of candidate vaccines. Three years of historical data, from more than 500 formulations of different antigen types (i.e., proteins, glycoconjugates, OMV/GMMA) injected into more than 5000 mice, was evaluated with two alternative statistical methodologies, both demonstrating that there is no significant relationship between actual endotoxin levels and mouse welfare. The calculation of thresholds was, therefore, performed by consistency versus formulations that demonstrated no impact on animal welfare.

Design of a Re-Dispersible High Drug Load Amorphous Formulation

Amorphous solid dispersions (ASD) are a commonly used enabling formulation technology to drive oral absorption of poorly soluble drugs. To ensure adequate solid-state stability and dissolution characteristics, the ASD formulation design typically has ≤ 25% drug loading. Exposed to aqueous media, ASD formulations can produce drug-rich colloidal dispersion with particle size < 500 nm. This in situ formation of colloidal particles requires incorporation of excess excipients in the formulation. The concept of using engineered drug-rich particles having comparable size as those generated by ASDs in aqueous media is explored with the goal of increasing drug loading in the solid dosage form. Utilizing ABT-530 as model compound, a controlled solvent-antisolvent precipitation method resulted in a dilute suspension that contained drug-rich (90% (w/w)) amorphous nanoparticles (ANP). The precipitation process was optimized to yield a suspension containing < 300 nm ANP. A systematic evaluation of formulation properties and process variables resulted in the generation of dry powders composed of 1-8 µm agglomerates of nanoparticles which in contact with water regenerated the colloidal suspension having particle size comparable to primary particles. Thus, this work demonstrates an approach to designing a re-dispersible ANP based powder containing ≥90% w/w ABT-530 that could be used in preparation of a high drug load solid dosage form.

Artemisinin Cocrystals for Bioavailability Enhancement. Part 2: In Vivo Bioavailability and Physiologically Based Pharmacokinetic Modeling

We report the evaluation and prediction of the pharmacokinetic (PK) performance of artemisinin (ART) cocrystal formulations, that is, 1:1 artemisinin/orcinol (ART-ORC) and 2:1 artemisinin/resorcinol (ART²-RES), using in vivo murine animal and physiologically based pharmacokinetic (PBPK) models. The efficacy of the ART cocrystal formulations along with the parent drug ART was tested in mice infected with Plasmodium berghei. When given at the same dose, the ART cocrystal formulation showed a significant reduction in parasitaemia at day 4 after infection compared to ART alone. PK parameters including C_max (maximum plasma concentration), T_max (time to C_max), and AUC (area under the curve) were obtained by determining drug concentrations in the plasma using liquid chromatography-high-resolution mass spectrometry (LC-HRMS), showing enhanced ART levels after dosage with the cocrystal formulations. The dose-response tests revealed that a significantly lower dose of the ART cocrystals in the formulation was required to achieve a similar therapeutic effect as ART alone. A PBPK model was developed using a PBPK mouse simulator to accurately predict the in vivo behavior of the cocrystal formulations by combining in vitro dissolution profiles with the properties of the parent drug ART. The study illustrated that information from classical in vitro and in vivo experimental investigations of the parent drug of ART formulations can be coupled with PBPK modeling to predict the PK parameters of an ART cocrystal formulation in an efficient manner. Therefore, the proposed modeling strategy could be used to establish in vitro and in vivo correlations for different cocrystals intended to improve dissolution properties and to support clinical candidate selection, contributing to the assessment of cocrystal developability and formulation development.

Discovery of Pemigatinib: A Potent and Selective Fibroblast Growth Factor Receptor (FGFR) Inhibitor

Aberrant activation of FGFR has been linked to the pathogenesis of many tumor types. Selective inhibition of FGFR has emerged as a promising approach for cancer treatment. Herein, we describe the discovery of compound 38 (INCB054828, pemigatinib), a highly potent and selective inhibitor of FGFR1, FGFR2, and FGFR3 with excellent physiochemical properties and pharmacokinetic profiles. Pemigatinib has received accelerated approval from the U.S. Food and Drug Administration for the treatment of adults with previously treated, unresectable locally advanced or metastatic cholangiocarcinoma with a FGFR2 fusion or other rearrangement. Additional clinical trials are ongoing to evaluate pemigatinib in patients with FGFR alterations.

