Release from or through a wax matrix system. I. Basic release properties of the wax matrix system

Transdermal delivery of atorvastatin calcium from novel nanovesicular systems using polyethylene glycol fatty acid esters: Ameliorated effect without liver toxicity in poloxamer 407-induced hyperlipidemic rats

CONTEXT

Atorvastatin calcium (ATV), a cholesterol-lowering agent, suffers from poor systemic availability (14%) after oral administration in addition to other side effects on the gastrointestinal tract, liver and muscle.

OBJECTIVE

The goal of the present investigation was to improve ATV bioavailability and overcome complications attendant with peroral administration by developing a new nanovesicular system encapsulating ATV for its delivery via the transdermal route.

METHODS

The vesicular systems were prepared by incorporating different polyethylene glycol fatty acid esters such as Labrasol, Cremophor EL, Gelucire 44/14 and Tween 80 as edge activators (EAs) in the lipid bilayer. The effect of the phosphatidylcholine (PC):EA molar ratio on the physicochemical properties of the vesicles was investigated. The pharmacokinetic studies of the optimized formulation were evaluated in rats. The optimized formulation was tested in poloxamer 407-induced hyperlipidemic rats. The plasma lipid profile, activity of liver enzymes, and oxidative stress parameters were measured using commercially available kits.

RESULTS

The results revealed high ATV entrapment efficiency (EE%) ranging from 55.62 to 83.91%. The formulations that contained Labrasol showed the highest EE%. The mean diameter of the vesicles was in the range of 186-583nm. T8 containing Gelucire 44/14 as an EA in the molar ratio of 15:1 (PC:EA) gave the smallest size and exhibited the best permeation parameters across the skin. The pharmacokinetic studies revealed that about three times statistically significant (p<0.05) improvement in bioavailability, after transdermal administration of nanotransfersomal ATV gel compared to oral ATV suspension. The transdermal vesicular system exhibited a significant decrease in plasma total cholesterol, triglycerides and LDL cholesterol comparable to oral ATV. Additionally, it lowered the malondialdehyde levels in plasma and abolished the increase in liver enzyme activity.

CONCLUSION

The results obtained suggest that the proposed transdermal vesicular system can serve as a promising alternative means for delivery of ATV.

Comparing different sterol containing solid lipid nanoparticles for targeted delivery of quercetin in hepatocellular carcinoma

Quercetin (QT) is a potential chemotherapeutic drug with low solubility that seriously limits its clinical use. The aim of this study was enhancing cellular penetration of QT by sterol containing solid lipid nanoparticles (SLNs) which make bilayers fluent for targeting hepatocellular carcinoma cells. Three variables including sterol type (cholesterol, stigmasterol and stigmastanol), drug and sterol content were studied in a surface response D-optimal design for preparation of QT-SLNs by emulsification solvent evaporation method. The studied responses included particle size, zeta potential, drug loading capacity and 24 h release efficiency (RE24%). Scanning electron and atomic force microscopy were used to study the morphology of QT-SLNs and their thermal behavior was studied by DSC analysis. Cytotoxicity of QT-SLNs was determined by MTT assay on HepG-2 cells and cellular uptake by fluorescence microscopy method. Optimized QT-SLNs obtained from cholesterol and QT with the ratio of 2:1 that showed particle size of 78.0 ± 7.0 nm, zeta potential of -22.7 ± 1.3 mV, drug loading efficiency of 99.9 ± 0.5% and RE24 of 56.3 ± 3.4%. IC50 of QT in cholesterol SLNs was about six and two times less than free QT and phytosterol SLNs, respectively, and caused more accumulation of QT in HepG2 cells. Blank phytosterol SLNs were toxic on cells.

Novel formulation of solid lipid microparticles of curcumin for anti-angiogenic and anti-inflammatory activity for optimization of therapy of inflammatory bowel disease

Objectives

This project was undertaken with a view to optimize the treatment of inflammatory bowel disease through a novel drug delivery approach for localized treatment in the colon. Curcumin has poor aqueous solubility, poor stability in the gastrointestinal tract and poor bioavailability. The purpose of the study was to prepare and evaluate the anti-inflammatory activity of solid lipid microparticles (SLMs) of curcumin for the treatment of inflammatory bowel disease in a colitis-induced rat model by a colon-specific delivery approach.

Methods

We have developed a novel formulation approach for treating experimental colitis in the rat model. SLMs of curcumin were prepared with various lipids, such as palmitic acid, stearic acid and soya lecithin, with an optimized percentage of poloxamer 188. The SLMs of curcumin were characterized for particle size, drug content, drug entrapment, in-vitro release, surface morphology and infrared, differential scanning calorimetry and X-ray studies. The colonic delivery system of SLM formulations of curcumin were further investigated for their anti-angiogenic and anti-inflammatory activity using chick embryo and rat colitis models.

