Variation in gastrointestinal transit of pharmaceutical dosage forms in healthy subjects

Mechanistic Modeling of In Vitro Biopharmaceutic Data for a Weak Acid Drug: A Pathway Towards Deriving Fundamental Parameters for Physiologically Based Biopharmaceutic Modeling

Mechanistic modeling of in vitro experiments using metabolic enzyme systems enables the extrapolation of metabolic clearance for in vitro-in vivo predictions. This is particularly important for successful clearance predictions using physiologically based pharmacokinetic (PBPK) modeling. The concept of mechanistic modeling can also be extended to biopharmaceutics, where in vitro data is used to predict the in vivo pharmacokinetic profile of the drug. This approach further allows for the identification of parameters that are critical for oral drug absorption in vivo. However, the routine use of this analysis approach has been hindered by the lack of an integrated analysis workflow. The objective of this tutorial is to (1) review processes and parameters contributing to oral drug absorption in increasing levels of complexity, (2) outline a general physiologically based biopharmaceutic modeling workflow for weak acids, and (3) illustrate the outlined concepts via an ibuprofen (i.e., a weak, poorly soluble acid) case example in order to provide practical guidance on how to integrate biopharmaceutic and physiological data to better understand oral drug absorption. In the future, we plan to explore the usefulness of this tutorial/roadmap to inform the development of PBPK models for BCS 2 weak bases, by expanding the stepwise modeling approach to accommodate more intricate scenarios, including the presence of diprotic basic compounds and acidifying agents within the formulation.

A Window for Enhanced Oral Delivery of Therapeutics via Lipid Nanoparticles

Oral administration of dosage forms is convenient and beneficial in several respects. Lipid nanoparticulate dosage forms have emerged as a useful carrier system in deploying low solubility drugs systemically, particularly class II, III, and IV drugs of the Biopharmaceutics Classification System. Like other nanoparticulate delivery systems, their low size-to-volume ratio facilitates uptake by phagocytosis. Lipid nanoparticles also provide scope for high drug loading and extended-release capability, ensuring diminished systemic side effects and improved pharmacokinetics. However, rapid gastrointestinal (GI) clearance of particulate delivery systems impedes efficient uptake across the mucosa. Mucoadhesion of dosage forms to the GI mucosa results in longer transit times due to interactions between the former and mucus. Delayed transit times facilitate transfer of the dosage form across the mucosa. In this regard, a balance between mucoadhesion and mucopenetration guarantees optimal systemic transfer. Furthermore, the interplay between GI anatomy and physiology is key to ensuring efficient systemic uptake. This review captures salient anatomical and physiological features of the GI tract and how these can be exploited for maximal systemic delivery of lipid nanoparticles. Materials used to impart mucoadhesion and examples of successful mucoadhesive lipid nanoformulations are highlighted in this review.

Thiolated Cellulose: A Dual-Acting Mucoadhesive and Permeation-Enhancing Polymer

This study aims to design an anionic, thiolated cellulose derivative and to evaluate its mucoadhesive and permeation-enhancing properties utilizing enoxaparin as a model drug. 2-Mercaptosuccinic acid-modified cellulose (cellulose-mercaptosuccinate) was synthesized by the reaction of cellulose with S-acetylmercaptosuccinic anhydride. The chemical structure of the target compound was confirmed by FTIR and 1H NMR spectroscopy. The thiol content was determined by Ellman's test. The conjugate exhibited 215.5 ± 25 μmol/g of thiol groups and 84 ± 16 μmol/g of disulfide bonds. Because of thiolation, mucoadhesion on porcine intestinal mucosa was 9.6-fold enhanced. The apparent permeability (Papp) of the model dye Lucifer yellow was up to 2.2-fold improved by 0.5% cellulose-mercaptosuccinate on a Caco-2 cell monolayer. Enoxaparin permeation through rat intestinal mucosa increased 2.4-fold in the presence of 0.5% cellulose-mercaptosuccinate compared with the drug in buffer only. In vivo studies in rats showed an oral bioavailability of 8.98% using cellulose-mercaptosuccinate, which was 12.5-fold higher than that of the aqueous solution of the drug. Results of this study show that the modification of cellulose with 2-mercaptosuccinic acid provides mucoadhesive and permeation-enhancing properties, making this thiolated polymer an attractive excipient for oral drug delivery.

Physiologically Based Biopharmaceutics Model for Selumetinib Food Effect Investigation and Capsule Dissolution Safe Space - Part I: Adults

OBJECTIVE

A physiologically based biopharmaceutics model (PBBM) was developed to mechanistically investigate the effect of formulation and food on selumetinib pharmacokinetics.

