Comparison of the mechanical destructive force in the small intestine of dog and human

Development of an In Vitro Drug Release Method to Enable In Vitro-In Vivo Correlation of Potassium Chloride Extended-Release Tablets

An in vitro drug release test was developed to establish a level A in vitro-in vivo correlation (IVIVC) for predicting the in vivo performance of potassium chloride extended-release (ER) matrix tablets. Three ER formulations of potassium chloride with different in vitro release rates were designed using the USP dissolution test, and their urinary pharmacokinetic profiles were evaluated in healthy subjects. Due to the lack of IVIVC with the USP method, experiments were designed to investigate the effects of in vitro test conditions on drug release in order to match in vitro drug release with in vivo behaviors of different formulations. The evaluated in vitro variables included the type of USP apparatus, surfactant, and ionic strength of the dissolution medium. Based on the study findings and data analysis, a discriminatory drug release method was successfully developed that enabled the establishment and validation of a level A IVIVC model of the potassium chloride ER tablet using urinary pharmacokinetic data. This method uses USP apparatus I at 50 rpm in 900 mL of 150 mM NaCl solution containing 40 mM sodium dodecyl sulfate at 37 °C. The current study highlights the value of investigating test conditions in developing a predictive in vitro test method for establishing IVIVC.

Alleviating the Influence of Circadian Rhythms and Drug Properties to the Release of Paliperidone Gel Matrix Tablets with Compression Coating Technology and Microenvironment Shaping

The influence of circadian rhythms is an important content in oral dosage form study which is shown as different pH conditions and gastrointestinal dynamics in the gastrointestinal tract. The purpose of this study was to alleviate the influence of circadian rhythms and drug properties to the release of gel matrix tablets in vitro and in vivo. In this study, the compression coating technology and microenvironment shaping were utilized to achieve the alleviation of the influence of circadian rhythms and drug properties. The compression coating technology was used to alleviate the influence of gastrointestinal dynamics, and microenvironment shaping was used to alleviate the interference of different pH condition variations. The self-made compression coating tablet could maintain a consistent release rate in different pH conditions and different dynamic environments in vitro for 24 h. In vivo, the pharmacokinetic parameters C_max and T_max were 3701.675 ng/mL and 24 h, respectively, and the release effect in vivo was similar to the paliperidone osmotic pump tablet with the ability to alleviate the influence of circadian rhythms. The correlation coefficient R² was 0.9914 for the self-made paliperidone compression coating tablet in vitro-in vivo correlation. The interference caused by circadian rhythms was alleviated so that the compression coating technology with microenvironment shaping could replace the osmotic pump technology with easier preparation process and cheaper costs in vitro and in vivo and achieve the effect of alleviating the interference of circadian rhythms.

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

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

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

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

Gel Strength of Hydrophilic Matrix Tablets in Terms of In Vitro Robustness

PURPOSE

The purpose of this study was to correlate the gel strength of swollen matrix tablets with their in vitro robustness against agitation intensity and applied mechanical forces. Five commercial products, i.e. Glucophage®, Alfuzosin®, Tromphyllin®, Preductal® MR and Quetiapin® formulated as water-soluble/erodible matrix tablets were investigated.

METHODS

Effect of agitation speed (50-150 rpm) on drug release, hydration/erosion and gel strength was investigated using USP paddle apparatus II. The gel strength of matrix tablets during dissolution at different conditions was characterized by a texture analyzer.

RESULTS

Commercial tablets formulated with HPMC of higher viscosity, such as K15M or K100M, demonstrated the gel strength in swollen state >0.02 MPa. In this case, the release mechanism was predominantly diffusional and, therefore, not affected by stirring speed and mechanical stress. In contrast, the Quetiapin® matrix tablet, formulated with HPMC K 4 M in amount of approx. 25%, demonstrated the gel strength dropped below 0.02 MPa after 6 h of release. In this case, the drug was predominantly released via erosional mechanism and very susceptible to stirring speed.

CONCLUSION

Sufficient gel strength of swollen tablets is an important prerequisite for unchanged in vitro performance in consideration of mechanical stress.

Capsule robot for gut microbiota sampling using shape memory alloy spring

BACKGROUND

Human gut microbiota can provide lifelong health information and even influence mood and behaviour. We currently lack the tools to obtain a microbial sample, directly from the small intestine, without contamination.