Key findings

Particle size, drug content, drug entrapment and in-vitro release studies showed that formulation F4 containing one part stearic acid and 0.5% surfactant had the smallest diameter of 108 μm, 79.24% entrapment and exhibited excellent in-vitro release characteristics when compared with other formulations and pure curcumin. SLMs of curcumin (F4) proved to be a potent angio-inhibitory compound, as demonstrated by inhibition of angiogenesis in the chorioallantoic membrane assay. Rats treated with curcumin and its SLM complex showed a faster weight gain compared with dextran sulfate solution (DSS) control rats. The increase in whole colon length appeared to be significantly greater in SLM-treated rats when compared with pure curcumin and DSS control rats. An additional finding in the DSS-treated rats was chronic cell infiltration with predominance of eosinophils. Decreased mast cell numbers in the mucosa of the colon of SLMs of curcumin and pure curcumin-treated rats was observed.

Conclusions

The degree of colitis caused by administration of DSS was significantly attenuated by colonic delivery of SLMs of curcumin. Being a nontoxic natural dietary product, curcumin could be useful in the therapeutic strategy for inflammatory bowel disease patients.

Enhancement of gastrointestinal absorption of quercetin by solid lipid nanoparticles

The aim of the present study is to design and characterize quercetin-loaded solid lipid nanoparticles (QT-SLNs), clarify the absorption mechanism of QT-SLNs and to evaluate the potential of using solid lipid nanoparticles (SLNs) as an oral delivery carrier for poorly water soluble drugs. QT-SLNs were prepared by an emulsification and low-temperature solidification method. The QT-SLNs presented as spherically shaped under transmission electron microscopy, with an average diameter of 155.3 nm. The average drug entrapment efficiency, drug loading and zeta potential were 91.1%, 13.2% and -32.2 mV, respectively. Drug release from QT-SLNs was fitted to a double phase kinetics model and the equation was as follows: 100-Q=98.87e(-0.1042t)+42.45e(-0.0258t). The absorption of QT-SLNs in the gastrointestinal (GI) tract was studied using an in situ perfusion method in rats. It was found that the absorption percent in the stomach for 2 h was only 6.20%, the absorption process of intestine was first-process with passive diffusion mechanism, and the main absorptive segments were ileum and colon. A pharmacokinetic study was conducted in rats after oral administration of quercetin at 50 mg/kg in the form of either QT-SLNs or suspension. The plasma concentration-time curves were both fitted to a one-compartment model. The relative bioavailability of QT-SLNs to quercetin suspension was 571.4%. The T(max) and MRT for quercetin in plasma were both delayed. Our studies provide evidence that SLNs are valuable as an oral delivery carrier to enhance the absorption of a poorly water soluble drug, quercetin.

Formulation and characterization of curcuminoids loaded solid lipid nanoparticles

Curcuminoids loaded solid lipid nanoparticles (SLNs) have been successfully developed using a microemulsion technique at approximately 75 degrees C. It was found that variation in the amount of ingredients had profound effects on the curcuminoid loading capacity, the mean particle size, and size distribution. At optimized process conditions, lyophilized curcuminoids loaded SLNs showed spherical particles with a mean particle size of approximately 450nm and a polydispersity index of 0.4. Up to 70% (w/w) curcuminoids incorporation efficacy was achieved. In vitro release studies showed a prolonged release of the curcuminoids from the solid lipid nanoparticles up to 12h following the Higuchi's square root model. After 6-month storage at room temperature in the absence of sunlight, the physical and chemical stabilities of the lyophilized curcuminoids loaded SLNs could be maintained, i.e. the mean particle size and the amount of curcuminoids showed no significant changes (P>0.05) compared to the freshly prepared SLNs. In addition, the chemical stability of curcuminoids incorporated into SLNs was further investigated by dispersing them into a model cream base. The results revealed that after storage in the absence of sunlight for 6 months, the percentages of the remaining curcumin, bisdemethoxycurcumin and demethoxycurcumin were 91, 96 and 88, respectively.

