Gastrointestinal release behaviour of modified-release drug products: Dynamic dissolution testing of mesalazine formulations

Colon targeting in rats, dogs and IBD patients with species-independent film coatings

Polysaccharides were identified, which allow for colon targeting in human Inflammatory Bowel Disease (IBD) patients, as well as in rats and dogs (which are frequently used as animals in preclinical studies). The polysaccharides are degraded by colonic enzymes (secreted by bacteria), triggering the onset of drug release at the target site. It has to be pointed out that the microbiota in rats, dogs and humans substantially differ. Thus, the performance of this type of colon targeting system observed in animals might not be predictive for patients. The aim of this study was to limit this risk. Different polysaccharides were exposed to culture medium inoculated with fecal samples from IBD patients, healthy dogs and "IBD rats" (in which colonic inflammation was induced). Dynamic changes in the pH of the culture medium were used as an indicator for the proliferation of the bacteria and, thus, the potential of the polysaccharides to serve as their substrate. Fundamental differences were observed with respect to the extent of the pH variations as well as their species-dependency. The most promising polysaccharides were used to prepare polymeric film coatings surrounding 5-aminosaliciylic acid (5-ASA)-loaded starter cores. To limit premature polysaccharide dissolution/swelling in the upper gastro intestinal tract, ethylcellulose was also included in the film coatings. Drug release was monitored upon exposure to culture medium inoculated with fecal samples from IBD patients, healthy dogs and "IBD rats". For reasons of comparison, also 5-ASA release in pure culture medium was measured. Most film coatings showed highly species-dependent drug release kinetics or limited colon targeting capacity. Interestingly, extracts from aloe vera and reishi (a mushroom) showed a promising potential for colon targeting in all species.

MMX mesalamine in ulcerative colitis: Major advantages towards classical mesalamine formulations

Medical therapy is the cornerstone of ulcerative colitis (UC) management and aims to induce and maintain remission. In case of mild-to-moderate UC, mesalamine (5-ASA) is the first-line option. 5-ASA requires local release at the level of the inflamed mucosa to exert its therapeutic action. While rectal preparations are useful in distal colitis, in cases of UC of at least rectosigmoid extent, guidelines suggest the association of oral and rectal 5-ASA. Mesalamine with Multi Matrix System® technology (MMX mesalamine) is an oral, high-strength (1.2 g/tablet), once-daily formulation of 5-ASA, designed to provide delayed and prolonged release throughout the entire colon. Clinical trials demonstrated a strong efficacy in inducing and maintaining clinical and endoscopic remission in active mild-to-moderate UC. The efficacy is related to specific colonic drug-delivery, to its high-dosage and once-daily administration, thus improving patients' adherence and outcomes. The specific colonic-delivery is also associated with very low rates of systemic absorption and adverse events (AEs). With this comprehensive review we aimed to summarize current knowledge on MMX mesalamine in mild-to-moderate UC, in terms of clinical pharmacology, efficacy and safety, also compared to other 5-ASA products. In addition we provided an expert opinion on the topic, examining the implications on clinical practice.

Comparison of 5-ASA layered or matrix pellets coated with a combination of ethylcellulose and Eudragits L and S in the treatment of ulcerative colitis in rats

The aim of this study was to evaluate and optimize the combination of time and pH-dependent polymers as a single coating for the design of the colon-specific drug delivery system of 5-aminosalicylic acid (5-ASA) pellets. 5-ASA matrix pellets with a 70% drug load were prepared by the extrusion-spheronization method. The optimal coating formula which included Eudragit S (ES)+Eudragit L (EL)+Ethylcellulose (EC) was predicted for the targeted drug delivery to the colonic area by a 3² factorial design. The ratio of ES:EL:EC and coating level were considered as independent variables while the responses were the release of less than 10% of the drug within 2 h (Y₁), the release of 60-70% within 10 h at pH 6.8 (Y₂) and lag time of less than 1 h at pH 7.2 (Y₃). Also, 5-ASA layered pellets were prepared by the powder layering of 5-ASA on nonpareils (0.4-0.6 mm) in a fluidized bed coater and then coated with the same optimum coating composition. The coated 5-ASA layered or matrix pellets were tested in a rat model of ulcerative colitis (UC) and compared with the commercial form of 5-ASA pellets (Pentasa®). The ratio of ES:EL:EC of 33:52:15 w/w at a coating level of 7% was discovered as the optimum coating for the delivery of 5-ASA matrix pellets to the colon. The coated 5-ASA pellets were spherical with uniform coating as shown by SEM and met all of our release criteria as predicted. In-vivo studies demonstrated that the optimum 5-ASA layered or matrix pellets had superior anti-inflammatory activities than Pentasa® in terms of colitis activity index (CAI), colon damage score (CDS), colon/body weight ratio and colon's tissue enzymes of glutathione (GSH) and malondialdehyde (MDA). The optimum coating formulation showed a high potential for colonic delivery of 5-ASA layered or matrix pellets and triggered drug release based on pH and time.

Colonic drug delivery: Formulating the next generation of colon-targeted therapeutics

Colonic drug delivery can facilitate access to unique therapeutic targets and has the potential to enhance drug bioavailability whilst reducing off-target effects. Delivering drugs to the colon requires considered formulation development, as both oral and rectal dosage forms can encounter challenges if the colon's distinct physiological environment is not appreciated. As the therapeutic opportunities surrounding colonic drug delivery multiply, the success of novel pharmaceuticals lies in their design. This review provides a modern insight into the key parameters determining the effective design and development of colon-targeted medicines. Influential physiological features governing the release, dissolution, stability, and absorption of drugs in the colon are first discussed, followed by an overview of the most reliable colon-targeted formulation strategies. Finally, the most appropriate in vitro, in vivo, and in silico preclinical investigations are presented, with the goal of inspiring strategic development of new colon-targeted therapeutics.

The effect of esomeprazole on the upper GI tract release and systemic absorption of mesalazine from colon targeted formulations

The aim of the present study was to investigate the effect of coadministration of the proton pump inhibitor (PPI) esomeprazole on the upper GI tract behavior and systemic exposure of mesalazine from two mechanistically different colon targeted delivery systems: Claversal (pH-dependent release) and Pentasa (prolonged release). To this end, gastric, jejunal and systemic concentrations of mesalazine and its metabolite N-acetyl mesalazine were monitored in 5 healthy volunteers following oral intake of Pentasa or Claversal with or without PPI pre-treatment (cross-over study). Our exploratory study demonstrated that pre-treatment with a PPI may affect the release and absorption of mesalazine from formulations with different modified release mechanisms. Upon intake of Claversal, the onset of mesalazine absorption was accelerated substantially by PPI pre-treatment. While the PPI-induced increase in pH initiated the disintegration process already in the upper GI tract, the release of mesalazine started beyond the proximal jejunum. Upon intake of Pentasa, PPI pre-treatment seemed to increase the systemic exposure, even though the underlying mechanism could not be revealed yet. The faster release of mesalazine in the GI tract and/or the increased systemic absorption following PPI pre-treatment may reduce the ability of mesalazine to reach the colon. Future research assessing mesalazine disposition in the lower GI tract is warranted.