METHODS

Shape memory alloy springs are used in concentric configuration to develop an axial actuator. A novel design of sampling mechanism is fabricated for collecting the sample from the gut. Storage chamber (500 µl) is used to protect the sample from downstream contamination.

RESULTS

The developed actuator occupies a small space (5 × Ø5.75 mm) and produces sufficient output force (1.75 N) to operate the sampling mechanism. A non-invasive capsule robot was tested ex vivo on the animal intestine, and it captured an average of 134 µl content which was sufficient for microbiome assessment.

CONCLUSIONS

Laboratory testing revealed that the collected sample had an amino acid signature indicative of microbiota, mucus and digesta, which provided a proof of concept for the proposed design.

Magnetic Resonance Methods as a Prognostic Tool for the Biorelevant Behavior of Xanthan Tablets

Hydrophilic matrix tablets with controlled drug release have been used extensively as one of the most successful oral drug delivery systems for optimizing therapeutic efficacy. In this work, magnetic resonance imaging (MRI) is used to study the influence of various pHs and mechanical stresses caused by medium flow (at rest, 80, or 150 mL/min) on swelling and on pentoxifylline release from xanthan (Xan) tablets. Moreover, a bimodal MRI system with simultaneous release testing enables measurements of hydrogel thickness and drug release, both under the same experimental conditions and at the same time. The results show that in water, the hydrogel structure is weaker and less resistant to erosion than the Xan structure in the acid medium. Different hydrogel structures affect drug release with erosion controlled release in water and diffusion controlled release in the acid medium. Mechanical stress simulating gastrointestinal contraction has no effect on the hard hydrogel in the acid medium where the release is independent of the tested stress, while it affects the release from the weak hydrogel in water with faster release under high stress. Our findings suggest that simultaneous MR imaging and drug release from matrix tablets together provide a valuable prognostic tool for prolonged drug delivery design.

Prediction of in vivo performance of oral extended release formulations prior to clinical evaluation: A case study for enteric coated polymeric beads formulation

To reduce cost and time for product development, an ideal strategy for the development of oral extended release (ER) product is to identify the desired formulation with minimum needsfor clinical evaluation. The aim of this work was to demonstrate the feasibility of adopting a "prediction-then-validation" strategy for the development of oral ER formulations. Instead of the traditional approach using multiple ER formulations for IVIVC development, an enteric-coated fast release formulation was successfully utilized for the development of a biopredictive tool to estimate the drug release from enteric coated polymeric ER formulations in the intestine. A TS1 (time scale factor between T_vitro and T_vivo equals to 1) system was designed and developed, based on which the in vivo pharmacokinetic (PK) performance of ER formulations in dog and in human were well predicted prior to in vivo evaluations. The model further passed a posteriori validation using the criteria for level A IVIVC and, as designed, provided a T_scale value of 1 for the IVIVC model.

IVIVC for Extended Release Hydrophilic Matrix Tablets in Consideration of Biorelevant Mechanical Stress

Purpose

When establishing IVIVC, a special problem arises by interpretation of averaged in vivo profiles insight of considerable individual variations in term of time and number of mechanical stress events in GI-tract. The objective of the study was to investigate and forecast the effect of mechanical stress on in vivo behavior in human of hydrophilic matrix tablets.

Methods

Dissolution profiles for the marketed products were obtained at different conditions (stirring speed, single- or repeatable mechanical stress applied) and convoluted into C-t profiles. Vice versa, published in vivo C-t profiles of the products were deconvoluted into absorption profiles and compared with dissolution profiles by similarity factor.

Results

Investigated hydrophilic matrix tablets varied in term of their resistance against hydrodynamic stress or single stress during the dissolution. Different scenarios, including repeatable mechanical stress, were investigated on mostly prone Seroquel® XR 50 mg. None of the particular scenarios fits to the published in vivo C-t profile of Seroquel® XR 50 mg representing, however, the average of individual profiles related to scenarios differing by number, frequency and time of contraction stress. When different scenarios were combined in different proportions, the profiles became closer to the original in vivo profile including a burst between 4 and 5 h, probably, due to stress-events in GI-tract.

Conclusion

For establishing IVIVC of oral dosage forms susceptible mechanical stress, a comparison of the deconvoluted individual in vivo profiles with in vitro profiles of different dissolution scenarios can be recommended.

