Transdermal delivery system for zidovudine:in vitro, ex vivo andin vivo evaluation

The objective of this study was to prepare a transdermal delivery system (TDS) for zidovudine (AZT) with a combination of menthol and oleic acid as penetration enhancers incorporated in hydroxypropyl methylcellulose, and to evaluate ex vivo as well as in vivo permeation across rat skin. It was found that AZT in gel formulation was stable in both refrigerated as well as accelerated stability conditions for 3 months and further, the gel did not significantly retard the permeability of AZT across the skin in comparison with solution formulation. Ex vivo steady state flux of AZT across rat skin from gel was 2.26 mg cm(-2) h(-1), which is sufficient to achieve therapeutic plasma concentrations. Intravenous pharmacokinetic parameters of AZT in rats were determined and used together with ex vivo flux data to generate theoretical plasma profiles of AZT and compared with plasma concentrations achieved after application of TDS. Further, steady state plasma concentrations of drug following multiple applications of TDS were determined and good correlations between ex vivo and in vivo data were observed. In addition, the combination of penetration enhancers used at 2.5% w/w in this study proved efficient in achieving sufficient enhancement in the transdermal permeability of AZT across rat skin with reduced skin irritation potential when compared with individual penetration enhancers at higher concentrations.

Inhibitory effect of water-soluble chitosan on growth of Streptococcus mutans

The present study was undertaken to evaluate the effects of pH and the degree of polymerization of chitosan on the inhibition of growth of Streptococcus mutans. Three types of chitosan, polymer, oligomer and monomer, were used at 4% (W/V) and three different levels of pH: 6.0, 6.5 and 7.4. Bactericidal activity was calculated by the growth ratio. Chitosan oligomer significantly inhibited bacterial growth at a pH value of 6.5. All three types of chitosan strongly inhibited bacterial growth at pH 6.0. Furthermore, nearly complete inhibition was obtained with 2%(W/V) chitosan solution at constant pH 6.5. This study is the first to report that water-soluble chitosan directly suppresses the growth of the typical cariogenic bacterium S. mutans even at pH 6.5, without causing demineralization of the tooth surface.

Mucosal Drug Delivery: Membranes, Methodologies, and Applications

In recent years, extensive research into novel forms of drug delivery has suggested that mucosal approaches offer a promising therapeutic alternative, especially for systemically acting drugs. Transmucosal drug delivery offers many benefits, including noninvasive administration, convenience, rapid onset, as well as elimination of hepatic first-pass metabolism. The investigated absorptive surfaces consist of the nasal, buccal, ocular, vaginal, and rectal mucosae. Among these, the nasal and buccal routes have proved the most promising to date. The bioavailability achieved mainly depends upon the pathophysiological state of the mucosa and the properties of both the drug and delivery systems. Various agents can increase the efficacy of transmucosal drug delivery. These include cyclodextrins, bile salts, surfactants, fusidic acid derivatives, microspheres, liposomes, and bioadhesive agents. The mechanisms of action, effectiveness, and toxicity profiles of these enhancers have been investigated extensively in both animal and human models.

Essential Oils from Sweet Basil (Ocimum basilicum) as Novel Enhancers to Accelerate Transdermal Drug Delivery

The purpose of this study was to evaluate the essential oils from sweet basil (Ocimum basilicum, OB) as skin permeation enhancers to promote the percutaneous absorption of drugs. The in vitro and in vivo irritancy of the essential oils was also examined. Terpenes with various carbon numbers (mono-, sesqui-, di-, and tri-) were identified in both the lower-polarity fraction (OB-1) and higher-polarity fraction (OB-2). In vitro skin permeation and deposition of indomethacin were significantly enhanced after treatment with OB essential oils. The enhancing effect of OB-1 was greater than that of OB-2 in the in vitro permeation and in vivo cutaneous microdialysis analyses as well as in the plasma concentration of indomethacin. On the other hand, the in vivo study showed that OB-2 had a greater ability to retain the drug within the skin than did OB-1. Enhancement of the skin permeation of drugs by OB essential oils might be mainly due to improvement in the partitioning of the drugs to the stratum corneum. Both in vitro cell cultures (keratinocytes and skin fibroblasts) and in vivo transepidermal water loss showed no or only negligible irritation to skin by OB essential oils.

