Improvement in site-specific intestinal absorption of furosemide by Eudragit L100-55

Design and evaluation of oseltamivir phosphate dual-phase extended-release tablets for the treatment of influenza

In this study, once-daily extended-release tablets with dual-phase release of oseltamivir phosphate were developed for the treatment of influenza. The goal was to improve patient adherence and offer more therapeutic choices. The tablets were manufactured using wet granulation, bilayer tablet compression, and enteric membrane-controlled coating processes. Various polymers, such as hydroxypropyl methylcellulose (HPMC K100MCR, K15MCR, K4MCR, K100LV), enteric polymers (HPMC AS-LF, Eudragit L100-55) and membrane-controlled polymers (OPADRY® CA), were used either individually or in combination with other common excipients. The formulations include enteric-coated extended-release tablet (F1), hydrophilic matrix extended-release tablet (F2), semipermeable membrane-controlled release tablet (F3) and a combination extended-release tablet containing both enteric and hydrophilic matrix (F4). The in vitro drug release profile of each formulation was fitted to the first-order model, and the Ritger-Peppas model suggested that Fickian diffusion was the primary mechanism for drug release. Comparative bioequivalence studies with Tamiflu® (oseltamivir phosphate) capsules revealed that formulations F1, F2, and F3 did not achieve bioequivalence. However, under fed conditions, formulation F4 achieved bioequivalence with a relative bioavailability of 95.30% (90% CI, 88.83%-102.15%). This suggests that the formulation F4 tablet could potentially be a new treatment option for patients with influenza.

Surviving process and transit: Controlled freeze drying, storage and enteric coated capsules for targeted delivery of probiotic Lactobacillusacidophilus

Viability loss of probiotics often occur during processing, storage and gastrointestinal transit. In this study, the viability of freeze-dried Lactobacillus acidophilus LA-5® was assessed after controlled freeze drying and storage at 4 °C and 25 °C over six months using glycerol, skim milk and trehalose as protectants. The freeze-dried probiotic was filled into hard gelatin capsules and enteric coated with the co-polymer Eudragit L100-55 using a fluidised bed coater to determine if the freeze-dried probiotic will survive the enteric coating process and remain viable during gastric transit. Empty hard gelatin capsules were also enteric coated by dipping in the co-polymer solution. These were dried, filled with microcrystalline cellulose and tested for their resistance to simulated gastric condition. The results showed that controlled freezing of the probiotic bacteria did not cause significant loss in viability when the cells were cryopreserved in the protectants. Viable cell loss was greater during the drying stage. Relatively better cell survival was recorded when the freeze-dried samples that were cryopreserved with skim milk were stored over six months at 4 °C. Freeze-dried samples that were preserved with trehalose stored better at 25 °C. The results also demonstrated that capsules coated with Eudragit L100-55 did not disintegrate in simulated gastric fluid. However, the capsules disintegrated in a simulated intestinal fluid. The enteric coating process resulted in about 95% recovery of viable cells. The high viable cell recovery after the coating process is likely due to the coating solution and conditions impacting the capsule body and cap rather than the cells directly. The study highlights that enteric coated capsules can offer gastric protection whilst minimizing viability losses associated with the enteric coating process.

Deep eutectic solvents based on sugars for oral applications

Solubility is a critical parameter in drug formulation to achieve the desired therapeutical concentration. Most drugs are weak acids or bases and, therefore, exhibit low solubility and poor oral availability. The main aim of this work is the use of Deep Eutectic Systems (DESs) for improving the solubility of drugs in aqueous medium. In this case, we use DESs formed by choline chloride and sugars (xylitol, fructose, glucose and sorbitol) at different proportions of water. These compounds present low toxicity, and thus can be used in syrups or liquid formulations. Different physicochemical properties, such as density, refractive index, and surface tension, were obtained. In addition, a rheological study of the different systems was carried out. Finally, these DESs were applied to analyse the solubility of the following active principles: caffeine (Class I) and furosemide (Class IV) of the Biopharmaceutics Classification System (BCS). The selection of the drugs attends to different reasons. On one hand, we want to develop a new liquid formulation for model drug furosemide and, on the other hand, the study of caffeine, instead, will be used as a model for comparing purposes. Solubility results show that the systems that best solubilize caffeine are those with the highest water content; however, they do not reach the levels of solubility of pure water. On the other hand, for furosemide, a great increase in solubility was observed, especially for systems formed by xylitol and, fundamentally, in the system with the lowest water content. Obtaining an increase in solubility of up to 4530 times. These systems provide an opportunity to improve the formulation of drugs in the liquid medium of active ingredients that are poorly soluble in an aqueous medium.