Deconstructing the physical processes of digestion: reductionist approaches may provide greater understanding

I provide a broad overview of the physical factors that govern intestinal digestion i.e. the admixture of food particles in digesta with secreted enzymes and the subsequent mass transfer of liberated nutrients from the surfaces of particles to the gut wall, with a view to outlining the quantitative work that is required to determine the relative importance of these factors in the digestion of particular foods. I first discuss what is known of the mechanical forces generated by contraction of the walls of the various segments of the gut and the level of diffusive, and advective mixing that it generates within the lumen. I then discuss the particular physical effects that may limit the digestion of solid, physically and/or chemically homogenous and heterogeneous food particles, notably capillarity, porosity, poro-elastic flow and compaction and their likely effects on diffusive and convective mass transfer at particulate surfaces. Similarly, I discuss mucins and morphology on mass transfer of nutrients to the gut wall i.e. the mucosa.

Development of Paroxetine Hydrochloride Single Layer Controlled-Release Tablets Based on 3² Factorial Design

Major depressive disorder (MDD) is one of the main contributors to disability and suicide mortality globally. Paroxetine hydrochloride (PHH) is the most potent antidepressant used for MDD treatment. Due to its reduced side effects PAXIL^® CR is a widely-used controlled-release formulation of PHH. However, the complicated double-layer production of PAXIL^® CR faces the risk of layer separation. In this study, PHH enteric coating single layer controlled-release tablets (PHH-EC-SLTs) were designed as a simplified substitution of PAXIL^® CR through a rational formulation screening. The optimized PHH-EC-SLTs showed similar release behaviors in vitro to PAXIL^® CR and the release profiles corresponded to a zero-order release model (R² = 0.9958). Polymer matrix erosion was the main release mechanism, according to the fitting exponents n > 1 in the Korsmeyer-Pappas model. Crucial pharmacokinetic parameters including peak-reaching time (T_max), peak concentration (C_max) and the area under the blood level-time curve (AUC_0-48) of PHH-EC-SLTs and PAXIL^® CR had no significant difference (p > 0.05) and the relative bioavailability (F = 97.97%) of PHH-EC-SLTs demonstrated their similar pharmacokinetic profiles in vivo. In view of avoiding layer separation risk and simplifying the preparation processing, the self-made PHH-EC-SLTs could be considered as a safe and economic alternative to PAXIL^® CR.

A pH-Responsive Amphiphilic Hydrogel Based on Pseudopeptides and Poly(ethylene glycol) for Oral Delivery of Hydrophobic Drugs

Oral administration is a noninvasive and convenient drug delivery route most preferred by patients. However, poor stability in the gastrointestinal tract and low bioavailability of hydrophobic drugs has greatly limited their oral administration. To address this problem, we report a pH-responsive, amphiphilic hydrogel drug carrier based on a pseudopeptide poly(l-lysine isophthalamide) (PLP) and poly(ethylene glycol) (PEG). The hydrogels were prepared by a simple N-(3-(dimethylamino)propyl)-N'-ethyl carbodiimide hydrochloride (EDC)/N-hydroxysuccinimide (NHS) coupling reaction, and the cross-linking was confirmed by infrared spectroscopy and differential scanning calorimetry analyses. Because of the pH-responsive conformational alteration of PLP, the hydrogels were relatively hydrophobic and collapsed at acidic pH, but became hydrophilic and swollen at neutral pH. The amphiphilicity enabled the hydrogels to well retain and protect hydrophobic model drugs in the simulated gastric fluid, but efficiently release them in the simulated intestinal fluid. These results suggested that the pH-responsive amphiphilic hydrogels are promising candidates for oral delivery of hydrophobic drugs.

Modification of drug delivery to improve antibiotic targeting to the stomach

The obstacles to the successful eradication of Helicobacter pylori infections include the presence of antibiotic-resistant bacteria and therapy requiring multiple drugs with complicated dosing schedules. Other obstacles include bacterial residence in an environment where high antibiotic concentrations are difficult to achieve. Biofilm production by the bacteria is an additional challenge to the effective treatment of this infection. Conventional oral formulations used in the treatment of this infection have a short gastric residence time, thus limiting the duration of exposure of drug to the bacteria. This review summarizes the current research in the development of gastroretentive formulations and the prospective future applications of this approach in the targeted delivery of drugs such as antibiotics to the stomach.

