The effects of three absorption-modifying critical excipients on the in vivo intestinal absorption of six model compounds in rats and dogs

A comprehensive mechanistic investigation of factors affecting intestinal absorption and bioavailability of two PROTACs in rats

AIM

Proteolysis targeting chimeras (PROTACs) exhibit a unique and promising pharmacology. However, this comes with molecular properties exceeding the 'drug-like' rule of five chemical space, which often limits gastrointestinal absorption. This in vivo study aimed to investigate the contribution of luminal and plasma stability, intestinal effective permeability, P-glycoprotein (P-gp) efflux, and bile excretion, on the rat intestinal absorption and systemic exposure of two PROTACs, ARV-110 (812 Da, LogD7.4 4.8) and ARV-471 (724 Da, LogD7.4 4.6).

METHODS

Luminal stability and effective intestinal permeability were determined directly from luminal disappearance using single-pass intestinal perfusion, with and without a protease inhibitor, or a P-gp/Cytochrome P450 CYP3A inhibitor (ketoconazole) in rats. Plasma stability was tested by in vitro incubations. Intestinal absorption, systemic exposure, and biliary excretion were examined after intraduodenal and intravenous dosing with ketoconazole or the P-gp selective inhibitor (encequidar).

RESULTS AND DISCUSSION

Both PROTACs were degraded in the intestinal lumen and in plasma by peptidases. The intestinal effective permeability in rats was moderate for ARV-110 (0.62 × 10-4 cm/s) and low for ARV-471 (0.23 × 10-4 cm/s). P-gp inhibition increased the permeability 1.6- and 2.3-fold for ARV-110 and ARV-471, respectively. After intraduodenal dosing with the P-gp inhibitors a corresponding increase in systemic exposure was observed for both PROTACs. There was only a minor difference in the increased systemic exposure induced by the two inhibitors, suggesting that the mechanisms were primarily P-gp inhibition, rather than gut-wall and hepatic extraction. Biliary excretion was a minor pathway and did not affect the absorption and systemic exposure of the PROTACs to a large extent.

CONCLUSION

In the rat, ARV-110 and ARV-471 were enzymatically degraded in the intestinal lumen and in plasma, and their intestinal permeability and systemic exposure seem to be reduced due to P-gp efflux.

Ex vivo permeability study of poorly soluble drugs across gastrointestinal membranes: acceptor compartment media composition

Ex vivo drug permeability testing across gastrointestinal (GI) membranes is crucial in drug discovery and oral drug delivery. It is a reliable method for drugs with good solubility, but it poses challenges for poorly soluble drugs, which are common in development pipelines today. Although enabling formulations increase the apparent solubility in the GI compartment (dissolution vessel or permeation chamber's donor compartment), maintaining solubilized drug in the acceptor compartment during ex vivo testing remains largely unresolved. This review compiles and critically evaluates the diverse compositions of acceptor media used in ex vivo permeability studies for poorly soluble drugs, highlighting this significant yet underexplored aspect of pharmaceutical science. An algorithm is proposed for selecting solubility-enhancing additives for the acceptor media in ex vivo permeability studies of poorly soluble drugs.

Brain drug delivery from the nasal olfactory region is enhanced using lauroylcholine chloride: An estimation using in vivo PET imaging

INTRODUCTION

Intranasal (IN) administration, often referred to as nose-to-brain (N2B) drug delivery, is an attractive approach for delivering drugs to the central nervous system. However, the efficacy of this method is limited because of the small size of the nasal olfactory region, which limits the drug dosage. Using permeation enhancers could improve drug delivery from this region to the brain, though their effects are not fully understood. We therefore investigated the effects of co-administration of permeation enhancers on N2B drug delivery of a model drug domperidone, a peripherally acting dopamine D2 receptor (D2R) blocker.

METHODS

We conducted in vitro permeability assays to evaluate the effects of sodium lauryl sulfate (SLS), a classical permeation enhancer, and lauroylcholine chloride (LCC) on domperidone permeation in human nasal mucosa-derived cells. We also used the D2R ligand [11C]raclopride to assess the in vivo effects of LCC on domperidone delivery in the rat brain using a positron emission tomography (PET) competition paradigm. In comparative PET experiments, we tested the effects of intravenously administered domperidone without LCC co-administration.

RESULTS

LCC effectively improved nasal mucosal permeation of domperidone in vitro compared to SLS. In rat IN administration experiments, striatal [11C]raclopride uptake was significantly decreased by the addition of LCC to domperidone. On the other hand, intravenously administered domperidone with or without intranasally administered LCC did not decrease [11C]raclopride brain uptake, suggesting a lesser influence of peripheral domperidone on [11C]raclopride brain uptake. PET studies showed that striatal D2R occupancy of domperidone was increased 2.4-fold by co-administration of LCC.

CONCLUSION

LCC effectively enhances the domperidone delivery from the rat olfactory region to the brain, probably not via a circulating blood. The combination of permeation enhancers and olfactory region-selective drug administration could be effective for N2B drug delivery.

Safety of surfactant excipients in oral drug formulations

Surfactants are a diverse group of compounds that share the capacity to adsorb at the boundary between distinct phases of matter. They are used as pharmaceutical excipients, food additives, emulsifiers in cosmetics, and as household/industrial detergents. This review outlines the interaction of surfactant-type excipients present in oral pharmaceutical dosage forms with the intestinal epithelium of the gastrointestinal (GI) tract. Many surfactants permitted for human consumption in oral products reduce intestinal epithelial cell viability in vitro and alter barrier integrity in epithelial cell monolayers, isolated GI tissue mucosae, and in animal models. This suggests a degree of mis-match for predicting safety issues in humans from such models. Recent controversial preclinical research also infers that some widely used emulsifiers used in oral products may be linked to ulcerative colitis, some metabolic disorders, and cancers. We review a wide range of surfactant excipients in oral dosage forms regarding their interactions with the GI tract. Safety data is reviewed across in vitro, ex vivo, pre-clinical animal, and human studies. The factors that may mitigate against some of the potentially abrasive effects of surfactants on GI epithelia observed in pre-clinical studies are summarised. We conclude with a perspective on the overall safety of surfactants in oral pharmaceutical dosage forms, which has relevance for delivery system development.

