Oral colon-specific drug delivery: a review

Delivery of Probiotic-Loaded Microcapsules in the Gastrointestinal Tract: A Review

Probiotics are live microorganisms that inhabit the gastrointestinal tract and confer health benefits to consumers. However, a sufficient number of viable probiotic cells must be delivered to the specific site of interest in the gastrointestinal tract to exert these benefits. Enhanced viability and tolerance to sublethal gastrointestinal stress can be achieved using appropriate coating materials and food matrices for orally consumed probiotics. The release mechanism and interaction of probiotic microcapsules with the gastrointestinal tract have been minimally explored in the literature to date. To the authors' knowledge, no review has been published to discuss the nature of release and the challenges in the targeted delivery of probiotics. This review addresses gastrointestinal-related complications in the formulation of targeted delivery and controlled release of probiotic strains. It investigates the impacts of environmental stresses during the transition stage and delivery to the target region in the gastrointestinal tract. The influence of factors such as pH levels, enzymatic degradation, and redox conditions on the release mechanisms of probiotics is presented. Finally, the available methods to evaluate the efficiency of a probiotic delivery system, including in vitro and in vivo, are reviewed and assessed. The paper concludes with a discussion highlighting the emerging technologies in the field and emphasising key areas in need of future study.

Oral liposomal delivery of an activatable budesonide prodrug reduces colitis in experimental mice

Inflammatory bowel disease (IBD) is one of the most common intestinal disorders, with increasing global incidence and prevalence. Numerous therapeutic drugs are available but require intravenous administration and are associated with high toxicity and insufficient patient compliance. Here, an oral liposome that entraps the activatable corticosteroid anti-inflammatory budesonide was developed for efficacious and safe IBD therapy. The prodrug was produced via the ligation of budesonide with linoleic acid linked by a hydrolytic ester bond, which was further constrained into lipid constituents to form colloidal stable nanoliposomes (termed budsomes). Chemical modification with linoleic acid augmented the compatibility and miscibility of the resulting prodrug in lipid bilayers to provide protection from the harsh environment of the gastrointestinal tract, while liposomal nanoformulation enables preferential accumulation to inflamed vasculature. Hence, when delivered orally, budsomes exhibited high stability with low drug release in the stomach in the presence of ultra-acidic pH but released active budesonide after accumulation in inflamed intestinal tissues. Notably, oral administration of budsomes demonstrated favorable anti-colitis effect with only ∼7% mouse body weight loss, whereas at least ∼16% weight loss was observed in other treatment groups. Overall, budsomes exhibited higher therapeutic efficiency than free budesonide treatment and potently induced remission of acute colitis without any adverse side effects. These data suggest a new and reliable approach for improving the efficacy of budesonide. Our in vivo preclinical data demonstrate the safety and increased efficacy of the budsome platform for IBD treatment, further supporting clinical evaluation of this orally efficacious budesonide therapeutic.

Solidification and oral delivery of biologics to the colon- A review

The oral delivery of biologics such as therapeutic proteins, peptides and oligonucleotides for the treatment of colon related diseases has been the focus of increasing attention over the last years. However, the major disadvantage of these macromolecules is their degradation propensity in liquid state which can lead to the undesirable and complete loss of function. Therefore, to increase the stability of the biologic and reduce their degradation propensity, formulation techniques such as solidification can be performed to obtain a stable solid dosage form for oral administration. Due to their fragility, stress exerted on the biologic during solidification has to be reduced with the incorporation of stabilizing excipients into the formulation. This review focuses on the state-of-the-art solidification techniques required to obtain a solid dosage form for the oral delivery of biologics to the colon and the use of suitable excipients for adequate stabilization upon solidification. The solidifying processes discussed within this review are spray drying, freeze drying, bead coating and also other techniques such as spray freeze drying, electro spraying, vacuum- and supercritical fluid drying. Further, the colon as site of absorption in both healthy and diseased state is critically reviewed and possible oral delivery systems for biologics are discussed.