Three-dimensional aspects of formulation excipients in drug discovery: a critical assessment on orphan excipients, matrix effects and drug interactions

Formulation/pharmaceutical excipients play a major role in formulating drug candidates, with the objectives of ease of administration, targeted delivery and complete availability. Many excipients used in pharmaceutical formulations are orphanized in preclinical drug discovery. These orphan excipients could enhance formulatability of highly lipophilic compounds. Additionally, they are safe in preclinical species when used below the LD50 values. However, when the excipients are used in formulating compounds with diverse physico-chemical properties, they pose challenges by modulating study results through their bioanalytical matrix effects. Excipients invariably present in study samples and not in the calibration curve standards cause over-/under- estimation of exposures. Thus, the mechanism by which excipients cause matrix effects and strategies to nullify these effects needs to be revisited. Furthermore, formulation excipients cause drug interactions by moderating the pathways of drug metabolizing enzymes and drug transport proteins. Although it is not possible to get rid of excipient driven interactions, it is always advised to be aware of these interactions and apply the knowledge to draw meaningful conclusions from study results. In this review, we will comprehensively discuss a) orphan excipients that have wider applications in preclinical formulations, b) bioanalytical matrix effects and possible approaches to mitigating these effects, and c) excipient driven drug interactions and strategies to alleviate the impacts of drug interactions.

Enhancing the Furosemide Permeability by Papain Minitablets Through a Triple Co-culture In Vitro Intestinal Cell Model

The administration of medicines by the oral route is the most used approach for being very convenient. Although it is the most popular, this route also has absorption, and consequently, bioavailability limitations. In this sense, several pharmacotechnical strategies have been used to improve drug absorption, one of which is the use of permeation promoters. Papain is a very versatile plant enzyme that can be used as a permeation promoter of various active compounds. This study aimed to evaluate the safety of papain and the formulation of native papain minitablets to promote in vitro permeation of furosemide through an innovative biomimetic triple co-culture model of Caco-2, HT29-MTX, and Raji cells. Regarding permeation, furosemide and metaprolol concentrations are determined with HPLC; those are used to calculate P_app. Monolayer integrity was evaluated using TEER and Lucifer Yellow. In the presence of papain, TEER decreased two-fold and the P_app of furosemide increased six-fold. The results suggest that native papain minitablets can be used as therapeutic adjuvants to enhance the permeation of drugs significantly improving bioavailability.

Preformulation Studies and Enabling Formulation Selection for an Insoluble Compound at Preclinical Stage-From In Vitro, In Silico to In Vivo

The objective of this work was to identify an enabling formulation for an insoluble compound ZL006 with potency of boosting leukocytes after chemotherapy. The low oral bioavailability (<1%) of its conventional suspension was the hurdle for the preclinical evaluation via oral administration. Preformulation studies including physical form screening and physicochemical properties determination were performed. Polymorphism was observed, and the more thermodynamically stable form was selected for further studies. ZL006 showed certain supersaturation solubility, although the thermodynamic solubility in FaSSIF was low, which indicated the supersaturating formulation might work. Parameter sensitivity analysis by in silico simulation predicted that in vivo exposure was sensitive to solubility, while particle size reduction would have limited impact on exposure. Based on in silico prediction and the understanding of the molecule from preformulation studies, solid dispersion approach was selected. A preliminary dose escalation pharmacokinetic study in rats demonstrated that in vivo exposure increased in dose-proportional manner from 12.5 mg/kg to 50 mg/kg with around 50% oral bioavailability after oral dosing of the solid dispersion. This work showed that combination of preformulation studies and in silico simulation could efficiently guide the selection of enabling formulation, which could save resources at preclinical stage.