Amorphous Drug Delivery Systems: Molecular Aspects, Design, and Performance

The biopharmaceutical properties-especially the solubility and permeability-of a molecule contribute to its overall therapeutic efficacy. The newer tools of drug discovery have caused a shift in the properties of drug-like compounds, resulting in drugs with poor aqueous solubility and permeability, which offer delivery challenges, thus requiring considerable pharmaceutical manning. The modulation of solubility is a more viable option for enhancing bioavailability than permeability, because of the lack of "safe" approaches to enhance the latter. Solid-state manipulation in general, and amorphization in particular, are preferred ways of enhancing solubility and optimizing delivery of poorly soluble drugs. This review attempts to address the diverse issues pertaining to amorphous drug delivery systems. We discuss the various thermodynamic phenomenon such as glass transition, fragility, molecular mobility, devitrification kinetics, and molecular-level chemical interactions that contribute to the ease of formation, the solubility advantage, and the stability of amorphous drugs. The engineering of pharmaceutical alloys by solubilizing and stabilizing carriers, commonly termed solid dispersions, provide avenues for exploiting the benefits of amorphous systems. Carrier properties, mechanisms of drug release, and study of release kinetics help to improve the predictability of performance. The review also addresses the various barriers in the design of amorphous delivery systems, use of amorphous form in controlled release delivery systems, and their in vivo performance.

Development of agglomerated directly compressible diluent consisting of brittle and ductile materials

The objective of this investigation was to develop a novel multifunctional coprocessed adjuvant consisting of three known diluents that show different consolidation mechanisms. The method of wet granulation was adopted for the preparation of coprocessed product. Microcrystalline cellulose (MCC) and colloidal silicon dioxide (X1), lactose monohydrate (X2), and dibasic calcium phosphate dihydrate (X3, DCP) were used as independent variables in a simplex lattice design. Croscarmellose sodium was used at 4% level intragranularly in all the batches. The granules (44/120 #) were characterized for angle of repose, bulk density, tapped density, and Carr's index. The tablets of coprocessed adjuvants were characterized for crushing strength, friability, and disintegration time. Multiple linear regression was adopted for evolving refined mathematical models. A checkpoint batch was prepared and evaluated for particle size distribution, moisture uptake, and dilution potential by using nimesulide as a model drug. Microcrystalline cellulose shows poor flowability due to irregular shape and interlocking. Moreover, it loses a part of its compactibility on wet granulation. To attend these problems, a physical blend of 97% microcrystalline cellulose and 3% colloidal silicon dioxide M5 was prepared and used. The blend of MCC and colloidal silicon dioxide showed better flow than that of the original MCC. Hence, it may be easier to mix with lactose and dibasic calcium phosphate. The loss in compactibility of microcrystalline cellulose on wet granulation was also reduced due to presence of colloidal silicon dioxide. As expected, all the batches exhibited acceptable angle of repose (<35 degrees) and quick disintegration (<1 min). Full and refined models for Carr's index and crushing strength were evaluated. Based on the results of grid analysis, a checkpoint (50% MCC, 40% lactose, and 10% DCP) that satisfies both the conditions of Carr's index and crushing strength was selected. The adjuvants absorb very little moisture in the moisture uptake study. The results of dilution potential study reveal that up to 30% nimesulide, a poorly compressible drug, can be incorporated in the coprocessed product. In vitro drug dissolution from capsules containing pure drug powder and compressed tablets was comparable (f2 = 79). The results reveal that the desired product characters can be obtained by varying the quantity of MCC (a ductile material that undergoes plastic deformation), lactose (brittle material with low-fragmentation propensity), and DCP (brittle material with high-fragmentation propensity).