METHODS

Selumetinib is presented as a hydrogen sulfate salt, and in vitro and in vivo data were used to verify the precipitation rate to apply to simulations. Dissolution profiles observed for capsules and granules were used to derive product-particle size distributions for model input. The PBBM incorporated gut efflux and first-pass gut metabolism, based on intravenous and oral pharmacokinetic data, alongside in vitro data for the main enzyme isoform and P-glycoprotein efflux. The PBBM was validated across eight clinical scenarios.

RESULTS

The quality-control dissolution method for selumetinib capsules was found to be clinically relevant through PBBM validation. A safe space for capsule dissolution was established using a virtual batch. The effect of food (low fat vs high fat) on capsules and granules was elucidated by the PBBM. For capsules, a lower amount was dissolved in the fed state due to a pH increase in the stomach followed by higher precipitation in the small intestine. First-pass gut extraction is higher for capsules in the fed state due to drug dilution in the stomach chyme and reduced concentration in the lumen. The enteric-coated granules dissolve more slowly than capsules after stomach emptying, attenuating the difference in first-pass gut extraction between prandial states.

CONCLUSIONS

The PBBM was instrumental in understanding and explaining the different behaviors of the selumetinib formulations. The model can be used to predict the impact of food in humans.

Microfluidic-Assisted Production of Gastro-Resistant Active-Targeted Diatomite Nanoparticles for the Local Release of Galunisertib in Metastatic Colorectal Cancer Cells

The oral route is highly desirable for colorectal cancer (CRC) treatment because it allows concentrating the drug in the colon and achieving a localized effect. However, orally administered drugs are often metabolized in the liver, resulting in reduced efficacy and the need for higher doses. Nanoparticle-based drug delivery systems can be engineered to prevent the diffusion of the drug in the stomach, addressing the release at the target site, and enhancing the efficacy of the delivered drug. Here, an orally administrable galunisertib delivery system is developed with gelatin-covered diatomite nanoparticles targeting the ligand 1-cell adhesion molecule (L1-CAM) on metastatic cells, and further encapsulated in an enteric matrix by microfluidics. The gastro-resistant polymer protects the nanoparticles from the action of the digestive enzymes and allows for a sustained release of galunisertib at the intestinal pH. The efficacy of antibody-antigen interactions to drive the internalization of nanoparticles in the targeted cells is investigated in CRC cells expressing abnormal (SW620) or basal levels (Caco-2, HT29-MTX) of L1-CAM. The combination of local drug release and active targeting enhances the effect of the delivered galunisertib, which inhibits the migration of the SW620 cells with greater efficiency compared to the free drug.

Impact of gastric and bowel surgery on gastrointestinal drug delivery

General surgical procedures on the gastrointestinal tract are commonly performed worldwide. Surgical resections of the stomach, small intestine, or large intestine can have a significant impact on the anatomy and physiological environment of the gastrointestinal tract. These physiological changes can affect the effectiveness of orally administered formulations and drug absorption and, therefore, should be considered in rational drug formulation design for specific pathological conditions that are commonly associated with surgical intervention. For optimal drug delivery, it is important to understand how different surgical procedures affect the short-term and long-term functionality of the gastrointestinal tract. The significance of the surgical intervention is dependent on factors such as the specific region of resection, the degree of the resection, the adaptive and absorptive capacity of the remaining tissue, and the nature of the underlying disease. This review will focus on the common pathological conditions affecting the gastric and bowel regions that may require surgical intervention and the physiological impact of the surgery on gastrointestinal drug delivery. The pharmaceutical considerations for conventional and novel oral drug delivery approaches that may be impacted by general surgical procedures of the gastrointestinal tract will also be addressed.

Current Advances in Chitosan Nanoparticles Based Oral Drug Delivery for Colorectal Cancer Treatment

As per the WHO, colorectal cancer (CRC) caused around 935,173 deaths worldwide in 2020 in both sexes and at all ages. The available anticancer therapies including chemotherapy, radiotherapy and anticancer drugs are all associated with limited therapeutic efficacy, adverse effects and low chances. This has urged to emerge several novel therapeutic agents as potential therapies for CRC including synthetic and natural materials. Orally administrable and targeted drug delivery systems are attractive strategies for CRC therapy as they minimize the side effects, enhance the efficacy of anticancer drugs. Nevertheless, oral drug delivery till today faces several challenges like poor drug solubility, stability, and permeability. Various oral nano-based approaches and targeted drug delivery systems have been developed recently, as a result of the ability of nanoparticles to control the release of the encapsulant, drug targeting and reduce the number of dosages administered. The unique physicochemical properties of chitosan polymer assist to overcome oral drug delivery barriers and target the colon tumour cells. Chitosan-based nanocarriers offered additional improvements by enhancing the stability, targeting and bioavailability of several anti-colorectal cancer agents. Modified chitosan derivatives also facilitated CRC targeting through strengthening the protection of encapsulant against acidic and enzyme degradation of gastrointestinal track (GIT). This review aims to provide an overview of CRC pathology, therapy and the barriers against oral drug delivery. It also emphasizes the role of nanotechnology in oral drug targeted delivery system and the growing interest towards chitosan and its derivatives. The present review summarizes the relevant works to date that have studied the potential applications of chitosan-based nanocarrier towards CRC treatment.