Excipient Impact on Fenofibrate Equilibrium Solubility in Fasted and Fed Simulated Intestinal Fluids Assessed Using a Design of Experiment Protocol

Solubility is a critical parameter controlling drug absorption after oral administration. For poorly soluble drugs, solubility is influenced by the complex composition of intestinal media and the influence of dosage form excipients, which can cause bioavailability and bioequivalence issues. This study has applied a small scale design of experiment (DoE) equilibrium solubility approach in order to investigate the impact of excipients on fenofibrate solubility in simulated fasted and fed intestinal media. Seven media parameters (bile salt (BS), phospholipid (PL), fatty acid, monoglyceride, cholesterol, pH and BS/PL ratio) were assessed in the DoE and in excipient-free media, and only pH and sodium oleate in the fasted state had a significant impact on fenofibrate solubility. The impact of excipients were studied at two concentrations, and for polyvinylpyrrolidone (PVP, K12 and K29/32) and hydroxypropylmethylcellulose (HPMC, E3 and E50), two grades were studied. Mannitol had no solubility impact in any of the DoE media. PVP significantly increased solubility in a media-, grade- and concentration-dependent manner, with the biggest change in fasted media. HPMC and chitosan significantly reduced solubility in both fasted and fed states in a media-, grade- and concentration-dependent manner. The results indicate that the impact of excipients on fenofibrate solubility is a complex interplay of media composition in combination with their physicochemical properties and concentration. The results indicate that in vitro solubility studies combining the drug of interest, proposed excipients along with suitable simulated intestinal media recipes will provide interesting information with the potential to guide formulation development.

Challenges in Permeability Assessment for Oral Drug Product Development

Drug permeation across the intestinal epithelium is a prerequisite for successful oral drug delivery. The increased interest in oral administration of peptides, as well as poorly soluble and poorly permeable compounds such as drugs for targeted protein degradation, have made permeability a key parameter in oral drug product development. This review describes the various in vitro, in silico and in vivo methodologies that are applied to determine drug permeability in the human gastrointestinal tract and identifies how they are applied in the different stages of drug development. The various methods used to predict, estimate or measure permeability values, ranging from in silico and in vitro methods all the way to studies in animals and humans, are discussed with regard to their advantages, limitations and applications. A special focus is put on novel techniques such as computational approaches, gut-on-chip models and human tissue-based models, where significant progress has been made in the last few years. In addition, the impact of permeability estimations on PK predictions in PBPK modeling, the degree to which excipients can affect drug permeability in clinical studies and the requirements for colonic drug absorption are addressed.

Novel food drug interaction mechanism involving acyclovir, chitosan and endogenous mucus

Drug absorption from drug products may be affected by pharmaceutical excipients and/or food additives through different mechanisms. Chitosan is a recognized nutraceutical, with potential as an excipient due to its permeability enhancer properties. While chitosan properties have been evaluated in in vitro and pre-clinical models, studies in humans are scarce. Unexpectedly, a controlled clinical trial showed chitosan actually reduced acyclovir bioavailability. The effect seems to be related to an interaction with gastrointestinal mucus that prevents further absorption, although more in depth research is needed to unravel the mechanism. In this paper, we propose a mechanism underlying this excipient effect. The mucus - chitosan interaction was characterized and its effect on acyclovir diffusion, permeation and bioaccessibility was investigated. Further, pharmacokinetic modeling was used to assess the clinical relevance of our findings. Results suggest that in situ coacervation between endogenous mucus and chitosan rapidly entrap 20-30% of acyclovir dissolved dose in the intestinal lumen. This local reduction of acyclovir concentration together with its short absorption window in the small intestine would explain the reduction in acyclovir C_max and AUC. This study highlights the importance of considering mucus in any biorelevant absorption model attempting to anticipate the effect of chitosan on drug absorption.

Intestinal epithelium penetration of liraglutide via cholic acid pre-complexation and zein/rhamnolipids nanocomposite delivery

BACKGROUND

Oral administration offered a painless way and improved compliance for diabetics. However, the emerging GLP-1 analog peptide drugs for diabetes primarily rely on the injection route, and the development of oral dosage forms was hampered by the low oral bioavailability due to the structural vulnerability to digestive enzymes and molecule impermeability in the gastrointestinal tract.

RESULTS

In this study, the non-covalent interaction between cholic acid (CA) and liraglutide (LIRA) was found and theoretically explained by molecular docking simulation. Formation of this physical complex of liraglutide and cholic acid (LIRA/CA Complex) reduced the self-aggregation of LIRA and accelerated intestinal epithelium penetration. By the anti-solvent method, LIRA/CA Complex was loaded into zein/rhamnolipids nanoparticles (LIRA/CA@Zein/RLs) with a loading efficiency of 76.8%. LIRA was protected from fast enzymatic degradation by the hydrophobic zein component. Meanwhile, Rhamnolipids, a glycolipid with surface activity, promoted endocytosis while also stabilizing the nanoparticles. The two components worked synergistically to ensure the delivery of LIRA/CA Complex to intestinal villi and improved oral absorption without disrupting tight junctions. LIRA/CA@Zein/RLs demonstrated a considerable intestinal epithelium absorption in mouse gastrointestinal section and a retention in vivo over 24 h, resulting in a significant and long-lasting hypoglycemic effect in Type 2 diabetes mice.

CONCLUSION

This study provided a promising oral delivery approach for LIRA and exhibited the potential for further translation into clinical application.