Exploration of melt granulation technique for the development of coprocessed directly compressible adjuvant containing lactose and microcrystalline cellulose

The objective of the present investigation was to prepare and evaluate lactose and microcrystalline cellulose based, directly compressible adjuvant using melt granulation technique. The percentage of polymer blend (PVP K 30 and PEG 4000; 5, 10, or 15%) and the polymer blend ratio (9:1, 1:1, or 1:9) were selected as independent variables in a 3(2) full factorial design. The lactose and microcrystalline cellulose blend (3:1) was mixed with the meltable binder on a water bath at 90 degrees C. The agglomerates were cooled to 35 degrees C and subsequently passed through 30 mesh. A batch containing 12.5% of the polymer blend containing 1:9 ratio of PVP:PEG was used for further studies. In an another 3(2) full factorial design, disintegrant (crospovidone, croscarmellose sodium, or sodium starch glycolate) and mode of addition of disintegrant (intragranular, extragranular, or combination of intragranular and extragranular) were used as independent variables. The agglomerates were evaluated for percentage fines and Carr's index. Tablets were prepared on a single-punch tablet machine, and they were evaluated for tensile strength, friability, and disintegration time. Regression analysis was carried out to evolve full and refined models. Contour plots are presented for graphical expression of the results. The use of composite index is demonstrated for the selection of an appropriate batch. The disintegration time of tablets reduced from 18 min to 6 min when 6% crospovidone was included in the product. The optimized adjuvant was characterized for particle size distribution, granular friability, Kawakita's and Kuno's equation, and dilution potential study. Turmeric, glycyrrhiza, acetaminophen, and metformin HCl were used as model drugs for the preparation of tablets. The present study underlines the fact that melt granulation technique may be adopted for the development of multifunctional directly compressible adjuvant for use in pharmaceuticals. The advantages of melt granulation technique over the classical wet granulation and spray-drying are presented.

The effect of long-term microcrystalline chitosan therapy on plasma lipids and glucose concentrations in subjects with increased plasma total cholesterol: a randomised placebo-controlled double-blind crossover trial in healthy men and women

OBJECTIVE

To evaluate the long-term effect of microcrystalline chitosan (MCC) on plasma lipids, especially the concentration of low-density lipoprotein (LDL) cholesterol, in subjects with a moderately increased concentration of plasma total cholesterol.

METHODS

A total of 130 middle-aged men and women without severe disease and with a total cholesterol of 4.8-6.8 mmol/l and triglycerides below 3.0 mmol/l were randomised into two treatment groups. At the beginning of the 10-month trial, all participants received placebo 1.2 g twice daily during a 1-month run-in period. Subsequently, group 1 first received 1.2 g placebo twice daily for 3 months and then 1.2 g MCC twice daily for 3 months. Correspondingly, group 2 received 1.2 g MCC twice daily during the first and 1.2 g placebo twice daily during the second 3-month period. During the final 3-month follow-up period, both groups received MCC. Altogether, 83 participants completed the study.

RESULTS

No difference was detected in the change in the LDL-cholesterol concentration between the treatments during the crossover trial ( P=0.98 for interaction between time period and treatment group, repeated-measures analysis of variance for crossover design). In an otherwise similar analysis, no differences were detected between the treatments in the concentrations of total cholesterol, high-density lipoprotein cholesterol, triglycerides and glucose.

CONCLUSIONS

Treatment with MCC had no effect on the concentrations of plasma lipids or glucose in healthy middle-aged men and women with moderately increased plasma cholesterol concentrations.

Application of chitin and chitosan derivatives in the pharmaceutical field

Chitin and chitosan derivatives are used as excipients and drug carriers in the pharmaceutical field. Their derivatization contributed to expansion of application and decrease toxicity. Chitosan is used as an excipient in oral dosage form. Chitosan tablet can exhibit a sustained drug release compared to commercial products. Films prepared using chitin or chitosan have been developed as wound dressings, oral mucoadhesive and water-resisting adhesive by virtue of their release characteristics and adhesion. Intratumoral administration of gadopentetic acid-chitosan complex nanoparticles (approximately 430 nm in diameter) has been more effective for gadolinium neutron-capture therapy compared with a group treated with the solution. Compared to intragastrical feeding with diphtheria toxoid (DT) in PBS, a strong enhancement of the systemic (IgG) and local (IgA) immune responses against DT has been observed in mice fed with DT loaded chitosan microparticles (approximately 4.7 microm in size). When DNA-loaded chitosan microspheres (1.15 - 1.28 microm) were intramuscularly administrated into mice, high beta-galactosidase and luciferase productions were obtained even after a long post-transfection period (12 weeks). N-Succinyl-chitosan (Suc-Chi) has been studied for cancer chemotherapy as a drug carrier and the conjugates of mitomycin C with Suc-Chi exhibited good antitumor activities against various tumors. Furthermore, trimethyl-chitosan and monocarboxymethyl-chitosan has been shown to be effective as intestinal absorption enhancers due to their physiological properties. Chitosan-thioglycolic acid conjugates has been found to be a promising candidate as scaffold material in tissue engineering due to their physicochemical properties. This review summarizes the application of chitin and chitosan derivatives for hospital preparations and drug carriers.