Clinical translation of advanced colonic drug delivery technologies

Targeted drug delivery to the colon offers a myriad of benefits, including treatment of local diseases, direct access to unique therapeutic targets and the potential for increasing systemic drug bioavailability and efficacy. Although a range of traditional colonic delivery technologies are available, these systems exhibit inconsistent drug release due to physiological variability between and within individuals, which may be further exacerbated by underlying disease states. In recent years, significant translational and commercial advances have been made with the introduction of new technologies that incorporate independent multi-stimuli release mechanisms (pH and/or microbiota-dependent release). Harnessing these advanced technologies offers new possibilities for drug delivery via the colon, including the delivery of biopharmaceuticals, vaccines, nutrients, and microbiome therapeutics for the treatment of both local and systemic diseases. This review details the latest advances in colonic drug delivery, with an emphasis on emerging therapeutic opportunities and clinical technology translation.

In Vitro Methodologies for Evaluating Colon-Targeted Pharmaceutical Products and Industry Perspectives for Their Applications

Several locally acting colon-targeted products to treat colonic diseases have been recently developed and marketed, taking advantage of gastrointestinal physiology to target delivery. Main mechanisms involve pH-dependent, time-controlled and/or enzymatic-triggered release. With site of action located before systemic circulation and troublesome colonic sampling, there is room for the introduction of meaningful in vitro methods for development, quality control (QC) and regulatory applications of these formulations. A one-size-fits-all method seems unrealistic, as the selection of experimental conditions should resemble the physiological features exploited to trigger the release. This article reviews the state of the art for bio-predictive dissolution testing of colon-targeted products. Compendial methods overlook physiological aspects, such as buffer molarity and fluid composition. These are critical for pH-dependent products and time-controlled systems containing ionizable drugs. Moreover, meaningful methods for enzymatic-triggered products including either bacteria or enzymes are completely ignored by pharmacopeias. Bio-predictive testing may accelerate the development of successful products, although this may require complex methodologies. However, for high-throughput routine testing (e.g., QC), simplified methods can be used where balance is struck between simplicity, robustness and transferability on one side and bio-predictivity on the other. Ultimately, bio-predictive methods can occupy a special niche in terms of supplementing plasma concentration data for regulatory approval.

Rheological and textural analysis as tools for investigation of drug-polymer and polymer-polymer interactions on the example of low-acyl gellan gum and mesalazine

PURPOSE

In the performed study, the rheological and textural parameters of gellan-based hydrogels were investigated and their dependence on three factors was taken into consideration: (i) The presence of the model drug, (ii) The presence and type of the ionic crosslinking agent, and (iii) the composition of the polymer network. The objective was to compare two analytical methods, regarded as complementary, and define to what extent the obtained results correlate with each other.

METHODS

The hydrogels contained low-acyl gellan gum or its mixtures with hydroxyethyl cellulose or κ-carrageenan. CaCl₂ and MgCl₂ were used as gelling agents. Mesalazine was used as a model drug. The rheological analysis included oscillatory stress and frequency sweeping. The texture profile analysis was performed to calculate texture parameters.

RESULTS

Placebo gels without the addition of gelling agents had the weakest structure. The drug had the strongest ability to increase the stiffness of the polymer network. The weakest structure revealed the placebo samples without the addition of gelling agents. Texture analysis revealed no significant influence of the drug on the strength of the gels, while rheological measurements indicated clear differences.

CONCLUSIONS

It can be concluded that in the case of some parameters methods correlate, that is, the effect related to gelling ions. However, the rheological analysis seems to be more precise and sensitive to some changes in the mechanical properties of the gels.

Integration of advanced methods and models to study drug absorption and related processes: An UNGAP perspective

This collection of contributions from the European Network on Understanding Gastrointestinal Absorption-related Processes (UNGAP) community assembly aims to provide information on some of the current and newer methods employed to study the behaviour of medicines. It is the product of interactions in the immediate pre-Covid period when UNGAP members were able to meet and set up workshops and to discuss progress across the disciplines. UNGAP activities are divided into work packages that cover special treatment populations, absorption processes in different regions of the gut, the development of advanced formulations and the integration of food and pharmaceutical scientists in the food-drug interface. This involves both new and established technical approaches in which we have attempted to define best practice and highlight areas where further research is needed. Over the last months we have been able to reflect on some of the key innovative approaches which we were tasked with mapping, including theoretical, in silico, in vitro, in vivo and ex vivo, preclinical and clinical approaches. This is the product of some of us in a snapshot of where UNGAP has travelled and what aspects of innovative technologies are important. It is not a comprehensive review of all methods used in research to study drug dissolution and absorption, but provides an ample panorama of current and advanced methods generally and potentially useful in this area. This collection starts from a consideration of advances in a priori approaches: an understanding of the molecular properties of the compound to predict biological characteristics relevant to absorption. The next four sections discuss a major activity in the UNGAP initiative, the pursuit of more representative conditions to study lumenal dissolution of drug formulations developed independently by academic teams. They are important because they illustrate examples of in vitro simulation systems that have begun to provide a useful understanding of formulation behaviour in the upper GI tract for industry. The Leuven team highlights the importance of the physiology of the digestive tract, as they describe the relevance of gastric and intestinal fluids on the behaviour of drugs along the tract. This provides the introduction to microdosing as an early tool to study drug disposition. Microdosing in oncology is starting to use gamma-emitting tracers, which provides a link through SPECT to the next section on nuclear medicine. The last two papers link the modelling approaches used by the pharmaceutical industry, in silico to Pop-PK linking to Darwich and Aarons, who provide discussion on pharmacometric modelling, completing the loop of molecule to man.