3-O-Ethyl-L-Ascorbic Acid Doped Enteric-Coated Gelatin Capsules towards the Advanced Oral Curcumin Delivery for Cancers

Among plant-derived polyphenols, curcumin has been recognized as a therapeutically potent nutrient presenting pleiotropic pharmacological effects on various cancers. However, the poor absorption and bioavailability of curcumin limit the use of this excellent naturally occurring polyphenol. 3-O-ethyl-L-ascorbic acid (EA) doped enteric-coated gelatin capsules were studied in the search for advanced oral curcumin delivery. The EA doped enteric-coated gelatin capsules were successfully created based on a developed inner dual enteric coating technique. When placed in four buffer solutions with different pHs (pH 2.0, 5.0, 6.0, and 7.3), the coated gelatin capsules showed delayed-release profiles of curcumin below pH 6.0. In contrast, both pristine and fabricated gelatin capsules showed similar curcumin release profiles at pH 7.3, which is a common pH observed in the lower gastrointestinal tract, especially intestinal regions. In conclusion, these results demonstrated the potential of the EA doped enteric-coated gelatin capsules in developing advanced oral delivery of curcumin targeting intestinal-specific regions.

The Effects of Bariatric Surgery and Gastrectomy on the Absorption of Drugs, Vitamins, and Mineral Elements

Bariatric surgery, which is an effective treatment for obesity, and gastrectomy, which is the primary treatment method for gastric cancer, alter the anatomy and physiology of the digestive system. Weight loss and changes in the gastrointestinal tract may affect the pharmacokinetic parameters of oral medications. Both bariatric and cancer patients use drugs chronically or temporarily. It is important to know how surgery affects their pharmacokinetics to ensure an effective and safe therapy. The Cochrane, PubMed, and Scopus databases were searched independently by two authors. The search strategy included controlled vocabulary and keywords. Studies show that bariatric surgery and gastrectomy most often reduce the time to maximum plasma concentration (t_max) and decrease the maximum plasma concentration (C_max) in comparison with the values of these parameters measured in healthy volunteers. Vitamin and mineral deficiencies are also observed. The effect depends on the type of surgery and the properties of the drug. It is recommended to use the drugs that have been tested on these groups of patients as it is possible to monitor them.

Factors and dosage formulations affecting the solubility and bioavailability of P-glycoprotein substrate drugs

Introduction: Expression of P-glycoprotein (P-gp) increases toward the distal small intestine, implying that the duodenum is the preferential absorption site for P-gp substrate drugs. Oral bioavailability of poorly soluble P-gp substrate drugs is low and varied but increases with high-fat meals that supply lipoidal components and bile in the duodenum.Areas covered: Absorption properties of P-gp substrate drugs along with factors and oral dosage formulations affecting their solubility and bioavailability were reviewed with PubMed literature searches. An overview is provided from the viewpoint of the 'spring-and-parachute approach' that generates supersaturation of poorly soluble P-gp substrate drugs.Expert opinion: The oral bioavailability of P-gp substrate drugs is difficult to predict because of their low solubility, preferential absorption sites, and overlapping substrate specificities with CYP3A4, along with the scattered intestinal P-gp expression/function. To attain high and steady oral bioavailability of poorly soluble P-gp substrate drugs, physicochemical modification of drugs to improve solubility, or oral dosage formulations that generate long-lasting supersaturation in the duodenum, is preferred. In particular, supersaturable lipid-based drug delivery systems that can increase passive diffusion and/or lymphatic absorption are effective and applicable to many poorly soluble P-gp substrate drugs.

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

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

Utilization of a Single Experimental Design for the Optimization of Furosemide Modified-Release Tablet Formulations

BACKGROUND

The loop diuretic drug furosemide is widely used for the treatment of edema in various conditions, such as pulmonary, cardiac and hepatic edema, as well as cardiac infarction. Furosemide, due to its poor water solubility and low bioavailability after oral administration of conventional dosage form, is categorized as class IV in the biopharmaceutical classification system.