A novel approach in distinguishing between role of hydrodynamics and mechanical stresses similar to contraction forces of GI tract on drug release from modified release dosage forms

The objective of this study was to determine the influence of mechanical stresses simulating gastrointestinal contraction forces of 2.0 N (stomach) and 1.2 N (intestine) on the gel properties and drug release characteristics from sustained release swelling and eroding hydrophilic matrices during dissolution studies. Two batches of tetracycline-sustained release tablets containing hydroxypropyl methyl cellulose (HPMC) were manufactured and subjected to USP apparatus II (pH 2.2 buffer) dissolution studies. Hydrated tablets were periodically removed, placed in a petri dish, and multiple times (six cycle) compressed with a flat-ended probe (diameter 1.3 cm) on a texture analyzer at preprogrammed force of either 2.0 or 1.2 N to determine force-distance profiles and changes in drug release rate. The calculated similarity factor values showed dissimilar dissolution profiles using standard dissolution profile as a reference. The similarity factor (f2) values were especially lower than 50 at 2.0 N and, when profiles between the two batches compressed at 1.2 and 2.0 N, were compared with each other. The changes in dissolution pattern and release rate were significantly different after 4 h of dissolution. At 8 h, tablets were fully hydrated and no force could be detected by the probe, indicating a very soft gel matrix. It appears that the contraction forces in the stomach and intestine are capable of altering drug release from modified release hydrophilic matrices during transit in the human GI tract. Accounting for these forces during dissolution can enhance predictions of in vivo drug release, achieve better in vitro and in vivo correlation, introduce improvement in dissolution methods, and better understand the critical quality attributes (CQAs) and factors in quality by design (QbD) during the product development process.

A novel beads-based dissolution method for the in vitro evaluation of extended release HPMC matrix tablets and the correlation with the in vivo data

The aim of this work was to establish alternative in vitro dissolution method with good discrimination and in vivo predictability for the evaluation of HPMC extended release matrix tablets. For this purpose, two different HPMC matrix tablet formulations were first evaluated by a range of conventional dissolution testing methods using apparatus 1, apparatus 2, and apparatus 3 according to US Pharmacopoeia. Obtained results showed low discrimination between the tested samples. Afterward, a novel dissolution testing method which combines plastic beads and apparatus 3 was developed with the aim to better mimic the mechanical forces that occur in vivo. Results showed that sufficiently large mechanical stress with high dips per minute program setting (apparatus 3) was needed to obtain in vitro discriminative results, which are in accordance with the in vivo data. The in vivo relevance of the method was confirmed with the establishment of the level A in vitro-in vivo correlation.

Correlating cellulose derivative intrinsic viscosity with mechanical susceptibility of swollen hydrophilic matrix tablets

Hydrophilic matrix tablets are prone to mechanical stress while passing through the gastrointestinal tract, which may result in inappropriate drug-release characteristics. Intrinsic viscosity is a physical polymer property that can be directly compared across various types and grades of polymers and correlated with the mechanical susceptibility of swollen matrix tablets. Five tablet formulations containing different HPMC and HPC polymers were prepared and analyzed using an in vitro glass bead manipulation test. The dissolution rate results were modeled using the Korsmeyer-Peppas equation and a correlation was found between the fit constants k and n, goodness-of-fit measure parameters, and intrinsic viscosity. Moreover, the dissolution profiles were used to calculate the degree of mechanical susceptibility for each formulation, defined as the ratio of the average dissolution rate after manipulation and the initial dissolution rate before manipulation. It was confirmed that an increased intrinsic viscosity polymer value resulted in a decrease in mechanical susceptibility. Considering this, two simple rules were defined for designing robust matrix tablets with respect to mechanical stresses.

A novel liquefied gas based oral controlled release drug delivery system for liquid drug formulations

A novel liquefied gas based drug delivery system for the oral delivery of liquid and semi-solid drug formulations is presented. The capsule-shaped system is equipped with a capillary as an element controlling the release rate. The delivery mechanism is based on a constant vapor pressure produced by isopentane as a low-boiling liquefied gas. The liquid drug valproic acid (VA) was used as a model compound. The viscosity was increased by the addition of povidone (PVP). The VA-PVP gel exhibited pseudoplastic rheological properties, the shear rate was above 0.1s(-1), similar to a Newtonian liquid. The gels tested in the gas based delivery system provided near-zero-order release kinetics. The longest delivery time was up to ca. 8h. The system is characterized by high flexibility of the delivery rate, which can be achieved by adjusting system parameters such as the diameter and length of the capillary, the vapor pressure of the propellant and the viscosity of the drug formulation.