Considerations in the developability of peptides for oral administration when formulated together with transient permeation enhancers

This paper reviews many of the properties of a peptide that need to be considered prior to development as an oral dosage form when co-formulated with a permeation enhancer to improve oral bioavailability, including the importance and implications of peptide half-life on variability in pharmacokinetic profiles. Clinical considerations in terms of food and drug-drug interactions are also discussed. The paper further gives a brief overview how permeation enhancers overcome barriers that limit oral absorption of peptides and thereby improve their oral bioavailability, albeit bioavailabilities are still low single digit and variability is high.

A simple and sensitive HPLC-FL method for bioanalysis of velpatasvir, a novel hepatitis C virus NS5A inhibitor, in rat plasma: Investigation of factors determining its oral bioavailability

Velpatasvir is a novel inhibitor of hepatitis C virus nonstructural protein 5A that received US Food and Drug Administration approval for the treatment of patients with chronic hepatitis C virus genotypes 1-6. In the present study, a sensitive bioanalytical method for velpatasvir was developed using high-performance liquid chromatography coupled with a fluorescence detector system, which was applied to elucidate the factors determining the oral bioavailability and disposition of velpatasvir. This method offered sufficient sensitivity, with a lower limit of quantification of 0.5 ng/mL, which is comparable to previously reported methods using liquid chromatography coupled with tandem mass spectrometry. Velpatasvir exhibited low oral bioavailability, moderate intestinal permeability, and significant biliary excretion in rats. It was also found to be significantly metabolized in the liver, with a low-to-moderate extraction ratio; however, its intestinal metabolism and enterohepatic circulation did not occur. Thus, our present results demonstrate that the oral bioavailability of velpatasvir is primarily dependent on gut absorption and hepatic first-pass metabolism. The fractions of velpatasvir dose unabsorbed from the gut and eliminated by the liver before reaching the systemic circulation following oral administration were estimated to be 32.8%-58.6% and 4.74%-30.54% of the oral dose, respectively. To our knowledge, this is the first systematic study to investigate the contributory roles of biopharmaceutical and pharmacokinetic factors on the oral bioavailability of velpatasvir, together with a new bioanalytical method for velpatasvir.

Study on the intestinal permeability of lamivudine using Caco-2 cells monolayer and Single-pass intestinal perfusion

Background

The aim of this work is to investigate the intestinal permeability of lamivudine and explore its absorption mechanism.

Method

Caco-2 cells monolayer and single-pass intestinal perfusion (SPIP) were selected for the investigation of lamivudine under different conditions, such as different concentration, absorption time, bidirectional transportation, and transportation with efflux transporters inhibitor. The concentration of lamivudine both in Caco-2 cells monolayer samples and SPIP samples was detected by HPLC-UV. Then the permeability parameters were calculated.

Results

The established HPLC-UV method reach the requirements for detection. There is no statistically difference between absorption parameters of lamivudine both in Caco-2 cells monolayer and SPIP (P > 0.05) under different dose groups. After transportation with efflux transporters inhibitor, the efflux rate of lamivudine in three dose groups was significantly decreased from 2.67, 2.59 and 2.59 to 1.78, 1.61, and 1.81 respectively. Lamivudine exhibits an absorption mechanism of passive diffusion.

Conclusion

The absorption of lamivudine may be related to efflux transporters. In addition, lamivudine is a moderate-permeability drug in Biopharmaceutics Classification System.

A Physiologically Based Pharmacokinetic Model for Studying the Biowaiver Risk of Biopharmaceutics Classification System Class I Drugs With Rapid Elimination: Dexketoprofen Trometamol Case Study

Biowaiver based on the biopharmaceutics classification system (BCS) has been widely used in the global market for the approval of new generic drug products to avoid unnecessary in vivo bioequivalence (BE) studies. However, it is reported that three out of four formulations of dexketoprofen trometamol (DEX) tablets (BCS class I drug) failed the first BE study. The aim of this study was to determine whether the current biowaiver standard is reasonable for DEX. Thus, we successfully established a physiologically based pharmacokinetic (PBPK) model for DEX and examined the effects of dissolution, permeability, and gastric emptying time on DEX absorption under BCS-based biowaiver conditions using sensitivity analyses. Parameter sensitivity analysis showed that the dissolution rate in pH 1.2 media, permeability, and liquid gastric emptying time were sensitive parameters of Cmax. Therefore, gastric emptying variation was introduced into the PBPK model, and virtual BE studys were conducted on original research formulation and the formulation of the boundary dissolution rate (f2 = 50) prescribed by the biowaiver guideline. The virtual BE results showed dissolution rate changes within the biowaiver range will not cause high non-BE ratio, indicate waive of DEX generic drugs would not lead the risk of Cmax when generic products satisfy the requirements of biowaiver guideline. However, the effect of excipients on gastric emptying as a sensitive factor needs to be further studied when the rapid elimination of BCS class I drug is biowaived.

Best practices in current models mimicking drug permeability in the gastrointestinal tract - an UNGAP review

The absorption of orally administered drug products is a complex, dynamic process, dependent on a range of biopharmaceutical properties; notably the aqueous solubility of a molecule, stability within the gastrointestinal tract (GIT) and permeability. From a regulatory perspective, the concept of high intestinal permeability is intrinsically linked to the fraction of the oral dose absorbed. The relationship between permeability and the extent of absorption means that experimental models of permeability have regularly been used as a surrogate measure to estimate the fraction absorbed. Accurate assessment of a molecule's intestinal permeability is of critical importance during the pharmaceutical development process of oral drug products, and the current review provides a critique of in vivo, in vitro and ex vivo approaches. The usefulness of in silico models to predict drug permeability is also discussed and an overview of solvent systems used in permeability assessments is provided. Studies of drug absorption in humans are an indirect indicator of intestinal permeability, but in vitro and ex vivo tools provide initial screening approaches are important tools for direct assessment of permeability in drug development. Continued refinement of the accuracy of in silico approaches and their validation with human in vivo data will facilitate more efficient characterisation of permeability earlier in the drug development process and will provide useful inputs for integrated, end-to-end absorption modelling.

