Image analysis studies of water transport and dimensional changes occurring in the early stages of hydration in cross-linked amylose matrices

Resistant starch as a carrier for oral colon-targeting drug matrix system

In this study, a novel tablet of protein drug matrix for colon targeting was developed using resistant starch as a carrier prepared by pre-gelatinization and cross-linking of starch. The effects of pre-gelatinization and cross-linking on the swelling and enzymatic degradation of maize starch as well as the release rate of drug from the matrix tablets were examined. Cross-linked pre-gelatinized maize starches were prepared by double modification of pre-gelatinization and cross-linked with POCl(3), and bovine serum albumin was used as a model drug. For in vitro drug release assays, the resistant starch matrix tablets were incubated in simulated gastric fluid, simulated intestinal fluid and simulated colonic fluid, respectively. The content of resistant starch and swelling property of maize starch were increased by pre-gelatinization and cross-linking, which retarded its enzymatic degradation. Drug release studies have shown that the matrix tablets of cross-linked pre-gelatinized maize starch could delivery the drug to the colon. These results indicate that the resistant starch carrier prepared by pre-gelatinization and cross-linking can be used for a potential drug delivery carrier for colon-targeting drug matrix delivery system.

Mechanistic study on hydration and drug release behavior of sodium alginate compacts

The influence of sodium alginate viscosity on the dynamics of matrix hydration, solvent front movement, swelling, erosion, and drug release from alginate matrix tablets were examined. The solvent front showed preferential penetration from the radial direction even though matrix swelling showed axial predominance. This study proposed alternative views for the anisotropic behavior of hydrating alginate compacts, namely, formation of gel barrier with different permeability characteristics, tension at the gel-core interface and preferential radial erosion, in addition to an in-depth examination on the contribution of stress relaxation of hydrated polymer as well as core expansion. Alginate matrices demonstrated pH-dependent hydration, swelling and erosion behavior, resulting in pH-dependent drug release mechanisms. Dissolution profiles for alginate matrices of different viscosities were similar in acid but differed upon increase of pH. This was due to the influence of alginate viscosity grade on liquid uptake, erosion and pronounced swelling at near neutral pH.

Dimensional changes, gel layer evolution and drug release studies in hydrophilic matrices loaded with drugs of different solubility

The objective of this investigation was to explore the effects of drug solubility on the evolution of matrix dimensions and gel layer's during drug release and investigate the relationship between these effects and the mechanism and the rate of drug release. Two hydrophilic swellable polymers Polyox (POL) and cross-linked Carbopol (CARB) were employed as carriers. Caffeine (CAF) and theophylline (THE), two drugs having similar chemical structure but different aqueous solubility, were used as model drugs. Both drug and polymer characteristics were found to influence the dimensional changes of matrices and the development of the gel layer formed around the glassy core. The dimensional expansion in CAF matrices was always more pronounced than the THE matrices. Also the CARB matrices demonstrated greater maximum expansion and lower drug release than the POL matrices, due to a smaller degree of erosion of CARB. The dimensions of CARB/CAF matrices, unlike all the other matrices studied, exhibited a biphasic increase at early times, which was attributed to the cross-linked structure of CARB and the high solubility of CAF. With both polymers, a thinner gel layer was developed in the matrices containing the less soluble THE compared to the CAF matrices. The thickness of the gel layer increased continuously with time in the CAF matrices whereas it increased initially and after reaching a maximum started to decrease in THE matrices. All formulations except those of CARB/THE exhibited burst release, which depended on drug and polymer characteristics. The gel layer thickness and erosion rate appeared to determine the rate of drug release from the CARB and POL formulations. The results clearly indicate that for these matrices gel thickness and fluctuation of gel thickness affect the release rate/h of drug proportionally. Analysis of the release kinetics indicated that CAF was released mainly through diffusion whereas, THE was released mainly through matrix erosion.