Smartphone-enabled 3D printing of medicines

3D printing is a manufacturing technique that is transforming numerous industrial sectors, particularly where it is key tool in the development and fabrication of medicinees that are personalised to the individual needs of patients. Most 3D printers are relatively large, require trained operators and must be located in a pharmaceutical setting to manufacture dosage forms. In order to realise fully the potential of point-of-care manufacturing of medicines, portable printers that are easy to operate are required. Here, we report the development of a 3D printer that operates using a mobile smartphone. The printer, operating on stereolithographic principles, uses the light from the smartphone's screen to photopolymerise liquid resins and create solid structures. The shape of the printed dosage form is determined using a custom app on the smartphone. Warfarin-loaded Printlets (3D printed tablets) of various sizes and patient-centred shapes (caplet, triangle, diamond, square, pentagon, torus, and gyroid lattices) were successfully printed to a high resolution and with excellent dimensional precision using different photosensitive resins. The drug was present in an amorphous form, and the Printlets displayed sustained release characterises. The promising proof-of-concept results support the future potential of this compact, user-friendly and interconnected smartphone-based system for point-of-care manufacturing of personalised medications.

Research-Based Product Innovation to Address Critical Unmet Needs of Patients with Inflammatory Bowel Diseases

Despite progress in recent decades, patients with inflammatory bowel diseases face many critical unmet needs, demonstrating the limitations of available treatment options. Addressing these unmet needs will require interventions targeting multiple aspects of inflammatory bowel disease pathology, including disease drivers that are not targeted by available therapies. The vast majority of late-stage investigational therapies also focus primarily on a narrow range of fundamental mechanisms. Thus, there is a pressing need to advance to clinical stage differentiated investigational therapies directly targeting a broader range of key mechanistic drivers of inflammatory bowel diseases. In addition, innovations are critically needed to enable treatments to be tailored to the specific underlying abnormal biological pathways of patients; interventions with improved safety profiles; biomarkers to develop prognostic, predictive, and monitoring tests; novel devices for nonpharmacological approaches such as minimally invasive monitoring; and digital health technologies. To address these needs, the Crohn's & Colitis Foundation launched IBD Ventures, a venture philanthropy-funding mechanism, and IBD Innovate®, an innovative, product-focused scientific conference. This special IBD Innovate® supplement is a collection of articles reflecting the diverse and exciting research and development that is currently ongoing in the inflammatory bowel disease field to deliver innovative and differentiated products addressing critical unmet needs of patients. Here, we highlight the pipeline of new product opportunities currently advancing at the preclinical and early clinical development stages. We categorize and describe novel and differentiated potential product opportunities based on their potential to address the following critical unmet patient needs: (1) biomarkers for prognosis of disease course and prediction/monitoring of treatment response; (2) restoration of eubiosis; (3) restoration of barrier function and mucosal healing; (4) more effective and safer anti-inflammatories; (5) neuromodulatory and behavioral therapies; (6) management of disease complications; and (7) targeted drug delivery.

Optimization study of combined enteric and time-dependent polymethacrylates as a coating for colon targeted delivery of 5-ASA pellets in rats with ulcerative colitis

Formulation design for colon-specific delivery of 5-aminosalicylic acid (5-ASA) could bring some therapeutic benefits in the treatment of ulcerative colitis (UC). In the current study, a 3² full factorial design was used to predict optimum coating composed of two enteric (poly methacrylic acid, methyl methacrylates 1:2 and 1:1) and time-dependent (poly ethyl acrylate, methyl methacrylate, trimethylammonio ethyl methacrylate chloride 1:2:0.1) polymethacrylates for colon-specific delivery of 5-ASA pellets. A unique coating composition and coating level predicted by the model was applied onto either inulin-free 5-ASA pellets or inulin-bearing 5-ASA pellets and the coated pellets were examined by dissolution test in-vitro. The coated pellets were also tested in a rat model of UC and compared with the a commercially available colonic delivery system of 5-ASA. The ratio of the two enteric polymethacrylates and time-dependet polymethacrylate of 16:64:20 w/w at a coating level of 15% was discovered as the optimum coating for delivery of 5-ASA pellets to the colon. In general, the coated pellets offered a better therapeutic outcome compared to commercially available colonic delivery system of 5-ASA and uncoated pellets in terms of colitis activity index and the colon's tissue enzymes of MDA and GSH. It seems that the coating composed of enteric and pH-dependent polymethacrylates could tune up the rate of drug release from 5-ASA-coated pellets and trigger drug release based on pH and time.

pH-dependent vs. constant release of mesalazine in the treatment of ulcerative colitis: Do drug delivery concepts determine therapeutic efficacy? (Review)

Inflammatory bowel diseases (IBD) have developed to become a major global health problem. Ulcerative colitis (UC) is one of two main types of IBD, and >90% of patients suffering from mild or moderate forms of UC are treated with mesalazine, a well-tolerated and cost-effective drug. To allow oral administration, the drug has to be protected from resorption before it can reach the affected sites in the colon. The drug is therefore released from most currently used medications either constantly slow (time-dependent) or triggered by an increased pH during gastrointestinal transition. Both variants are widely used in clinical practice and it is surprising that they have not yet been compared directly in a large clinical study. In this overview, the evidence that may suggest preferential use of one type of mesalazine formulation over the other in general or for defined subgroups of patients is summarized and evaluated. Data from in vitro modelling of drug release and measurements of drug concentrations in colonic mucosa suggest that in many cases, constant release and pH-dependent formulations are of similar therapeutic efficiency; however, pH-triggered release may be superior in patients with proctitis-type UC or sites of inflammation in the proximal colon. Additionally, patients with a long gastric residence time, slow small intestinal transition, disease-related diarrhea or sensitivity to systemic adverse effects may benefit more from pH-dependent release formulations. In general, medications based on both concepts show similar efficacies, but the pH-dependent release formulations seem to be more robust in the treatment of a not further classified group of patients with UC. Future comparative clinical studies are required to clearly define the subgroups of patients that should be treated preferably with constant or pH-dependent release formulations of mesalazine.

Development of Anti-fibrotic Therapy in Stricturing Crohn's Disease: Lessons from Randomized Trials in Other Fibrotic Diseases

Intestinal fibrosis is considered an inevitable complication of Crohn's disease (CD) that results in symptoms of obstruction and stricture formation. Endoscopic or surgical treatment is required to treat the majority of patients. Progress in the management of stricturing CD is hampered by the lack of effective anti-fibrotic therapy; however, this situation is likely to change because of recent advances in other fibrotic diseases of the lung, liver and skin. In this review, we summarized data from randomized controlled trials (RCT) of anti-fibrotic therapies in these conditions. Multiple compounds have been tested for the anti-fibrotic effects in other organs. According to their mechanisms, they were categorized into growth factor modulators, inflammation modulators, 5-hydroxy-3-methylgultaryl-coenzyme A (HMG-CoA) reductase inhibitors, intracellular enzymes and kinases, renin-angiotensin system (RAS) modulators and others. From our review of the results from the clinical trials and discussion of their implications in the gastrointestinal tract, we have identified several molecular candidates that could serve as potential therapies for intestinal fibrosis in CD.