Effects of fatty acids and iontophoresis on the delivery of midodrine hydrochloride and the structure of human skin

PURPOSE

The purpose of this work was to investigate if fatty acids can increase the iontophoretic delivery of midodrine hydrochloride through human dermatomed skin and to observe the effects of iontophoresis and fatty acids on skin using SEM.

METHODS

After prehydration for 1 h, human dermatomed skin was treated with 0-0.3 M fatty acids (oleic acid, linoleic acid, decanoic acid, and lauric acid) in propylene glycol (PG) for 1 h. Then the fatty acid solution was replaced by 1% midodrine hydrochloride aqueous solution, and 0.1 mA/cm2 constant current was applied. Samples were taken over 24 h and analyzed by HPLC. After the treatments outlined above, the epidermis was separated, fixed with glutaraldehyde, and dehydrated for SEM.

RESULTS

SEM studies revealed that only 1 h of treatment with fatty acids opened up the tightly compact stratum corneum cell layer, and the permeation study showed a significant increase of the permeability of skin to midodrine hydrochloride after fatty acid treatment.

CONCLUSIONS

Using 5% oleic acid pretreatment, with the electrical current offset at 0.1 mA/cm2, the daily delivery of midodrine hydrochloride can provide an adequate clinical application. The enhancement of passive and iontophoretic delivery by fatty acids may be occurring through the same mechanism.

Effect of lecithin on epicutaneous absorption of diclofenac epolamine

The epicutaneous application of nonsteroidal antiinflammatory drugs in localized rheumatic diseases results in a highly targeted antiinflammatory action and is associated with reduced systemic effects. The new diclofenac epolamine (DHEP) salt is much more soluble both in water and in lipid solvent than other diclofenac salts. The pharmaceutical addition of lecithin to DHEP leads to the formation of mixed micelles with high affinity to the cellular component, which guarantees the absorption of the active ingredient. We performed a bioavailability randomized, cross-over study to compare the plasma profiles of diclofenamic acid after repeated epicutaneous administration of the new topical formulation with those of the marketed DHEP formulation without lecithin. Based on a randomization list, 12 healthy volunteers were asked to apply one of the two formulations twice a day for 10 consecutive days. The other formulation was given after a washout period of 1 week. Blood samples were collected before the morning epicutaneous dose on days 1, 3, 5 and 8 of treatment and on day 10 at different sampling times until 24 h after the application. The pharmacokinetic analysis showed a significantly higher plasma concentration of diclofenamic acid after the application of DHEP lecithin, which indicates a better saturation of the subcutaneous tissues underlying the application site. This also indicates increased local availability of the active principle. In conclusion, the new DHEP formulation with lecithin should have a therapeutic advantage compared with the formulation without lecithin, even in cases of short- to medium-term treatments.

Mucoadhesive buccal patches of miconazole nitrate: in vitro/in vivo performance and effect of ageing

Mucoadhesive patches containing 10mg miconazole nitrate were evaluated. The patches were prepared with ionic polymers, sodium carboxymethyl cellulose (SCMC) and chitosan, or non-ionic polymers, polyvinyl alcohol (PVA), hydroxyethyl cellulose (HEC) and hydroxypropylmethyl cellulose (HPMC). Convenient bioadhesion, acceptable elasticity, swelling and surface pH were obtained. Patches exhibited sustained release over more than 5h and the addition of polyvinyl pyrrolidone (PVP) generally enhanced the release rate. Optimum release behaviour was shown with patches containing 10% w/v PVA and 5% w/v PVP. Study of the in vivo release from this formulation revealed uniform and effective salivary levels with adequate comfort and compliance during at least 6h. On the contrary, in vivo release of the commercial oral gel product resulted in a burst and transient release of miconazole, which diminished sharply after the first hour of application. Storage of these patches for 6 months did not affect the elastic properties, however, enhanced release rates were observed due to marked changes in the crystal habit of the drug.