Emerging technologies to increase gastrointestinal transit times of drug delivery systems

Apart from already established technologies to increase gastrointestinal transit times, including devices rapidly increasing in size once they have reached the stomach in order to retard the passage through the pylorus, formulations that float on gastric fluids and mucoadhesive drug delivery systems adhering to the gastrointestinal mucosa, there are new technologies emerging that might be game changing. They include mucus permeating nanocarriers that are able to diffuse deeply into the mucus gel layer of the gastric and intestinal mucosa remaining there for a prolonged time period (i), charge-converting nanocarriers that shift their zeta potential from negative to positive within the mucus gel layer providing strong ionic bonds with anionic mucus glycoproteins (ii) and thiolated nanocarriers and cyclodextrins form even covalent bonds with cysteine-rich subdomains of mucus glycoproteins (iii). Within this review we will provide an overview about these emerging new technologies and will critically discuss their potential and shortcomings.

Effect of Colonic Absorption on the Pharmacokinetic Properties of Delayed-Release and Extended-Release Methylphenidate: In Vivo, In Vitro, and Modeling Evaluations

Most stimulants used to treat attention‐deficit/hyperactivity disorder are administered in the morning and absorbed in the upper gastrointestinal tract. DR/ER‐MPH (formerly HLD200), an evening‐dosed delayed‐release and extended‐release methylphenidate, is predicted to be absorbed in the proximal colon. The pharmacokinetic (PK) profile of DR/ER‐MPH is characterized by an 8‐ to 10‐hour delay in initial methylphenidate absorption and a subsequent gradual increase in plasma concentration, followed by a slow decline. To examine the relationship of absorption site to pharmacokinetics, the DR/ER‐MPH formulation was altered to release methylphenidate in the small intestine and distal colon. The 3 formulations were administered in an open‐label, 3‐way, crossover study in healthy adults (N = 18). Compared with the small intestine formulation, the PK profile of the proximal colon (DR/ER‐MPH) formulation exhibited a longer delay before initial methylphenidate absorption, decreased peak methylphenidate concentration, increased time to peak concentration, and decreased bioavailability; these characteristics were amplified in the distal colon formulation. Safety profiles fell within the expectations for methylphenidate products. Modeled PK profiles were similar between the small intestine formulation and a morning‐dosed extended‐release methylphenidate (both predicted to release methylphenidate in the upper gastrointestinal tract), providing additional evidence that the PK profile of DR/ER‐MPH is shaped by colonic absorption.

Review of paediatric gastrointestinal physiology relevant to the absorption of orally administered medicines

Despite much progress in regulations to improve paediatric drug development, there remains a significant need to develop better medications for children. For the design of oral dosage forms, a detailed understanding of the specific gastrointestinal (GI) conditions in children of different age categories and how they differ from GI conditions in adults is essential. Several review articles have been published addressing the ontogeny of GI characteristics, including luminal conditions in the GI tract of children. However, the data reported in most of these reviews are of limited quality because (1) information was cited from very old publications and sometimes low quality sources, (2) data gaps in the original data were filled with textbook knowledge, (3) data obtained on healthy and sick children were mixed, (4) average data obtained on groups of patients were mixed with data obtained on individual patients, and (5) results obtained using investigative techniques that may have altered the outcome of the respective studies were considered. Consequently, many of these reviews draw conclusions that may be incorrect. The aim of the present review was to provide a comprehensive and updated overview of the available original data on the ontogeny of GI luminal conditions relevant to oral drug absorption in the paediatric population. To this end, the PubMed and Web of Science metadatabases were searched for appropriate studies that examined age-related conditions in the oral cavity, esophagus, stomach, small intestine, and colon. Maturation was observed for several GI parameters, and corresponding data sets were identified for each paediatric age group. However, it also became clear that the ontogeny of several GI traits in the paediatric population is not yet known. The review article provides a robust and valuable data set for the development of paediatric in vitro and in silico biopharmaceutical tools to support the development of age-appropriate dosage forms. In addition, it provides important information on existing data gaps and should provide impetus for further systematic and well-designed in vivo studies on GI physiology in children of specific age groups in order to close existing knowledge gaps and to sustainably improve oral drug therapy in children.