Cellulose Nanofibers Improve the Performance of Retrograded Starch/Pectin Microparticles for Colon-Specific Delivery of 5-ASA

Cellulose nanofibers (CNF) were employed as the nanoreinforcement of a retrograded starch/pectin (RS/P) excipient to optimize its colon-specific properties. Although starch retrogradation ranged from 32 to 73%, CNF addition discretely disfavored the RS yield. This result agrees with the finding that in situ CNF reduces the presence of the RS crystallinity pattern. A thermal analysis revealed that the contribution of pectin improves the thermal stability of the RS/CNF mixture. Through a complete factorial design, it was possible to optimize the spray-drying conditions to obtain powders with high yield (57%) and low moisture content (1.2%). The powders observed by Field Emission Gum Scanning Electron Microscopy (FEG-SEM) had 1–10 µm and a circular shape. The developed methodology allowed us to obtain 5-aminosalicilic acid-loaded microparticles with high encapsulation efficiency (16–98%) and drug loading (1.97–26.63%). The presence of CNF in RS/P samples was responsible for decreasing the burst effect of release in simulated gastric and duodenal media, allowing the greatest mass of drug to be targeted to the colon. Considering that spray-drying is a scalable process, widely used by the pharmaceutical industry, the results obtained indicate the potential of these microparticles as raw material for obtaining other dosage forms to deliver 5-ASA to the distal parts of gastrointestinal tract, affected by inflammatory bowel disease.

3D printing and enteric coating of a hollow capsular device with controlled drug release characteristics prepared using extruded Eudragit® filaments

This work focuses on the extrusion of a brittle, tacky, cationic copolymer i.e. Eudragit® E-100 to prepare filament and subsequent 3D printing of hollow capsular device using the extruded filament. An optimum amount of talc and triethyl citrate was used for the possible extrusion of the polymer. There was no thermal and chemical degradation of the polymer observed after extrusion confirmed by DSC and FTIR analysis. Microscopic analysis of the printed capsule showed the layer-by-layer manner of 3D printing. Capsule parts were printed according to the set dimensions (00 size) with minimal deviation. Printed capsule showed the soluble behaviour in gastric fluid pH 1.2 where within 15 min the encapsulated drug encounters with the dissolution medium and almost 70% drug was dissolved within 4 hr. In case of phosphate buffer pH 6.8, the printed capsule showed a longed swelling behaviour up to 12 hr and then gradually bursting of capsule occurred wherein more than 90% encapsulated drug was dissolved within 36 hr. Enteric coating of the printed capsule showed similar behaviour in alkaline medium that observed with non-enteric capsule. This indicates the potential application of this printed capsules for both gastric and intestinal specific delayed drug delivery by a single step enteric coating process.

Differential effects of mesalazine formulations on thiopurine metabolism through thiopurine S-methyltransferase inhibition

BACKGROUND AND AIM

Thiopurines are often used in combination with mesalazine for the treatment of ulcerative colitis (UC). Mesalazine formulations are delivered to the digestive tract by various delivery systems and absorbed as 5-aminosalicylic acid (5-ASA). 5-ASA is known to inhibit thiopurine S-methyltransferase (TPMT) activity and to affect thiopurine metabolism. There have been no studies comparing TPMT inhibition by multimatrix mesalazine (MMX) with other formulations. We investigated the difference in TPMT inhibition by different mesalazine formulations and prospectively confirmed the clinical relevance.

METHODS

Plasma concentrations of 5-ASA, N-acetyl-5-aminosalicylic acid (N-Ac-5-ASA), and TPMT activities were measured in UC patients receiving various mesalazine formulations (time-dependent or pH-dependent mesalazine or MMX) as monotherapy. Patients already on both time-dependent or pH-dependent mesalazine and thiopurines switched their mesalazine to MMX, examining 6-thioguanine nucleotide (6-TGN) and 6-methylmercaptopurine (6-MMP) 0 and 8 weeks after switching. Clinical relapse after switching was also monitored for 24 weeks.

RESULTS

Plasma 5-ASA and N-Ac-5-ASA levels were significantly higher in patients receiving time-dependent mesalazine (n = 12) compared with pH-dependent mesalazine (n = 12) and MMX (n = 15), accompanied by greater TPMT inhibition. Prospective switching from time-dependent mesalazine to MMX decreased 6-TGN levels, increased those of 6-MMP, and increased 6-MMP/6-TGN ratios. Furthermore, this resulted in significantly more relapses than switching from pH-dependent mesalazine to MMX.

CONCLUSIONS

Time-dependent mesalazine has higher plasma 5-ASA and N-Ac-5-ASA levels and greater TPMT inhibition than MMX. Therefore, switching from time-dependent mesalazine to MMX may lead to an increase of 6-MMP/6-TGN, which may reduce the clinical effectiveness of thiopurines, warranting close monitoring after switch.

5-Aminosalicylic Acid Loaded Chitosan-Carrageenan Hydrogel Beads with Potential Application for the Treatment of Inflammatory Bowel Disease

The aim of our work is to prepare mucoadhesive particles with biopolymers and 5-Aminosalicylic acid (5ASA) using the ionotropic gelation technique to ensure a controlled drug release at the colon level with potential applications in the treatment of intestinal bowel disease (IBD). The preparation of particles through the crosslinking of Chitosan (CS) with sodium tripolyphosphate (TPP) using different mass ratios and the influence of the k-Carrageenan (kCG) layer were studied. UV–VIS spectrometry was employed to assess encapsulation efficiency and drug release profile of 5ASA. The particles were investigated using FT-IR spectrometry for chemical characterization and the DLS results highlighted a monodisperse particle size distribution. The morphology of the polymeric beads was investigated using micro-computer tomography (µCT) and Scanning Electron Microscopy (SEM). Particles based on Chitosan and k-Carrageenan were able to incorporate and preserve 5ASA in an acidic and alkaline medium. The 5ASA loaded polymeric particles obtained after immersion for 1 h in kCG solution exhibited the lowest release rate in pH = 1.2. Biocompatibility studies performed on all of the particles displayed a good viability for the CCD 841 CoN cells and low cytotoxicity. All of the results have shown that these new biomaterials could be a versatile platform of targeted carriers with potential applications in inflammatory bowel disease treatment.