Ultrasonication of chitosan and chitosan nanoparticles

The objective of this study was to evaluate the effects of ultrasonication on chitosan molecules and nanoparticles. Molecular weight (M(v)) of chitosan HCl (M(v) 146 kDa and degree of deacetylation (DD) 96%) decreased linearly with increasing duration and amplitude of ultrasonication. DD and FTIR absorption were unaffected. X-ray diffraction (XRD) analysis suggested greater chain alignment in the ultrasonicated chitosan samples. Chitosan nanoparticles had mean diameter of 382 nm, polydispersity of 0.53 and zeta potential of 47 mV. Ultrasonication administered at increasing duration or amplitude decreased the mean diameter and polydispersity of the nanoparticles. Zeta potential and FTIR absorbance were unaffected, while XRD suggested a greater disarray of chain alignment in the nanoparticle matrix. Under the transmission electron microscope (TEM), freshly prepared nanoparticles were dense spherical structures which became fragmented after ultrasonication for 10 min at amplitude of 80. Untreated nanoparticle formulation turned turbid upon storage for 3 weeks at ambient conditions due to substantial swelling of the nanoparticles. Ultrasonicated nanoparticle formulation remained clear on storage. Although the particles had also swelled, they were no longer spherical, assuming instead an irregular shape with branching arms. In conclusion, high-intensity ultrasonication induced considerable damage on the chitosan nanoparticles which could affect their function as drug carriers.

Improvement in the bioavailability of poorly absorbed glycyrrhizin via various non-vascular administration routes in rats

The purpose of this study was to examine the improvement of the bioavailability of glycyrrhizin (GL) via extra-vascular, i.e. oral, rectal, and nasal routes with or without the aid of an absorption enhancer in place of the vascular intravenous route in rats. Pharmacokinetic behavior following administration via vascular routes, i.e. the intravenous and portal-venous routes was examined in rats. The area under the plasma concentration-time curve (AUC) after administration of GL via the portal vein was decreased slightly, suggesting that the first elimination of GL in the liver may be one of the factors contributing to the low bioavailability after administration via the oral route. When GL was administered orally as a solution (30 mg/kg), the plasma concentration of GL was extremely low. However, after rectal or nasal administration of GL solution (30 mg/kg) with or without sodium caprate, the mean AUC value was remarkably increased compared with oral administration. In particular, the absolute bioavailability of GL after nasal administration was estimated to be approximately 20%, which was approximately 80-fold greater compared with after oral administration despite of the absence of an enhancer. Furthermore, the fatty acids co-administered orally with GL produced an increase in GL absorption in the following order: sodium caprate>sodiumlaurate>sodiumcaprylate>sodium oleate. These results indicate that the rectum and nasal cavity are useful administration routes for systemic delivery of GL. It was also found that the fatty acids were enhancers for the absorption of GL.

Effect of the degree of phosphate substitution in aluminum hydroxide adjuvant on the adsorption of phosphorylated proteins

Aluminum hydroxide adjuvant was pretreated with six concentrations of potassium dihydrogen phosphate to produce a series of adjuvants with various degrees of phosphate substitution for surface hydroxyl. The adsorption of three phosphorylated proteins (alpha casein, dephosphorylated alpha casein, and ovalbumin) by the phosphate-treated aluminum hydroxide adjuvants was studied. The phosphorylated proteins were adsorbed by ligand exchange of phosphate for hydroxyl even when an electrostatic repulsive force was present. However, the extent (adsorptive capacity) and strength (adsorptive coefficient) of adsorption was inversely related to the degree of phosphate substitution of the aluminum hydroxide adjuvant. Exposure of vaccines containing aluminum hydroxide adjuvant and phosphorylated antigens to phosphate ion in the formulation or during manufacture should be minimized to produce maximum adsorption of the antigen.