Mechanistic Models for USP2 Dissolution Apparatus, Including Fluid Hydrodynamics and Sedimentation

Drug product dissolution is a key input to Physiologically Based Biopharmaceutics Models (PBBM) to be able to predict in vivo dissolution. The integration of product dissolution in PBBMs for immediate release drug products should be mechanistic, i.e. allow to capture the main determinants of the in vitro dissolution experiment, and extract product batch specific parameter(s). This work focussed on the Product Particle Size Distribution (P-PSD), which was previously shown to integrate the effect of dose, volume, solubility (pH), size and concentration of micelles in the calculation of a batch specific input to PBBMs, and proposed new hydrodynamic (HD) models, which integrate the effect of USP2 apparatus paddle rotation speed and medium viscosity on dissolution. In addition, new models are also proposed to estimate the quantitative impact of formulation and drug sedimentation or "coning" on dissolution. Model "HDC-1" predicts coning in the presence of formulation insoluble excipients and "HDC-2" predicts the sedimentation of the drug substance only. These models were parameterized and validated on 166 dissolution experiments and 18 different drugs. The validation showed that the HD model average fold errors (AFE) for dissolution rate prediction of immediate release formulations, is comprised between 0.85 and 1.15, and the absolute average fold errors (AAFE) are comprised between 1.08 and 1.28, which shows satisfactory predictive power. For experiments where coning was suspected, the HDC-1 model improved the precision of the prediction (defined as ratio of "AAFE-1"values) by 2.46 fold compared to HD model. The calculation of a P-PSD integrating the impact of USP2 paddle rotation, medium viscosity and coning, will improve the PBBM predictions, since these parameters could have an influence on in vitro dissolution, and could open the way to better prediction of the effect of prandial state on human exposure, by developing new in silico tools which could integrate variation of velocity profiles due to the chyme viscosity.

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.

In vivo models to evaluate ingestible devices: Present status and current trends

Evaluation of orally ingestible devices is critical to optimize their performance early in development. Using animals as a pre-clinical tool can provide useful information on functionality, yet it is important to recognize that animal gastrointestinal physiology, pathophysiology and anatomy can differ to that in humans and that the most suitable species needs to be selected to inform the evaluation. There has been a move towards in vitro and in silico models rather than animal models in line with the 3Rs (Replacement, Reduction and Refinement) as well as the better control and reproducibility associated with these systems. However, there are still instances where animal models provide the greatest understanding. This paper provides an overview of key aspects of human gastrointestinal anatomy and physiology and compares parameters to those reported in animal species. The value of each species can be determined based upon the parameter of interest from the ingested device when considering the use of pre-clinical animal testing.

Treating colon cancers with a non-conventional yet strategic approach: An overview of various nanoparticulate systems

Regardless of progress in therapy management which are developed for colon cancer (CC), it remains the third most common cause of mortality due to cancers around the world. Conventional medicines pose side effects due to untoward action on non-target cells. Their inability to deliver drugs to the affected regions of the colon locally, in a reproducible manner raises a concern towards the efficacy of therapy. In this regard, nanoparticles emerged as a promising drug delivery system due to their flexibility in designing, drug release modulation and cancer cell targeting. Not only are nanoparticles making their way into colon cancer research in the revolution of conventional onco-therapeutics, but they also offer promising scope in the development of colon cancer vaccines and theranostic tools. However, there are challenges with respect to drug delivery using nanoparticles, which may hamper the delivery of these novel carriers to the colon. The present review addresses recent advents in nanotechnology for colon-specific drug delivery (CDDS) which may help to overcome the existing challenges and intends to recognize futuristic potentials in the treatment of CC with CDDS.

Evaluating the Impact of Physiological Properties of the Gastrointestinal Tract On Drug In Vivo Performance Using Physiologically Based Biopharmaceutics Modeling and Virtual Clinical Trials

The physiological properties of the gastrointestinal tract, such as pH, fluid volume, bile salt concentration, and gastrointestinal transit time, are highly variable in vivo. These properties can affect the dissolution and absorption of a drug, depending on its properties and formulation. The effect of gastrointestinal physiology on the bioperformance of a drug was studied in silico for a delayed-release pantoprazole tablet and an immediate-release dolutegravir tablet. Physiologically based absorption models were developed and virtual clinical trials were performed. Reasons for the variability in drug bioperformance between subjects were investigated, taking into account differences in gastrointestinal tract characteristics, pharmacokinetic parameters, and additional parameters (e.g., permeability). Default software parameters describing gastrointestinal physiology in the fasted and fed states, and variation in these parameters, were altered to match variability in these parameters reported in vivo. The altered model physiologies better described the variability of gastrointestinal conditions, and therefore the results of virtual trials using these physiologies are likely to be more relevant in vivo. With such altered gastrointestinal physiologies used to develop models, it is possible to obtain additional knowledge and improve the understanding of subject-formulation interactions.

pH-Dependent Molecular Gate Mesoporous Microparticles for Biological Control of Giardia intestinalis

Giardiasis is a parasitism produced by the protozoa Giardia intestinalis that lives as trophozoite in the small intestine (mainly in the duodenum) attached to the intestinal villus by means of billed discs. The first line treatment is metronidazole, a drug with high bioavailability, which is why to obtain therapeutic concentrations in duodenum, it is necessary to administer high doses of drug to patients with the consequent occurrence of side effects. It is necessary to developed new therapeutical approaches to achieve a local delivery of the drug. In this sense, we have developed gated mesoporous silica microparticles loaded with metronidazole and with a molecular gate pH dependent. In vitro assays demonstrated that the metronidazole release is practically insignificant at acidic pHs, but in duodenum conditions, the metronidazole delivery from the microparticles is effective enough to produce an important parasite destruction. In vivo assays indicate that this microparticulate system allows to increase the concentration of the drug in duodenum and reduce the concentration in plasma avoiding systemic effects. This system could be useful for other intestinal local treatments in order to reduce doses and increase drug availability in target tissues.