OBJECTIVE

In the case of furosemide, this release profile is responsible for various physiological problems, acute diuresis being the most serious. This adverse effect can be circumvented by the modified release of furosemide from tablet formulations compared to those forms designed for immediate release.

METHODS

In this report, a D-optimal combined experimental design was applied for the development of furosemide containing bilayer and compression coated tablets, aiming at lowering the drug's burst release in the acidic environment of the stomach. A D-optimal combined design was selected in order to include all requirements in one design with many levels for the factors examined. The following responses were selected as the ones reflecting better criteria for the desired drug release: dissolution at 120 min (30-40%), 300 min (60-70%) and 480 min >95%. The new formulations, suggested by the Doptimal combined design, incorporated different grades of Eudragit ® polymers (Eudragit® E100 and Eudragit® L100-55), lactose monohydrate and HPMC K15M. The dissolution profile of furosemide from these systems was probed via in vitro dissolution experiments in buffer solutions simulating the pH of the gastrointestinal tract.

RESULTS

The results indicate that the use of Eudragit® E100 in conjunction with lactose monohydrate led to 21.32-40.85 % drug release, in the gastric medium, in both compression-coated and bilayer tablets. This is lower than the release of the mainstream drug Lasix® (t=120 min, 44.5% drug release), implying longer gastric retention and drug waste minimization.

CONCLUSION

Furosemide's release in the intestinal environment, from compression coated tablets incorporating Eudragit® L100-55 and HPMC K15M in the inner core or one of the two layers of the bilayer tablets, was delayed, compared to Lasix®.

Modified release of furosemide from Eudragits® and poly(ethylene oxide)-based matrices and dry-coated tablets

Modified release of furosemide from tablet formulations is preferred by patients, because of physiological problems, acute diuresis being the most serious, compared to the forms designed for immediate release. With this in view, we aimed at achieving furosemide's longer gastric retention and waste minimization by preparing matrix and compression coated tablets incorporating different grades of Eudragit® and poly(ethylene oxide) (PEO), polyvinylpyrrolidone (PVP) and lactose monohydrate. Dissolution profiles of the new formulations were compared with that of the main stream drug Lasix®, 40 mg tablets. The results indicate that the use of Eudragit® in conjunction with either PVP or lactose monohydrate led to a slower release rate in the intestinal fluids compared to Lasix®. Moreover, furosemide release in the intestinal pH from matrix tablets and compression coated tablets was not noticeably different. Formulations incorporating PEO led to sustained release, in intestinal fluids, which depended on the molecular weight of PEO.

Development and Characterization of Eudragit®-Based Electrospun Nanofibrous Mats and Their Formulation into Nanofiber Tablets for the Modified Release of Furosemide

Furosemide, a chloride channel blocker ordinarily used as a high-ceiling or loop diuretic, is practically insoluble in water and dilute acids. Due to its acidic nature, furosemide is mostly absorbed in the stomach and in the upper small intestine. Efforts have focused on the development of sustained release systems of furosemide in order to improve the effectiveness of the drug, which exhibits poor aqueous solubility and poor permeability. Recently, electrospun nanofibrous drug delivery systems have emerged as promising alternative solid-dosage forms due to their advantages of high porosity, high surface to volume ratio, and high drug-loading efficacy. Herein, a number of nanofibrous mats composed of different types of Eudragit® polymers in various concentrations and combinations loaded with furosemide were designed, successfully electrospun, and characterized using SEM, FTIR, DSC, and TGA analyses. The nanofibrous nonwovens were formulated in nanofiber tablets and the release profile of furosemide from them was evaluated at pH 1.2 and 6.8 and compared to that of physical mixture matrix tablets of analogous composition as well as to that of a commercial formulation. It was found that the release of furosemide was compatible with the gastroretentive and slower intestinal release requirements with a well-defined absorption window, while some nanofiber formulations could act as furosemide carriers in emergency situations where a relatively fast onset of its action is required, as in the case of critically ill post-traumatic patients.