Low-frequency dielectric spectroscopy as a tool for studying the compatibility between pharmaceutical gels and mucous tissue

This interdisciplinary work demonstrates how low-frequency dielectric spectroscopy, a technique that is frequently used within physics, can be used to assess the possibilities of intimate surface contact between a polymer gel and mucous tissue, which is generally considered to be the first step in the mucoadhesion process. The dielectric responses of five different gels, of freshly excised porcine nasal mucosa and of systems made by combining the two were measured. All spectra were modeled by a Randles electric circuit containing a diffusion element, a barrier resistance in parallel with a capacitance, and a high-frequency resistance. The results were used to create a measure of the compatibility between the gel and the mucus, which we have named the compatibility factor. Thus, the compatibility factor provides us with a measure of the ease with which a charged species passes the interface between a gel and the mucus layer. The compatibility factor is calculated from the high frequency (kHz region) response of the gel, of the mucosa, and of the combined system. The two highest compatibility factors in this study were obtained for gels based on crosslinked poly(acrylic acid) and chitosan, which was in agreement with the results from mucoadhesion measurements that were performed using a tensile strength method.

The use of complexation with alkanolamines to facilitate skin permeation of mefenamic acid

The preparation of mefenamic acid (MH)-alkanolamine [monoethanolamine, diethanolamine, triethanolamine and propanolamine] complexes was attempted to increase the transdermal flux of MH. A lipophilic enhancer system consisting of isopropyl myristate (IPM) and ethanol (9:1; EI system) produced a marked enhancement of MH flux from the alkanolamine complexes through hairless rat skin membrane. Among the alkanolamines examined, the propanolamine complex had the greatest enhancing effect on the permeation of MH. The observed permeation enhancement of MH-alkanolamine complexes by the EI system was explained by an analysis based on a two-layer diffusion model. The stratum corneum immersed in IPM forms a continuous phase of vehicle and stratum corneum and, from the phase, ethanol transport the MH-alkanolamine complexes to the epidermis and dermis, and the complexes, which are more water soluble than MH, exhibit increased partition into the epidermis and dermis, as the flux increases.

Microsphere design for the colonic delivery of 5-fluorouracil

The treatment of colon cancer has been aimed by approaches of oral drug administration. 5-Fluorouracil is the standard treatment still nowadays and would be a candidate to be delivered orally to the colon. A pH-sensitive polymer Eudragit P-4135F was used to prepare microspheres by a simple oil/water emulsification process. Process parameters were analyzed in order to optimize the drug loading and release profiles. In further attempts mixtures with Eudragit RS100 were prepared to prolong drug release. Scanning electron microscopy and confocal laser scanning microscopy permitted a structural analysis. The solvent extraction was preferable over solvent evaporation with a view to the encapsulation rate (extraction: 37%; evaporation: 19%) due to the hydrophilic character of the drug while release pattern were nearly unchanged. Eudragit P-4135F, pure or in mixture, was found to retain drug release at pH 6.8 lower than 35% within 6 h. At pH 7.4, nearly immediate release (within 30 min) was observed for pure P-4135F, while mixtures enabled to prolong the release slightly. Analysis of the morphology led to an inhomogeneous polymer distribution of P-4135F and RS100 throughout the particle core. A capsule-like structure was concluded which allowed only slight changes of the release kinetics by the addition of RS100. However, the formulation proved its applicability in-vitro as a promising device for pH-dependent colon delivery of 5-fluorouracil.

Release phenomena of insulin from an implantable device composed of a polyion complex of chitosan and sodium hyaluronate

An implant controlled-release system for protein drug delivery based on a polyion complex device composed of chitosan (CS) and sodium hyaluronate (HA) was investigated. The conditions which generated the greatest amount of the polyion solid complex were studied to ascertain the formation of polyion complex between CS and HA. The greatest amount of the polyion complex was formed at the weight ratio of 3 to 7 (CS:HA) at pH 3.5. Furthermore, the CS-HA pellets were prepared and then drug release from CS-HA pellets was evaluated using insulin as a model drug. The results demonstrated that the insulin release from CS-HA pellets was markedly influenced by both the change in the polymer mixing ratio and the total pellet weight, whereas the compression pressure did not affect the release significantly. An artificial neural network (ANN) and biharmonic spline interpolation (HSI) were employed to predict the actual relation between causal factors and the release rate constant of insulin. Although both the ANN and HSI successfully represented a non-linear relationship between the formulation factors and the release rate constant, HSI methodology gave a better estimation than that of the ANN.