Formulation strategies to improve the efficacy of intestinal permeation enhancers. Adv Drug Deliv Rev 2021;177:113925. [PMID: 34418495 DOI: 10.1016/j.addr.2021.113925]

The use of chemical permeation enhancers (PEs) is the most widely tested approach to improve oral absorption of low permeability active agents, as represented by peptides. Several hundred PEs increase intestinal permeability in preclinical bioassays, yet few have progressed to clinical testing and, of those, only incremental increases in oral bioavailability (BA) have been observed. Still, average BA values of ~1% were sufficient for two recent FDA approvals of semaglutide and octreotide oral formulations. PEs are typically screened in static in vitro and ex-vivo models where co-presentation of active agent and PE in high concentrations allows the PE to alter barrier integrity with sufficient contact time to promote flux across the intestinal epithelium. The capacity to maintain high concentrations of co-presented agents at the epithelium is not reached by standard oral dosage forms in the upper GI tract in vivo due to dilution, interference from luminal components, fast intestinal transit, and possible absorption of the PE per se. The PE-based formulations that have been assessed in clinical trials in either immediate-release or enteric-coated solid dosage forms produce low and variable oral BA due to these uncontrollable physiological factors. For PEs to appreciably increase intestinal permeability from oral dosage forms in vivo, strategies must facilitate co-presentation of PE and active agent at the epithelium for a sustained period at the required concentrations. Focusing on peptides as examples of a macromolecule class, we review physiological impediments to optimal luminal presentation, discuss the efficacy of current PE-based oral dosage forms, and suggest strategies that might be used to improve them.

An Assessment of Occasional Bio-Inequivalence for BCS1 and BCS3 Drugs: What are the Underlying Reasons?

Despite having adequate solubility properties, bioequivalence (BE) studies performed on immediate release formulations containing BCS1/3 drugs occasionally fail. By systematically evaluating a set of 17 soluble drugs where unexpected BE failures have been reported and comparing to a set of 29 drugs where no such reports have been documented, a broad assessment of the risk factors leading to BE failure was performed. BE failures for BCS1/3 drugs were predominantly related to changes in C_max rather than AUC. C_max changes were typically modest, with minimal clinical significance for most drugs. Overall, drugs with a sharp plasma peak were identified as a key factor in BE failure risk. A new pharmacokinetic term (t½C_max) is proposed to identify drugs at higher risk due to their peak plasma profile shape. In addition, the analysis revealed that weak acids, and drugs with particularly high gastric solubility are potentially more vulnerable to BE failure, particularly when these features are combined with a sharp C_max peak. BCS3 drugs, which are often characterised as being more vulnerable to BE failure due to their potential for permeation and transit to be altered, particularly by excipient change, were not in general at greater risk of BE failures. These findings will help to inform how biowaivers may be optimally applied in the future.

Effect of paracellular permeation enhancers on intestinal permeability of two peptide drugs, enalaprilat and hexarelin, in rats

Transcellular permeation enhancers are known to increase the intestinal permeability of enalaprilat, a 349 Da peptide, but not hexarelin (887 Da). The primary aim of this paper was to investigate if paracellular permeability enhancers affected the intestinal permeation of the two peptides. This was investigated using the rat single-pass intestinal perfusion model with concomitant blood sampling. These luminal compositions included two paracellular permeation enhancers, chitosan (5 mg/mL) and ethylenediaminetetraacetate (EDTA, 1 and 5 mg/mL), as well as low luminal tonicity (100 mOsm) with or without lidocaine. Effects were evaluated by the change in lumen-to-blood permeability of hexarelin and enalaprilat, and the blood-to-lumen clearance of 51chromium-labeled EDTA (CLCr-EDTA), a clinical marker for mucosal barrier integrity. The two paracellular permeation enhancers increased the mucosal permeability of both peptide drugs to a similar extent. The data in this study suggests that the potential for paracellular permeability enhancers to increase intestinal absorption of hydrophilic peptides with low molecular mass is greater than for those with transcellular mechanism-of-action. Further, the mucosal blood-to-lumen flux of 51Cr-EDTA was increased by the two paracellular permeation enhancers and by luminal hypotonicity. In contrast, luminal hypotonicity did not affect the lumen-to-blood transport of enalaprilat and hexarelin. This suggests that hypotonicity affects paracellular solute transport primarily in the mucosal crypt region, as this area is protected from luminal contents by a constant water flow from the crypts.

Comparison of Canine and Human Physiological Factors: Understanding Interspecies Differences that Impact Drug Pharmacokinetics

This review is a summary of factors affecting the drug pharmacokinetics (PK) of dogs versus humans. Identifying these interspecies differences can facilitate canine-human PK extrapolations while providing mechanistic insights into species-specific drug in vivo behavior. Such a cross-cutting perspective can be particularly useful when developing therapeutics targeting diseases shared between the two species such as cancer, diabetes, cognitive dysfunction, and inflammatory bowel disease. Furthermore, recognizing these differences also supports a reverse PK extrapolations from humans to dogs. To appreciate the canine-human differences that can affect drug absorption, distribution, metabolism, and elimination, this review provides a comparison of the physiology, drug transporter/enzyme location, abundance, activity, and specificity between dogs and humans. Supplemental material provides an in-depth discussion of certain topics, offering additional critical points to consider. Based upon an assessment of available state-of-the-art information, data gaps were identified. The hope is that this manuscript will encourage the research needed to support an understanding of similarities and differences in human versus canine drug PK.