Successful oral delivery of poorly water-soluble drugs both depends on the intraluminal behavior of drugs and of appropriate advanced drug delivery systems

Poorly water-soluble drugs continue to be a problematic, yet important class of pharmaceutical compounds for treatment of a wide range of diseases. Their prevalence in discovery is still high, and their development is usually limited by our lack of a complete understanding of how the complex chemical, physiological and biochemical processes that occur between administration and absorption individually and together impact on bioavailability. This review defines the challenge presented by these drugs, outlines contemporary strategies to solve this challenge, and consequent in silico and in vitro evaluation of the delivery technologies for poorly water-soluble drugs. The next steps and unmet needs are proposed to present a roadmap for future studies for the field to consider enabling progress in delivery of poorly water-soluble compounds.

Low colonic absorption drugs: risks and opportunities in the development of oral extended release products

INTRODUCTION

Currently numerous drugs have been observed with lower colonic absorption than small intestine absorption, which can significantly impact in vivo performance of their oral extended release (ER) products.

AREAS COVERED

We reviewed over 300 publications, patents, book chapters, and commercial reports of drug products from regulatory agencies for low colonic absorption (LCA) drugs and critical findings are discussed. The focuses of this article are (1) current findings on the causes of low colonic absorption to support early assessment of LCA candidates, and (2) current knowledge on successful ER strategies and technical platforms used for LCA drugs in commercial drug products to facilitate oral ER product development.

EXPERT OPINION

Colonic drug absorption is one of the critical considerations in successful development of oral ER products. The root causes of low colonic absorption in many LCA drugs are still unclear. It is recommended to evaluate colonic drug absorption of drug candidate at early stage of oral ER product development. After evaluation, the selection of a formulation platform to develop an oral ER product needs to be carefully considered for LCA drugs. Based on the current commercial oral ER formulation platforms for LCA drugs, compounds are first divided into five types (I-V) and different ER formulation approaches with higher success rate are recommended for each type.

A simple and inexpensive enteric-coated capsule for delivery of acid-labile macromolecules to the small intestine

Understanding the ecology of the gastrointestinal tract and the impact of the contents on the host mucosa is emerging as an important area for defining both wellness and susceptibility to disease. Targeted delivery of drugs to treat specific small intestinal disorders such as small bowel bacterial overgrowth and targeting molecules to interrogate or to deliver vaccines to the remote regions of the small intestine has proven difficult. There is an unmet need for methodologies to release probes/drugs to remote regions of the gastrointestinal tract in furthering our understanding of gut health and pathogenesis. In order to address this concern, we need to know how the regional delivery of a surrogate labeled test compound is handled and in turn, if delivered locally as a liquid or powder, the dynamics of its subsequent handling and metabolism. In the studies we report on in this paper, we chose (13)C sodium acetate ((13)C-acetate), which is a stable isotope probe that once absorbed in the small intestine can be readily measured non-invasively by collection and analysis of (13)CO2 in the breath. This would provide information of gastric emptying rates and an indication of the site of release and absorptive capacity. In a series of in vitro and in vivo pig experiments, we assessed the enteric-protective properties of a commercially available polymer EUDRAGIT(®) L100-55 on gelatin capsules and also on DRcaps(®). Test results demonstrated that DRcaps(®) coated with EUDRAGIT(®) L100-55 possessed enhanced enteric-protective properties, particularly in vivo. These studies add to the body of knowledge regarding gastric emptying in pigs and also begin the process of gathering specifications for the design of a simple and cost-effective enteric-coated capsule for delivery of acid-labile macromolecules to the small intestine.

Colloidal carriers for extended absorption window of furosemide

Objectives

The aim was to investigate the potential of self-microemulsifying drug delivery systems (SMEDDS) and niosomes as carriers for widening the gastrointestinal absorption window of furosemide (model acidic drug).

Methods

The drug was incorporated in SMEDDS and was encapsulated into niosomes. The intestinal absorption was monitored at two anatomical sites (duodenum and jejuno-ileum). This employed in situ rabbit intestinal perfusion technique.