The Macromolecular Polymers for the Preparation of Hydrodynamically Balanced Systems—Methods of Evaluation

Evaluation of macromolecular polymers used as excipients for the preparation of hydrodynamically balanced systems (HBS) was carried out. Hard gelatine capsules were filled with polymeric substances belonging to various chemical groups (chitosan, sodium alginate, hydroxypropylmethycellulose--HPMC). The following properties of the HBS were investigated: density, hydration, erosion and floating force. The solvent penetration process into the HBS was visualized using magnetic resonance imaging (MRI) technique. Densities of the HBS in hydrochloric acid (0.1 M) ranged from 0.37 g/cm3 to 0.71 g/cm3. Each polymer demonstrated different hydration/erosion abilities and floating properties. The maximum floating force (F(float max)) for capsules size 0, ranged from 26.7 mN (sodium alginate) to 64.7 mN (chitosan). HBS formulations also varied in time to reach maximum floating force (T(float max)). HPMC and sodium alginate formulation reached F(float max) within half an hour after immersion, while in the case of chitosan formulations (deacetylation degree (d.d.) 66% and d.d. 93%), the time was 184 minutes and 218 minutes respectively. The floating properties of the dosage forms were reliant on type of the polymer and the medium-fasted state simulated gastric fluid (FaSSGF) or fed state simulated gastric fluid (FeSSGF). The size of the HBS influenced the floating force value. The mechanisms of erosion and swelling of the polymeric matrices play a dominant role in flotation of the dosage forms.

Cross-linked high amylose starch derivatives for drug release

Acetate (Ac-), aminoethyl (AE-), and carboxymethyl (CM-) high amylose starch cross-linked 6 (HASCL-6) derivatives were previously shown to control the release of drugs over 20 h from monolithic tablets highly loaded (up to 60% drug). This report describes the swelling characteristics, which allow a better understanding of the mechanisms involved in the control of the drug release from the said polymeric matrices. The tablet swelling of HASCL-6, Ac-HASCL-6, and AE-HASCL-6 was found to not be affected by the ionic strength and by the pH between 1.2 (gastric) and 7 (intestinal), whereas the swelling of CM-HASCL-6 was shown to depend on both ionic strength and pH of the release medium. For all the studied polymers the drug loading did not change the equilibrium swelling ratio but affected the initial swelling velocity, seemingly due to the competition between drug and polymer for water uptake, a phenomenon probably influenced by the loading and the drug solubility. It was also shown that the increase of ionic strength would slightly increase the drug release time probably by decreasing the amount of free water still available to solubilize the drug present into the matrix.

NMR imaging of high-amylose starch tablets. 2. Effect of tablet size

Carbohydrate polymers are widely used for pharmaceutical applications such as the controlled release of drugs. The swelling and water mobility in high-amylose starch tablets are important parameters to be determined for these applications. They have been studied at different time intervals by nuclear magnetic resonance imaging (NMRI) after the immersion of the samples in water. These tablets have a hydrophilic matrix, which swells anisotropically and forms a hydrogel in water. NMRI shows clearly the anisotropy of the water penetration and the swelling along the radial and axial dimensions of the tablets. Empirical relationships are established to describe the kinetics of water penetration and swelling of the tablets. Results show that water uptake and tablet swelling strongly depend on the size of the tablets. Gravimetric measurements of water uptake were also performed in comparison with the NMRI results.

Influence of physical parameters and lubricants on the compaction properties of granulated and non-granulated cross-linked high amylose starch

Cross-linked high amylose starch (CLA) is a pharmaceutical excipient used in direct compression for the preparation of controlled release tablets and implants. In this work the compression properties of CLA in bulk and granulated forms (without binder) were evaluated for the first time. Tablets were prepared on an instrumented single punch machine. The flow properties and the compression characteristics (compressibility, densification behavior, work of compression) of the materials as well as the mechanical strength of the finished compacts (compactibility) were systematically examined. Wet granulation was found to improve the flowability and the compressibility of CLA but concomitantly reduced its compactibility. It was demonstrated that CLA was a plastically deforming material with a plasticity index and a yield pressure value comparable to those of pregelatinized starch. The compactibility of granulated CLA was independent of particle size in the range of 75 to 500 microm, but slightly decreased when the percentage of the fine particles (<75 microm) in the bulk powder was increased. Water and colloidal silicone dioxide facilitated the consolidation of CLA, while magnesium stearate had an opposite effect on the tablet crushing force.