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

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 therapeutic improvement with fewer adverse effects. Future perspectives to the treatment of this disease include the elucidation of molecular basis of IBD diseases in order to design more specific treatments, and the performance of more in vivo assays to validate the specificity and stability of the obtained systems.

Similar pharmacokinetics of three dosing regimens comprising two oral delayed-release mesalamine formulations in healthy adult volunteers: Randomised, open-label, parallel-group study

Aims

Mesalamine is the first‐line therapy for treating mild‐to‐moderate ulcerative colitis. Multiple mesalamine formulations are available, with similar safety and efficacy profiles. Mesalamine is commonly administered as divided dosing, although once‐daily dosing may provide benefits for patients. We evaluated the pharmacokinetics of three dosing regimens of two oral delayed‐release mesalamine formulations in healthy adult volunteers.

Methods

A randomised, open‐label, parallel‐group study of mesalamine pharmacokinetics following Lialda 2 × 1.2 g once daily (QD) (dose A), Asacol 6 × 400 mg QD (dose B), or Asacol 2 × 400 mg three times daily (TID) (dose C) over 7 days. Assessments included 5‐aminosalicylic acid (5‐ASA) and N‐acetyl 5‐aminosalicylic acid (N‐Ac‐5‐ASA, primary metabolite) pharmacokinetics (A_e(%), AUC_0‐24 and C_max), safety and tolerability.

Results

All enrolled volunteers (n = 37) completed the study. Steady state was achieved for all treatments by day 4. Ratios (95% CI) of means for steady‐state AUC_0‐24 (dose A vs B 90.3% [39.8, 204.8], dose A vs C 123.5% [55.3, 275.7], dose B vs C 136.8% [61.3, 305.5]) and C_max (dose A vs B 106.0% [46.4, 242.2], dose A vs C 133.0% [59.1, 299.0], dose B vs C 125.5% [55.8, 282.1]) were similar for all 5‐ASA treatments. Mean urinary excretion of 5‐ASA plus N‐Ac‐5‐ASA was comparable between treatments (dose A 21.3%, dose B 20.2%, dose C 17.9%). All treatment regimens were well tolerated; no safety issues were observed.

Conclusions

Plasma and urine pharmacokinetics for Asacol TID, Asacol QD, and Lialda QD are similar, suggesting similar daily systemic exposures can be obtained with either TID or QD dosing. NCT00751699.

pH-dependent ileocolonic drug delivery, part I: in vitro and clinical evaluation of novel systems

After the pH dependency of novel pH-dependent ileocolonic drug delivery systems is confirmed in vitro, their performance should be evaluated in human volunteers.

Advances in Oral Drug Delivery for Regional Targeting in the Gastrointestinal Tract - Influence of Physiological, Pathophysiological and Pharmaceutical Factors

The oral route is by far the most common route of drug administration in the gastrointestinal tract and can be used for both systemic drug delivery and for treating local gastrointestinal diseases. It is the most preferred route by patients, due to its advantages, such as ease of use, non-invasiveness, and convenience for self-administration. Formulations can also be designed to enhance drug delivery to specific regions in the upper or lower gastrointestinal tract. Despite the clear advantages offered by the oral route, drug delivery can be challenging as the human gastrointestinal tract is complex and displays a number of physiological barriers that affect drug delivery. Among these challenges are poor drug stability, poor drug solubility, and low drug permeability across the mucosal barriers. Attempts to overcome these issues have focused on improved understanding of the physiology of the gastrointestinal tract in both healthy and diseased states. Innovative pharmaceutical approaches have also been explored to improve regional drug targeting in the gastrointestinal tract, including nanoparticulate formulations. This review will discuss the physiological, pathophysiological, and pharmaceutical considerations influencing drug delivery for the oral route of administration, as well as the conventional and novel drug delivery approaches. The translational challenges and development aspects of novel formulations will also be addressed.