Physiologically relevant dissolution conditions towards improved in vitro - in vivo relationship - A case study with enteric coated pantoprazole tablets

There are many hurdles in the development of generic formulations. In vitro biopredictive dissolution conditions together with alternative in vitro - in vivo relationship (IVIVR) approaches can be a powerful tool to support the development of such formulations. In this study, we hypothesized that the release profile of enteric coated (EC) formulations of pantoprazole in physiologically relevant bicarbonate buffer (BCB) would detect possible performance differences between test and reference formulations resulting in more accurate IVIVR results and predictability when compared to a pharmacopeial dissolution test. We correlated the in vitro performance of test and reference formulations (both in BCB and pharmacopeial phosphate buffer) with the in vivo data from a failed bioequivalence study. Test and reference formulations of EC pantoprazole tablets passed the USP dissolution criteria. However, they failed statistical similarity in vitro both in compendial and BCB. Bicarbonate buffer was additionally more discriminative while being more physiologically relevant. Having BCB as an additional test to evaluate EC products in vitro might improve the comparison of formulations. This can de-risk the development of generic EC formulations.

Oral delivery of micro/nanoparticulate systems based on natural polysaccharides for intestinal diseases therapy: Challenges, advances and future perspectives

Colon-targeted oral delivery of drugs remains as an appealing and promising approach for the treatment of prevalent intestinal diseases (ID), such as inflammatory bowel disease (IBD) and colorectal cancer (CRC). Notwithstanding, there are numerous challenges to effective drug delivery to the colon, which requires the design of advanced strategies. Micro- and nanoparticles have received great attention as colon-targeted delivery platforms due to their reduced size and structural composition that favors the accumulation and/or residence time of drugs at the site of action and/or absorption, contributing to localized therapy. The choice by natural polysaccharides imparts key properties and advantages to the nano-in-microparticulate systems to effective colon-specific oral delivery. This review proposes to discuss the physiological barriers imposed by the gastrointestinal tract (GIT) against oral administration of drugs, as well as pathological factors and challenges of the ID for oral delivery of colon-targeted systems. We then provide an updated progress about polysaccharides-based colon-targeted drug delivery systems, including microparticulate, nanoparticulate and nano-in-microparticulate systems, highlighting their key properties, advantages and limitations to achieving targeted delivery and efficacious therapy within the colon. Lastly, we provide future perspectives, towards advances in the field and clinical translation of colon-targeted oral delivery systems for ID therapy.

Application of inulin/Eudragit RS in 5-ASA pellet coating with tuned, sustained-release feature in an animal model of ulcerative colitis

A tunable release of 5-aminosalicylic acid (5-ASA) could bring therapeutic benefits in the treatment of inflammatory bowel disease (IBD). A 3² factorial design was used to achieve a tuned delivery of 5-ASA pellets in the small and large intestine using a coating composed of inulin/Eudragit RS (RS). The ratio of inulin/RS and coating level were independent variables while the dependent variables were the percent of drug release at pH 1.2 in 2 h and total release of drug in 10 h at pH 6.8. 5-ASA release from pellets was examined at different pH levels and the therapeutic efficacy of the optimum pellets was compared to 5-ASA pellets of Pentasa in rats with ulcerative colitis. The inulin/RS of 18/82 at a coating level of 16% was found to be the optimum for delivery of the drug to the small and large intestine. The coated pellets offered a superior therapeutic outcome compared to uncoated pellets and Pentasa in terms of colitis activity index (CAI), and the colon's tissue enzymes of GSH and MDA. The optimum coating composed of inulin and RS could offer a tuned sustained release of 5-ASA throughout the small and large intestine with the sensitivity of drug release to microbial degradation.

Physicochemical, pharmacokinetic, and pharmacodynamic characterization of isradipine tablets for controlled release

Isradipine is a dihydropyridine calcium channel blocker (CCB) commonly used as vasodilator with antihypertensive properties. A remote-controlled release formulation for isradipine would substantially improve the clinical outcomes of the patients requiring chronic long-term treatment. In this work, sustained release (SR) tablets of isradipine, composed of hydroxypropylmethyl cellulose (HPMC), have been produced by wet granulation and their in vitro and in vivo characterization was compared to a conventional tablet dosage form of immediate release (IR) as preliminary assessment. Tablets composed of 15.0% (wt/wt) HPMC exhibited a SR profile over a period of 24 hours. The release of isradipine followed a Fickian diffusion pattern obeying to the first order kinetics and the extent of absorption was even higher in comparison to the developed conventional tablets, which showed immediate drug release. In vivo studies were carried out in rabbits, showing that the extent of isradipine absorption from the developed tablets was higher in comparison to IR tablets due to the modified release profile obtained for the former (p < 0.05). Our results suggest that SR tablets of isradipine are an efficient solid dosage form to overcome the limitations encountered in conventional IR tablets.

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.

Artificial Neural Network (ANN) Approach to Predict an Optimized pH-Dependent Mesalamine Matrix Tablet

Background

Severe bleeding and perforation of the colon and rectum are complications of ulcerative colitis which can be treated by a targeted drug delivery system.

Purpose

Development of colon-targeted delivery usually involves a complex formulation process and coating steps of pH-sensitive methacrylic acid based Eudragit^®. The current work was purposefully designed to develop dicalcium phosphate (DCP) facilitated with Eudragit-S100-based pH-dependent, uncoated mesalamine matrix tablets.

Materials and Methods

Mesalamine formulations were compressed using wet granulation technique with varying compositions of dicalcium phosphate (DCP) and Eudragit-S100. The developed formulations were characterized for physicochemical and drug release profiles. Infrared studies were carried out to ensure that there was no interaction between active ingredients and excipients. Artificial neural network (ANN) was used for the optimization of final DCP-Eudragit-S100 complex and the experimental data were employed to train a multi-layer perception (MLP) using quick propagation (QP) training algorithm until a satisfactory root mean square error (RMSE) was reached. The ANN-aided optimized formulation was compared with commercially available Masacol^®.

Results

Compressed tablets met the desirability criteria in terms of thickness, hardness, weight variation, friability, and content uniformity, ie, 5.34 mm, 7.7 kg/cm^2, 585±5 mg (%), 0.44%, and 103%, respectively. In-vitro dissolution study of commercially available mesalamine and optimized formulation was carried out and the former showed 100% release at 6 h while the latter released only 12.09% after 2 h and 72.96% after 12 h which was fitted to Weibull release model with b value of 1.3, indicating a complex release mechanism.

