Swellable matrices for controlled drug delivery: gel-layer behaviour, mechanisms and optimal performance

Design and evaluation of novel barrier layer technologies for controlling venlafaxine hydrochloride release from tablet dosage form

CONTEXT

Venlafaxine Hydrochloride (VH) is a highly soluble and highly permeable antidepressant compound. Thus controlling VH release from tablet dosage form over a prolonged period is a challenge.

OBJECTIVE

The objective of this work was to study the effect of various barrier layer formulation compositions, its orientations and manufacturing technology on release profile of highly soluble VH.

MATERIALS AND METHODS

Different barrier compositions and orientations were established on the same extended release formulations of VH using compression as well as film coating technologies. Barrier effectiveness in reducing the VH release was verified through in vitro dissolution studies.

RESULTS AND DISCUSSION

The "belly band" portion of the tablets was successfully oriented in different ways to develop bilayer as well as trilayer tablets. The compression technology had substantially reduced the VH release up to 16% in various compositions and orientation as compared to core tablet. The film coating technology had reduced the VH release up to 14% effectively; thereby shifting the dissolution curve to downside.

CONCLUSION

The explored "belly band" portion of the tablets had reduced the VH release substantially. These innovatively created different barrier orientation technologies hold the great promise of commercialization in future.

Quantifying the release of lactose from polymer matrix tablets with an amperometric biosensor utilizing cellobiose dehydrogenase

The release of lactose (hydrophilic) from polymer tablets made with hydrophobically modified poly(acrylic acid) (HMPAA) have been studied and compared to the release of ibuprofen, a hydrophobic active substance. Lactose is one of the most used excipients for tablets, but lactose release has not been widely studied. One reason could be a lack of good analytical tools. A novel biosensor with cellobiose dehydrogenase (CDH) was used to detect the lactose release, which has a polydiallyldimethylammonium chloride (PDADMAC) layer that increases the response. A sample treatment using polyethylenimine (PEI) was developed to eliminate possible denaturants. The developed methodology provided a good approach to detect and quantify the released lactose. The release was studied with or without the presence of a model amphiphilic substance, sodium dodecyl sulphate (SDS), in the release medium. Ibuprofen showed very different release rates in the different media, which was attributed to hydrophobic interactions between the drug, the HMPAA and the SDS in the release medium. The release of hydrophilic lactose, which did not associate to any of the other components, was rapid and showed only minor differences. The new methodology provides a useful tool to further evaluate tablet formulations by a relatively simple set of experiments.

High-amylose sodium carboxymethyl starch matrices: development and characterization of tramadol hydrochloride sustained-release tablets for oral administration

Substituted amylose (SA) polymers were produced from high-amylose corn starch by etherification of its hydroxyl groups with chloroacetate. Amorphous high-amylose sodium carboxymethyl starch (HASCA), the resulting SA polymer, was spray-dried to obtain an excipient (SD HASCA) with optimal binding and sustained-release (SR) properties. Tablets containing different percentages of SD HASCA and tramadol hydrochloride were produced by direct compression and evaluated for dissolution. Once-daily and twice-daily SD HASCA tablets containing two common dosages of tramadol hydrochloride (100 mg and 200 mg), a freely water-soluble drug, were successfully developed. These SR formulations presented high crushing forces, which facilitate further tablet processing and handling. When exposed to both a pH gradient simulating the pH variations through the gastrointestinal tract and a 40% ethanol medium, a very rigid gel formed progressively at the surface of the tablets providing controlled drug-release properties. These properties indicated that SD HASCA was a promising and robust excipient for oral, sustained drug-release, which may possibly minimize the likelihood of dose dumping and consequent adverse effects, even in the case of coadministration with alcohol.