Analysis of the Release Process of Phenylpropanolamine Hydrochloride from Ethylcellulose Matrix Granules III. Effects of the Dissolution Condition on the Release Process

In the pharmaceutical preparation of a controlled release drug, it is very important and necessary to understand the entire release properties. As the first step, the dissolution test under various conditions is selected for the in vitro test, and usually the results are analyzed following Drug Approval and Licensing Procedures. In this test, 3 time points for each release ratio, such as 0.2-0.4, 0.4-0.6, and over 0.7, respectively, should be selected in advance. These are analyzed as to whether their values are inside or outside the prescribed aims at each time point. This method is very simple and useful but the details of the release properties can not be clarified or confirmed. The validity of the dissolution test in analysis using a combination of the square-root time law and cube-root law equations to understand all the drug release properties was confirmed by comparing the simulated value with that measured in the previous papers. Dissolution tests under various conditions affecting drug release properties in the human body were then examined, and the results were analyzed by both methods to identify their strengths and weaknesses. Hereafter, the control of pharmaceutical preparation, the manufacturing process, and understanding the drug release properties will be more efficient. It is considered that analysis using the combination of the square-root time law and cube-root law equations is very useful and efficient. The accuracy of predicting drug release properties in the human body was improved and clarified.

Release from or through a Wax Matrix System. VI. Analysis and Prediction of the Entire Release Process of the Wax Matrix Tablet

Analysis of the entire release process of the wax matrix tablet was examined. Wax matrix tablet was prepared from a physical mixture of drug and wax powder to obtain basic or clear release properties. The release process began to deviate from Higuchi equation when the released amount reached at around the half of the initial drug amount. Simulated release amount increase infinitely when the Higuchi equation was applied. Then, the Higuchi equation was modified to estimate the release process of the wax matrix tablet. The modified Higuchi equation was named as the H-my equation. Release process was well treated by the H-my equation. Release process simulated by the H-my equation fitted well with the measured entire release process. Also, release properties from and through wax matrix well coincident each other. Furthermore, it is possible to predict an optional release process when the amount of matrix and composition of matrix system were defined.

Analysis of the Release Process of Phenylpropanolamine Hydrochloride from Ethylcellulose Matrix Granules II. Effects of the Binder Solution on the Release Process

The release properties of phenylpropanolamine hydrochloride (PPA) from ethylcellulose (EC) matrix granules prepared by an extrusion granulation method were examined. The release process could be divided into two parts; the first and second stages were analyzed by applying square-root time law and cube-root law equations, respectively. The validity of the treatments was confirmed by the fitness of a simulation curve with the measured curve. In the first stage, PPA was released from the gel layer of swollen EC in the matrix granules. In the second stage, the drug existing below the gel layer dissolved and was released through the gel layer. The effect of the binder solution on the release from EC matrix granules was also examined. The binder solutions were prepared from various EC and ethanol (EtOH) concentrations. The media changed from a good solvent to a poor solvent with decreasing EtOH concentration. The matrix structure changed from loose to compact with increasing EC concentration. The preferable EtOH concentration region was observed when the release process was easily predictable. The time and release ratio at the connection point of the simulation curves were also examined to determine the validity of the analysis.

Release from or through a wax matrix system. V. Applicability of the square-root time law equation for release from a wax matrix tablet

To obtain basic and clear release properties, wax matrix tablets were prepared from a physical mixture of drug and wax powder at a fixed mixing ratio. Properties of release from the single flat-faced surface, curved side surface, and/or whole surface of the wax matrix tablet were examined. Then tortuosity and the applicability of Higuchi's square-root time law equation were examined. The Higuchi equation well analyzed the release processes of different release manners. However, the region fitted to the Higuchi equation differed with the release manner. Tortuosity obtained with release from the single flat-faced surface and curved side surface was comparable with that obtained with the release from a reservoir device tablet, whereas tortuosity obtained with release from the whole surface was larger. As the wax matrix tablets were prepared at a fixed mixing ratio, their internal structures should be similar. Therefore changes in the matrix volume or volume fraction with release were examined, and an extra volume where dissolved drug stray becomes large with release time in the case of release from the whole surface. These factors should be taken into account for evaluation of applicability and release properties. Furthermore, the entire release process should be analyzed using a combination of the square-root time law and other suitable equations in accordance with release manner or condition.

Controlled release formulation of tramadol hydrochloride using hydrophilic and hydrophobic matrix system

The effect of concentration of hydrophilic (hydroxypropyl methylcellulose [HPMC]) and hydrophobic polymers (hydrogenated castor oil [HCO], ethylcellulose) on the release rate of tramadol was studied. Hydrophilic matrix tablets were prepared by wet granulation technique, while hydrophobic (wax) matrix tablets were prepared by melt granulation technique and in vitro dissolution studies were performed using United States Pharmacopeia (USP) apparatus type II. Hydrophobic matrix tablets resulted in sustained in vitro drug release (>20 hours) as compared with hydrophilic matrix tablets (<14 hours). The presence of ethylcellulose in either of the matrix systems prolonged the release rate of the drug. Tablets prepared by combination of hydrophilic and hydrophobic polymers failed to prolong the drug release beyond 12 hours. The effect of ethylcellulose coating (Surelease) and the presence of lactose and HPMC in the coating composition on the drug release was also investigated. Hydrophobic matrix tablets prepared using HCO were found to be best suited for modulating the delivery of the highly water-soluble drug, tramadol hydrochloride.