Effect of 1-O-ethyl-3-butylcyclohexanol on the skin permeation of drugs with different physicochemical characteristics

The effects of 1-O-ethyl-3-butylcyclohexanol (OEBC) on the in vitro skin permeation of ten model drugs with different physicochemical properties across excised rat skin were evaluated. The results showed that the addition of OEBC significantly improved the in vitro skin permeation of the model drugs compared with the control (without OEBC). To clarify the promoting mechanism of OEBC, a multiple regression analysis was employed. When the permeation study was performed without OEBC, the permeability coefficient was quantitatively predicted as a linear function of molecular weight (log MW) and their lipophilicity (partition coefficient of drugs between octanol and water (log K(o/w)) with a sufficiently high correlation coefficient (r=0.842). It was suggested that skin permeation of drugs without OEBC was explained as a function of diffusion of drugs through the skin and partitioning of drugs to the skin. Although OEBC was administered, the permeability coefficient of drugs cannot be predicted as a linear function of log MW and log K(o/w) (r=0.572).

Relationships between the hydrophilic-lipophilic balance values of pharmaceutical excipients and their multidrug resistance modulating effect in Caco-2 cells and rat intestines

The effects of a series of pharmaceutical excipients, including Span 80, Brij 30, Tween 20, Tween 80, Myrj 52, and sodium lauryl sulfate (with increasing hydrophilic-lipophilic balance (HLB) values) on the intracellular accumulation, transport kinetics, and intestinal absorption of epirubicin were investigated in both the human colon adenocarcinoma (Caco-2) cell line and the everted gut sacs of rat jejunum and ileum. The possible use of these excipients as multidrug resistance (MDR) reversing agents also was examined. Epirubicin uptake experiments using a flow cytometer showed that these selected excipients markedly enhanced the intracellular accumulation of epirubicin in Caco-2 cells in a dose-dependent manner. The optimal effect on the epirubicin uptake was characteristic of excipients with intermediate HLB values ranging from 10 to 17. Moreover, the optimal net efficacy was observed for excipients with polyoxyethylene chains and intermediate chain length of fatty acid and fatty alcohol (monolaurate for Tween 20, monooleate for Tween 80, monostearate for Myrj 52, and lauryl alcohol for Brij 30). These excipients significantly increased apical to basolateral absorption and substantially reduced basolateral to apical efflux of epirubicin across Caco-2 monolayers. Furthermore, the addition of Tween 20, Tween 80, Myrj 52, and Brij 30 markedly enhanced mucosal to serosal absorption of epirubicin in the rat jejunum and ileum. This study suggests that inhibition of intestinal P-glycoprotein (P-gp), multidrug resistance associated protein family (MRPs), or other transporter proteins by pharmaceutical excipients may improve oral absorption of drugs in MDR spectrum. The optimal HLB values of surfactant systems with suitable hydrocarbon chains and polar groups are an important factor in designing promising epirubicin formulations for reversing MDR. In conclusion, therapeutic efficacy of epirubicin may be enhanced by the use of such low toxicity excipients as absorption enhancers and MDR modulators in formulations. This provides a potential strategy for improving bioavailability in the optimization of formulations for drugs performing intestinal absorption and secretion.

Structure-activity relationship for chemical skin permeation enhancers: probing the chemical microenvironment of the site of action