The design of controlled-release formulations resistant to alcohol-induced dose dumping--a review

The concomitant intake of alcoholic beverages together with oral controlled-release opioid formulations poses a serious safety concern since alcohol has the potential to alter the release rate controlling mechanism of the dosage form which may result in an uncontrolled and immediate drug release. This effect, known as alcohol-induced dose dumping, has drawn attention of the regulatory authorities. Thus, the Food and Drug Administration (FDA) recommends that in vitro drug release studies of controlled-release dosage forms containing drugs with narrow therapeutic range should be conducted in ethanolic media up to 40%. So far, only a limited number of robust dosage forms that withstand the impact of alcohol are available and the development of such dosage forms is still a challenge. This review deals with the physico-chemical key factors which have to be considered for the preparation of alcohol-resistant controlling dosage forms. Furthermore, appropriate matrix systems and promising technological strategies, which are suitable to prevent alcohol-induced dose dumping, are discussed.

Characterization and properties of carboxymethyl cellulose hydrogels crosslinked by polyethylene glycol

Novel hydrogels were prepared from carboxymethyl cellulose (CMC) sodium salt by crosslinking with polyethylene glycol diglycidyl ether (PEGDE). The detailed structures of the hydrogels were determined via FTIR and solid-state NMR spectroscopic analyses. Increasing the feed ratio of PEGDE to CMC in the reaction mixture led to an increase in the crosslinking degree, which enhanced the physical strength of the hydrogels. The hydrogels exhibited enzyme degradability, and after 3 days of incubation with cellulase, 62-28 wt% of the CMC in the hydrogel was degraded under the conditions employed in this study. In addition, the hydrogels exhibited protein adsorption and release abilities, and the amounts of proteins adsorbed on the hydrogels and the release profile of the proteins depended on the protein sizes and crosslinking degree of the hydrogels. These unique properties might enable the use of CMC-based hydrogels as drug delivery system carriers for protein-based drugs if the biological safety of the hydrogel can be verified.

Using NMR chemical shift imaging to monitor swelling and molecular transport in drug-loaded tablets of hydrophobically modified poly(acrylic acid): methodology and effects of polymer (in)solubility

A new technique has been developed using NMR chemical shift imaging (CSI) to monitor water penetration and molecular transport in initially dry polymer tablets that also contain small low-molecular weight compounds to be released from the tablets. Concentration profiles of components contained in the swelling tablets could be extracted via the intensities and chemical shift changes of peaks corresponding to protons of the components. The studied tablets contained hydrophobically modified poly(acrylic acid) (HMPAA) as the polymer component and griseofulvin and ethanol as hydrophobic and hydrophilic, respectively, low-molecular weight model compounds. The water solubility of HMPAA could be altered by titration with NaOH. In the pure acid form, HMPAA tablets only underwent a finite swelling until the maximum water content of the polymer-rich phase, as confirmed by independent phase studies, had been reached. By contrast, after partial neutralization with NaOH, the polyacid became fully miscible with water. The solubility of the polymer affected the water penetration, the polymer release, and the releases of both ethanol and griseofulvin. The detailed NMR CSI concentration profiles obtained highlighted the clear differences in the disintegration/dissolution/release behavior for the two types of tablet and provided insights into their molecular origin. The study illustrates the potential of the NMR CSI technique to give information of importance for the development of pharmaceutical tablets and, more broadly, for the general understanding of any operation that involves the immersion and ultimate disintegration of a dry polymer matrix in a solvent.

An innovative matrix controlling drug delivery produced by thermal treatment of DC tablets containing polycarbophil and ethylcellulose

An innovative matrix, produced by thermal treatment on direct compression (DC) tablets containing polycarbophil (POL) and ethylcellulose (EC), identified as matrix forming polymers, and able to control the release of diltiazem hydrochloride, was developed. At pH 7.2, 72 ± 1.2% (w/w) of drug loaded was released in 25 h, mostly at constant rate. This swellable and unerodible matrix controls drug release by an anomalous transport mechanism. The modifications induced by the thermal treatment are irreversible and can be used to control and characterize the matrix. A 3-component constrained mixture design allowed the investigation of the experimental domain in which the matrix forms and the computation of a mathematical model that can be used to optimize the formulation properties. The release rate can be modulated (0.032-0.064% drug released/min) through the choice of suitable treatment conditions and tablet composition. The maximum amount of diltiazem hydrochloride released by zero-order kinetics, at the lowest release rate, occurs for POL:EC ratio in the range of 1:1-2:3 with 20-30% of diluent. The tablets are able to load up to 50% (w/w) of diltiazem hydrochloride without losing their properties. A stability study performed on a selected formulation containing DTZ showed stability for at least 2.7 years at RT conditions.