In vivo models and decision trees for formulation development in early drug development: A review of current practices and recommendations for biopharmaceutical development

The ability to predict new chemical entity performance using in vivo animal models has been under investigation for more than two decades. Pharmaceutical companies use their own strategies to make decisions on the most appropriate formulation starting early in development. In this paper the biopharmaceutical decision trees available in four EFPIA partners (Bayer, Boehringer Ingelheim, Bristol Meyers Squibb and Janssen) were discussed by 7 companies of which 4 had no decision tree currently defined. The strengths, weaknesses and opportunities for improvement are discussed for each decision tree. Both pharmacokineticists and preformulation scientists at the drug discovery & development interface responsible for lead optimization and candidate selection contributed to an overall picture of how formulation decisions are progressed. A small data set containing compound information from the database designed for the IMI funded OrBiTo project is examined for interrelationships between measured physicochemical, dissolution and relative bioavailability parameters. In vivo behavior of the drug substance and its formulation in First in human (FIH) studies cannot always be well predicted from in vitro and/or in silico tools alone at the time of selection of a new chemical entity (NCE). Early identification of the risks, challenges and strategies to prepare for formulations that provide sufficient preclinical exposure in animal toxicology studies and in FIH clinical trials is needed and represents an essential part of the IMI funded OrBiTo project. This article offers a perspective on the use of in vivo models and biopharmaceutical decision trees in the development of new oral drug products.

Acid-base properties of phosphoric and acetic acid in aprotic organic solvents - A complete thermodynamic characterisation

Knowledge regarding the acid-base behaviour in non-aqueous media has remained relatively scarce in spite of its importance for many aspects of chemistry. The research presented in this work fills some of particularly important gaps in the corresponding thermodynamic data. We report on a detailed study of acid-base properties of dihydrogen phosphate and acetate in aprotic organic solvents (acetonitrile, dimethyl sulfoxide, and dimethylformamide). It was found that several processes, i.e. protonation, homoassociation, and dimerisation play important roles in defining the basicity of these widely important anions. In the case of dihydrogen phosphate, formation of higher homoassociates (two anions, one acid molecule and vice versa) was detected, whereas acetate formed only simple homoassociates of 1:1 stoichiometry. The dimerisation of dihydrogen phosphate and acetic acid were confirmed to be important processes as well. The thermodynamics of the above mentioned reactions was characterised in detail by means of various experimental methods: ITC, spectrophotometry, NMR-spectroscopy, and conductometry. Reliable equilibrium constants and other thermodynamic reaction functions were determined. The obtained results were discussed in terms of hydrogen bonding potential of the anions and their conjugated acids, as well as solvent properties, i.e. their ability to solvate the species involved in the studied processes.

Potential of Cocoa Pod Husk Pectin-Based Modified Release Capsules as a Carrier for Chronodelivery of Hydrocortisone in Sprague-Dawley Rats

The potential of cocoa pod husk (CPH) pectin-based modified release (MR) capsules as a carrier for chronodelivery of hydrocortisone in Sprague-Dawley rats was assessed. Extemporaneously formulated CPH pectin-based hydrocortisone (10 mg) capsules crosslinked with calcium chloride (Formulation A) or zinc (Formulation B) and a commercial immediate release hydrocortisone formulation were administered orally to Sprague-Dawley rats and the pharmacokinetic parameters were evaluated using noncompartmental analysis. Formulation A had a 2 h lag phase followed by an increase in serum drug concentration in the treated rats. Peak concentrations (C_max) of 21.799 ± 1.993 ng/ml and 20.844 ± 2.661 ng/ml were achieved after 6 ± 0.23 h and 6 ± 0.35 h (T_max), respectively, for capsules A and B. The immediate release formulation had a peak concentration of 15.322 ± 0.313 ng/ml within 1 ± 0.2 h. The relative bioavailability of the CPH pectin-based capsules A and B was 213% and 274%, respectively. Formulations A and B had half-lives more than three times that of the immediate release formulation. The MR capsules exhibited a higher exposure, greater bioavailability, and versatility in release of cortisol than the commercial immediate release formulation. Additionally, the MR capsules exhibited an extended drug release with overnight cortisol rise and early morning cortisol peak and hold promise in the management of adrenal insufficiency.