Conclusion

DCP-Eudragit-S100 blend was found explicative for mesalamine release without coating in gastric and colonic regions. This combination may provide a better control of ulcerative colitis.

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Regulating the pH of bicarbonate solutions without purging gases: Application to dissolution testing of enteric coated tablets, pellets and microparticles

Dissolution media based on bicarbonate buffers closely mimic the environment of intestinal fluids and thus improve in vitro in vivo correlation compared to phosphate buffers. Purging gases into the medium is used as a method to stabilise bicarbonate buffers; however, this causes issues due to the disturbance of the hydrodynamics in the dissolution vessel. The aim of this study was to develop a novel system to regulate and stabilise the pH of bicarbonate buffers without purging gases for the application of dissolution testing of enteric coated products. A novel enclosure system was applied to the USP II dissolution vessel to supply N₂ and CO₂ gases above the dissolution medium without purging into the solution. Drug release from enteric coated predinisolone microparticles (216.9 µm), pellets (1.25 mm) and commercially available tablets was determined in 0.1 M HCl and subsequently in pH 6.8 phosphate buffer or pH 6.2-6.8 bicarbonate buffers generated by titration of the acidic medium in situ using USP II apparatus. Supplying N₂ at 3-4 bar and CO₂ at 0.1 bar were able to increase the pH of the bicarbonate buffer from pH 6.2 to 6.8 within 45 min and subsequently stabilise the medium pH at 6.8 ± 0.05 pH units. Enteric coated microparticles showed much faster drug release in the physiological bicarbonate buffers than tablets and pellets. The novel bicarbonate-based dissolution system moves forward the application of the physiological bicarbonate buffers for testing pharmaceutical products to meet compendial requirements.

A dual pH and microbiota-triggered coating (Phloral™) for fail-safe colonic drug release

Enteric-coated dosage forms are widely used for targeting the ileo-colonic region of the gastrointestinal (GI) tract. However, accurate targeting is challenging due to intra- and inter-individual variability in intestinal paramaters such as fluid pH and transit times, which occasionally lead to enteric coating failure. As such, a unique coating technology (Phloral™), which combines two independent release mechanisms - a pH trigger (Eudragit® S; dissolving at pH 7) and a microbiota-trigger (resistant starch), has been developed, offering a fail-safe approach to colonic targeting. Here, we demonstrate that the inclusion of resistant starch in the coating does not affect the pH mediated drug release mechanism or the robustness of the coating in the upper GI tract. In order to make the resistant starch more digestible by bacterial enzymes, heat treatment of the starch in the presence of butanol was required to allow disruption of the crystalline structure of the starch granules. Under challenging conditions of limited exposure to high pH in the distal small intestine fluid and rapid transit through the colon, often observed in patients with inflammatory bowel disease, particularly in ulcerative colitis, this dual-trigger pH-enzymatic coating offers a revolutionary approach for site specific drug delivery to the large intestine.

OPTICORE™, an innovative and accurate colonic targeting technology

Inflammatory bowel disease (IBD) is a debilitating condition, estimated to affect 7 million people worldwide. Current IBD treatment strategies are substandard, relying on colonic targeting using the pH gradient along the gastrointestinal tract. Here, we describe an innovative colonic targeting concept, OPTICORE™ coating technology. OPTICORE™ combines two release triggers (pH and enzyme: Phloral™) in the outer layer, with an inner layer promoting a release acceleration mechanism (Duocoat™). The technology comprises an inner layer of partially neutralized enteric polymer with a buffer agent and an outer layer of a mixture of Eudragit® S and resistant starch. 5-aminosalicylic acid (5-ASA) tablets were coated with different inner layers, where the type of polymer, buffer salt concentration and pH of neutralization, were investigated for drug release acceleration. Buffer capacity of polymethacrylate neutralized polymer significantly contributes to the buffer capacity of the inner layer formulation, while buffer salt concentration is a major contributor to dispersion buffer capacity in the case of hypromellose enteric polymer formulations. An interplay between buffer capacity, pH and ionic strength contributes to an accelerated drug release. Resistant starch does not impact the enteric properties but allows for drug release mediated by colonic bacterial enzymes, ensuring complete drug release. Therefore, OPTICORE™ technology is designed to offer significant advantages over standard enteric coatings, particularly allowing for more accurate colonic drug delivery in ulcerative colitis patients.

Nanoparticle-Mediated Drug Delivery Systems For The Treatment Of IBD: Current Perspectives

Inflammatory bowel disease (IBD), which mainly consists of Crohn’s disease and ulcerative colitis, is a chronic and relapsing inflammatory condition of the gastrointestinal tract. The traditional treatment strategies relied on frequent administration of high dosages of medications, including antibiotics, non-steroidal anti-inflammatory drugs, biologics, and immunomodulators, with the goal of reducing inflammation. Some of these medications were effective in alleviating the early-stage inflammatory symptoms, but their long-term efficacies were compromised by the accumulation of toxicities. Recently, nanoparticle (NP)-based drugs have been widely studied for their potential to solve such problems. Various mechanisms/strategies, including size-, charge-, pH-, pressure-, degradation-, ligand-receptor-, and microbiome- dependent drug delivery systems, have been exploited in preclinical studies. A certain number of NP delivery systems have sought to target drugs to the inflamed intestine. Although several NP-based drugs have entered clinical trials for the treatment of IBD, most have failed due to premature drug release, weak targeting ability, and the high immune toxicity of some of the synthetic nanomaterials that have been used to fabricate the NPs. Therefore, there is still a need for rationally designed and stable NP drug delivery system that can specifically target drugs to the disease site, prolong the drug’s residence time, and minimize systemic side effects. This review will analyze the current state of the art in NP-mediated drug delivery for IBD treatment. We will focus on topics such as deliverable targets (at the tissue or cellular level) for treating inflammation; the target-homing NP materials that can interact with such targets; and the major administration routes for treating IBD. These discussions will integrate notable trends in the research and development of IBD medications, including multi-responsive NP-mediated delivery and naturally-derived targeting NPs. Finally, current challenges and future directions will be presented in the hopes of advancing the study of NP-mediated strategies for treating IBD.