Selection of the most suitable dissolution method for an extended release formulation based on IVIVC level A obtained on cynomolgus monkey

OBJECTIVE

The purpose of this study is primarily to identify the most suitable in vitro dissolution method(s) for their ability to predict the in vivo performance of extended release prototype tablet formulations designed for a new chemical entity, Biopharmaceutic Classification System class II drug, weak base, based on the data collected in cynomolgus monkey.

MATERIALS AND METHODS

Different types of buffer at different pH were selected as dissolution medium resulting in a broad variety of release patterns (slow to fast). The in vivo and in vitro data were put in relation.

RESULTS

As a consequence of the discrimination between both tested formulations, the in vitro-in vivo correlation (IVIVC) qualities and shapes changed significantly. The obtained level A showed that the simple HCl medium was superior to biorelevant media and media containing surfactant when investigating IVIVCs in cynomolgus monkey. In addition, the results of dissolution in HCl suggested rather a diffusion mechanism of the extended release matrix formulation as the main factor of the release.

CONCLUSION

Adjusting dissolution testing conditions to match the behavior of the formulations in vitro with that in vivo by taking into account the properties of the drug and the formulation is a straightforward and useful approach in identifying a predictive method in the development of the IVIVC. These investigations will definitely help by derisking of new formulations as well as by rating changes in existing formulations with regard to their impact on bioavailability before entry into human.

A new pressure-controlled colon delivery capsule for chronotherapeutic treatment of nocturnal asthma

The purpose of this study was to prepare a pressure-controlled colon delivery capsule (PCDC) containing theophylline (TPH) dispersion in a lipid matrix as a chronotherapeutic drug delivery system for the treatment of nocturnal asthma. The system was made by film coating using Eudragit S100- based formula over the sealed-hard gelatin capsules containing the drug-lipid dispersion. The lipid formula was composed mainly of Gelucire 33/01 (G33) with different ratios of surfactants (1-10%). The efficiency of the prepared system was evaluated in vitro for its ability to withstand both the gastric and intestinal medium. In addition, the drug plasma concentrations were monitored after single administration to Beagle dogs and compared to that obtained after administration of a reference marketed, generic, sustained-release TPH tablets, Avolen(®) SR. It was found that the optimum lipid formula was GL2 containing 90% G33 and 10% Labrasol. The film-coated capsules showed complete resistance to both the acidic environment (pH 1.2) for 2 hours and phosphate buffer pH 6.8 for 3 hours at 37°C. In vivo evaluation of the TPH-based PCDCs showed longer lag time compared TO the marketed formula followed by sudden increase in TPH blood levels, which recommends the high potential of this system as a chronotherapeutic drug delivery for nocturnal asthma. The prepared PCDCs exhibited a significantly higher C(max) and T(max) and a nonsignificantly different AUC compared with Avolen(®) SR. Higher TPH blood levels from 1 to 8 hours postadministration was detected in the case of the prepared PCDCs.

Preparation and evaluation of a novel delayed-onset sustained-release system of propranolol hydrochloride

The objective of this work was to prepare and evaluate a new delayed-onset sustained-release system, comprising a sustained-release core tablet with hydroxypropyl methylcellulose as polymer matrix and an ethylcellulose/Eudragit L coating capable of delaying the drug release. The sustained core containing propranolol hydrochloride as the model drug was prepared by granulate tableting and the polymer coating was applied in a computer-controlled coating pan. The dissolution tests demonstrated that the in-vitro drug release was pH-dependent with sufficient gastric resistance, and the lag time (t10%) could be controlled by adjusting the coating level. Three dosage forms including commercial tablet, sustained-release tablet and the delayed-onset sustained-release tablet were administrated to six beagle dogs and the plasma levels of propranolol hydrochloride were measured with high-performance liquid chromatography. The delayed-onset sustained-release tablet had a lag time of 3.0 h in-vitro and 3.5 h in-vivo, and a tmax of 7.0 h. The relative bioavailability for delayed-onset sustained-release tablet was 96.98% compared with commercial tablets. The results indicate that the new propranolol delayed-onset sustained-release system could achieve a relatively constant drug release followed by a programmed lag time, and this may provide a promising drug delivery form for chronopharmacotherapy of certain cardiovascular diseases.