Eudragit-Coated Sporopollenin Exine Microcapsules (SEMC) of Phoenix dactylifera L. of 5-Fluorouracil for Colon-Specific Drug Delivery

In this study, 5-fluorouracil (5-FU)-loaded pollens of Phoenix dactylifera and their coating with ERS was done and evaluated for the colon-targeted delivery of 5-FU to treat colon cancer. Sporopollenin exine microcapsules (SEMC) from the pollens of Phoenix dactylifera were extracted by the reflux method and 5-FU into SEMC was encapsulated by the vacuum-assisted loading method. 5-FU loaded SEMC was coated with Eudragit^® RS-100 (ERS) by the organic solvent-evaporation technique under vacuum to avoid the discharge of 5-FU in the stomach and small intestine. Morphological and physicochemical characterization of drug-loaded SEMC (coated/uncoated) was performed by scanning electron microscopy (SEM), FTIR, XRD, and DSC. The encapsulation and drug loading were determined by the direct method, and an in vitro release study was performed in simulated gastric and intestinal fluids (SGF/SIF). The colon-specific delivery of 5-FU from the SEMC was assessed in terms of pharmacokinetics and gastrointestinal tract distribution after oral administration in rats. The successful encapsulation and loading of 5-FU into SEMC by a vacuum-assisted loading technique and its coating with ERS by a solvent-evaporation technique were achieved. SEM images of uncoated SEMC have shown porous structures, and coating with ERS reserved their morphology with a smooth surface and discrete microstructures and the 5% w/v ERS acetone solution. ERS-coated SEMC sustained the release of 5-FU until 24 h in SIF, while it was up to 12 h only from uncoated SEMC. The maximum plasma concentration (Cmax) of 5-FU from uncoated SEMC was 102.82 μg/mL after 1 h, indicating a rapid release of 5-FU in the upper gastrointestinal tract. This concentration decreased quickly with a half-life of 4 h, AUC0-t was 264.1 μg/mL.h, and MRT0-inf was 5.2 h. The Cmax of 5-FU from ERS-coated SEMC was 19.47 μg/mL at 16 h. The Cmax of 5-FU in small intestines was 406.2 μg/g at 1 h from uncoated SEMC and 1271.5 μg/g at 12 h from coated SEMC. Conclusively, a 249.9-fold higher relative bioavailability of 5-FU was achieved with the ERS-coated SEMC in colon tissues than that from uncoated SEMC.

Just how prevalent are peptide therapeutic products? A critical review

How prevalent are peptide therapeutic products? How innovative are the formulations used to deliver peptides? This review provides a critical analysis of therapeutic peptide products and the formulations approved by the United States Food and Drug administration (FDA), the European Medicines Agency (EMA), and the Japanese Pharmaceuticals and Medical Devices Agency (PMDA). This review also provides an in-depth analysis of dosage forms and administration routes for delivering peptide therapeutics, including injectables, oral dosage forms, and other routes of administration. We discuss the function of excipients in parenteral formulations in detail, since most peptide therapeutics are parenterally administered. We provide case studies of alternate delivery routes and dosage forms. Based on our analysis, therapeutic peptides administered as injectables remain the most commonly used dosage forms, particularly in the form of subcutaneous, intravenous, or intramuscular injections. In addition, therapeutic peptides are formulated to achieve prolonged release, often through the use of polymer carriers. The limited number of oral therapeutic peptide products and their poor absorption and subsequent low bioavailability indicate a need for new technologies to broaden the formulation design space. Therapeutic peptide products may also be delivered through other administration routes, including intranasal, implant, and sublingual routes. Therefore, an in-depth understanding of how therapeutic peptides are now formulated and administered is essential to improve peptide delivery, improve patient compliance, and reduce the healthcare burden for these crucial therapeutic agents.

Development and Evaluation of Controlled and Simultaneous Release of Compound Danshen Based on a Novel Colon-Specific Osmotic Pump Capsule