3D Printing of a Multi-Layered Polypill Containing Six Drugs Using a Novel Stereolithographic Method

Three-dimensional printing (3DP) has demonstrated great potential for multi-material fabrication because of its capability for printing bespoke and spatially separated material conformations. Such a concept could revolutionise the pharmaceutical industry, enabling the production of personalised, multi-layered drug products on demand. Here, we developed a novel stereolithographic (SLA) 3D printing method that, for the first time, can be used to fabricate multi-layer constructs (polypills) with variable drug content and/or shape. Using this technique, six drugs, including paracetamol, caffeine, naproxen, chloramphenicol, prednisolone and aspirin, were printed with different geometries and material compositions. Drug distribution was visualised using Raman microscopy, which showed that whilst separate layers were successfully printed, several of the drugs diffused across the layers depending on their amorphous or crystalline phase. The printed constructs demonstrated excellent physical properties and the different material inclusions enabled distinct drug release profiles of the six actives within dissolution tests. For the first time, this paper demonstrates the feasibility of SLA printing as an innovative platform for multi-drug therapy production, facilitating a new era of personalised polypills.

Simulated, biorelevant, clinically relevant or physiologically relevant dissolution media: The hidden role of bicarbonate buffer

In-vitro dissolution testing of pharmaceutical formulations has been used as a quality control test for many years. At early drug product development, in vivo predictive dissolution testing can be used for guidance in the rational selection of candidate formulations that best fit the desired in vivo dissolution characteristics. At present, the most widely applied dissolution media are phosphate-based buffers and, in some cases, the result of dissolution tests performed in such media have demonstrated reasonable/acceptable IVIVCs. However, the presence of phosphates in human GI luminal fluids is insignificant, which makes the use of such media poorly representative of the in vivo environment. The gastrointestinal lumen has long been shown to be buffered by bicarbonate. Hence, much interest in the development of suitable biorelevant in vitro dissolution media based on bicarbonate buffer systems has evolved. However, there are inherent difficulties associated with these buffers, such as maintaining the pH throughout the dissolution test, as CO₂ tends to leave the system. Various mathematical models have been proposed to analyze bicarbonate buffers and they are discussed in this review. Approaches such as using simpler buffer systems instead of bicarbonate have been proposed as surrogate buffers to produce an equivalent buffer effect on drug dissolution on a case-by-case basis. There are many drawbacks related to simpler buffers systems including their poor in vivo predictability. Considerable discrepancies between phosphate and bicarbonate buffer dissolution results have been reported for certain dosage forms, e.g. enteric coated formulations. The role and need of bicarbonate-based buffers in quality control testing requires scientific analysis. This review also encompasses on the use of bicarbonate-based buffers as a potentially in vivo predictive dissolution medium for enteric coated dosage forms.

Mass Transport Analysis of Bicarbonate Buffer: Effect of the CO2-H2CO3 Hydration-Dehydration Kinetics in the Fluid Boundary Layer and the Apparent Effective p Ka Controlling Dissolution of Acids and Bases

The main buffering system influencing ionizable drug dissolution in the human intestinal fluid is bicarbonate-based; however, it is rarely used in routine pharmaceutical practice due to the volatility of dissolved CO₂. The typical pharmaceutical buffers used fail to capture the unique aspects of the hydration-dehydration kinetics of the bicarbonate-CO₂ system. In particular, CO₂ is involved in a reversible interconversion with carbonic acid (H₂CO₃), which is the actual conjugate acid of the system, as follows CO₂ + H₂O ⇌ H₂CO₃. In contrast to ionization reactions, this interconversion does not equilibrate very rapidly compared to the diffusional processes through a typical fluid diffusion boundary layer at a solid-liquid interface. In this report, a mathematical mass transport analysis was developed for ionizable drug dissolution in bicarbonate using the rules of conservation of mass and electric charge in addition to accounting for the diffusional times and reaction rate constants of the CO₂-H₂CO₃ interconversion. This model, which includes both the hydration reaction rate and dehydration reaction rate, we called the "reversible non-equilibrium" (RNE) model. The predictions made by this RNE approach for ionizable drug dissolution rates were compared to the experimental data generated by an intrinsic dissolution method for three ionizable drugs, indomethacin, ibuprofen, and haloperidol. The results demonstrate the superiority of predictions for the RNE approach compared to the predictions of a model assuming equilibrium between CO₂ and H₂CO₃, as well as models ignoring reactions. The analysis also shows that bicarbonate buffer can be viewed as having an effective p K_a in the boundary layer that is different from that in bulk and is hydrodynamics-dependent.

3D Printed Pellets (Miniprintlets): A Novel, Multi-Drug, Controlled Release Platform Technology

Selective laser sintering (SLS) is a single-step three-dimensional printing (3DP) process that can be leveraged to engineer a wide array of drug delivery systems. The aim of this work was to utilise SLS 3DP, for the first time, to produce small oral dosage forms with modified release properties. As such, paracetamol-loaded 3D printed multiparticulates, termed miniprintlets, were fabricated in 1 mm and 2 mm diameters. Despite their large surface area compared with a conventional monolithic tablet, the ethyl cellulose-based miniprintlets exhibited prolonged drug release patterns. The possibility of producing miniprintlets combining two drugs, namely paracetamol and ibuprofen, was also investigated. By varying the polymer, the dual miniprintlets were programmed to achieve customised drug release patterns, whereby one drug was released immediately from a Kollicoat Instant Release matrix, whilst the effect of the second drug was sustained over an extended time span using ethyl cellulose. Herein, this work has highlighted the versatility of SLS 3DP to fabricate small and intricate formulations containing multiple active pharmaceutical ingredients with distinct release properties.

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

Enteric coatings have shown in vivo dissolution rates that are poorly predicted by traditional in vitro tests, with the in vivo dissolution being considerably slower than in vitro. To provide a more mechanistic understanding of this, the dependence of the release properties of various enteric-coated (EC) products on bulk pH and bicarbonate molarity was investigated. It was found that, at presumably in vivo-relevant values, the bicarbonate molarity is a more significant determinant of the dissolution profile than the bulk pH. The findings also indicate that this steep relationship between the dissolution of enteric coatings and bicarbonate molarity limits those coatings' performance in vivo. This is attributed to the relatively low bicarbonate molarities in human intestinal fluids. Further, the hydration and dehydrations kinetics of carbonic acid and carbon dioxide are not sufficiently rapid to reach equilibrium in the diffusion layer surrounding a dissolving ionizable solid. This results in the effective pKa of bicarbonate in the diffusion layer being lower than that determined potentiometrically at equilibrium in the bulk surrounding fluid. These results demonstrate the importance of thoroughly investigating the intestinal bicarbonate concentrations and using bicarbonate buffers or properly designed surrogates (if possible) when evaluating enteric drug products during product development and quality control.

