The influence of buffer species and strength on diltiazem HCl release from beads coated with the aqueous cationic polymer dispersions, Eudragit RS, RL 30D

Effect of Eudragit RS 30D and talc powder on verapamil hydrochloride release from beads coated with drug layered matrices

The aim of this study was to investigate the effect of Eudragit RS 30D, talc, and verapamil hydrochloride on dissolution and mechanical properties of beads coated with "drug-layered matrices". This was accomplished with the aid of a three-factor multiple-level factorial design using percent drug release in 1 and 2 h, T(50), tensile strength, brittleness, stiffness and toughness as the responses. Beads were coated in a fluidized-bed coating unit. Surface morphology and mechanical properties were evaluated by surface profilometry and texture analysis, respectively. No cracks, flaws and fissures were observed on the surfaces. The mechanical properties were dependent on the talc/polymer ratio. The release of verapamil from the beads was influenced by matrix components. Increasing the level of both talc and Eudragit decreased the percent drug released from 67% to 4.8% and from 80.7% to 6.7% in 1 and 2 h, respectively, and increased T(50) from 0.8 to 25.7 h. It was concluded that beads could be efficiently coated with "drug-layered matrices". The release of drug, however, depends on a balance between the levels of drug, talc, and polymer, whereby desired dissolution and mechanical properties could be controlled by the talc/polymer ratio and the level of drug loading.

Evaluation of Sterculia foetida gum as controlled release excipient

The purpose of the research was to evaluate Sterculia foetida gum as a hydrophilic matrix polymer for controlled release preparation. For evaluation as a matrix polymer; characterization of Sterculia foetida gum was done. Viscosity, pH, scanning electronmicrographs were determined. Different formulation aspects considered were: gum concentration (10-40%), particle size (75-420 microm) and type of fillers and those for dissolution studies; pH, and stirring speed were considered. Tablets prepared with Sterculia foetida gum were compared with tablets prepared with Hydroxymethylcellulose K15M. The release rate profiles were evaluated through different kinetic equations: zero-order, first-order, Higuchi, Hixon-Crowell and Korsemeyer and Peppas models. The scanning electronmicrographs showed that the gum particles were somewhat triangular. The viscosity of 1% solution was found to be 950 centipoise and pH was in range of 4-5. Suitable matrix release profile could be obtained at 40% gum concentration. Higher sustained release profiles were obtained for Sterculia foetida gum particles in size range of 76-125 microm. Notable influences were obtained for type of fillers. Significant differences were also observed with rotational speed and dissolution media pH. The in vitro release profiles indicated that tablets prepared from Sterculia foetida gum had higher retarding capacity than tablets prepared with Hydroxymethylcellulose K15M prepared tablets. The differential scanning calorimetry results indicated that there are no interactions of Sterculia foetida gum with diltiazem hydrochloride. It was observed that release of the drug followed through surface erosion and anomalous diffusion. Thus, it could be concluded that Sterculia foetida gum could be used a controlled release matrix polymer.

Influence of plasticizer level on the drug release from sustained release film coated and hot-melt extruded dosage forms