In the study, we developed a novel oral dosage form of Compound Danshen to resolve the problems of low bioavailability, disequilibrium in drug release, and stomach degradation of active components of Compound Danshen in conventional formulas. A colon-specific osmotic pump capsule (COPC) of Compound Danshen was prepared using a semipermeable shell with the core components. Using a single-factor method, we obtained the optimal formulation that consisted of Salvia miltiorrhiza extract, Panax notoginseng extract, Borneol, sodium chloride, polyethylene oxide wsr-N10, hydroxypropyl-β-cyclodextrin, and ludipress. Moreover, in vitro dissolution test showed simultaneous releases of active ingredients from Compound Danshen COPC over 12 h at pH 7.8, displaying zero-order release characteristics. The impetus of drug release mainly depended on the difference in osmotic pressure across the capsule shell. Next, scanning electron microscopy showed morphological changes in the capsule shell during the dissolution test. More importantly, pharmacokinetic study in beagle dogs indicated that relative bioavailability was 330.58% and retention time was greatly prolonged in Compound Danshen COPC, compared with those in marketed Compound Danshen tablet products. Finally, in vivo imaging studies in beagle dogs showed that COPC was stable in gastrointestinal tract and the drug was specifically released in the colon region. A colon-specific osmotic pump capsule (COPC) of Compound Danshen was developed and optimized to achieve simultaneous zero-order release of multiple active components of Compound Danshen in the colon. More importantly, the COPC have proved to improve the bioavailability and prolong the retention time of Compound Danshen, compared with those in a marketed product.

A review on the strategies for oral delivery of proteins and peptides and their clinical perspectives

In the modern world, a number of therapeutic proteins such as vaccines, antigens, and hormones are being developed utilizing different sophisticated biotechnological techniques like recombinant DNA technology and protein purification. However, the major glitches in the optimal utilization of therapeutic proteins and peptides by the oral route are their extensive hepatic first-pass metabolism, degradation in the gastrointestinal tract (presence of enzymes and pH-dependent factors), large molecular size and poor permeation. These problems can be overcome by adopting techniques such as chemical transformation of protein structures, enzyme inhibitors, mucoadhesive polymers and permeation enhancers. Being invasive, parenteral route is inconvenient for the administration of protein and peptides, several research endeavors have been undertaken to formulate a better delivery system for proteins and peptides with major emphasis on non-invasive routes such as oral, transdermal, vaginal, rectal, pulmonary and intrauterine. This review article emphasizes on the recent advancements made in the delivery of protein and peptides by a non-invasive (peroral) route into the body.

Photoresponsive amphiphilic azobenzene–PEG self-assembles to form supramolecular nanostructures for drug delivery applications

Self-assembled smart nanostructures have emerged as controlled and site-specific systems for drug delivery applications.

Microbial fuel cell as power supply for implantable medical devices: a novel configuration design for simulating colonic environment

This study focused on providing power for implantable medical devices (IMDs) using a microbial fuel cell (MFC) implanted in human transverse colon. Considering the condition of colonic environment, a continuous-flow single-chamber MFC without membrane was set up. The performance of the MFC was investigated. The power output of 1.6 mW under the steady state was not rich enough for some high energy-consuming IMDs. Moreover, the parameters of the simulated colonic environment, such as pH and ORP value, varied along with the time. Hence, a new MFC configuration was developed. In this novel model, pH transducers were placed in cathodic and anodic areas, so as to regulate the reactor operation timely via external intervention. And two ORP transducers were inserted next to the pH transducers, for monitoring and adjusting the MFC operation efficiently. Besides, colonic haustra were designed in order to increase the difference between cathodic and anodic areas.

Synthesis and characterization of ionic liquid functionalized polymers for drug delivery of an anti-inflammatory drug

Polymeric forms of ionic liquids have many potential applications because of their ionic nature. Two ionic liquid monomers, 1-(4-vinylbenzyl)-3-methyl imidazolium hexafluorophosphate (VMIH) and 1-(4-vinylbenzyl)-4-(dimethylamino)-pyridinium hexafluorophosphate (VDPH), were synthesized through the quaternization of N-methylimidazole and 4-(dimethylamino) pyridine with 4-vinylbenzylchloride, respectively, and a subsequent anion exchange reaction with potassium hexafluorophosphate. The homopolymers of VMIH, VDPH, and its copolymers with methyl styrene (in various mole ratios) were synthesized by free radical polymerizations at 70 °C using α,α'-azobis(isobutyronitrile) as an initiator. Anionic drug molecule, naproxen (an anti-inflammatory drug), was effectively loaded into these positive charges polymers (PCP) and remained inside of the PCP under acidic environment (pH 2-6.5). The amount of loading of drug was increased with increasing positive charge densities resulting from the increasing number of ionic liquids groups. PCP as a controllable release of anionic drug molecules can be used as an oral delivery drug systems targeting at intestine. This drug can be remained trapped in the polymers when passing through the acidic and neutral environment and be released in intestine, where the environmental pH is close to basic.