Quantification of swelling and erosion in the controlled release of a poorly water-soluble drug using synchrotron X-ray computed microtomography

The hydration layer plays a key role in the controlled drug release of gel-forming matrix tablets. For poorly water-soluble drugs, matrix erosion is considered as the rate limiting step for drug release. However, few investigations have reported on the quantification of the relative importance of swelling and erosion in the release of poorly soluble drugs, and three-dimensional (3D) structures of the hydration layer are poorly understood. Here, we employed synchrotron radiation X-ray computed microtomography with 9-μm resolution to investigate the hydration dynamics and to quantify the relative importance of swelling and erosion on felodipine release by a statistical model. The 3D structures of the hydration layer were revealed by the reconstructed 3D rendering of tablets. Twenty-three structural parameters related to the volume, the surface area (SA), and the specific surface area (SSA) for the hydration layer and the tablet core were calculated. Three dominating parameters, including SA and SSA of the hydration layer (SA hydration layer and SSA hydration layer ) and SA of the glassy core (SA glassy core ), were identified to establish the statistical model. The significance order of independent variables was SA hydration layer > SSA hydration layer > SA glassy core , which quantitatively indicated that the release of felodipine was dominated by a combination of erosion and swelling. The 3D reconstruction and structural parameter calculation methods in our study, which are not available from conventional methods, are efficient tools to quantify the relative importance of swelling and erosion in the controlled release of poorly soluble drugs from a structural point of view.

Surfactants modify the release from tablets made of hydrophobically modified poly (acrylic acid)

Many novel pharmaceutically active substances are characterized by a high hydrophobicity and a low water solubility, which present challenges for their delivery as drugs. Tablets made from cross-linked hydrophobically modified poly (acrylic acid) (CLHMPAA), commercially available as Pemulen™, have previously shown promising abilities to control the release of hydrophobic model substances. This study further investigates the possibility to use CLHMPAA in tablet formulations using ibuprofen as a model substance. Furthermore, surfactants were added to the dissolution medium in order to simulate the presence of bile salts in the intestine.

The release of ibuprofen is strongly affected by the presence of surfactant and/or buffer in the dissolution medium, which affect both the behaviour of CLHMPAA and the swelling of the gel layer that surrounds the disintegrating tablets. Two mechanisms of tablet disintegration were observed under shear, namely conventional dissolution of a soluble tablet matrix and erosion of swollen insoluble gel particles from the tablet. The effects of surfactant in the surrounding medium can be circumvented by addition of surfactant to the tablet. With added surfactant, tablets that may be insusceptible to the differences in bile salt level between fasted or fed states have been produced, thus addressing a central problem in controlled delivery of hydrophobic drugs. In other words CLHMPAA is a potential candidate to be used in tablet formulations for controlled release with poorly soluble drugs.

Formulation development and stability studies of norfloxacin extended-release matrix tablets

The aim of this research was to develop a new hydrophilic matrix system containing norfloxacin (NFX). Extended-release tablets are usually intended for once-a-day administration with benefits to the patient and lower discontinuation of the therapy. Formulations were developed with hydroxypropylmethylcellulose or poly(ethylene oxide) as hydrophilic polymers, with different molecular weights (MWs) and concentrations (20 and 30%). The tablets were found to be stable (6 months at 40 ± 2°C and 75 ± 5% relative humidity), and the film-coating process is recommended to avoid NFX photodegradation. The dissolution profiles demonstrated an extended-release of NFX for all developed formulations. Dissolution curves analyzed using the Korsmeyer exponential equation showed that drug release was controlled by both drug diffusion and polymer relaxation or erosion mechanisms. A more erosion controlled system was obtained for the formulations containing lower MW and amount of polymer. With the increase in both MW and amount of polymer in the formulation, the gel layer became stronger, and the dissolution was more drug-diffusion dependent. Formulations containing intermediate MW polymers or high concentration (30%) of low MW polymers demonstrated a combination of extended and complete in vitro drug release. This way, these formulations could provide an increased bioavailability in vivo.