Fos Protein as a Marker of Neuronal Activity: a Useful Tool in the Study of the Mechanism of Action of Natural Products with Analgesic Activity

Pain treatment is still ineffective in many conditions and remains one of the greatest challenges of modern medicine. Historically, due to the incredible variety of pharmacologically promising natural products (NPs) and the chemical complexity of their compounds, scientists have explored their use as a source of treatment for diseases or symptomatology. Fos protein and its precursor, the gene c-Fos, have been the subject of study in relation to the pathophysiology of pain as a possible tool to aid in its understanding. More recently, it has become a useful tool in the study of NPs with analgesic profile. Thus, this systematic review aimed to investigate the analgesic effect of NPs and derivatives through changes in Fos protein or c-Fos expression in nervous system central. The search terms "analgesics," "Fos," and "drug effects" were used in the databases PubMed, MEDLINE, Scopus, and Embase. Forty-six articles were identified. Twenty-five articles investigated Fos expression in the spinal cord, 1 in dorsal root ganglion, 11 in brain areas, and 9 investigated the association between the spinal cord and brain areas. Although Fos protein expression has been used as a tool in the studies of the mechanism of action of pain in relation to NPs with analgesic activity, the associations between brain areas and the spinal cord-and the possible pathways involved-have not yet been fully elucidated and deserve further study.

Pokharkar V. Understanding peroral absorption: regulatory aspects and contemporary approaches to tackling solubility and permeability hurdles

Oral drug absorption is a process influenced by the physicochemical and biopharmaceutical properties of the drug and its inter-relationship with the gastrointestinal tract. Drug solubility, dissolution and permeability across intestinal barrier are the key parameters controlling absorption. This review provides an overview of the factors that affect drug absorption and the classification of a drug on the basis of solubility and permeability. The biopharmaceutical classification system (BCS) was introduced in early 90׳s and is a regulatory tool used to predict bioavailability problems associated with a new entity, thereby helping in the development of a drug product. Strategies to combat solubility and permeability issues are also discussed.

The formation of a host-guest inclusion complex system between β-cyclodextrin and baicalin and its dissolution characteristics

Objectives

Baicalin (BCL) has potential therapeutic benefits, but its clinical outcomes are restricted mainly because of low water solubility. This study sought to improve the water solubility of BCL by the formation of inclusion complex with β-cyclodextrin (β-CD).

Methods

The inclusion complex was studied by solubility test, differential scanning calorimeter (DSC), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), 1H Nuclear magnetic resonance (1HNMR) and scanning electron microscopy (SEM). Molecular docking was conducted to verify the experimental findings. The dissolution rate was determined by dialysis membrane method. In vivo absorption studies in rats were conducted and high-performance liquid chromatography (HPLC) was used to analyse the plasma level of BCL after oral administration.

Key findings

The DSC, FTIR, XRD, 1HNMR and SEM findings suggested the formation of inclusion complex between BCL and β-CD in 1 : 1 stoichiometry. Molecular docking demonstrated the insertion of benzene ring of BCL into β-CD cavity by hydrophobic interactions and possible H-bond formation. Moreover, β-CD markedly improved the solubility of BCL and displayed AL-type phase diagrams. The improvement in dissolution rate of the inclusion complex was reflected in the earlier Tmax, higher Cmax and larger AUC0–t than that of BCL after oral administration.

Conclusions

β-cyclodextrin complex can be used as an effective formulation strategy for development of BCL-loaded delivery system with better therapeutic outcomes.