In-vitro evaluation of khaya and albizia gums as compression coatings for drug targeting to the colon

Khaya and albizia gums were evaluated as compression coatings for target drug delivery to the colon using indometacin (a water insoluble drug) and paracetamol (a water soluble drug) as model drugs. The core tablets were compression-coated with 300 and 400mg of 100% khaya gum, 100% albizia gum and a mixture of khaya and albizia gum (1:1). Drug release studies were carried out in 0.1M HCI (pH 1.2) for 2h, Sorensen's buffer (pH 7.4) for 3 h and then in phosphate-buffered saline (pH 6.8) or in simulated colonic fluid for the rest of the experiment to mimic the physiological conditions from the mouth to colon. The results indicated that khaya and albizia gums were capable of protecting the core tablet in the physiological environment of the stomach and small intestine, with albizia gum showing greater ability than khaya gum. The release from tablets coated with the mixture of khaya and albizia gums was midway between the two individual gums, indicating that there was no interaction between the gums. Studies carried out using rat caecal matter in phosphate-buffered saline at pH 6.8 (simulated colonic fluid) showed that the gums were susceptible to degradation by the colonic bacterial enzymes, leading to release of the drug. The results demonstrate that khaya gum and albizia gum have potential for drug targeting to the colon.

In-vitroandIn-vivoEvaluation of Mesalazine–Guar Gum Matrix Tablets for Colonic Drug Delivery

The aim of this study was to develop colon-specific delivery systems for mesalazine (5-ASA) using guar gum as a carrier. A colon specific matrix tablet of mesalazine with guar gum was evaluated by in vitro and in vivo X-ray studies in humans. Two different types of guar gum were used in the experiments. Tablets were prepared by the slugging method. The physical properties of tablets were tested and in vitro release studies were performed by a flow-through cell apparatus with and without galactomannanase enzyme. The type and the amount of guar gum affected the in vitro release of drug from the matrix tablets. High viscosity guar gum, in the form of a matrix tablet was capable of protecting the drug from being released in the upper region of gastrointestinal (GI) system, i.e. stomach and small intestine. X-ray imaging technique was used to monitor the tablets throughout the GI system on 8 healthy volunteers. Barium sulphate was used as a marker in the tablets for in vivo studies. These results showed that, the matrix tablets reached the colon; not being subjected to disintegration in the upper region of the GI system in all the subjects.

Cross-linked guar gum microspheres: a viable approach for improved delivery of anticancer drugs for the treatment of colorectal cancer

In the present work, guar gum microspheres containing methotrexate (MTX) were prepared and characterized for local release of drug in the colon, which is a prerequisite for the effective treatment of colorectal cancer. Guar gum microspheres were prepared by the emulsification method using glutaraldehyde as a cross-linking agent. Surface morphological characteristics were investigated using scanning electron microscopy. Particle size, shape, and surface morphology were significantly affected by guar gum concentration, glutaraldehyde concentration, emulsifier concentration (Span 80), stirring rate, stirring time, and operating temperature. MTX-loaded microspheres demonstrated high entrapment efficiency (75.7%). The in vitro drug release was investigated using a US Pharmacopeia paddle type (type II) dissolution rate test apparatus in different media (phosphate-buffered saline [PBS], gastrointestinal fluid of different pH, and rat cecal content release medium), which was found to be affected by a change to the guar gum concentration and glutaraldehyde concentration. The drug release in PBS (pH 7.4) and simulated gastric fluids followed a similar pattern and had a similar release rate, while a significant increase in percent cumulative drug release (91.0%) was observed in the medium containing rat cecal content. In in vivo studies, guar gum microspheres delivered most of their drug load (79.0%) to the colon, whereas plain drug suspensions could deliver only 23% of their total dose to the target site. Guar gum microspheres showed adequate potential in achieving local release of drug in in vitro release studies, and this finding was further endorsed with in vivo studies.

