Enhanced transdermal delivery of triprolidine from the ethylene-vinyl acetate matrix

Status of surfactants as penetration enhancers in transdermal drug delivery

Surfactants are found in many existing therapeutic, cosmetic, and agro-chemical preparations. In recent years, surfactants have been employed to enhance the permeation rates of several drugs via transdermal route. The application of transdermal route to a wider range of drugs is limited due to significant barrier to penetration across the skin which is associated with the outermost stratum corneum layer. Surfactants have effects on the permeability characteristics of several biological membranes including skin. They have the potential to solubilize lipids within the stratum corneum. The penetration of the surfactant molecule into the lipid lamellae of the stratum corneum is strongly dependent on the partitioning behavior and solubility of surfactant. Surfactants ranging from hydrophobic agents such as oleic acid to hydrophilic sodium lauryl sulfate have been tested as permeation enhancer to improve drug delivery. This article reviews the status of surfactants as permeation enhancer in transdermal drug delivery of various drugs.

Controlled Release of Pranoprofen from the Ethylene-Vinyl Acetate Matrix Using Plasticizer

An ethylene-vinyl acetate (EVA) matrix containing pranoprofen was prepared using the casting method and the release patterns of pranoprofen were observed. The solubility of pranoprofen was determined to be a function of the volume fraction of polyethylene glycol 400. The release of the drug from the matrix was examined as a function of temperature and drug concentration. Plasticizers such as the citrates and the phthalates were added to prepare the membrane in order to increase the flexibility of the EVA matrix. The solubility of pranoprofen was the highest when the PEG 400 concentration was 20% (v/v). The rate of drug release from the EVA matrix increased with increasing temperature and drug loading dose. There was a linear relationship between the flux of pranoprofen and the square root of the loading dose. The activation energy of release (Ea), which was measured from the slope of the log P versus 1000/T plots, was estimated to be 17.44, 16.14, 14.88, and 14.78 kcal/mol for loading doses of 0.5, 1, 1.5, and 2%, respectively. Among the plasticizers used such as the citrate and the phthalate groups, diethyl phthalate had the best enhancing effects on drug release. In conclusion, the application of an EVA matrix containing a plasticizer might be useful in the development of a controlled drug delivery system.

OCULAR TISSUE DISTRIBUTION OF BETAMETHASONE AFTER ANTERIOR-EPISCLERAL, POSTERIOR-EPISCLERAL, AND ANTERIOR-INTRASCLERAL PLACEMENT OF NONBIODEGRADABLE IMPLANTS

PURPOSE

To investigate the intraocular distribution of betamethasone (BM) after implantation of transscleral drug delivery devices at three different sites in the eye: anterior episclera, posterior episclera, and anterior intrasclera.

METHODS

Nonbiodegradable implants designed to release BM for at least 1 month were placed at three different sites in albino rabbit eyes. The concentrations of BM in the aqueous humor, vitreous, and retina-choroid were determined by high-performance liquid chromatography at 4 weeks after placement. The distribution of BM in the retina-choroid was also evaluated.

RESULTS

In the in vitro and in vivo release study, the release of BM from implants in vivo correlated comparatively with those in vitro in all studied devices. The concentrations of BM in ocular tissues were measured after the implantations. The concentrations of BM after anterior-intrascleral placement of the implants were highest in the vitreous and retina-choroid among the three sites. The concentrations of BM in the three different sections of retina-choroid, which were around the placement site, opposite the placement site and posterior pole, were also determined. The concentration of BM in the retina-choroid around the placement site was higher than that in other parts of the retina-choroid after anterior-episcleral and anterior-intrascleral placement of implants. The implants at the anterior-intrascleral site yielded the highest concentrations of BM in the anterior part and posterior pole of the retina-choroid among the three placement sites. Only the implant at the posterior-episcleral site showed a higher concentration of BM at the posterior pole of the retina-choroid than at the other anterior part.

CONCLUSIONS

Transscleral drug delivery devices may be feasible systems to deliver BM to intraocular tissues. The placement site of the device should be selected according to the location of the targeted lesions.