Key findings

Perfusion of drug solution (control) revealed poor intestinal permeability with per cent fraction absorbed (%Fa) from the duodenum and jejuno-ileum being 1.3 and 0.6 % per cm, respectively. Formulation of furosemide as SMEDDS increased the %Fa from the duodenum and jejuno-ileum to reach 1.7 and 1 % per cm, respectively. Niosomal encapsulation increased the %Fa from duodenum and jejuno-ileum to record 1.9 and 1.2 % per cm, respectively. The increase in the %Fa was also revealed as a reduction in the length required for 95 % absorption of the drug which was reduced from 557.2 to 245.8 cm and to 279.8 cm after delivery as niosomes or SMEDDS, respectively, in case of jejuno-ileum. The same trend was recorded with the duodenum.

Conclusion

The recorded results highlighted the potential for SMEDDS and niosomes for widening the absorption window of acidic drugs after oral administration.

Electrospun polyurethane/Eudragit ® L100-55 composite mats for the pH dependent release of paclitaxel on duodenal stent cover application

A nanofiber composite mat of PU and Eudragit(®) L100-55 was created using electrospinning process. The pH dependent release of paclitaxel was successfully done with the use of PU/EL100-55 nanocomposite mats as the controlling platform. The morphology of the nanofiber composites was surveyed using FESEM and ratios of the polymers affects the diameter of the nanofiber. Characterization of the nanofiber composite mat was done using FTIR, DSC-TGA method. The release rate of paclitaxel was determined and analyzed by in vitro drug release method. In order to mimic the condition of a human duodenum, the fibers were submersed on PBS of different pH levels (4.0, 6.0,) respectively, and then analyzed using high performance liquid chromatography (HPLC). Composite mats submersed in PBS with pH 4.0 showed lesser release profile compared to mats submersed in PBS with pH of 6.0. The composite mat has adequate mechanical properties and in vitro cell biocompatibility indicating that the material can be used for drug eluting stent cover application.

Diuretic bioactivity optimization of furosemide in rats

Furosemide is a loop diuretic widely used by patients with congestive heart failure (CHF) to rid excess body water, reducing blood pressure, and mobilizing edemas. However, due to the narrow window of furosemide absorption, occurring only in the proximal gastrointestinal tract, only immediate release oral formulations are clinically available. Comparisons of bolus and continuous administration of furosemide in intravenous settings demonstrate that continuous administration at lower concentrations produced greater diuretic efficiency and reduced subsequent hospitalization rates in patients experiencing severe CHF. We report a systematic investigation of the diuretic bioactivity profiles of phase inversion micronized furosemide and furosemide co-precipitated with Eudragit L100, as well as their blends with stock furosemide, targeted at reducing the rapid spike in diuresis associated with immediate release formulations while maintaining cumulative urine output. Of the formulations tested, an equal parts blend of micronized furosemide and stock furosemide demonstrated optimal diuretic bioactivity profiles in a rat model.

Diverse approaches for the enhancement of oral drug bioavailability

In conscious and co-operating patients, oral drug delivery remains the preferable route of drug administration. However, not all drugs possess the desirable physicochemical and pharmacokinetic properties which favor oral administration mainly due to poor bioavailability. This has in some cases led to the choice of other routes of administration, which may compromise the convenience and increase the risk of non-compliance. Poor bioavailability has necessitated the administration of higher than normally required oral doses which often leads to economic wastages, risk of toxicity, erratic and unpredictable responses. The challenge over the years has been to design techniques that will allow oral administration of most drugs, irrespective of their properties, to achieve a therapeutic systemic availability. This will be a worthy achievement since over 90% of therapeutic compounds are known to possess oral bioavailability limitations. In this review, an attempt has been made to explore various approaches that have been used in recent years to improve oral drug bioavailability, including physical and chemical means. This review strives to provide a comprehensive overview of advances made over the past 10 years (2000-2010) in the improvement of the oral bioavailability of drugs. Briefly, the design of prodrugs to bypass metabolism or to enhance solubility as well as modification of formulation techniques such as the use of additives, permeation enhancers, solubilizers, emulsifiers and non-aqueous vehicles have been discussed. Arising approaches, such as formulation modification techniques; novel drug delivery systems, which exploit the gastrointestinal regionality of drugs, and include the pharmaceutical application of nanotechnology as an emerging area in drug delivery; inhibition of efflux pumps; and inhibition of presystemic metabolism have been more extensively addressed. This critical review sought to assess each method aimed at enhancing the oral bioavailability of drugs in terms of the purpose, scientific basis, limitations, commercial application, as well as the areas in which current research efforts are being focused and should be focused in the future.