In the current study, the influence of plasticizer level on drug release was investigated for solid dosage forms prepared by hot-melt extrusion and film coating. The properties of two highly water-soluble compounds, diltiazem hydrochloride (DTZ) and chlorpheniramine maleate (CPM), and a poorly water-soluble drug, indomethacin (IDM), were investigated in the melt extrudates containing either Eudragit RSPO or Eudragit RD 100 and triethyl citrate (TEC) as the plasticizer. In addition, pellets containing DTZ were film coated with Eudragit RS 30D and varying levels of TEC using a fluidized bed coating unit. Differential scanning calorimetry (DSC) demonstrated that both CPM and IDM exhibited a plasticization effect on the acrylic polymers, whereas no plasticizing effect by DTZ on Eudragit RSPO was observed. Thermogravimetric analysis (TGA) was used to investigate the thermal stability of the DTZ, Eudragit RSPO and TEC at 140 degrees C, the maximum temperature used in the hot-melt extrusion process. The chemical stability of DTZ and IDM in the extrudate following hot-melt processing was determined by high pressure liquid chromatography (HPLC). Drug release rates of both DTZ and CPM from hot-melt extrudates increased with an increase in the TEC level in the formulations, while the release rate of DTZ from the Eudragit RS 30D-coated pellets decreased with an increase in TEC in the coating dispersion. This phenomenon was due to the formation of a reservoir polymeric structure as a result of the thermal stress and shear stress involved in the hot-melt extrusion process regardless of the TEC level. In contrast, coalescence of the polymer particles in the film coating process was enhanced with higher levels of TEC, as demonstrated by scanning electron microscopy (SEM). The addition of TEC (0% to 8%) in the IDM hot-melt extrudate formulation had no influence on the drug release rate as the drug release rate was controlled by drug diffusion through the inside of the polymeric materials rather than between the polymer particles.

Permeability and swelling studies on free films containing inulin in combination with different polymethacrylates aimed for colonic drug delivery

The aim of this study was to assess some permeability and swelling characteristics of free films prepared by combination of inulin as a bacterially degradable system and time- or pH-dependent polymers as a coating formulation for colonic drug delivery. Different free films were prepared by casting and solvent evaporation method. Formulations containing inulin with Eudragit RS, Eudragit RL, Eudragit RS-Eudragit RL, Eudragit FS and Eudragit RS-Eudragit S with different ratios of inulin were prepared. After preparation, free films were evaluated by water vapor transmission test, swelling experiment and permeability to indomethacin and theophylline in different media. Formulations containing Eudragit FS had high resistance to water vapor permeation; but were unable to protect premature swelling and drug release in simulated small intestine media. Also, combination of Eudragit RS and Eudragit S had no suitable characteristics for colon delivery. However, Eudragit RS and Eudragit RL in combination with inulin made free films which had more swelling and permeation of drug in the colonic medium rather than the other media. It was shown that formulations containing sustained release polymethacrylates in combination with inulin have more potential as a coating system for specific colon delivery compared with pH-dependent polymers.

Drug-polymer mixed coating: a new approach for controlling drug release rates in pellets

A new approach to developing a drug-polymer mixed coat for highly water-soluble diltiazem pellets was investigated at different coating levels. Drug layering and the coating procedures were performed using a bottom spray fluidized bed coater. Drug pellets were coated with Eudragit NE40 (NE40) alone and in combination with diltiazem and hydrophilic cellulose derivatives. Dissolution studies revealed that incorporation of hydrophilic substances such as methylcellulose (MC), hydroxypropyl methylcellulose (HPMC), and the drug itself considerably increased the release rates. The release from mixed polymer coatings was fast compared to pellets coated with NE40 only. The major portion of the drug was released in about 2 hours in case of MC and NE40 mixed coat compared to hours from coated pellets containing HPMC or diltiazem. Incorporation of 15% to 25% drug with respect to the polymer coat helped to achieve a drug-release profile at a desirable rate over a 12 hour period. Moreover, the test formulation comprising 25% diltiazem with respect to 7% NE40 had a dissolution profile that matched the commercial product, Herbesser SR capsules. The release of diltiazem from the coated pellets was slightly affected by the pH of dissolution media.