A review on 5-aminosalicylic acid colon-targeted oral drug delivery systems

Site-specific colon drug delivery is a practical approach for the treatment of local diseases of the colon with several advantages such as rapid onset of action and reduction of the dosage of the drug as well as minimization of harmful side effects. 5-aminosalicylic acid (5-ASA) is a drug of choice in the treatment of inflammatory bowel disease and colitis. For the efficient delivery of this drug, it is vital to prevent 5-ASA release in the upper part of the gastrointestinal tract and to promote its release in the proximal colon. Different approaches including chemical manipulation of drug molecule for production of prodrugs or modification of drug delivery systems using pH-dependent, time-dependent and/or bacterially biodegradable materials have been tried to optimize 5-ASA delivery to the colon. In the current review, the different strategies utilized in the design and development of an oral colonic delivery dosage form of 5-ASA are presented and discussed.

Influence of Geometry on the Drug Release Profiles of Stereolithographic (SLA) 3D-Printed Tablets

Additive manufacturing (3D printing) permits the fabrication of tablets in shapes unattainable by powder compaction, and so the effects of geometry on drug release behavior is easily assessed. Here, tablets (printlets) comprising of paracetamol dispersed in polyethylene glycol were printed using stereolithographic 3D printing. A number of geometric shapes were produced (cube, disc, pyramid, sphere and torus) with either constant surface area (SA) or constant surface area/volume ratio (SA/V). Dissolution testing showed that printlets with constant SA/V ratio released drug at the same rate, while those with constant SA released drug at different rates. A series of tori with increasing SA/V ratio (from 0.5 to 2.4) were printed, and it was found that dissolution rate increased as the SA/V ratio increased. The data show that printlets can be fabricated in multiple shapes and that dissolution performance can be maintained if the SA/V ratio is constant or that dissolution performance of printlets can be fine-tuned by varying SA/V ratio. The results suggest that 3D printing is therefore a suitable manufacturing method for personalized dosage forms.

Local delivery of macromolecules to treat diseases associated with the colon

Current treatments for intestinal diseases including inflammatory bowel diseases, irritable bowel syndrome, and colonic bacterial infections are typically small molecule oral dosage forms designed for systemic delivery. The intestinal permeability hurdle to achieve systemic delivery from oral formulations of macromolecules is challenging, but this drawback can be advantageous if an intestinal region is associated with the disease. There are some promising formulation approaches to release peptides, proteins, antibodies, antisense oligonucleotides, RNA, and probiotics in the colon to enable local delivery and efficacy. We briefly review colonic physiology in relation to the main colon-associated diseases (inflammatory bowel disease, irritable bowel syndrome, infection, and colorectal cancer), along with the impact of colon physiology on dosage form design of macromolecules. We then assess formulation strategies designed to achieve colonic delivery of small molecules and concluded that they can also be applied some extent to macromolecules. We describe examples of formulation strategies in preclinical research aimed at colonic delivery of macromolecules to achieve high local concentration in the lumen, epithelial-, or sub-epithelial tissue, depending on the target, but with the benefit of reduced systemic exposure and toxicity. Finally, the industrial challenges in developing macromolecule formulations for colon-associated diseases are presented, along with a framework for selecting appropriate delivery technologies.

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

The bicarbonate buffer capacity is usually considered in a phase-homogeneous system, at equilibrium, with no CO₂ transfer between the liquid buffer phase and another phase. However, typically, an in vitro bicarbonate buffer-based system is a phase-heterogeneous system, as it entails continuously sparging (bubbling) the dissolution medium with CO₂ in a gas mixture, at constant ratio, to maintain a constant partial pressure of CO_2 (g) and CO_2(aq) molarity at a prescribed value, with CO₂ diffusing freely between the gas and the aqueous phases. The human gastrointestinal tract is also a phase-heterogeneous system, with CO₂ diffusing across the mucosal membrane into the mesenteric arterial blood, which serves as a sink for CO₂ from the intestinal lumen. In this report, a mass transport analysis of the apparent buffer capacity of a phase-heterogeneous bicarbonate-CO₂ system is developed. It is shown that, most significantly, a phase-heterogeneous bicarbonate-CO₂ system can have a much higher buffer capacity than a phase-homogeneous system such that the buffer capacity is dependent on the bicarbonate concentration. It is double that of a phase-homogeneous system at the pH = p K_a for a monoprotic buffer at the same concentration. This buffer capacity enhancement increases hyperbolically with pH above the p K_a, thus providing a much stronger buffering to keep the pH in the physiologically neutral range. The buffer capacity will be dependent on the bicarbonate molarity (which in vivo will depend on the bicarbonate secretion rate) and not the pH of the luminal fluid. Further, there is no conjugate acid accumulation as a result of bicarbonate neutralization, since the resulting carbonic acid (H₂CO₃) rapidly dehydrates producing CO₂ and H₂O. The mass transport analysis developed in this report is further supported by in vitro experimental results. This enhanced bicarbonate buffer capacity in a phase-heterogeneous system is of physiological significance as well as significant for the dissolution and absorption of ionizable drugs.

The Influence of Simulated Fasted Gastrointestinal pH Profiles on Diclofenac Sodium Dissolution in a Glass-Bead Flow-Through System

High inter- and intra-individual variability in the pH of fluids in the human gastrointestinal (GI) tract has been described in the literature. The aim of this study was to assess the influence of physiological variability in fasted pH profiles of media along the GI tract on diclofenac sodium (DF-Na) dissolution from matrix tablets. Four individual in vivo fasted pH profiles were selected from the literature that differed in pH values and transit times from the stomach to the proximal colon. Using a glass-bead device flow-through dissolution system, these pH profiles were simulated in vitro using a specific media sequence and considering simulated intestinal buffer capacities corresponding to in vivo literature data. Dissolution experiments were then performed in the same system with media sequence following individual pH profiles. In dissolution experiments, where influences of simulated gastric emptying time (GET), gastric pH value, small intestinal transit time, and colonic pH were studied; high influence of gastric pH value and GET on DF-Na dissolution was observed. The effect of variability in pH profiles in the range of individual in vivo data on DF-Na dissolution was also clearly observed in experiments, where dissolution studies were performed following three simulated in vivo individual pH profiles. The differences in DF-Na release between three individual pH profiles were substantial; they also reflected in simulated plasma concentration profiles and can be attributed to pH dependent diclofenac solubility.

Layered gadolinium hydroxides for simultaneous drug delivery and imaging

Drug intercalates of a layered gadolinium hydroxide have been prepared, and their drug delivery and imaging properties explored.