The developability classification system: application of biopharmaceutics concepts to formulation development

A revised classification system for oral drugs was developed using the biopharmaceutics classification system (BCS) as a starting point. The revised system is designed to have a greater focus on drug developability. Intestinal solubility, the compensatory nature of solubility and permeability in the small intestine and an estimate of the particle size needed to overcome dissolution rate limited absorption were all considered in the revised system. The system was then validated by comparison with literature on the in vivo performance of a number of test compounds. Observations on the test compounds were consistent with the revised classification, termed the developability classification system (DCS), showing it to be of greater value in predicting what factors are critical to in vivo performance than the widely used BCS.

Drug Absorption in the Management of Congestive Heart Failure: Loop Diuretics

Congestive heart failure is a disease state distinguished by the regular presence of both renal and hepatic abnormalities in drug handling. One such abnormality involves flaws in the process of drug absorption. In most instances, congestive heart failure-related abnormalities in drug absorption are of inconsequential significance. However, this is not the case with loop diuretics. Loop diuretic action ordinarily tracks the rate and extent of absorption if a sufficient amount of diuretic has been given to exceed the threshold for diuretic effect. In congestive heart failure, both the rate and absolute amount of loop diuretic absorbed can be reduced as a function of the heart failure state itself. In this setting, drug dissolution characteristics can assume added significance. Furosemide is the loop diuretic with the widest intra- and interpatient variability of absorption. Alternatively, the loop diuretic torsemide is rapidly and fairly completely absorbed independent of the heart failure state. This pattern of absorption establishes it as the preferred loop diuretic in the otherwise diuretic-resistant heart failure patient. However, the exact role of torsemide in the outpatient management of congestive heart failure remains to be determined.

Formulation strategies for absorption windows

Absorption windows in the proximal gut can limit the bioavailability of orally administered compounds and can be a major obstacle to the development of controlled release formulations for important drugs. Methods to increase the residence of drug formulations at or above the absorption window are discussed in this review. Two main approaches are presently being explored: (i) bioadhesive microspheres that have a slow intestinal transit; and (ii) the gastroretentive dosage system, which is based on multiparticulates or large single unit systems. A good understanding of gastrointestinal transit in humans and the effect of factors such as food can be helpful in the design of rational systems that will have clinical benefit.

Effect of microenvironment pH of swellable and erodable buffered matrices on the release characteristics of diclofenac sodium

The aim of this work is to design pH-dependent swellable and erodable-buffered matrices and to study the effect of the microenvironment pH on the release pattern of diclofenac sodium. Buffered matrix tablets containing diclofenac sodium, physically mixed with hydrophilic polymer (hydroxypropyl methylcellulose [HPMC]) and pH-dependent solubility polymer (Eudragit L100-55) were prepared with different microenvironment pHs. The release of diclofenac sodium from the buffer matrices was studied in phosphate buffer solutions of pH 5.9 and 7.4. The swelling and erosion matrices containing only HPMC and Eudragit L100-55 were studied in phosphate buffer solution of pH similar to the microenvironment pHs of the matrices. Drug release from matrices was found to be linear as a function of time. Amount of drug released was found to be higher in the medium of pH 7.4 than that of pH 5.9. The rate of drug release increased with the increase of the microenvironment pH of the matrices as determined from the slope. The pattern of drug release did not change with the change of microenvironment pH. The swelling and erosion occurred simultaneously from matrices made up of HPMC and Eudragit L100-55. Both extent of swelling and erosion increased with increase of the medium pH. It was concluded from this study that changing the pH within the matrix influenced the rate of release of the drug without affecting the release pattern.