Controlled release of ropinirole hydrochloride from a multiple barrier layer tablet dosage form: effect of polymer type on pharmacokinetics and IVIVC

The purpose of the present study was to control in vitro burst effect of the highly water-soluble drug, ropinirole hydrochloride to reduce in vivo dose dumping and to establish in vitro-in vivo correlation. The pharmacokinetics of two entirely different tablet formulation technologies is also explored in this study. For pharmacokinetics study, FDA recommends at least 10% difference in drug release for formulations to be studied but here a different approach was adopted. The formulations F8A and F9A having similar dissolution profiles among themselves and with Requip® XL™ (f 2 value 72, 77, 71 respectively) were evaluated. The C max of formulation F8A comprising hypromellose 100,000 cP was 1005.16 pg/ml as compared to 973.70 pg/ml of formulation F9A comprising hypromellose 4000 cP irrespective of T max of 5 and 5.75 h, respectively. The difference in release and extent of absorption in vivo was due to synergistic effect of complex RH release mechanism; however, AUC0-t and AUC0-∞ values were comparable. The level A correlation using the Wagner-Nelson method supported the findings where R (2) was 0.7597 and 0.9675 respectively for formulation F8A and F9A. Thus, in vivo studies are required for proving the therapeutic equivalency of different formulation technologies even though f 2 ≥ 50. The technology was demonstrated effectively at industrial manufacturing scale of 200,000 tablets.

The influence of vitamin E succinate on the stability of polyethylene oxide PEO controlled release matrix tablets

Hydrophilic matrices are a principal technology used for extended release (ER) oral dosage forms and a recent review concluded that their development is currently one of the most important challenges in pharmaceutical research. High molecular weight polyethylene oxides (PEOs) have been proposed as an alternative to hydroxypropylmethylcellulose (HPMC) for the manufacture of controlled release matrix tablets. It is known that PEO's are prone to oxidative degradation which can occur by chain scission and can be catalyzed by metal ions. In this study, we investigated the stability of PEO matrix tablets, of different molecular weight, containing diltiazem hydrochloride, when stored at 40 °C. The results show that there were dramatic increases in the release rate of the diltiazem following storage over only a few weeks, resulting in immediate release profiles after eight weeks, even for the highest molecular weight grade. We employed Gel permeation chromatography (GPC), viscosity and differential scanning calorimetry (DSC) techniques to try and determine the underlying causes of these dramatic shifts in dissolution profiles on storage. The results showed that there were significant decreases in the molecular weight of the PEO's during storage. The second part of the study looked at the addition of three different levels of vitamin E succinate to the tablets. The results clearly demonstrate the ability of the added antioxidant to reverse the significant reductions in molecular weight seen using GPC, viscosity and DSC. Importantly the addition of the antioxidant was able to stabilize the release profile of the diltiazem especially when present at a 1% level. Researchers and those working in pharmaceutical development should be aware of the potential stability risks when making matrix tablets containing PEO's and may wish to consider the addition of an antioxidant to the tablet formulation.

Starch-based microspheres for sustained-release of curcumin: preparation and cytotoxic effect on tumor cells

Curcumin (CUR) has been proved to be highly cytotoxic against different tumor cell lines. However, its poor solubility in aqueous medium and fast degradation in physiological pH are the common drawbacks preventing its efficient practical use. Herein, we report the development of original microspheres based on the biopolymer starch crosslinked with N,N-methylenebisacrylamide (MBA) to be applied as an efficient delivering system for CUR. The starch-based microspheres showed high loading efficiency even in loading solution with different CUR concentrations. In vitro release assays data showed that the CUR release is governed by anomalous transport (n=0.73) and it is pH-dependent. Cytotoxicity assays showed that starch microspheres could improve the cytotoxicity of CUR toward Caco-2 and HCT-116 tumor cell lines up to 40 times than that found for pure CUR. This behavior was attributed to the slowly and sustained release of CUR from the microspheres.