The study of a remote-controlled gastrointestinal drug delivery and sampling system

A micromachined capsule based on microelectromechanical systems (MEMS) technology is introduced in this paper. It is an effective tool for diagnosing and treating gastrointestinal diseases. The microcapsule can carry out real-time drug release and the gastrointestinal fluid sampling in the gastrointestinal tract. According to the structural and metabolic characters of the gastrointestinal tract, the configuration of the microcapsule was designed as a cylinder. This nondigestible oral device can smoothly pass through the gastrointestinal tract for drug delivery and liquid sampling. The working mechanism of the capsule was the mechanic movement mode of a piston, which was regulated through a MEMS calorific element. The action of drug delivery and gastrointestinal fluid sampling in the gastrointestinal tract was performed wirelessly. The remote control device can be connected with a computer through a serial port (RS-232), and it can be used in telemedicine applications. Some experimental research has been carried out to validate the design. The experimental results indicated that the microcapsule can achieve drug delivery and liquid sample reliably.

Disintegration of solid foods in human stomach

Knowledge of the disintegration of solid foods in human stomach is essential to assess the bioavailability of nutrients in the gastrointestinal (GI) tract. A comprehensive review of food gastric digestion, focusing on disintegration of solid foods, is presented. Most of the research reviewed in this paper is contained in the medical, pharmaceutical, food, and nutritional literature. Stomach physiology is briefly introduced, including composition and rheological properties of gastric contents, stomach wall motility in fed/fasted states, and hydrodynamic and mechanical forces that act on the ingested food. In vivo and in vitro methods used for studying food and drug digestion in GI are summarized. Stomach emptying rate, which controls the rate of absorption of nutrients, is highly related to the disintegration of foods. This topic is highlighted with focus on the important mechanisms and the influence of chemical and physical properties of foods. Future research in this area is identified to increase our fundamental understanding of the food digestion process in the stomach as related to the food composition, material properties such as texture and microstructure, and chemical characteristics. This information is necessary to develop new guidelines for seeking innovative processing methods to manufacture foods specifically targeted for health.

Theoretical comparison of hydrodynamic diffusion layer models used for dissolution simulation in drug discovery and development

The effective hydrodynamic diffusion layer thickness (h(eff)) of a drug particle dissolving into an agitated fluid is of great importance for oral absorption simulation. The purpose of the present study was to: (1) introduce a h(eff) estimation method based on the fluid dynamic theory (FD model), and (2) compare the FD model with the non-FD-based approximation models previously reported by Hintz and Johnson (HJ model) and Wang and Flanagan (WF model). In the FD model, the relative velocity of a particle suspended in an agitated fluid was estimated from the terminal slip velocity and the microeddy effect. For small particles (particle radius (r(p))<ca. 15microm), the HJ, WF and FD models resulted in the similar h(eff) values, whereas they resulted in different h(eff) values for large particles (r(p)>ca. 15microm). One of the merits of the FD model is that it provides the a priori theoretical estimation of h(eff) from particle radius, drug density, agitation strength, fluid viscosity, and diffusion coefficient. The hydrodynamic conditions in the gastrointestinal (GI) tract differ among human and animals, the GI sites, and fasted/fed conditions, etc. Therefore, the FD model could provide a more comprehensive and sophisticated simulation of oral absorption.

Solubility and dissolution profile assessment in drug discovery

The purposes of the review are to: a) Provide a comprehensible introduction of the-state-of-the-art sciences of solubility and dissolution, b) introduce typical technologies to assess solubility and dissolution, and c) propose the best practice strategy. The theories of solubility and dissolution required in drug discovery were reviewed especially from the view point of oral absorption. The physiological conditions in the gastrointestinal fluid in humans and animals were then briefly summarized. Technologies to assess solubility and dissolution in drug discovery were then introduced. Recently, these technologies have been improved by the laboratory automation and computational technologies. Finally, the strategies to apply these technologies for a drug discovery project were discussed.

In-vitro/in-vivo correlation of pulsatile drug release from press-coated tablet formulations: A pharmacoscintigraphic study in the beagle dog

The aim of the current study was to investigate the in-vitro and in-vivo performance of a press-coated tablet (PCT) intended for time delayed drug release, consisting of a rapidly disintegrating theophylline core tablet, press-coated with barrier granules containing glyceryl behenate (GB) and low-substituted hydroxypropylcellulose (L-HPC). The PCTs showed pulsatile release with a lag time dependent upon the GB and L-HPC composition of the barrier layer. In-vivo gamma-scintigraphic studies were carried out for PCTs containing GB:L-HPC at 65:35 w/w and 75:25 w/w in the barrier layer in four beagle dogs, in either the fed or fasted state. The in-vivo lag time in both the fed and fasted states did not differ significantly (p>0.05) from the in-vitro lag time. Additionally, no significant difference (p<0.05) between in-vivo fed and fasted disintegration times was observed, demonstrating that in-vivo performance of the PCT was not influenced by the presence or absence of food in the gastrointestinal tract. A distinct lag time was obtained prior to the appearance of drug in plasma and correlated (R2=0.98) with disintegration time observed from scintigraphic images. However, following disintegration, no difference in pharmacokinetic parameters (AUC(0-6 dis), K(el), Cmax) was observed. The current study highlighted the potential use of these formulations for chronopharmaceutical drug delivery.