Modulated release metoprolol succinate formulation based on ionic interactions: In vivo proof of concept

A modulated release, multiunit oral drug delivery technology using a system based on ionic interactions of anions of salts with quaternary ammonium ions of the ammoniomethacrylate polymer is described. The system consisted of a drug layered, EUDRAGIT NE-coated salt core which was further coated with EUDRAGIT RS. The relative effects of different anions on the polymer permeability have been investigated by studying their influence on the in vitro drug release. A prototype formulation of metoprolol succinate using this technology was developed and the drug release from the formulation was adjusted to have a release profile which would match the circadian rhythm i.e. a higher amount of drug would be available after an initial lower release (accelerated type of release). The formulation was tested in vivo in 12 healthy human volunteers in an open label, randomized, two-treatment, two-period, single dose crossover bio-study with reference formulation Beloc-zok. The in vivo release demonstrated that compared to the reference, a higher amount of drug was available in the plasma from the 7th hour onwards. A higher AUC of the drug was also observed compared to the reference formulation. An in vitro-in vivo correlation was attempted to identify a bio-relevant in vitro dissolution medium for the formulation.

Anion-induced water flux as drug release mechanism through cationic Eudragit RS 30D film coatings

The objective of this study was to investigate the anion-controlled drug release mechanism through the cationic coating polymer Eudragit RS 30 D as a function of the anion attraction toward the polymer's quarternary ammonium group (QAG), anion valence, and film composition. The mechanism was investigated by dissolution testing, determination of chloride ion exchange using ion chromatography, plasticizer leaching by means of differential scanning calorimetry, and water uptake by Karl Fischer titration. All experiments were performed on coated theophylline micro tablets or isolated films of various compositions using 0.01 M sodium nitrate, sodium sulfate, disodium succinate, sodium acetate, and succinic acid as dissolution media. The mechanism of drug release involved an immediate penetration of dissolution medium into the polymer followed by an instant exchange of chloride against the medium's anion species at completely different rates compared with the drug release. Dependent on the attraction of the anion toward the QAGs, a water flux was induced by back and forth exchanging anions. Strong attraction (nitrate, sulfate) resulted in a low water flux while weak attraction resulted in a high flux (acetate, succinic acid). The water flux increased at increasing number of QAGs. Plasticizer acted as a diluent in respect of the number of QAGs, thus higher plasticizer concentrations led to lower drug release.

Quantification of the leaching of triethyl citrate/polysorbate 80 mixtures from Eudragit® RS films by differential scanning calorimetry

The influence of triethyl citrate and polysorbate 80 (Tween 80) on the glass transition temperature (T(G)) of Eudragit RS membranes was investigated using differential scanning calorimetry (DSC). The T(G)-decreasing effect of TEC and Tween 80 displayed an almost identical performance in extent at a linear relationship between weight proportion and T(G) resulting in a specific T(G)-decrease (T(G,spec.)) of -1.98(K/%TEC) and -1.86(K/%Tween), respectively. Thus, the proportion of each adjuvant could be summarized as the plasticizer complex weight proportion (PC) with T(G,spec.)=1.96(K/%PC). Vice versa this linear relationship could be used to determine the proportion of plasticizer complex within the polymer membrane after swelling and diffusion processes, i.e. plasticizer leaching. For membranes containing 20% (w/w) TEC and 8% (w/w) Tween 80 as plasticizer complex a fast leaching resulted during the dissolution test reaching an equilibrium at 6.08% (+/-0.5) PC after 30 min in demineralised water. The DSC method proved to be a simple method to determine plasticizer leaching via T(G), however, without respect on the film forming properties of the two different excipients. Plasticizing with TEC or TEC/Tween 80 mixtures led to smooth and continuous films, while plasticizing with Tween 80 only resulted in mosaic like fissured films.

Physicochemical and release properties of pellets coated with Kollicoat® SR 30 D, a new aqueous polyvinyl acetate dispersion for extended release

Kollicoat SR 30 D is a new aqueous colloidal polyvinyl acetate dispersion used for extended release coatings. Kollicoat SR 30 D is stable against sedimentation, has a low viscosity (54 mPas) and a negative zeta potential of -23.2 mV because of the presence of the anionic surfactant, sodium dodecyl sulfate. Because of its low minimum film formation temperature (MFT = 18 degrees C), plasticizer addition and a thermal after-treatment (curing) of coated pellets was not required. Coated pellets showed no aging or curing effect. The rate of release could be easily adjusted by varying the coating level. A subcoating layer of the hydrophilic polymer, polyvinyl alcohol, between an ibuprofen-containing core and the Kollicoat SR coating prevented the diffusion of the lipophilic, low melting ibuprofen into the polymer coating during storage. The drug release from Kollicoat SR 30 D coated pellets was almost independent of the pH and ionic strength of release medium.