Gelucire and Gelucire-PEG400 formulations; tolerability in species used for non-clinical safety testing after oral (gavage) dosing

The selection of a vehicle for oral formulations of compounds to be used in non-clinical safety studies is a challenge for poorly soluble compounds. Typically a compromise between solubility and tolerability has to be reached. Vehicle tolerability data are not readily available for a number of vehicles, and a series of oral tolerability studies were, therefore, conducted with Gelucire and Gelucire:PEG400 formulations in rats, dogs and minipigs in order to determine tolerable daily dose volumes in these species. Gelucire and Gelucire:PEG400 formulations were assessed in studies for up to 5 days in minipigs, 7 days in rats and up to 39 weeks in dogs. Gastrointestinal side effects in terms of soft and/or liquid faeces were noted in all species, but the sensitivity to these effects differed between species with the dog being the most sensitive. It was concluded that Gelucire:PEG400 (90:10) was tolerated in Beagle dogs when administered at 1 ml kg(-1) once daily for 39 weeks, and 100% Gelucire was tolerated in the rat and the minipig when administered once daily at 5 ml kg(-1) for 5 days. Copyright © 2016 John Wiley & Sons, Ltd.

Design and development of an in situ synthesized layered double hydroxide structure of Fe-induced hydroxyapatite for drug carriers

Possible mechanisms: (i) formation of LDH structure of Fe-induced hydroxyapatite (HA), (ii) intercalation of Aceclofenac (AF) drug in LDH structure of FH carriers and (iii) releasing of drug via hydrolysis and/or reaction with other biomolecules.

Studies and methodologies on vaginal drug permeation

The vagina stands as an important alternative to the oral route for those systemic drugs that are poorly absorbed orally or are rapidly metabolized by the liver. Drug permeation through the vaginal tissue can be estimated by using in vitro, ex vivo and in vivo models. The latter ones, although more realistic, assume ethical and biological limitations due to animal handling. Therefore, in vitro and ex vivo models have been developed to predict drug absorption through the vagina while allowing for simultaneous toxicity and pathogenesis studies. This review focuses on available methodologies to study vaginal drug permeation discussing their advantages and drawbacks. The technical complexity, costs and the ethical issues of an available model, along with its accuracy and reproducibility will determine if it is valid and applicable. Therefore every model shall be evaluated, validated and standardized in order to allow for extrapolations and results presumption, and so improving vaginal drug research and stressing its benefits.

Supramolecular cyclodextrin-based drug nanocarriers

Hosting of polymers, lipids and drug conjugates makes cyclodextrins suitable to prepare biocompatible, targetable and stimuli-responsive supramolecular drug nanocarriers.

An oral redox-sensitive self-immolating prodrug strategy

We report a novel oral prodrug approach where a solubilizing polymer conjugated to the drug is designed to be released by the action of an exogenously administered agent in the intestine.

Preclinical formulations: insight, strategies, and practical considerations

A lot of resources and efforts have been directed to synthesizing potentially useful new chemical entities (NCEs) by pharmaceutical scientists globally. Detailed physicochemical characterization of NCEs in an industrial setup begins almost simultaneously with preclinical testing. Most NCEs possess poor water solubility posing bioavailability issues during initial preclinical screening, sometimes resulting in dropping out of an NCE with promising therapeutic activity. Selection of right formulation approach for an NCE, based on its physicochemical properties, can aid in improving its solubility-related absorption and bioavailability issues. The review focuses on preclinical formulations stressing upon different preclinical formulation strategies and deciphers the understanding of formulation approaches that could be employed. It also provides detailed information related to a vast pool of excipients available today, which is of immense help in designing preclinical formulations. Few examples mentioned, throw light on key aspects of preclinical formulation development. The review will serve as an important guide for selecting the right strategy to improve bioavailability of NCEs for academic as well as industrial formulation scientists.