Development of a controlled release low dose class II drug-Glipizide

The purpose of this study was to develop a new monolithic matrix system to completely deliver glipizide, a Biopharmaceutics Classification System (BCS) Class II drug in a zero order manner over an extended time period. Two approaches were examined using drug in formulations that contain swellable hydroxypropylmethylcellulose (HPMC) or erodible polyethylene oxide (PEO). The matrices were prepared by dry blending selected ratios of polymers and ingredients using direct compression technique. Dissolution was assessed using modified USP apparatus II. Glucotrol XL push-pull osmotic pump (PPOP) was used as the reference. The interrelationship between matrix hydration, erosion and textural properties were determined and analyzed under the dissolution test conditions. Linear and reproducible release similar to that of Glucotrol XL was achieved for optimized matrices (f2>50) independent of hydrodynamic conditions. The kinetics of drug delivery was directly related to the synchronization of swelling, erosion and fractional release. HPMC matrices showed a significantly greater degree of hydration and swelling and stronger texture property relative to PEO matrices. Results indicate that in the case of low dose/low soluble drug, total drug release in a zero order manner heavily depends on the synchronization of erosion and swelling fronts during the entire dissolution study.

Analysis of macromolecular changes and drug release from hydrophilic matrix systems

The influence of water-soluble and insoluble excipients on dynamics of hydration, front movement, erosion, and drug release from hydrophilic matrix tablets containing water-soluble drug was studied. Tablets were manufactured by direct compression, and their un-constrained swelling behavior and gel strength were assessed with a texture analyzer. Dissolution was performed using USP 26 apparatus II modified by insertion of a mesh to prevent sticking of tablets to the bottom of the vessel and to allow free three-dimensional matrix swelling. Significant release differences between tablet batches were observed and this was consistent with changes in swelling rate, gel thickness, and swelling front movement within the tablets. Matrices containing approximately 30% drug load and water-soluble lactose, demonstrated more pronounced swelling front movement and hence drug release relative to the matrix tablets containing dicalcium phosphate dihydrate. The observed differences in release were verified by calculating the similarity and difference factors. The interdependence of front movement and mass erosion in relation to excipient types on progression of swelling front movement and alteration of water penetration, erosion, and drug release are explained. It is concluded that unlike in conventional dosage forms inclusion of excipients in hydrophilic controlled-release tablets containing water-soluble drugs should be carefully analyzed as their various physico-chemical properties may have significant implications on swelling dynamics, front movement, drug release kinetics, and consequently in vivo performance.

Pharmacokinetics of an immediate release, a controlled release and a two pulse dosage form in dogs

Clinical studies have shown that circadian patterns influence the pharmacokinetics of certain drugs used in the treatment of different diseases. For such drugs, the bioavailability is influenced by the time of administration. The objective of this study was to investigate differences in the pharmacokinetic patterns between a pulsatile drug delivery system using a pulsatile capsule, an immediate release tablet and a controlled release tablet. Metoprolol was chosen as a model drug because of its high solubility and high permeability pattern throughout the GI tract. The dosage forms were administered to four dogs and the plasma levels were measured using LC-MS/MS. Pharmacokinetic parameters were determined for each dosage form. Fluctuations in the plasma time curves over the observation period indicated that physiological factors like motility have an influence on the drug absorption. The comparison of the plasma time curves of the dosage forms showed that each dosage form caused significant differences in the drug plasma levels. The pulsatile drug delivery capsule caused two defined C(max) values for each dose between 1-1.75 and 2.5-3.5h. Implications for the use of a pulsatile drug delivery device for chronopharmacotherapy are discussed. Pulsatile drug delivery offers a promising way for chronopharmacotherapy if the time of administration and pulse time are adjusted to the circadian pattern.