Application of Eudragit RS to thermo-sensitive drug delivery systems

The Eudragit RS and polyethylene glycol 400 (PEG 400) blend polymer (EPG) membranes were prepared by the solvent casting method to pioneer a novel application of Eudragit RS to a thermo-sensitive material. The EPG membranes containing 2.5-10% PEG 400 (2.5-10% EPG) showed the glass transition temperatures (Tgs) around the body temperature (32-42 degrees C). Drug permeation studies through the EPG membranes were carried out using acetaminophen (AAP) and aminopyrine (AMP) as the model drugs. The permeability of AAP and AMP through the EPG membranes has been shown to be a discontinuous function of temperature, that is, their permeability increased steeply above the Tg of the membranes. The amount of AMP permeated at 42 degrees C was nearly eight times as much as that at 36 degrees C. Arrhenius plots of the steady-state permeability coefficient (P) of AAP indicated two straight lines that intersect at the Tg of the 10% EPG membrane. In the water uptake study for the 10% EPG membrane, the degree of the swelling for the membrane tended to increase with increasing temperature above the Tg of the membrane. The thermo-sensitive permeation mechanism for the EPG membranes might be based on the structure change of the membranes caused by the glass transition, so that the membranes could absorb more water. Considering the high biological safety of Eudragit RS and PEG 400, the EPG membranes might be used to develop a novel thermo-sensitive drug delivery system.

Chronopharmaceutics: gimmick or clinically relevant approach to drug delivery?

Due to advances in chronobiology, chronopharmacology, and global market constraints, the traditional goal of pharmaceutics (e.g. design drug delivery systems with a constant drug release rate) is becoming obsolete. However, the major bottleneck in the development of drug delivery systems that match the circadian rhythm (chronopharmaceutical drug delivery systems: ChrDDS) may be the availability of appropriate technology. The last decade has witnessed the emergence of ChrDDS against several diseases. The increasing research interest surrounding ChrDDS may lead to the creation of a new sub-discipline in pharmaceutics known as chronopharmaceutics. This review introduces the concept of chronopharmaceutics, addresses theoretical/formal approaches to this sub-discipline, underscores potential disease-targets, revisits existing technologies and examples of ChrDDS. Future development in chronopharmaceutics may be made at the interface of other emerging disciplines such as system biology and nanomedicine. Such novel and more biological approaches to drug delivery may lead to safer and more efficient disease therapy in the future.

Lactic acid-induced modifications in films of Eudragit RL and RS aqueous dispersions

Eudragit RL (ERL) and RS (ERS) are polymethacrylate co-polymers, used in film coating of sustained release dosage forms, possessing some hydrophilic properties due to the presence of quaternary ammonium groups (QAG), where ERL contains more of such groups, hence more permeable, than ERS. However, because these groups ionize in solution, they undergo electrostatic interaction with negatively charged species. This phenomenon was utilized in this study to introduce modification in the film properties of ERL and ERS by interaction with lactic acid (LA). Thermal and mechanical analyses were carried out on polymeric free films. DSC showed a shift in Tg of the film while 1H NMR spectroscopy revealed a significant deshielding in the peak of QAGs protons after interaction with LA. Stress-strain test showed an increase in three mechanical parameters of the new film (containing LA): tensile strength to modulus ratio, relative surface energy and toughness index, indicating an enhancement in the mechanical stress resistance. Tablets coated with LA-containing films showed an increase in the release rate and extent and good stability upon aging, compared to those coated with the original film.