Time-controlled oral delivery systems for colon targeting

In recent years, many research efforts have been spent in the achievement of selective delivery of drugs into the colon following oral administration. Indeed, colonic release is regarded as a beneficial approach to the pharmacological treatment or prevention of widespread large bowel pathologies, such as inflammatory bowel disease and adenocarcinoma. In addition, it is extensively explored as a potential means of enhancing the oral bioavailability of peptides, proteins and other biotechnological molecules, which are known to be less prone to enzymatic degradation in the large, rather than in the small, intestine. Based on these premises, several formulation strategies have been attempted in pursuit of colonic release, chiefly including microflora-, pH-, pressure- and time-dependent delivery technologies. In particular, this review is focused on the main design features and release performances of time-controlled devices, which rely on the relative constancy that is observed in the small intestinal transit time of dosage forms.

Oral colon-specific drug delivery for bee venom peptide: development of a coated calcium alginate gel beads-entrapped liposome

Colon-specific drug delivery systems (CDDSs) can be used to improve the bioavailability of protein and peptide drugs through the oral route. A novel formulation for oral administration using coated calcium alginate gel beads-entrapped liposome and bee venom peptide as a model drug has been investigated for colon-specific drug delivery in vitro. Drug release studies under conditions mimicking stomach to colon transit have shown that the drug was protected from being released completely in the physiological environment of the stomach and small intestine. The release rate of bee venom from the coated calcium alginate gel beads-entrapped liposome was dependent on the concentration of calcium and sodium alginate, the amount of bee venom in the liposome, as well as the coating. Furthermore, a human gamma-scintigraphy technique was used in vivo to determine drug delivery more precisely. The colonic arrival time of the tablets was found to be 4-5 h. The results clearly demonstrated that the coated calcium alginate gel beads-entrapped liposome is a potential system for colon-specific drug delivery.

Challenges for the oral delivery of macromolecules

The rapid integration of new technologies by the pharmaceutical industry has resulted in numerous breakthroughs in the discovery, development and manufacturing of pharmaceutical products. In particular, the commercial-scale production of high-purity recombinant proteins has resulted in important additions to treatment options for many large therapeutic areas. In addition to proteins, other macromolecules, such as the animal-derived mucopolysaccharide heparins, have also seen dramatic growth as injectable pharmaceutical products. To date, macromolecules have been limited as therapeutics by the fact that they cannot be orally delivered. This article will address the current status and future possibilities of oral macromolecular drug delivery.

Dendrimers conjugates for colonic delivery of 5-aminosalicylic acid

The water-soluble polyamidoamine (PAMAM) dendrimer conjugates for colonic delivery of 5-aminosalicylic acid (5-ASA) were designed. The drug was bound to the dendrimer using two different spacers containing azo-bond, p-aminobenzoic acid (PABA) and p-aminohippuric acid (PAH). Incubation of PAMAM dendrimer conjugates containing PABA and PAH spacers with rat cecal contents at 37 degrees C gradually released 5-ASA with time and the amount of drug released was 45.6 and 57.0% of the dose in 24 h, respectively. The release of the drug from the commercial prodrug, sulfasalazine was significantly faster than both conjugates (80.2% of the dose in 6 h). No 5-ASA was detected from the incubation of dendrimer conjugates with the homogenate of the stomach or phosphate buffer, pH 1.2 and 6.8. Only a small amount of 5-ASA was found after incubation of both conjugates with the homogenate of the small intestine for 12 h. It appears that this PAMAM dendrimer can be developed for use as a carrier for colon-specific drug delivery.

Studies on the development of oral colon targeted drug delivery systems for metronidazole in the treatment of amoebiasis