Effect of excipients on oral absorption process according to the different gastrointestinal segments

INTRODUCTION

Excipients are necessary to develop oral dosage forms of any Active Pharmaceutical Ingredient (API). Traditionally, excipients have been considered inactive and inert substances, but, over the years, numerous studies have contradicted this belief. This review focuses on the effect of excipients on the physiological variables affecting oral absorption along the different segments of the gastrointestinal tract. The effect of excipients on the segmental absorption variables are illustrated with examples to help understand the complexity of predicting their in vivo effects.

AREAS COVERED

The effects of excipients on disintegration, solubility and dissolution, transit time, and absorption are analyzed in the context of the different gastrointestinal segments and the physiological factors affecting release and membrane permeation. The experimental techniques used to study excipient effects and their human predictive ability are reviewed.

EXPERT OPINION

The observed effects of excipient in oral absorption process have been characterized in the past, mainly in vitro (i.e. in dissolution studies, in vitro cell culture methods or in situ animal studies). Unfortunately, a clear link with their effects in vivo, i.e. their impact on Cmax or AUC, which need a mechanistic approach is still missing. The information compiled in this review leads to the conclusion that the effect of excipients in API oral absorption and bioavailability is undeniable and shows the need of implementing standardized and reproducible preclinical tools coupled with mechanistic and predictive physiological-based models to improve the current empirical retrospective approach.

In Vitro Biopredictive Methods: A Workshop Summary Report

This workshop report summarizes the proceedings of Day 1 of a three-day workshop on "Current State and Future Expectations of Translational Modeling Strategies to Support Drug Product Development, Manufacturing Changes and Controls". Physiologically based biopharmaceutics models (PBBM) are tools which enable the drug product quality attributes to be linked to the in vivo performance. These tools rely on key quality inputs in order to provide reliable predictions. After introducing the objectives of the workshop and the expectations from the breakout sessions, Day 1 of the workshop focused on the best practices and challenges in measuring in vitro inputs needed for modeling, such as the drug solubility, the dissolution rate of the drug product, potential precipitation of the drug and drug permeability. This paper reports the podium presentations and summarizes breakout session discussions related to A) the best strategies for determining solubility, supersaturation and critical supersaturation; B) the best strategies for the development of biopredictive (clinically relevant) dissolution methods; C) the challenges associated with describing gastro-intestinal systems parameters such as mucus, liquid volume and motility; and D) the challenges with translating biopharmaceutical measures of drug permeability along the gastrointestinal tract to a meaningful model parameter.

Intestinal absorption of BCS class II drugs administered as nanoparticles: A review based on in vivo data from intestinal perfusion models

An established pharmaceutical strategy to increase oral drug absorption of low solubility–high permeability drugs is to create nanoparticles of them. Reducing the size of the solid-state particles increases their dissolution and transport rate across the mucus barrier and the aqueous boundary layer. Suspensions of nanoparticles also sometimes behave differently than those of larger particles in the fed state. This review compares the absorption mechanisms of nano- and larger particles in the lumen at different prandial states, with an emphasis on data derived from in vivo models. Four BSC class II drugs—aprepitant, cyclosporine, danazol and fenofibrate—are discussed in detail based on information from preclinical intestinal perfusion models.

Physiologically based pharmacokinetic-pharmacodynamic modeling for prediction of vonoprazan pharmacokinetics and its inhibition on gastric acid secretion following intravenous/oral administration to rats, dogs and humans

Vonoprazan is characterized as having a long-lasting antisecretory effect on gastric acid. In this study we developed a physiologically based pharmacokinetic (PBPK)-pharmacodynamic (PD) model linking to stomach to simultaneously predict vonoprazan pharmacokinetics and its antisecretory effects following administration to rats, dogs, and humans based on in vitro parameters. The vonoprazan disposition in the stomach was illustrated using a limited-membrane model. In vitro metabolic and transport parameters were derived from hepatic microsomes and Caco-2 cells, respectively. We found the most predicted plasma concentrations and pharmacokinetic parameters of vonoprazan in rats, dogs and humans were within twofold errors of the observed data. Free vonoprazan concentrations (f_u × C₂) in the stomach were simulated and linked to the antisecretory effects of the drug (I) (increases in pH or acid output) using the fomula dI/dt = k × f_u × C₂ × (I_max − I) − k_d × I. The vonoprazan dissociation rate constant k_d (0.00246 min⁻¹) and inhibition index K_I (35 nM) for H⁺/K⁺-ATPase were obtained from literatures. The vonoprazan-H⁺/K⁺-ATPase binding rate constant k was 0.07028 min⁻¹· μM⁻¹ using ratio of k_d to K_I. The predicted antisecretory effects were consistent with the observations following intravenous administration to rats (0.7 and 1.0 mg/kg), oral administration to dogs (0.3 and 1.0 mg/kg) and oral single dose or multidose to humans (20, 30, and 40 mg). Simulations showed that vonoprazan concentrations in stomach were 1000-fold higher than those in the plasma at 24 h following administration to human. Vonoprazan pharmacokinetics and its antisecretory effects may be predicted from in vitro data using the PBPK-PD model of the stomach. These findings may highlight 24-h antisecretory effects of vonoprazan in humans following single-dose or the sustained inhibition throughout each 24-h dosing interval during multidose administration.