Improved Stability of Rifampicin in the Presence of Gastric-Resistant Isoniazid Microspheres in Acidic Media

The degradation of rifampicin (RIF) in an acidic medium to form 3-formyl rifamycin SV, a poorly absorbed compound, is accelerated in the presence of isoniazid, contributing to the poor bioavailability of rifampicin. This manuscript presents a novel approach in which isoniazid is formulated into gastric-resistant sustained-release microspheres and RIF into microporous floating sustained-release microspheres to reduce the potential for interaction between RIF and isoniazid (INH) in an acidic environment. Hydroxypropyl methylcellulose acetate succinate and Eudragit^® L100 polymers were used for the manufacture of isoniazid-loaded gastric-resistant sustained-release microspheres using an o/o solvent emulsification evaporation approach. Microporous floating sustained-release microspheres for the delivery of rifampicin in the stomach were manufactured using emulsification and a diffusion/evaporation process. The design of experiments was used to evaluate the impact of input variables on predefined responses or quality attributes of the microspheres. The percent degradation of rifampicin following 12 h dissolution testing in 0.1 M HCl pH 1.2 in the presence of isoniazid gastric-resistant sustained-release microspheres was only 4.44%. These results indicate that the degradation of rifampicin in the presence of isoniazid in acidic media can be reduced by encapsulation of both active pharmaceutical ingredients to ensure release in different segments of the gastrointestinal tract, potentially improving the bioavailability of rifampicin.

Physiological and Pharmaceutical Considerations for Rectal Drug Formulations

Although the oral route is the most convenient route for drug administration, there are a number of circumstances where this is not possible from either a clinical or pharmaceutical perspective. In these cases, the rectal route may represent a practical alternative and can be used to administer drugs for both local and systemic actions. The environment in the rectum is considered relatively constant and stable and has low enzymatic activity in comparison to other sections of the gastrointestinal tract. In addition, drugs can partially bypass the liver following systemic absorption, which reduces the hepatic first-pass effect. Therefore, rectal drug delivery can provide significant local and systemic levels for various drugs, despite the relatively small surface area of the rectal mucosa. Further development and optimization of rectal drug formulations have led to improvements in drug bioavailability, formulation retention, and drug release kinetics. However, despite the pharmaceutical advances in rectal drug delivery, very few of them have translated to the clinical phase. This review will address the physiological and pharmaceutical considerations influencing rectal drug delivery as well as the conventional and novel drug delivery approaches. The translational challenges and development aspects of novel formulations will also be discussed.

In Vitro and In Vivo Test Methods for the Evaluation of Gastroretentive Dosage Forms

More than 50 years ago, the first concepts for gastroretentive drug delivery systems were developed. Despite extensive research in this field, there is no single formulation concept for which reliable gastroretention has been demonstrated under different prandial conditions. Thus, gastroretention remains the holy grail of oral drug delivery. One of the major reasons for the various setbacks in this field is the lack of predictive in vitro and in vivo test methods used during preclinical development. In most cases, human gastrointestinal physiology is not properly considered, which leads to the application of inappropriate in vitro and animal models. Moreover, conditions in the stomach are often not fully understood. Important aspects such as the kinetics of fluid volumes, gastric pH or mechanical stresses have to be considered in a realistic manner, otherwise, the gastroretentive potential as well as drug release of novel formulations cannot be assessed correctly in preclinical studies. This review, therefore, highlights the most important aspects of human gastrointestinal physiology and discusses their potential implications for the evaluation of gastroretentive drug delivery systems.

Effect of polymer concentration and solution pH on viscosity affecting integrity of a polysaccharide coat of compression coated tablets

Tablets, compression coated with certain polysaccharides and intended for colon delivery, retain the integrity of the coat for an initial period of about 6 h (lag period) beyond which (post-lag period) the coat is degraded by colonic enzymes to induce drug release. This work was undertaken to investigate the factors which influence the integrity of the coat during the lag period. Core tablets containing two model drugs were compression coated with various amounts of carboxymethyl locust bean gum (CMLBG). In-vitro release of drugs, erosion of coat, and steady shear viscosity of CMLBG solutions having different concentrations and solution pH were determined. The viscosity of CMLBG that depended primarily on CMLBG concentration and partly on solution pH was responsible for erosion and integrity of the coat in the lag period. Evaluation of polymer viscosity could describe the integrity of coat of a polysaccharide coated tablet in the lag period.

Pharmacokinetics and efficacy of orally administered polymeric chloroquine as macromolecular drug in the treatment of inflammatory bowel disease