Characterization of crosslinked high amylose starch matrix implants. 1. In vitro release of ciprofloxacin

The objective of this study was to characterize in vitro the potential of crosslinked high amylose starch (CLHAS) as an implant matrix for the delivery of ciprofloxacin (CFX). Direct compression of dry blends of four different matrices: control CLHAS; CLHAS with 1% hydrogenated vegetable oil (HVO); and CLHAS with 10 or 20% hydroxypropylmethylcellulose (HPMC), each of them with three CFX loadings (2.5, 5.0 and 7.5%) was performed to prepare twelve implant formulations. All CLHAS implants were used for 24-h dissolution tests to evaluate swelling, erosion, water uptake and CFX release. Additionally, 1%-HVO- CLHAS implants were used for an extended dissolution test. The presence of HPMC in the matrix increased CFX release rate, swelling, erosion and water uptake in a concentration-dependent manner whereas HVO had no effect. With increasing drug loading, a decrease of cumulative CFX percent release was observed in both 24-h and extended dissolution tests. Of the different formulations tested, CLHAS implants with 1% HVO and 7.5% CFX provided the longest period of drug delivery without any initial burst effect.

Characterization of subcutaneous Contramid implantation: host response and delivery of a potent analog of the growth hormone-releasing factor

Cross-linked high amylose starch (Contramid) was investigated as a solid implant for evaluation of host response in mice and as a possible delivery system for a human growth hormone-releasing factor analog (Hex-hGRF) release profile in pigs. Seventy mice were administered subcutaneously one 3 mm diameter Contramid pellet and host reaction was evaluated over 6 months. Thirty pigs were divided into four groups. All animals of the three implanted groups were administered subcutaneously 15 mg Hex-hGRF, (1) one pure Hex-hGRF implant; (2) four 30/70 w/w Hex-hGRF/Contramid implants; or (3) eight 15/85 w/w Hex-hGRF/Contramid implants. The fourth group (n=6) was injected subcutaneously twice daily with 10 microg/kg of Hex-hGRF over 5 consecutive days. Serum insulin-like growth factor-I (IGF-I) was monitored over 1 month. In mice, no adverse reaction occurred after implantation. Macroscopic and microscopic inflammatory reactions were always localized. Polymorphonuclear cells (PMNs) and macrophages predominated within and around the pellets, respectively. Thin fibrovascular septas eventually subdivided Contramid pellets which were progressively phagocytosed by macrophages. In pigs, serum IGF-I concentrations were increased over a 10 day period in all implanted groups. The initial IGF-I peak observed in the daily injected group was avoided in both Contramid implant groups but not in the pure Hex-hGRF implant group. These encouraging results warrant the development of Contramid implants as a sustained delivery system for peptidic drugs.

NMR imaging of high-amylose starch tablets. 1. Swelling and water uptake

Pharmaceutical tablets made of modified high-amylose starch have a hydrophilic polymer matrix into which water can penetrate with time to form a hydrogel. Nuclear magnetic resonance imaging was used to study the water penetration and the swelling of the matrix of these tablets. The tablets immersed in water were imaged at different time intervals on a 300 MHz NMR spectrometer. Radial images show clearly the swelling of the tablets and the water concentration profile. The rate constants for water diffusion and the tablet swelling were extracted from the experimental data. The water diffusion process was found to follow case II kinetics at 25 degrees C. NMR imaging also provided spin density profiles of the water penetrating inside the tablets.