Regional Intestinal Drug Permeability and Effects of Permeation Enhancers in Rat

Sufficient colonic absorption is necessary for all systemically acting drugs in dosage forms that release the drug in the large intestine. Preclinically, colonic absorption is often investigated using the rat single-pass intestinal perfusion model. This model can determine intestinal permeability based on luminal drug disappearance, as well as the effect of permeation enhancers on drug permeability. However, it is uncertain how accurate the rat single-pass intestinal perfusion model predicts regional intestinal permeability and absorption in human. There is also a shortage of systematic in vivo investigations of the direct effect of permeation enhancers in the small and large intestine. In this rat single-pass intestinal perfusion study, the jejunal and colonic permeability of two low permeability drugs (atenolol and enalaprilat) and two high-permeability ones (ketoprofen and metoprolol) was determined based on plasma appearance. These values were compared to already available corresponding human data from a study conducted in our lab. The colonic effect of four permeation enhancers—sodium dodecyl sulfate, chitosan, ethylenediaminetetraacetic acid (EDTA), and caprate—on drug permeability and transport of chromium EDTA (an established clinical marker for intestinal barrier integrity) was determined. There was no difference in jejunal and colonic permeability determined from plasma appearance data of any of the four model drugs. This questions the validity of the rat single-pass intestinal perfusion model for predicting human regional intestinal permeability. It was also shown that the effect of permeation enhancers on drug permeability in the colon was similar to previously reported data from the rat jejunum, whereas the transport of chromium EDTA was significantly higher (p < 0.05) in the colon than in jejunum. Therefore, the use of permeation enhancers for increasing colonic drug permeability has greater risks than potential medical rewards, as indicated by the higher permeation of chromium EDTA compared to the drugs.

The In Vivo Effect of Transcellular Permeation Enhancers on the Intestinal Permeability of Two Peptide Drugs Enalaprilat and Hexarelin

Permeation enhancers like sodium dodecyl sulfate (SDS) and caprate increase the intestinal permeability of small model peptide compounds, such as enalaprilat (349 Da). However, their effects remain to be investigated for larger low-permeability peptide drugs, such as hexarelin (887 Da). The objective of this single-pass perfusion study in rat was to investigate the effect of SDS at 5 mg/mL and of caprate administered at different luminal concentrations (5, 10, and 20 mg/mL) and pH (6.5 and 7.4). The small intestinal permeability of enalaprilat increased by 8- and 9-fold with SDS at 5 mg/mL and with caprate at 10 and 20 mg/mL but only at pH 7.4, where the free dissolved caprate concentration is higher than at pH 6.5 (5 vs. 2 mg/mL). Neither SDS nor caprate at any of the investigated luminal concentrations enhanced absorption of the larger peptide hexarelin. These results show that caprate requires doses above its saturation concentration (a reservoir suspension) to enhance absorption, most likely because dissolved caprate itself is rapidly absorbed. The absent effect on hexarelin may partly explain why the use of permeation enhancers for enabling oral peptide delivery has largely failed to evolve from in vitro evaluations into approved oral products. It is obvious that more innovative and effective drug delivery strategies are needed for this class of drugs.

Suitability of RPMI 2650 cell models for nasal drug permeability prediction

The RPMI 2650 cell line has been a subject of evaluation as a physiological and pharmacological model of the nasal epithelial barrier. However, its suitability for drug permeability assays has not yet been established on a sufficiently large set of model drugs. We investigated two RPMI 2650 cell models (air-liquid and liquid-liquid) for nasal drug permeability determination by adopting the most recent regulatory guidelines on showing suitability of in vitro permeability methods for drug permeability classification. The permeability of 23 model drugs and several zero permeability markers across the cell models was assessed. The functional expression of two efflux transporters P-glycoprotein (P-gp) and Breast Cancer Resistant Protein (BCRP) was shown to be negligible by bidirectional transport studies using appropriate transporter substrates and inhibitors. The model drug permeability determined in the two RPMI 2650 cell models was correlated with the fully differentiated nasal epithelial model (MucilAir™). Additionally, correlations between the drug permeability in the investigated cell models and the ones determined in the Caco-2 cells and isolated rat jejunum were established. In conclusion, the air-liquid RPMI 2650 cell model is a promising pharmacological model of the nasal epithelial barrier and is much more suitable than the liquid-liquid model for nasal drug permeability prediction.

Intestinal Permeability and Drug Absorption: Predictive Experimental, Computational and In Vivo Approaches

The main objective of this review is to discuss recent advancements in the overall investigation and in vivo prediction of drug absorption. The intestinal permeability of an orally administered drug (given the value P_eff) has been widely used to determine the rate and extent of the drug’s intestinal absorption (F_abs) in humans. Preclinical gastrointestinal (GI) absorption models are currently in demand for the pharmaceutical development of novel dosage forms and new drug products. However, there is a strong need to improve our understanding of the interplay between pharmaceutical, biopharmaceutical, biochemical, and physiological factors when predicting F_abs and bioavailability. Currently, our knowledge of GI secretion, GI motility, and regional intestinal permeability, in both healthy subjects and patients with GI diseases, is limited by the relative inaccessibility of some intestinal segments of the human GI tract. In particular, our understanding of the complex and highly dynamic physiology of the region from the mid-jejunum to the sigmoid colon could be significantly improved. One approach to the assessment of intestinal permeability is to use animal models that allow these intestinal regions to be investigated in detail and then to compare the results with those from simple human permeability models such as cell cultures. Investigation of intestinal drug permeation processes is a crucial biopharmaceutical step in the development of oral pharmaceutical products. The determination of the intestinal P_eff for a specific drug is dependent on the technique, model, and conditions applied, and is influenced by multiple interactions between the drug molecule and the biological membranes.