Studies were previously conducted in our laboratory on the influence of n-alkanols, 1-alkyl-2-pyrrolidones, N,N-dimethlyalkanamides, and 1,2-alkanediols as skin permeation enhancers on the transport of a model permeant, corticosterone (CS). The experiments were conducted with hairless mouse skin (HMS) in a side-by-side, two-chamber diffusion cell, with enhancer present in an aqueous buffer in both chambers. The purpose of the present study was to extend these studies and investigate in greater detail the hypothesis that a suitable semipolar organic phase may mimic the microenvironment of the site of enhancer action, and that the enhancer partitioning tendency into this organic phase may be used to predict the enhancer potency. CS flux enhancement along the lipoidal pathway of HMS stratum corneum was determined with the 1-alkyl-2-azacycloheptanones, 1-alkyl-2-piperidinones, 1,2-dihydroxypropyl decanoate, 1,2-dihydroxypropyl octanoate, n-alkyl-beta-D-glucopyranosides, 2-(1-alkyl)-2-methyl-1,3-dioxolanes, 1,2,3-nonanetriol, and trans-hydroxyproline-N-decanamide-C-ethylamide as enhancers. Enhancement factors (E values) were calculated from the permeability coefficient and solubility data over a range of E values. Comparisons of the enhancer potencies for all studied homologous series and the carbon number of the n-alkyl group revealed a nearly semilogarithmic linear relationship with a slope of approximately 0.55, which is consistent with the hydrophobic effect. Moreover, comparisons of the enhancer potencies of all the enhancers with the n-hexanol-phosphate buffered saline (PBS), n-octanol-PBS, n-decanol-PBS, and n-hexane-PBS partition coefficients showed very good correlations for the n-alkanol solvents but not for n-hexane. This result supports the interpretation that the enhancer potency is directly related to the ability of the enhancer molecule to translocate to a site of action via its free energy of transfer from the bulk aqueous phase to a semipolar microenvironment in the stratum corneum lipid lamella that is well mimicked by water-saturated n-alkanols.

Development and characterization of naproxen-chitosan solid systems with improved drug dissolution properties

The solubilizing and amorphizing properties toward naproxen (a poorly water-soluble antiinflammatory drug) of chitosan, an emerging pharmaceutical biopolymer, have been investigated. Solid binary systems at different drug/polymer ratios have been prepared according to different techniques (mixing, cogrinding, kneading, coevaporation) using chitosan at low (CS-L(w)) and medium (CS-M(w)) molecular weight, and tested for dissolution properties. Drug-carrier interactions were investigated in both the liquid and solid state, by phase solubility analysis, differential scanning calorimetry, X-ray powder diffractometry, FT-IR spectroscopy, and scanning electron microscopy. Drug dissolution parameters improved with increasing the polymer amount in the mixture, reaching the highest values at the 1:9 (w/w) drug/polymer ratio, and CS-L(w) was more efficacious than CS-M(w). Cogrinding was the most effective technique, showing the strongest amorphizing effect toward the drug and enabling an increase of more than ten times its relative dissolution rate. Coground mixtures at 3:7 (w/w) drug/polymer ratio were able to give directly compressed tablets which maintained unchanged the improved drug dissolution properties. Enhancer dissolution properties combined with its direct compression feasibility and antiulcerogenic action make CS-L(w) an optimal carrier for developing fast-release oral solid dosage forms of naproxen.

Functions of a chitosan-orotic acid salt in the gastrointestinal tract

A chitosan (CS)-orotic acid salt (CS-OT) was prepared, and the release of orotic acid (OT) from CS-OT as well as the adsorption of bile acids by CS-OT was investigated in vitro. The amount of OT released from CS-OT was about 2-2.7 micromol/mg CS-OT and this changed depending on the species of CS. CS-OT also adsorbed bile acids and the amount increased incrementally according to the number of amino group contained in CS. Furthermore, CS-OT was given to rats as feed in order to investigate the influence on serum cholesterol levels. A decrease in serum cholesterol levels was observed in the group, which was fed a diet containing CS-OT or CS for 1-2 weeks, but no differences in body weight changes were recognized. Therefore, CS-OT may be applied to treating hyperlipidemia.

Buccal Delivery Systems

The oral cavity is an attractive site for drug delivery due to ease of administration and avoidance of possible drug degradation in gastrointestinal tract and first-pass metabolism. Buccal drug delivery specifically refers to the delivery of drugs within/ through buccal mucosa to affect local/systemic pharmacological actions. This review briefly describes advantages and limitations of buccal drug delivery, anatomical structure of oral mucosa, and methodology in evaluating buccal drug delivery system, focusing on physiology, pharmacology, pathology, and formulation design in line with recent developments in buccal delivery systems.