A type of esophageal stent coating composed of one 5-fluorouracil-containing EVA layer and one drug-free protective layer: In vitro release, permeation and mechanical properties

A type of esophageal stent coating was investigated, which consists of one 5-fluorouracil (5-FU)-containing ethylene-vinyl acetate (EVA) copolymer layer and one drug-free EVA protective layer. The amount of 5-FU permeated through the protective layer (100 mum) is thousands of times lower than that of 5-FU released from the drug-loaded layer, indicating that the coating releases drug molecules in a unidirectional fashion. The barrier of the protective layer can be attributed to a tiny flux of 5-FU through the EVA film. In vitro release profiles of the stent coatings with various drug contents were investigated in pH 6.5 phosphate buffer solution. The results show that, the burst effect is not obvious for the coatings with 20-50% of 5-FU and the release profiles can be characterized by a first faster release rate phase followed by a decrease in release rate. The release data in the early and late stages can all be well fitted with zero-order kinetics, and the possible reasons for the release profiles were discussed. The rate of 5-FU permeation through porcine esophageal mucosa from the coatings can be adjusted by changing drug content of the coatings. The increase of drug content of the coatings significantly leads to the decrease of the maximum elongation, maximum tensible strength and maximum tear strength, and the increase of the modulus of elasticity. The coatings with 20-60% of drug attached to a stent can endure repeated binding and liberation via a stent introducer.

Transdermal delivery system of triamcinolone acetonide from a gel using phonophoresis

Triamcinolone acetonide (TA) is a corticosteroid that is used in the systemic and topical treatment of many inflammatory diseases. In this study, a phonophoretic drug delivery system was designed to enhance the TA permeability and the influence of ultrasound was examined. In order to establish the transdermal delivery system for TA, a hydrophilic carbopol gel containing TA was prepared after adopting phonophoresis. A permeation study through mouse skin was performed at 37 degrees C using a Franz diffusion cell, and the ultrasound treatment was carried out for 10 h. The level of TA permeation through the skin was evaluated under various ultrasound conditions including the frequency (1.0, 3.0 MHz), intensity (1.0, 2.5 W/cm2), and duty cycle (continuous, pulse mode) using a 0.5% TA gel. The highest permeation was observed under the ultrasound treatment conditions of low frequency, high intensity, and in continuous mode.

Release characteristics of quinupramine from the ethylene-vinyl acetate matrix

An ethylene-vinyl acetate (EVA) matrix containing quinupramine was prepared in an attempt to develop a controlled delivery system for quinupramine. Permeation studies of quinupramine through the EVA copolymer membrane were carried out using a two-chamber diffusion cell. The rate of drug permeation through the EVA membrane was proportional to the PEG 400 volume fraction. The release of quinupramine from the EVA matrix was examined using a modified Franz diffusion cell. A plasticizer was added to prepare the pore structure of the EVA matrix in order to increase the rate of drug release. The effects of PEG 400, membrane thickness, drug concentration, temperature, and plasticizer on drug release rate were investigated. The drug release rate from the EVA matrix increased with increasing PEG 400 volume fraction, temperature and drug loading dose. The activation energy for drug release was 5.91, 5.39, 4.68 and 4.52 kcal/mol for a loading dose of 0.5%, 1%, 1.5%, and 2%, respectively. Among the plasticizers used, diethyl phthalate showed the best results. The release of quinupramine from the EVA matrix follows a diffusion-controlled model, where the quantity released per unit area is proportional to the square root of time. The controlled release of quinupramine was achieved using the EVA polymer including a plasticizer.

Controlled release of furosemide from the ethylene-vinyl acetate matrix

The ethylene-vinyl acetate (EVA) matrix containing furosemide was prepared by the casting method and the release patterns were observed. The solubility of furosemide was determined as a function of volume fraction of polyethylene glycol 400. The release of drug from the matrix was studied as a function of temperature and drug concentration. Plasticizers such as the citrates and the phthalates were added for preparing the membrane to increase the flexibility of the EVA matrix. The solubility of furosemide was the highest when the concentration of PEG 400 was 40% (v/v). The release rate of drug from the EVA matrix increased with increasing temperature and drug loading doses. A linear relationship was found between the release rate and the square root of the loading dose. The activation energy (Ea), which was measured from the slope of the logP versus 1000/T plots, was 12.33 kcal/mol for the 0.5% loading dose, and 11.58 kcal/mol for the 1.0% loading dose, and 11.00 kcal/mol for the 1.5% loading dose. Among the plasticizers used such as the citrates and the phthalates groups, diethyl phthalate showed the best enhancing effects in drug release. In conclusion, the application of an EVA matrix containing a plasticizer might be useful in the development of a controlled drug delivery system.