Effects of absorption-modifying excipients on jejunal drug absorption in simulated fasted and fed luminal conditions

Oral administration of drug products is the preferred administration route. In recent decades there has been an increase in drug candidates with low solubility and/or low permeability. To increase the possibility of oral administration for the poorly permeating drugs, the use of absorption modifying excipients (AMEs) has been proposed. These types of AMEs may also affect the regulatory assessment of a novel drug delivery system if they affect the absorption of a drug from any of the four BCS classes. The effects of AMEs have previously been investigated in various animal models, including the single-pass intestinal perfusion (SPIP) in rats. To further improve the biorelevance and the in vivo predictiveness of the SPIP model, four compounds (atenolol, enalaprilat, ketoprofen, metoprolol) were perfused in fasted or fed state simulated intestinal fluid (FaSSIF or FeSSIF) together with the AMEs N-acetyl-cysteine, caprate, or sodium dodecyl sulfate. For the highly soluble and poorly permeating compounds enalaprilat and atenolol (BCS class III), the flux was increased the most by the addition of SDS in both FaSSIF and FeSSIF. For ketoprofen (BCS class II), the flux decreased in the presence of all AMEs in at least one of the perfusion media. The flux of metoprolol (BCS class I) was not affected by any of the excipients in none of simulated prandial states. The changes in magnitude in the absorption of the compounds were in general smaller in FeSSIF than in FaSSIF. This may be explained by a reduced free concentration AMEs in FeSSIF. Further, the results in FeSSIF were similar to those from intrajejunal bolus administration in rat in a previous study. This suggests that the biorelevance of the SPIP method may be increased when investigating the effects of AMEs, by the addition of intraluminal constituents representative to fasted and/or fed state to the inlet perfusate.

Evaluation of drug permeability calculation based on luminal disappearance and plasma appearance in the rat single-pass intestinal perfusion model

The rat single-pass intestinal perfusion (SPIP) model is commonly used to investigate gastrointestinal physiology and membrane drug transport. The SPIP model can be used with the intestinal segment inside or outside the abdomen. The rats can also be treated with parecoxib, a selective cycloxygenase-2 inhibitor that has been shown to affect some intestinal functions following abdominal surgery, such as motility, epithelial permeability, fluid flux and ion transport. However, the impact of extra-abdominal placement of the intestinal segment in combination with parecoxib on intestinal drug transport has not been investigated. There is also uncertainty how well intestinal permeability determinations based on luminal drug disappearance and plasma appearance correlate in the rat SPIP model. The main objective of this rat in vivo study was to investigate the effect of intra- vs. extra-abdominal SPIP, with and without, pretreatment with parecoxib. The effect was evaluated by determining the difference in blood-to-lumen ⁵¹Cr-EDTA clearance, lumen-to-blood permeability of a cassette-dose of four model compounds (atenolol, enalaprilat, ketoprofen, and metoprolol), and water flux. The second objective was to compare the jejunal permeability values of the model drugs when determined based on luminal disappearance or plasma appearance. The study showed that the placement of the perfused jejunal segment, or the treatment with parecoxib, had minimal effects on membrane permeability and water flux. It was also shown that intestinal permeability of low permeability compounds should be determined on the basis of data from plasma appearance rather than luminal disappearance. If permeability is calculated on the basis of luminal disappearance, it should preferably include negative values to increase the accuracy in the determinations.

Potential for pharmaceutical excipients to impact absorption: A mechanistic review for BCS Class 1 and 3 drugs

The potential for certain excipients to impact drug absorption is the subject of numerous publications. Reflecting this, current Biopharmaceutics Classification System (BCS) guidelines place restrictions on the level of change in excipients to be eligible for a BCS biowaiver. The degree of change permitted between test and reference formulations varies between BCS Class 1 and 3, and also across different regulatory authorities. This article reviews the literature evidence for excipients to impact drug absorption, with a particular focus on identifying effects which may be important for BCS Class 1 and 3 compounds and formulations. Literature examples were categorised according to the mechanism by which the excipient was believed to impact drug absorption, and the relevance of these mechanisms for compounds within BCS Class 1 and 3 was assessed. The likelihood of using the excipient in solid oral immediate release formulations (i.e. formulation types which would be eligible for BCS biowaivers) was also considered. Using this mechanistic and risk-based approach, potential critical excipients for BCS Class 1 and 3 compounds were identified. Based on the literature data, there are only a limited number of mechanisms by which excipients could affect the absorption of a BCS Class 3 drug. For BCS1, absorption is very unlikely to be affected by excipient changes. For many of these excipients, there is no in vivo evidence of such an effect having occurred. The risk can be mitigated to a large extent by applying some compound-specific understanding of the absorption site, rate and mechanism of the particular API under consideration.

Development of daidzein nanosuspensions: Preparation, characterization, in vitro evaluation, and pharmacokinetic analysis

The purpose of this investigation was to improve the solubility and oral bioavailability of daidzein via preparing nanosuspensions (NS) with steric stabilizers, electrostatic stabilizers, or a combination of both. Based on particle size and zeta potential, daidzein NS stabilized by HP-β-CD, soy lecithin, HP-β-CD + soy lecithin, TPGS, TPGS + SBE-β-CD, SDS, or HPMC E5 + SDS were generated and characterized by scanning electron microscopy, powder X-ray diffraction, and Fourier transform-infrared spectroscopy. In addition, the stability, cytotoxicity, solubility, dissolution, and pharmacokinetics of NS were evaluated. The resulting daidzein NS were physically stable and biocompatible and presented as regular shapes with homogenous particle sizes of 360-600 nm and decreased crystallinity. Due to the increased solubility and dissolution rate, the oral bioavailability of daidzein NS in rats was 1.63-2.19 times greater than that of crude daidzein. In particular, among the investigated seven daidzein NS formulations, daidzein NS prepared with the costabilizers HPMC E5 + SDS is an optimal formulation for increased daidzein bioavailability. The present study proposes that the combined usage of steric and electrostatic stabilizers is a promising strategy for improving the bioavailability of water-insoluble flavonoid compounds by an NS approach.