Engineered nanocrystal technology: in-vivo fate, targeting and applications in drug delivery

Formulation of nanocrystals is a robust approach which can improve delivery of poorly water soluble drugs, a challenge pharmaceutical industry has been facing since long. Large scale production of nanocrystals is done by techniques like precipitation, media milling and, high pressure homogenization. Application of appropriate stabilizers along with drying accords long term stability and commercial viability to nanocrystals. These can be administered through oral, parenteral, pulmonary, dermal and ocular routes showing their high therapeutic applicability. They serve to target drug molecules in specific regions through size manipulation and surface modification. This review dwells upon the in-vivo fate and varying applications in addition to the facets of drug nanocrystals stated above.

Water-Dilutable Biocompatible Microemulsion Systems: Design and Characterisation

The present study describes a screening approach in design of microemulsion preconcentrates (self-microemulsifying systems) comprising: PEG-8 caprylic/capric glycerides (Labrasol®) (surfactant), PEG-40 hydrogenated castor oil (Cremophor® RH40) (cosurfactant) (at surfactant-to-cosurfactant mass ratios 9:1, 7:3, 5:5, 3:7 and 1:9), and 10% w/w or 20% w/w of medium-chain triglycerides or olive oil (oil). The self-microemulsifying ability of the prepared surfactant/cosurfactant/oil mixtures in water and 0.1 M HCl (pH 1.2), was evaluated by droplet size and zeta potential analysis and cross-polarized light microscopy. The formation of microemulsions was observed only in the presence of medium-chain triglycerides at surfactant-to-cosurfactant ratios 7:3 and 5:5 (in the mixtures containing 10% w/w of the oil phase) and 3:7 and 1:9 (when 20% w/w of the same oil was used). The obtained results provide new implications for development of microemulsion preconcentrates suitable as delivery systems for food and pharmaceutical applications.

Strategies to address low drug solubility in discovery and development

Drugs with low water solubility are predisposed to low and variable oral bioavailability and, therefore, to variability in clinical response. Despite significant efforts to "design in" acceptable developability properties (including aqueous solubility) during lead optimization, approximately 40% of currently marketed compounds and most current drug development candidates remain poorly water-soluble. The fact that so many drug candidates of this type are advanced into development and clinical assessment is testament to an increasingly sophisticated understanding of the approaches that can be taken to promote apparent solubility in the gastrointestinal tract and to support drug exposure after oral administration. Here we provide a detailed commentary on the major challenges to the progression of a poorly water-soluble lead or development candidate and review the approaches and strategies that can be taken to facilitate compound progression. In particular, we address the fundamental principles that underpin the use of strategies, including pH adjustment and salt-form selection, polymorphs, cocrystals, cosolvents, surfactants, cyclodextrins, particle size reduction, amorphous solid dispersions, and lipid-based formulations. In each case, the theoretical basis for utility is described along with a detailed review of recent advances in the field. The article provides an integrated and contemporary discussion of current approaches to solubility and dissolution enhancement but has been deliberately structured as a series of stand-alone sections to allow also directed access to a specific technology (e.g., solid dispersions, lipid-based formulations, or salt forms) where required.

Cell-based in vitro models for predicting drug permeability

INTRODUCTION

In vitro cell models have been used to predict drug permeation in early stages of drug development, since they represent an easy and reproducible method, allowing the tracking of drug absorption rate and mechanism, with an advantageous cost-benefit ratio. Such cell-based models are mainly composed of immortalized cells with an intrinsic ability to grow in a monolayer when seeded in permeable supports, maintaining their physiologic characteristics regarding epithelium cell physiology and functionality.

AREAS COVERED

This review summarizes the most important intestinal, pulmonary, nasal, vaginal, rectal, ocular and skin cell-based in vitro models for predicting the permeability of drugs. Moreover, the similitude between in vitro cell models and in vivo conditions are discussed, providing evidence that each model may provisionally resemble different drug absorption route.

EXPERT OPINION

Despite the widespread use of in vitro cell models for drug permeability and absorption evaluation purposes, a detailed study on the properties of these models and their in vitro-in vivo correlation compared with human data are required to further use in order to consider a future drug discovery optimization and clinical development.