Inflammatory bowel disease is a chronic inflammation of the gastrointestinal tract with poor understanding of its pathogenesis and no effective cure. The goal of this study was to evaluate the feasibility of orally administered non-degradable polymeric chloroquine (pCQ) to locally reduce colon inflammation. The pCQ was synthesized by radical copolymerization of N-(2-hydroxypropyl)methacrylamide with methacryloylated hydroxychloroquine (HCQ). The anti-inflammatory activity of orally administered pCQ versus HCQ was tested in a mouse model of colitis induced by Citrobacter rodentium (C. rodentium). Single-dose pharmacokinetic and biodistribution studies performed in the colitis model indicated negligible systemic absorption (p ≤ 0.001) and localization of pCQ in the gastrointestinal tract. A multi-dose therapeutic study demonstrated that the localized pCQ treatment resulted in significant reduction in the colon inflammation (p ≤ 0.05). Enhanced suppression of pro-inflammatory cytokines IL-6 (p ≤ 0.01) and IL1-β and opposing upregulation of IL-2 (p ≤ 0.05) recently reported to be involved in downstream anti-inflammatory events suggested that the anti-inflammatory effects of the pCQ are mediated by altering mucosal immune homeostasis. Overall, the reported findings demonstrate a potential of pCQ as a novel polymer therapeutic option in inflammatory bowel disease with the potential of local effects and minimized systemic toxicity.

All disease begins in the gut: Influence of gastrointestinal disorders and surgery on oral drug performance

The term "disease" conjures a plethora of graphic imagery for many, and the use of drugs to combat symptoms and treat underlying pathology is at the core of modern medicine. However, the effects of the various gastrointestinal diseases, infections, co-morbidities and the impact of gastrointestinal surgery on the pharmacokinetic and pharmacodynamic behaviour of drugs have been largely overlooked. The better elucidation of disease pathology and the role of underlying cellular and molecular mechanisms have increased our knowledge as far as diagnoses and prognoses are concerned. In addition, the recent advances in our understanding of the intestinal microbiome have linked the composition and function of gut microbiota to disease predisposition and development. This knowledge, however, applies less so in the context of drug absorption and distribution for orally administered dosage forms. Here, we revisit and re-evaluate the influence of a portfolio of gastrointestinal diseases and surgical effects on the functionality of the gastrointestinal tract, their implications for drug delivery and attempt to uncover significant links for clinical practice.

Influence of pH and phosphate concentration on the phosphate binding capacity of five contemporary binders. An in vitro study

AIM

Hyperphosphataemia is associated with increased mortality and morbidity in end stage renal disease. Despite phosphate binder therapy, a large proportion of patients do not reach the treatment target. In five contemporary binders we explored the influence of pH and phosphate concentration on phosphate binding. This interaction could be of relevance in clinical practice.

METHODS

Phosphate binding was quantified in vitro in 25 mL of purified water containing phosphate concentrations of 10, 15 and 20 mM and baseline pH values of 3.0 or 6.0, with a binder over 6 h. Lanthanum carbonate, calcium acetate/magnesium carbonate, sevelamer carbonate, calcium carbonate and sucroferric oxyhydroxide, 67 mg of each, were used. The experiments were performed in duplicate. The primary outcome was the difference in the amount of bound phosphate for each binder after 6 h in solutions at two different pH values. Secondary outcomes were the influence of phosphate concentration on phosphate binding, next to binding patterns and phosphate binder saturation.

RESULTS AND CONCLUSION

In this specific in vitro setting, lanthanum carbonate, sevelamer carbonate, calcium carbonate and sucroferric oxyhydroxide bound more phosphate in the solution with baseline pH of 3.0. Differences however were small except for lanthanum carbonate. Calcium acetate/magnesium carbonate was most effective in a solution with baseline pH of 6.0. All phosphate binders bound more phosphate in solutions with higher concentrations of phosphate. Sevelamer carbonate, calcium acetate/magnesium carbonate and sucroferric oxyhydroxide bound most phosphate in the first hour and reached maximum binding capacity in less than 6 h.

Application Potential of Polymeric Nanoconstructs for Colon-Specific Drug Delivery

Numerous applications of colon-specific drug delivery have been found in a wide array of diseases like irritable bowel syndrome (IBS), inflammatory bowel diseases (ulcerative colitis and Crohn's disease), colorectal cancer, and diverticulitis. Drug delivery to the colon has different anatomic and pathophysiological barriers. In recent advancements, these barriers were overcome by using biodegradable polymeric nanoconstructs, which are exhibiting minimal systemic adverse effects. Various polymeric nanoconstructs (PNCs) such as nanoparticles, micelles, and dendrimers have been exploited for effective targeting to pathological sites of colon. PNCs on oral administration not only protect the bioactive from physicochemical degradation but also prevent premature leakage in the upper parts of gastrointestinal tract. The chapter summarizes various PNCs-based approaches for colon-specific drug delivery.