Carboxymethyl starch and lecithin complex as matrix for targeted drug delivery: I. Monolithic mesalamine forms for colon delivery

For drugs expected to act locally in the colon, and for successful treatment, a delivery device is necessary, in order to limit the systemic absorption which decreases effectiveness and causes important side effects. Various delayed release systems are currently commercialized; most of them based on pH-dependent release which is sensitive to gastrointestinal pH variation. This study proposes a novel excipient for colon delivery. This new preparation consists in the complexation between carboxymethyl starch (CMS) and Lecithin (L). As opposed to existing excipients, the new complex is pH-independent, inexpensive, and easy to manufacture and allows a high drug loading. FTIR, X-ray, and SEM structural analysis all support the hypothesis of the formation of a complex. By minor variation of the excipient content within the tablet, it is possible to modulate the release time and delivery at specific sites of the gastrointestinal tract. This study opens the door to a new pH-independent delivery system for mesalamine targeted administration. Our novel formulation fits well with the posology of mesalamine, used in the treatment of Inflammatory Bowel Disease (IBD), which requires repeated administrations (1g orally four times a day) to maintain a good quality of life.

Improvement of dissolution behavior of poorly water soluble drugs by biodegradable polymeric submicron carriers containing sparingly methylated β-cyclodextrin

The objective of this study was to develop submicron carriers of two drugs that are practically insoluble in water, i.e. meloxicam and aceclofenac, to improve their dissolution behavior. The phase solubility of the drugs was studied using different concentrations of sparingly methylated β-cyclodextrin, Kleptose(®) Crysmeβ (Crysmeb), in the presence and absence of 0.2 % w/v water-soluble chitosan. Drug-loaded submicron particles (SMPs) were prepared using chitosan chlorhydrate and Crysmeb by the ionotropic gelation method. The SMPs were characterized in terms of powder X-ray diffraction, Fourier transforms infrared spectroscopy, size determination, process yield, drug loading, encapsulation efficiency, surface morphology and in vitro release. The drug loading in the SMPs was enhanced in the presence of Crysmeb. The in vitro drug release was found to be enhanced with SMPs prepared using higher concentrations of Crysmeb. These results indicate that SMPs formed from chitosan chlorhydrate and Crysmeb are promising submicron carriers for enhancing the dissolution of meloxicam and aceclofenac.

Matrix tablets: the effect of hydroxypropyl methylcellulose/anhydrous dibasic calcium phosphate ratio on the release rate of a water-soluble drug through the gastrointestinal tract I. In vitro tests

Different hydroxypropyl methylcellulose (HPMC)/anhydrous dibasic calcium phosphate (ADCP) matrix tablets have been developed aiming to evaluate the influence of both components ratio in the control release of a water-soluble drug (theophylline). In order to characterise the matrix tablets, swelling, buoyancy and dissolution studies have been carried out in different aqueous media (demineralised water, progressive pH medium, simulated gastric fluid, simulated intestinal fluid and simulated colonic fluid). The HPMC/ADCP ratio has turned out to be the determinant in the matrix behaviour: the HPMC characteristic swelling behaviour was modulated, in some cases, by the ADCP characteristic acidic dissolution. When the HPMC/ADCP ratio was ≥0.69, buoyancy, continuous swelling and low theophylline dissolution rate from the matrices (H1, H2 and H3) were observed in all dissolution media. Consequently, these formulations could be adequate as gastro-retentive drug delivery systems. Additionally, HPMC/ADCP ratio ≤0.11 (H5 and H6) induces a pH-dependent drug release which could be applied to design control drug release enteric formulations (with a suitable enteric coating). Finally, a HPMC/ADCP ratio between 0.11 and 0.69 (H4) yield a gastrointestinal controlled drug release, due to its time-dependent buoyancy (7 h) and a total drug delivery in 17 h in simulated colonic fluid.

The role of oral controlled release matrix tablets in drug delivery systems

Formulations that are able to control the release of drug have become an integral part of the pharmaceutical industry. In particular oral drug delivery has been the focus of pharmaceutical research for many years. This type of drug delivery has been at the centre of research due to its many benefits over conventional dosage. The focus of this review is on matrix tablets due to their widely use and simplicity of the formulation. This includes the discussion of various types of matrix tablets and factors affecting the drug release from these formulations. The mechanism of drug release from HPMC matrices is also discussed.