Fronts movement as a useful tool for hydrophilic matrix release mechanism elucidation

The purpose of this study was to modify the fronts movement method proposed by Colombo et al. in order to apply it to uncoloured drugs and hydrophilic non-swellable matrices. Matrix tablets were prepared using theophylline as a model drug and sodium carboxymethylcellulose (NaCMC) or a new graft copolymer, hydroxypropylcellulose methylmethacrylate dried by lyophilization (HCMMAL), as polymer carriers. Drug release experiments were performed from the whole tablets. Radial drug release and fronts movement were also evaluated using special devices consisting of two Plexiglass(R) discs joined by means of four stainless steel screws. Release kinetics were determined by means of Higuchi, Korsmeyer and Peppas equations and were related to the fronts movement data. The analysis of drug release and fronts movement kinetics revealed a different release mechanism for both matrices. Drug release from NaCMC matrices was mostly controlled by relaxation, whereas drug diffusion through the porous network regulated drug release from HCMMAL matrices. A reduction in the surface exposed to the dissolution medium led to a decrease in the drug release rate, but the release mechanism was not essentially modified. Fronts movement was shown as a useful tool for matrix release mechanism elucidation. A new denomination for the different fronts observed in HCMMAL matrices was proposed.

Analysis of film coating thickness and surface area of pharmaceutical pellets using fluorescence microscopy and image analysis

A method is presented which enables geometrical characterisation of pharmaceutical pellets and their film coating. It provides a high level of details on the single pellet level. Image analysis was used to determine the coating thickness (h) applied on the pellets and the surface area (A) of the pellet cores. Different definitions of A and h are evaluated. Hierarchical analysis of variance was used to resolve different sources contributing to the total variance. The variance within pellets and the variance between pellets were found as significant sources of variation. Special emphasis was put on evaluation of A/h due to its influence on the release rate of an active drug substance from the pellet core. The pellet images were thus used to predict variations in the release rate using a mathematical model as a link between the image data and the release rate. General aspects of image analysis are discussed. The method would be useful in calibration of near infrared spectra to h in process analytical chemistry.

Cross-linked high amylose starch for controlled release of drugs: recent advances

Cross-linked high amylose starches have been developed as excipients for the formulation of controlled-release solid dosage forms for the oral delivery of drugs. Advantages of this new class of excipients include cost-effectiveness, readily accessible industrial manufacturing technology, high active ingredient core loading and the possibility of achieving a quasi zero-order release for most drugs. In addition to the latter, other features distinguish cross-linked high amylose starches from other excipients used to prepare hydrophilic matrices. Among these are the absence of erosion, the limited swelling and the fact that increasing cross-linking degrees results in increased water uptake rate, drug release rate and equilibrium swelling. Thus the goal of the present study was to gain some insights into the mechanism of drug release control by matrices of cross-linked high amylose starch. Water transport kinetics and dimensional changes were studied in matrices placed in water at 37 degrees C by an image analysis technique. The results show that in the first 5 min, a gel layer is formed at the surface of the tablet, after which the gel front seems to halt its progression toward the center of the tablet. Water continues to diffuse through the front and to invade the core. As a consequence, this latter swells, with a predominance for radial swelling. Equilibrium swelling is reached over 3 days, when the water concentration in the tablet becomes homogeneous and the whole tablet gelifies. Solid-state 13C-NMR were acquired on cross-linked high amylose starch powders, tablets and hydrated tablets with varying cross-linking degrees. They show a predominance of the V-type single helix arrangement of amylose in the dry state irrespective of the cross-linking degree. Upon hydration, the homologues with a low cross-linking degrees show a transition from the V to the B-type double helix arrangement. It is therefore hypothesized that the capacity of amylose to undergo the V to B transition is an important factor in controlling water transport and drug release rate. Finally applications to different drugs are reviewed briefly. They illustrate the versatility of this technology as generic versions of zero order OROS drug (Efidac) and Fickian release conventional matrices (Voltaren SR) were developed and successfully tested in pilot clinical studies to be bioequivalent to the references. These studies further showed that cross-linked high amylose starch matrices have the lowest inter-subject variability among the systems tested and show a total absence of food effect.