Rate and extent of ion-exchange process: the effect of physico-chemical characteristics of salicylate anions

Ten salicylate anions were used as model compounds in order to investigate systematically the impact of compound lipophilicity, valence, aqueous solubility and hydrogen bonding on binding into and release from a strong anion-exchange fiber, Smopex DS-218v. The release of salicylates from the fiber was studied at 1/10, 1/1 or 10/1 molar ratios of the external chloride-ions versus the salicylate bound in the fiber. The Donnan potential between the fiber and external solution (electrostatic interaction) appeared to be the main factor affecting the release of salicylates from the strong base anion-exchange fiber--an increase in the molar amount of the external chloride-ions resulted in a more effective release of all the salicylates from the fiber. The highest chloride-ion concentration (10/1) released the monovalent salicylates practically completely, while the lowest concentration (1/10) released only 10-35% of the loaded salicylates. The nature and strength of salicylate binding to the fiber by non-electrostatic interactions affected also the ion-exchange process, especially in dilute Cl- solutions. Hydrophobic interactions decreased the rate and amount of drug release from the fiber with the most lipophilic salicylates. Hydrogen bonding between the fiber and the compound restricted also the rate and extent of ion-exchange process of the hydrophilic 5-aminosalicylic acid and 5-hydroxysalicylic acid. The amount of divalent 5-carboxylsalicylic acid bound into and released from the fiber was clearly smaller as compared to the monovalent salicylates potentially due to cross-linking of the fiber chains.

Pediatric drug formulations of sodium benzoate: II. Coated granules with a lipophilic binder

Sodium benzoate is used as a therapeutic agent in the treatment of some rare disorders that predominantly affect children. In preliminary investigations, liquid and semi-solid formulations of sodium benzoate failed because children refuse the oral uptake due to the bad taste of the drug. Recently developed microcapsules with macrogol as a hydrophilic binder raise concern in high-dose treatment regimens because acceptable daily intake limits are exceeded. A novel microcapsule formulation was developed consisting of a lipophilic core with high sodium benzoate load and a saliva-resistant coating. A new powder quality of saturated triglycerides from plant origin was introduced which complies with the Ph. Eur. monograph 'Hard fat'. Sodium benzoate and the triglyceride were mixed and directly extruded at room temperature. The extrudates were spheronized and coated in a fluidized-bed process. The resulting coated granules are small-sized microcapsules and taste neutrally. They can be mixed with food before administration. As the amount of released sodium benzoate is negligible within the first minutes, children do not recognize the bad taste and accept the medication. Recently, sodium benzoate in this novel formulation has been designated by the European Community as an orphan drug in the treatment of non-ketotic hyperglycinemia.

Floating matrix tablets based on low density foam powder: effects of formulation and processing parameters on drug release

The aim of this study was to develop and physicochemically characterize single unit, floating controlled drug delivery systems consisting of (i). polypropylene foam powder, (ii). matrix-forming polymer(s), (iii). drug, and (iv). filler (optional). The highly porous foam powder provided low density and, thus, excellent in vitro floating behavior of the tablets. All foam powder-containing tablets remained floating for at least 8 h in 0.1 N HCl at 37 degrees C. Different types of matrix-forming polymers were studied: hydroxypropyl methylcellulose (HPMC), polyacrylates, sodium alginate, corn starch, carrageenan, gum guar and gum arabic. The tablets eroded upon contact with the release medium, and the relative importance of drug diffusion, polymer swelling and tablet erosion for the resulting release patterns varied significantly with the type of matrix former. The release rate could effectively be modified by varying the "matrix-forming polymer/foam powder" ratio, the initial drug loading, the tablet geometry (radius and height), the type of matrix-forming polymer, the use of polymer blends and the addition of water-soluble or water-insoluble fillers (such as lactose or microcrystalline cellulose). The floating behavior of the low density drug delivery systems could successfully be combined with accurate control of the drug release patterns.