Formulation development and human in vitro-in vivo correlation for a novel, monolithic controlled-release matrix system of high load and highly water-soluble drug niacin

Novel, controlled-release formulations for high drug load, highly water soluble compound niacin based on polyethylene oxide (PEO) and hydroxypropylmethyl cellulose (HPMC) matrices were developed and investigated. The effect of sodium bicarbonate as a modulator of swelling, erosion, and drug release and its impact on changes in the kinetics of axial swelling and gel strength were evaluated by textural analysis during dissolution study. The drug release rate from PEO-based matrices was faster and correlated with lower gel strength, greater water uptake, and greater matrix erosion. Slower release rate and greater release duration correlated significantly with greater matrix swelling with negligible matrix erosion for the HPMC-based matrix system. Inclusion of sodium bicarbonate in the polymeric matrix salted out the macromolecules and increased gel strength and gel viscosity, especially in the vicinity of the swelling fronts. An in vivo study in human subjects after administration of the formulations and a commercial product exhibited similar plasma concentrations. For the formulation of interest, the mean drug fraction absorbed by the body was calculated by the Wagner-Nelson technique, and a level A "in vitro-in vivo correlation" was observed between the percent released in vitro and percent absorbed in vivo. The developed formulations appear to be robust and easy to manufacture with maximum flexibility with respect to drug dose, polymeric carriers, duration, and kinetics of drug release.

Suitability of the cynomolgus monkey as an animal model for drug absorption studies of oral dosage forms from the viewpoint of gastrointestinal physiology

To determine the usefulness of the monkey as an animal model, which can predict in vivo performance of humans, the major gastrointestinal physiological parameters of this animal were evaluated. The pH of gastric juice collected by a fiberscope from the stomach in fasted cynomolgus monkeys showed a high acidity level, which ranged from 1.2 to 4.3. The gastric emptying time of oral dosage forms (solution, granules and tablets) showed that the larger size dosage forms seemed to be emptied more slowly, and three dosage forms were prolonged by feeding. The gastrointestinal agitation intensity of monkeys was estimated using controlled-release tablets of acetoaminophen, which showed a slow erosion rate. The in vivo release amount-time profiles of the tablet in fasted monkeys corresponded to their in vitro profiles with paddle agitation conditions of between 10 rpm and 50 rpm of the paddle method; this result was smaller than in dogs (100 rpm) but equivalent to that in humans (10 rpm). Further, the small intestinal transit time (SITT), estimated using a double marker method, ranged from 2.2 to 4.2 h in the fasting state and from 2.2 to 3.2 h in the fed state; the SITT was not significantly delayed by feeding. Comparison with the published data about dogs and humans showed these gastrointestinal physiological parameters of monkeys to be more similar to those of humans. Consequently, it is assumed that the monkey is useful as an animal model for bioavailability studies of oral dosage forms.

Drug formulations intended for the global market should be tested for stability under tropical climatic conditions

RATIONALE OBJECTIVE

The quality of drugs imported into developing countries having a tropical climate may be adversely affected if their formulations have not been optimized for stability under these conditions. The present study investigated the influence of tropical climate conditions (class IV: 40 degrees C, 75% relative humidity) on the drug content, in vitro dissolution and oral bioavailability of different formulations of two essential drugs marketed in Tanzania: diclofenac sodium and ciprofloxacin tablets.

METHODS

Before and after 3 and 6 months storage under class IV conditions the drug content and in vitro dissolution were evaluated using United States Pharmacopoeia (USP) 24 methods. Following a randomized four-period cross-over study, the pharmacokinetic parameters of drug formulations stored for 3 months under class IV conditions were compared with those stored at ambient conditions.

RESULTS

Drug content and drug release from all tested ciprofloxacin formulations were within USP-24 requirements and remained stable during storage at simulated tropical conditions. Oral bioavailability was also not influenced by tropical conditions. The dissolution rate of two diclofenac formulations (Diclo 50 manufactured by Camden and Dicloflame 50 manufactured by Intas) reduced significantly during storage under class IV conditions. After oral administration Camden tablets stored for 3 months under class IV conditions showed a reduction in C(max) (90% CI of C(max) ratio: 0.59 - 0.76). This reduction was smaller than expected based on the in vitro tests.

CONCLUSIONS

Some drug formulations imported into Tanzania are not optimized for stability in a tropical climate. Manufacturers and regulatory authorities should pay more attention to the WHO recommendations for testing the stability of drugs under tropical climate conditions. Efforts should be made to improve the in vitro tests to better predict the bioavailability.