Study on sustained-release metformin hydrochloride from matrix tablet: Influence of hydrophilic polymers and in vitro evaluation

The overall objective of the present work was to develop an oral sustained-release (SR) metformin tablet prepared by the direct compression method, using hydrophilic hydroxylpropylmethylcellulose (HPMC) and Guar gum polymer alone and in combination at different concentrations. Metformin hydrochloride (HCl), a biguanide, has a relatively short plasma half-life and low absolute bioavailability. All the batches were evaluated for thickness, weight variation, hardness and drug content uniformity and in vitro drug release. Mean dissolution time is used to characterize the drug release rate from a dosage form, and indicates the drug release-retarding efficiency of the polymer. The hydrophilic matrix of HPMC alone could not control the Metformin release effectively for 12 h whereas when combined with Guar gum, it could slow down the release of drug and, thus, can be successfully employed for formulating SR matrix tablets. Fitting the data to the Korsmeyer equation indicated that diffusion along with erosion could be the mechanism of drug release. Similarity factor ƒ2 values suggest that the test and reference profiles are identical.

A horse of a different color: how formulation influences medication effects

A medication's pharmacokinetic properties can be as important as its efficacy in determining how successful a treatment is. Formulation plays a critical role in absorption, distribution, and elimination of a drug, which in turn can influence the clinical profile of a medication, including onset and duration of action, consistency of plasma levels, ability to cross the blood-brain barrier, and other factors. Advances in drug delivery technology mean that formulation is now an integral component in the development of a drug. Likewise, formulation is one of the factors that may influence selection of a medication to suit the needs of a particular patient. This article briefly reviews the technologies commonly applied in the development of psychotropic medications, with emphasis on the various oral modified-release formulations, and discusses how formulation can be used to optimize the efficacy and tolerability of psychotropic drugs.

Nano-hydroxyapatite/chitosan/konjac glucomannan scaffolds loaded with cationic liposomal vancomycin: preparation, in vitro release and activity against Staphylococcus aureus biofilms

The objective of this study was to design a novel artificial bone scaffold for the therapy and prevention of refractory bacterial infections. Porous nano-hydroxyapatite/chitosan/konjac glucomannan (n-HA/CS/KGM) scaffolds were loaded with cationic liposomal vancomycin (CLV) to form a novel complex drug carrier (LLS). The kinetics of CLV release from LLS and the effects of the amount of konjac glucomannan (KGM) and CLV in LLS were examined in vitro. The anti-biofilm activity of LLS was also studied. Electron microscopy indicated that the liposomes were well preserved in the scaffold, and that CLV rather than free vancomycin is released from the scaffold. The weight percentage of KGM or CLV greatly influenced the release behavior of the scaffolds. LLS could provide sustained CLV release and inhibited the formation of Staphylococcus aureus biofilms better than scaffolds without CLV loaded. LLS may be a novel, effective drug-delivery system for the antibiotic treatment of osteomyelitis caused by biofilm infections.

Characterization of indomethacin release from polyethylene glycol tablet fabricated with mold technique

The purpose of this study was to use polyethylene glycol as a carrier to improve the solubility of an aqueous insoluble drug by melting and molding method. The release of dissolved drug was designed to be subsequently sustained with an addition of xanthan gum. The release of indomethacin from the developed system into phosphate buffer pH 6.2 was conducted using the dissolution apparatus. This carrier system could effectively enhance the solubility of indomethacin and an addition of xanthan gum could sustain the drug release. Eudragit L100 film coating could protect the carrier not to be disturbed with HCl buffer pH 1.2 and could dissolve in phosphate buffer pH 6.2, therefore, the drug release from coated tablet was initially very low but subsequently gradually released and prolonged in phosphate buffer pH 6.2. Differential scanning calorimetry study indicated the amorphous state of drug in polyethylene glycol carrier. Scanning electron microscopy photomicrograph indicated the drug diffusion outward through the porous network of matrix tablets into the dissolution fluid and curve fitting signified that the drug release kinetic was Fickian diffusion.