Gated Mesoporous Silica Nanocarriers for a "Two-Step" Targeted System to Colonic Tissue

Colon targeted drug delivery is highly relevant not only to treat colonic local diseases but also for systemic therapies. Mesoporous silica nanoparticles (MSNs) have been demonstrated as useful systems for controlled drug release given their biocompatibility and the possibility of designing gated systems able to release cargo only upon the presence of certain stimuli. We report herein the preparation of three gated MSNs able to deliver their cargo triggered by different stimuli (redox ambient (S1), enzymatic hydrolysis (S2), and a surfactant or being in contact with cell membrane (S3)) and their performance in solution and in vitro with Caco-2 cells. Safranin O dye was used as a model drug to track cargo fate. Studies of cargo permeability in Caco-2 monolayers demonstrated that intracellular safranin O levels were significantly higher in Caco-2 monolayers when using MSNs compared to those of free dye. Internalization assays indicated that S2 nanoparticles were taken up by cells via endocytosis. S2 nanoparticles were selected for in vivo tests in rats. For in vivo assays, capsules were filled with S2 nanoparticles and coated with Eudragit FS 30 D to target colon. The enteric coated capsule containing the MSNs was able to deliver S2 nanoparticles in colon tissue (first step), and then nanoparticles were able to deliver safranin O inside the colonic cells after the enzymatic stimuli (second step). This resulted in high levels of safranin O in colonic tissue combined with low dye levels in plasma and body tissues. The results suggested that this combination of enzyme-responsive gated MSNs and enteric coated capsules may improve the absorption of drugs in colon to treat local diseases with a reduction of systemic effects.

Design and evaluation of an extended-release matrix tablet formulation; the combination of hypromellose acetate succinate and hydroxypropylcellulose

The purpose of this study was to develop an extended-release (ER) matrix tablet that shows robust dissolution properties able to account for the variability of pH and mechanical stress in the GI tract using a combination of enteric polymer and hydrophilic polymer. Hypromellose acetate succinate (HPMCAS) and hydroxypropylcellulose (HPC) were selected as ER polymers for the ER matrix tablet (HPMCAS/HPC ER matrix tablet). Oxycodone hydrochloride was employed as a model drug. Dissolution properties of the HPMCAS/HPC ER matrix tablets were evaluated and were not affected by the pH of the test medium or paddle rotating speed. In a USP apparatus 3 (bio-relevant dissolution method), dissolution profiles of the HPMCAS/HPC ER matrix tablets containing oxycodone hydrochloride were similar to that of the reference product (OxyContin). Moreover, in vivo performance after oral administration of the HPMCAS/HPC ER matrix tablets to humans was simulated by GastroPlus based on dissolution profiles from the USP apparatus 3. The plasma concentration-time profile simulated was similar to that of the reference product. These results suggest that the combination of HPMCAS and HPC shows a robust dissolution profile against pH and paddle rotating speed and indicates the appropriate extended-release profile in humans.

Thiomers and their potential applications in drug delivery

INTRODUCTION

Thiomers are the product of the immobilization of sulfhydryl-bearing ligands onto the polymer backbone of a conventional polymer, which results in a significant improvement in mucoadhesion; in situ gelation and efflux inhibition compare with unchanged polymers. Because of thiol groups, thiomers have more reactivity and enhanced protection against oxidation. Since the late 1990s, extensive work has been conducted on these promising polymeric excipients in the pharmaceutical field. Areas covered: This review covers thiomers, their classification and their different properties. Various techniques for the synthesis, purification and characterization of thiomers are described in detail. This review also encompasses their various properties such as mucoadhesion, permeation enhancement, in situ gelation and efflux inhibition, as well as different formulations based on thiomers. In addition to the use of thiomers as multifunctional excipients, this review also encompasses their use as drugs. Expert opinion: The synthesis is realized by linkage of sulfhydryl-bearing ligands but reported methods give low yields. Higher degrees of modification are not necessary and would probably lead to extreme changes in properties. Nevertheless, an accurate characterization of the final product is important. The scale-up procedure for industrial manufacturing has been adapted to produce GMP materials; Lacrimera® eye drops have already entered the European market.

Is it possible to achieve bio-equivalence between an oral solid immediate-release and an analogue enteric-coated formulation?

Objectives

While bioequivalence between enteric-coated and immediate-release formulations can be achieved in terms of AUC, gastric emptying of enteric-coated dosage forms is a stochastic event, usually leading to lower Cmax values than those observed with the corresponding immediate release. This article examines challenges of developing enteric-coated dosage forms which are bioequivalent to the corresponding immediate-release formulations in terms of both AUC and Cmax using rasagiline as a model compound.

Methods

In vitro drug release profiles of enteric-coated formulations were obtained and compared to those of the immediate-release formulation by dissolution testing. Pharmacokinetics was evaluated in bioequivalence studies in healthy human volunteers after single oral administration of enteric-coated and immediate-release formulations.

Key findings

The initial enteric-coated pellet formulation prototype was equivalent in terms of AUC, but differed in Cmax; a second formulation prototype, consisting of a single-unit core and enteric-coating film, proved to be bioequivalent to immediate-release rasagiline tablets in terms of AUC and Cmax. In vitro, it released rasagiline rapidly at a pH of 6.8.

Conclusions

Despite differences in gastric emptying between disintegrating immediate-release and enteric-coated solid dosage forms, bioequivalence in pharmacokinetic studies was achieved.