Enhanced Intestinal Absorption of Drugs by Activation of Peptide Transporter PEPT1 Using Proton‐Releasing Polymer

Utilization of carrier-mediated transport systems in the gastrointestinal tract to increase the bioavailability of drugs is of great interest. In the present study, an increased supply of the driving force for peptide transporter PEPT1 by utilizing a proton-releasing polymer, Eudragit L100-55, was employed to increase the intestinal transport activity. Intestinal absorption of zwitterionic cefadroxil and dianionic cefixime was studied in rats by using in situ ileal closed loops and by in vivo oral administration of the drugs concomitantly with Eudragit L100-55. The results showed that Eudragit L100-55 decreased the pH in the intestinal loops, and increased the disappearance of both cefadroxil and cefixime from the loops. In rats, the plasma concentration after oral administration was increased significantly by coadministration of Eudragit L100-55, whereas a proton-nonreleasing analogous polymer, Eudragit RSPO, did not have any effect. Furthermore, the increased absorption of cefixime caused by Eudragit L100-55 was blocked by simultaneous administration of cefadroxil, a PEPT1 substrate/inhibitor, in a concentration-dependent manner. These results demonstrate that improvement of intestinal absorption of peptide-mimetics via a peptide transporter is possible by optimizing the transporter activity through coadministration of a proton-releasing polymer that supplies the driving force for the transporter.

Pharmacokinetic strategies in deciphering atypical drug absorption profiles

Drug absorption is a very complex process that manifests itself through potential interaction with a host of physicochemical and physiological variables. Some factors that may affect the absorption processes include presystemic metabolism/efflux, the "absorption window" along the gastrointestinal tract, disease states, demographics (gender, age, ethnicity), and biopharmaceutical classification of solid dosage forms. Despite the complexity of the absorption processes, the analysis of the absorption kinetic data is mostly empirical, and the assumption of first-order absorption is axiomatic. Nevertheless, we often encounter irregular drug absorption profiles (such as double-peak, absorption window-type absorption profiles, etc.) that cannot be satisfactorily described by a simple first-order absorption process. The selection of an inappropriate absorption model would result in the misspecification of the pharmacokinetic model and subsequent erroneous prediction of the dosing regimen. This article presents several pharmacokinetic strategies in analyzing typical and atypical absorption profiles. The atypical absorption profiles discussed in this article include parallel first-order absorption, mixed zero-order and first-order absorption, Weibull-type absorption, absorption window with or without Michaelis-Menton absorption, time-dependent absorption, and inverse Gaussian density absorption. In any event, intravenous drug concentration-time data are generally needed to avoid the ambiguousness in the absorption analyses.

Effect of the biologically active fragment of zonula occludens toxin, delta G, on the intestinal paracellular transport and oral absorption of mannitol

OBJECTIVE

Many therapeutically active agents experience low bioavailability upon oral administration due to low permeability, low solubility, interaction with efflux transporters or first pass metabolism. In general, absorption enhancers are agents that can modulate the paracellular permeability of drugs, thus, potentially increasing oral bioavailability. The objective of this study was to examine the effect of the active fragment of Zonula occludens toxin (Zot), deltaG, on the transport of a paracellular marker, mannitol, using in vitro (Caco-2 cell monolayers) and in vivo (intraduodenal administration in rats) experimental methods.

METHODS

The transport of [14C]mannitol with deltaG (0, 50, 80, or 100 microg/ml) was determined across Caco-2 cells. Male Sprague-Dawley rats were assigned to receive one of the following treatments: [14C] mannitol (40 microCi/kg), [14C]mannitol/deltaG (417 microg/kg), or [14C] mannitol/deltaG/Protease inhibitors (PI).

RESULTS

The mean (+/-S.E.M.) apparent mannitol permeability coefficients (P(app)) observed after incubation with 0, 50, 80, and 100 microg/ml deltaG were 3.5 (+/-0.4), 4.17 (+/-0.27), 4.33 (+/-0.61), and 9.94 (+/-0.24)x10(-6) cm/s. After oral administration, C(max) (3.8 x 10(-4) vs. 4.4 x 10(-4) mM) and AUC(0-6 h) (0.096 vs. 0.088 mM min), obtained for [14C]mannitol and [14C]mannitol/deltaG, respectively, were not statistically different. However, both C(max) (7.6 x 10(-4) mM) and AUC(0-6 h) (0.25 mM min) were significantly higher for the [14C]mannitol/deltaG/PI treatment.

CONCLUSIONS

The 12 kDa fragment of Zot, deltaG, enhanced the in vitro transport and oral absorption of the paracellular marker, mannitol, in the presence of protease inhibitors (PI).