Analysis of the release process of phenylpropanolamine hydrochloride from ethylcellulose matrix granules

The release properties of phenylpropanolamine hydrochloride (PPA) from ethylcellulose (EC, ethylcellulose 10 cps (EC#10) and/or 100 cps (EC#100)) matrix granules prepared by the extrusion granulation method were examined. The release process could be divided into two parts, and was well analyzed by applying square-root time law and cube root law equations, respectively. The validity of the treatments was confirmed by the fitness of the simulation curve with the measured curve. At the initial stage, PPA was released from the gel layer of swollen EC in the matrix granules. At the second stage, the drug existing below the gel layer dissolved, and was released through the gel layer. Also, the time and release ratio at the connection point of the simulation curves was examined to determine the validity of the analysis. Comparing the release properties of PPA from the two types of EC matrix granules, EC#100 showed more effective sustained release than EC#10. On the other hand, changes in the release property of the EC#10 matrix granule were relatively more clear than that of the EC#100 matrix granule. Thus, it was supposed that EC#10 is more available for controlled and sustained release formulations than EC#100.

Release from or through a wax matrix system. IV. Generalized expression of the release process for a reservoir device tablet

Generalization of the release process through the wax matrix layer was examined by use of a reservoir device tablet. The wax matrix layer of the reservoir device tablet was prepared from a physical mixture of lactose and hydrogenated castor oil to simplify the release properties. Release through the wax matrix layer showed zero-order kinetics in a steady state after a given lag time, and could be divided into two stages. The first stage was the formation process of water channel by dissolving the soluble component in the wax matrix layer. The lag time obtained by applying the square root law equation was well connected with the amount of the matrix layer and mixed weight ratio of components in this layer. The second stage was the zero-order release process of drug in the reservoir through the wax matrix layer, because the effective surface area was fixed. The release rate constants were connected with thickness of the matrix layer and permeability coefficient, and the permeability coefficients were connected with the diffusion coefficient of drug and porosity. Hence the release rate constant could be connected with the amount of matrix layer and the mixed weight ratio of components in the matrix layer. It was therefore suggested that the release process could be generalized using the amount of matrix layer and the mixed weight ratio of components in the matrix layer.

Release from or through a wax matrix system. III. Basic properties of release through the wax matrix layer

Release property of reservoir device matrix tablet was examined. Wax matrix layer was prepared from physical mixture of lactose and hydrogenated castor oil to obtain basic release properties. Release process showed zero order kinetics in a steady state after a given lag times, and could be divided into two stages. The first stage was the formation process of water channel by dissolving the soluble component in the wax matrix layer. The lag time was considered to be the time required forming water channel and the time begun to release drug through the wax matrix layer at the same time. The lag time obtained by applying the square root law equation was well connected with the amount of matrix layer and mixed weight fraction of component in matrix layer. The second stage was the zero order release process of drug in the reservoir through the wax matrix layer. The release rate constants were calculated by taking into accounts of the thickness of matrix layer and permeability coefficient, and were well connected with the amount of matrix layer and mixed weight fraction of component. Also it was suggested that the tortuosity of matrix layer could be expressed by a function of the porosity defined by the mixed weight fraction.

Release from or through a wax matrix system. II. Basic properties of release from or through the wax matrix layer

In order to examine basic properties of release from and through wax matrix layer, reservoir device matrix tablet was prepared from a physical mixture of hydrogenated caster oil and drug that was the same one in the reservoir. Release process could be divided into two stages. The first stage was the formation process of water channel by dissolving the drug in the wax matrix layer, and dissolved drug was released from the matrix layer following the square-root-of-time law equation. Hence, the drug penetration coefficient and tortuosity in the matrix layer were estimated. The second stage was the zero order release process of drug in the reservoir through the wax matrix layer. The release rate constant was calculated from the slope of line. Hence, the drug permeability coefficient and tortuosity were estimated. Fundamentally, tortuosity can not be expressed by some meaningful factors, and is obtained as an experimental result. By preparing wax matrix system from a physical mixture other than melted granule method, it was suggested that the matrix structure was uniform three-dimensionally. As a result, tortuosity could be expressed by a function of porosity, because unrecognized factors such as the surface coverage and thickness of melted wax on the soluble component should not be involved.