Influence of chloride ion exchange on the permeability and drug release of Eudragit RS 30 D films

The objective of this study was to investigate the permeability of the cationic acrylic copolymer Eudragit RS 30 D as a function of the anionic buffer species of the dissolution media with special emphasis on the chloride ion exchange of the polymer. Indirect impedance measurement on isolated Eudragit RS films was used to investigate the mechanisms controlling membrane permeability. The chloride ion exchange was determined using capillary electrophoresis during dissolution testing of Eudragit RS 30 D-coated theophylline beads. The dissolution media investigated included various concentrations of sodium acetate, succinic acid and di-sodium succinate. The results of this study demonstrated that the degree of polymer swelling and related drug release was a function of the chloride counterion interaction with the polymer's quarternary ammonium groups. Chloride exchange during the dissolution test with other anions including acetate or succinate ions, resulted in significant changes in the polymer diffusion properties. The ion exchange proved to be the responsible mechanism of controlling polymer permeability as a function of anionic species and concentration. The order of anion permeability enhancing effect was acetate>mono-succinate>disuccinate. The ion exchange could be inhibited significantly by the addition of chloride ions to the dissolution medium.

Transport properties of ionic drugs in the ammonio methacrylate copolymer membranes

PURPOSE

Ammonio methacrylate copolymer is a pharmaceutical excipient widely used as a coating material for encapsulation of pellet and tablet dosage forms. Because of the charged ammonio function groups within the polymer, ionic drugs may interact with the coating film while transporting through it. The kinetic swelling and drug permeation properties of the ammonio methacrylate copolymer membranes were studied to delineate the effect of ionic interaction between the ionic drugs and the membranes.

METHODS

The pH and ionic strength of the solutions and the charged properties of drugs were varied to study the effects on the transport properties through the membranes. Ambroxol was chosen as a model cationic drug and aspirin as a model anionic drug.

RESULTS

The degree of membrane swelling in the drug-free solution decreases as the ionic strength increases but it is irrelevant to the pH. With the presence of ionic drugs, the degree of membrane swelling is affected by the drug species as well as the pH of the solutions in addition to the effect of ionic strength. The degree of swelling for a membrane in a solution containing aspirin is higher at a lower pH and ambroxol is lower at a lower pH. Aspirin experiences a three-stage permeation and ambroxol a two-stage one. The ion-exchange reaction between the anionic carboxylic groups in aspirin and the cationic ammonio groups in the membranes results in a slow permeation stage during the transient state. The pseudo steady-state permeability for each drug follows the trend as the degree of membrane swelling in the drug media at various pH and ionic strengths. However, it is much higher for aspirin than ambroxol although the degree of membrane swelling is higher in an ambroxol solution than that in an aspirin solution. The permeability of ambroxol through the membrane is largely reduced because of the Donnan exclusion effect.

CONCLUSIONS

The interaction between ionic drugs with the cationic groups in the membranes affects the ionic strength of the solutions and results in a pH-dependent degree of swelling. The ionic interaction also determines the drug permeation rates as well as the transient permeation behaviors.

The effects of plasticizers on the release of metoprolol tartrate from granules coated with a polymethacrylate film

For coating metoprolol tartrate granules, coating dispersions of Eudragit RS 30 D containing 6%, 12%, or 18% (based on polymer weight) of one of the following plasticizers were used: polyethylene glycol 400 (PEG400), propylene glycol (PG), tributyl citrate (TBC), and triethyl citrate (TEC). The release of metoprolol tartrate from these coated granules was determined at pH 1.2 and 7.4. Slower release resulted from the use of each plasticizer, being slower with increasing concentration of the plasticizer. Release was faster with the more water soluble PEG400 and PG than with TBC and TEC. pH-dependent release was observed with PEG400, PG, and TBC, while TEC gave pH-independent release of drug.