Mechanistic Studies on the Absorption-Enhancing Effects of Gemini Surfactant on the Intestinal Absorption of Poorly Absorbed Hydrophilic Drugs in Rats

Generally, the use of absorption enhancers might be the most effective approaches to ameliorate the enteric absorption of poorly absorbed substances. Among numerous absorption enhancers, we already reported that a gemini surfactant, sodium dilauramidoglutamide lysine (SLG-30) with two hydrophobic and two hydrophilic moieties, is a novel and promising adjuvant with a high potency in improving the absorption safely. Here, we examined and elucidated the absorption-improving mechanisms of SLG-30 in the enteric absorption of substances. SLG-30 increased the intestinal absorption of 5(6)-carboxyfluorescein (CF) to a greater level than the typical absorption enhancers, including sodium glycocholate and sodium laurate, as evaluated by an in situ closed-loop method. Furthermore, SLG-30 significantly lowered the fluorescence anisotropy of dansyl chloride (DNS-Cl), suggesting that it might increase the fluidity of protein sections in the intestinal cell membranes. Moreover, SLG-30 significantly lowered the transepithelial-electrical resistance (TEER) values of Caco-2 cells, suggesting that it might open the tight junctions (TJs) between the enteric epithelial cells. Additionally, the levels of claudin-1 and claudin-4 expression decreased in the presence of SLG-30. These outcomes propose that SLG-30 might improve the enteric transport of poorly absorbed substances through both transcellular and paracellular routes.

Effects of Drugs and Excipients on Hydration Status

Despite being the most essential nutrient, water is commonly forgotten in the fields of pharmacy and nutrition. Hydration status is determined by water balance (the difference between water input and output). Hypohydration or negative water balance is affected by numerous factors, either internal (i.e., a lack of thirst sensation) or external (e.g., polypharmacy or chronic consumption of certain drugs). However, to date, research on the interaction between hydration status and drugs/excipients has been scarce. Drugs may trigger the appearance of hypohydration by means of the increase of water elimination through either diarrhea, urine or sweat; a decrease in thirst sensation or appetite; or the alteration of central thermoregulation. On the other hand, pharmaceutical excipients induce alterations in hydration status by decreasing the gastrointestinal transit time or increasing the gastrointestinal tract rate or intestinal permeability. In the present review, we evaluate studies that focus on the effects of drugs/excipients on hydration status. These studies support the aim of monitoring the hydration status in patients, mainly in those population segments with a higher risk, to avoid complications and associated pathologies, which are key axes in both pharmaceutical care and the field of nutrition.

Time-dependent effects on small intestinal transport by absorption-modifying excipients

The relevance of the rat single-pass intestinal perfusion model for investigating in vivo time-dependent effects of absorption-modifying excipients (AMEs) is not fully established. Therefore, the dynamic effect and recovery of the intestinal mucosa was evaluated based on the lumen-to-blood flux (J_abs) of six model compounds, and the blood-to-lumen clearance of ⁵¹Cr-EDTA (CL_Cr), during and after 15- and 60-min mucosal exposure of the AMEs, sodium dodecyl sulfate (SDS) and chitosan, in separate experiments. The contribution of enteric neurons on the effect of SDS and chitosan was also evaluated by luminal coadministration of the nicotinic receptor antagonist, mecamylamine. The increases in J_abs and CL_Cr (maximum and total) during the perfusion experiments were dependent on exposure time (15 and 60 min), and the concentration of SDS, but not chitosan. The increases in J_abs and CL_Cr following the 15-min intestinal exposure of both SDS and chitosan were greater than those reported from an in vivo rat intraintestinal bolus model. However, the effect in the bolus model could be predicted from the increase of J_abs at the end of the 15-min exposure period, where a six-fold increase in J_abs was required for a corresponding effect in the in vivo bolus model. This illustrates that a rapid and robust effect of the AME is crucial to increase the in vivo intestinal absorption rate before the yet unabsorbed drug in lumen has been transported distally in the intestine. Further, the recovery of the intestinal mucosa was complete following 15-min exposures of SDS and chitosan, but it only recovered 50% after the 60-min intestinal exposures. Our study also showed that the luminal exposure of AMEs affected the absorptive model drug transport more than the excretion of ⁵¹Cr-EDTA, as J_abs for the drugs was more sensitive than CL_Cr at detecting dynamic mucosal AME effects, such as response rate and recovery. Finally, there appears to be no nicotinergic neural contribution to the absorption-enhancing effect of SDS and chitosan, as luminal administration of 0.1 mM mecamylamine had no effect.

Effect of absorption-modifying excipients, hypotonicity, and enteric neural activity in an in vivo model for small intestinal transport

The small intestine mucosal barrier is physiologically regulated by the luminal conditions, where intestinal factors, such as diet and luminal tonicity, can affect mucosal permeability. The intestinal barrier may also be affected by absorption-modifying excipients (AME) in oral drug delivery systems. Currently, there is a gap in the understanding of how AMEs interact with the physiological regulation of intestinal electrolyte transport and fluid flux, and epithelial permeability. Therefore, the objective of this single-pass perfusion study in rat was to investigate the effect of three AMEs on the intestinal mucosal permeability at different luminal tonicities (100, 170, and 290 mOsm). The effect was also evaluated following luminal administration of a nicotinic receptor antagonist, mecamylamine, and after intravenous administration of a COX-2 inhibitor, parecoxib, both of which affect the enteric neural activity involved in physiological regulation of intestinal functions. The effect was evaluated by changes in intestinal lumen-to-blood transport of six model compounds, and blood-to-lumen clearance of ⁵¹Cr-EDTA (a mucosal barrier marker). Luminal hypotonicity alone increased the intestinal epithelial transport of ⁵¹Cr-EDTA. This effect was potentiated by two AMEs (SDS and caprate) and by parecoxib, while it was reduced by mecamylamine. Consequently, the impact of enteric neural activity and luminal conditions may affect nonclinical determinations of intestinal permeability. In vivo predictions based on animal intestinal perfusion models can be improved by considering these effects. The in vivo relevance can be increased by treating rats with a COX-2 inhibitor prior to surgery. This decreases the risk of surgery-induced ileus, which may affect the physiological regulation of mucosal permeability.