The aim of the present study is to develop colon targeted drug delivery systems for metronidazole using guar gum as a carrier. Matrix, multilayer and compression coated tablets of metronidazole containing various proportions of guar gum were prepared. All the formulations were evaluated for the hardness, drug content uniformity, and were subjected to in vitro drug release studies. The amount of metronidazole released from tablets at different time intervals was estimated by high performance liquid chromatography method. Matrix tablets and multilayer tablets of metronidazole released 43-52% and 25-44% of the metronidazole, respectively, in the physiological environment of stomach and small intestine depending on the proportion of guar gum used in the formulation. Both the formulations failed to control the drug release within 5 h of the dissolution study in the physiological environment of stomach and small intestine. The compression coated formulations released less than 1% of metronidazole in the physiological environment of stomach and small intestine. When the dissolution study was continued in simulated colonic fluids, the compression coated tablet with 275 mg of guar gum coat released another 61% of metronidazole after degradation by colonic bacteria at the end of 24 h of the dissolution study. The compression coated tablets with 350 and 435 mg of guar gum coat released about 45 and 20% of metronidazole, respectively, in simulated colonic fluids indicating the susceptibility of the guar gum formulations to the rat caecal contents. The results of the study show that compression coated metronidazole tablets with either 275 or 350 mg of guar gum coat is most likely to provide targeting of metronidazole for local action in the colon owing to its minimal release of the drug in the first 5 h. The metronidazole compression coated tablets showed no change either in physical appearance, drug content or in dissolution pattern after storage at 40 degrees C/75% RH for 6 months.

In vitro biodegradation study of acetyl and methyl inulins by Bifidobacteria and inulinase

The purpose of this study was to investigate if acetylated and methylated inulins can be degraded by inulinase from Aspergillus niger and by Bifidobacteria, in order to determine their potential in colonic drug delivery. Methyl and acetyl inulins were synthesized by the reaction of inulin (Raftiline HP) with methyl sulfate and acetic anhydride, respectively. The degree of substitution (DS) and the structure of the reaction products were confirmed by 13C-NMR. Degradation by inulinase was investigated in a citrate buffer (0.05 M, pH 4) or with a mixture of citrate buffer and DMSO at 37 degrees C. Biodegradation by Bifidobacteria was investigated under anaerobic conditions using an in-house prepared broth at 37 degrees C for 2 days. The resulting products were analyzed chromatographically; the formation of short chain fatty acids was followed by measuring the pH of the incubation media. The results obtained suggest that acetylated and methylated inulins are not biodegradable, since no degradation product could be detected after incubation; a decrease in pH was clearly observed in control samples (pure fructose and inulin), but not in the derivatized inulin samples. The results can probably be explained by a change in conformation of inulin due to derivatization.

Gamma scintigraphic studies on guar gum matrix tablets for colonic drug delivery in healthy human volunteers

A novel colon-specific drug delivery system based on a polysaccharide, guar gum, was evaluated by conducting gamma scintigraphic studies using technetium-99m-DTPA as tracer, in six healthy male human volunteers. Scintigraphs taken at regular intervals have shown that some amount of tracer present on the surface of the tablets was released in stomach and small intestine and the bulk of the tracer present in the tablet mass was delivered to the colon. The colonic arrival time of the tablets was found to be 2 to 4 h. On entering the colon, the tablets were found to be degraded in five out of six volunteers thereby releasing a larger amount of the tracer. The study clearly demonstrates that guar gum, in the form of directly compressed matrix tablets, is a potential carrier for colon-specific drug delivery.

In vitro evaluation of guar gum as a carrier for colon-specific drug delivery

A novel tablet formulation for oral administration using guar gum as the carrier and indomethacin as a model drug has been investigated for colon-specific drug delivery using in vitro methods. Drug release studies under conditions mimicking mouth to colon transit have shown that guar gum protects the drug from being released completely in the physiological environment of stomach and small intestine. Studies in pH 6.8 phosphate buffered saline (PBS) containing rat caecal contents have demonstrated the susceptibility of guar gum to the colonic bacterial enzyme action with consequent drug release. The pre-treatment of rats orally with 1 ml of 2% w/v aqueous dispersion of guar gum for 3 days induced enzymes specifically acting on guar gum thereby increasing drug release. A further increase in drug release was observed with rat caecal contents obtained after 7 days of pre-treatment. The presence of 4% w/v of caecal contents obtained after 3 days and 7 days of enzyme induction showed biphasic drug release curves. The results illustrate the usefulness of guar gum as a potential carrier for colon-specific drug delivery. The study also reveals that the use of 4% w/v of rat caecal contents in PBS, obtained after 7 days of enzyme induction provide the best conditions for in vitro evaluation of guar gum.