Electrolyte-induced compositional heterogeneity: a novel approach for rate-controlled oral drug delivery

In this work a new approach for in situ interactions between drug and electrolyte(s) is devised to control the release of highly water soluble drugs from oral hydrophilic monolithic systems. The model drug diltiazem hydrochloride (water solubility in excess of 50% at 25 degrees C), in conjunction with specific electrolytes, was principally employed in the design of swellable tablet formulations comprised of hydrophilic polymers such as hydroxypropylmethlcellulose (HPMC) or poly(ethylene oxide) (PEO). Electrolytes such as sodium bicarbonate or pentasodium tripolyphosphate were used to modulate intragel pH dynamics, swelling kinetics, and gel properties. Through in situ ionic interactions (an intragel matrix system composed of different chemical species that promote competition for water of hydration), a compositionally heterogeneous structure referred to as a "metamorphic scaffold" was established. It is shown that this latter structure results in the inhibition of drug dissolution, induction of a differential swelling rate, and attainment of "matrix stiffening" and axially provides a uniform gel layer. Presence of such phases in matrix structure and its influence on swelling dynamics enabled control of diltiazem hydrochloride release in a zero-order manner in different pH environments over a 24-h period. From kinetic analysis using the power law expressions [M(t)/M(infinity) = k(1)t(n), M(t)/M(infinity) = k(1)t(n) + k(2)t(2)(n)] and Hopfenberg model [M(t)/M(infinity) = 1 - (1 - k(1)t)(n)], it became apparent that the dynamics of matrix relaxation and controlled erosion were major factors involved in the release mechanism, while the composite rate constant k(1) (in Hopfenberg model) decreased by approximately 2-fold in the presence of electrolyte(s). These findings indicated that the dynamics of swelling and gel formation in the presence of ionizable species within hydrophilic matrices provide an attractive alternative for zero-order drug delivery from a simple monolithic system.

Influence of ionic strength on drug adsorption onto and release from a poly(acrylic acid) grafted poly(vinylidene fluoride) membrane

Ion exchange resins have several applications in pharmacy for controlled or sustained release of drugs. In the present study, effects of the ionic strengths of adsorption medium and dissolution medium on drug adsorption onto and release from a acrylic acid grafted poly(vinylidene fluoride) (PAA-PVDF) were studied. Despite their porosity, PAA-PVDF membranes act reasonable well as cation exchange membranes. It was observed, that ionic strength of adsorption medium, degree of grafting and concentration of propranolol-HCl in adsorption medium affect propranolol-HCl adsorption onto the membrane. The fluxes of smaller molecules (MW < 500) across the membrane decreased with ionic strength of buffer solution, whereas the fluxes of the large molecules (FITC-dextran, MW 4400) increased with ionic strength. Release rate of adsorbed propranolol-HCl from the membrane into phosphate buffer was greatly affected by ionic strength of adsorption medium. These results can be explained by a cation exchange process between membrane and cations present in the buffer solution and swelling behavior of the grafted PAA chains.

Guar gum-based sustained release diltiazem

PURPOSE

This study was performed to examine the use of guar gum to sustain the release of diltiazem under in vitro and in vivo conditions.

METHODS

Guar gum tablet formulations were prepared and evaluated under a variety of in vitro dissolution conditions. The formulations, along with Dilacor XR, were administered to a group eight fasted, healthy volunteers in a four period crossover study.

RESULTS

Varying the lot of guar gum as well as using guar from different suppliers had little effect on diltiazem dissolution. Also, dissolution of diltiazem from guar gum tablets was essentially independent of stir speed under normal conditions (USP Apparatus II) The stability of guar-based formulations under stressed conditions (40 degrees C/75% relative humidity for 3 months) was also established. All four formulations gave similar plasma concentrations over time in the healthy volunteers pharmacokinetic study.

CONCLUSIONS

Guar gum-based matrix tablets represent a simple and economical alternative to existing diltiazem sustained release dosage forms.