Enhanced efficacy of triprolidine by transdermal application of the EVA matrix system in rabbits and rats

The bioavailability of triprolidine from the ethylene vinyl acetate (EVA) matrix system containing polyoxyethylene-2-oleyl ether was studied to determine the feasibility of enhanced transdermal delivery of triprolidine in rabbits. The antihistamine effects were also confirmed to determine the percutaneous absorption of triprolidine from the EVA matrix system containing a penetration enhancer and plasticizer in rats. The triprolidine-EVA matrix (50mg/kg) was applied to the abdominal skin of rabbits. Blood samples were collected via the femoral artery for 36 h and the plasma concentrations of triprolidine were determined by HPLC. The pharmacokinetic parameters were calculated using the LAGRAN computer program. The area under the curve(AUC) was significantly higher in the enhancer group (4582+/-1456 ng/mL h) than that (2958+/-997 ng/mL h) in the control group (P<0.05), showing an approximate 155% increased bioavailability. The average Cmax in the enhancer group (241+/-46.5 ng/mL) was significantly higher than that in the control group (198+/-28.9 ng/mL), (P<0.05). The mean Tmax in the enhancer group (8.0+/-2.57 h) was higher than that in the control group (6.0+/-2.24 h, but this was not statistically significantly. The relative bioavailability of triprolidine in the transdermal application was 35.9% in the control group and 55.6% in the enhancer group compared comparing with that after oral administration. As the triprolidine-EVA matrix, which contains polyoxyethylene-2-oleyl ether as an enhancer and triethyl citrate as a plasticizer was administered to the rabbits via the transdermal routes, the relative bioavailability increased approximately 1.55 fold compared with that in the control group, showing a relatively constant, sustained blood concentration with minimal fluctuation. The antihistamine effect was determined using the Evans blue dye procedure by comparing the changes in the vascular permeability increase following the transdermal application. The vascular permeability increase was reduced significantly by the transdermal application of the EVA-triprolidine system containing triethyl citrate and polyoxyethylene-2-oleyl ether. These results show that the plasticizer and penetration enhancer increase the skin permeation of triprolidine and the triprolidine-EVA matrix system could be developed as a transdermal delivery system providing the increased constant plasma concentration and antihistamine effects.

Development of the Bioadhesive Tetracaine Gels for Enhanced Local Anesthetic Effects

To develop the new local anesthetic formulations with a suitable bioadhesive property, hydroxypropyl methylcellulose (HPMC)-based gel was formulated. As the drug concentration in the gels, and the temperature of surrounding solutions increased, the drug release increased. The activation energy of tetracaine permeation was 4.47 kcal/mol. The effects of permeation enhancers on the permeation rate of drug through skin were studied using various enhancers, such as the glycols, the nonionic surfactants, and the bile salts. Among the enhancers used, polyoxyethylene 2-oleyl ether showed the highest enhancing effects on drug permeation through skin. The analgesic activity was examined using a tail-flick analgesimeter. In the AUEC (area under the efficacy curve) of the rat-tail flick test, tetracaine gel containing polyoxyethylene 2-oleyl ether showed about 3.2-fold increase in analgesic activity compared with the control. The results of this study support that the tetracaine gels with efficient anesthetic effects could be developed using HPMC and poloxamer with combination of enhancer and vasoconstrictor.

The use of polymers for dermal and transdermal delivery

The use of polymers for skin preparations is manifold. Requirements of such polymers are dependent on the formulation types. The most applied polymers on skin belong to various classes, for example to cellulose derivatives, chitosan, carageenan, polyacrylates, polyvinylalcohol, polyvinylpyrrolidone and silicones. They are gelating agents, matrices in patches and wound dressings, anti-nucleants and penetration enhancers. Correlations between commercially available products and results of new scientific investigations are often difficult or not possible, because of the lack of comparative data especially for transdermal patches. Finally, two promising future trends of polymeric systems, gene delivery and tissue engineering, are discussed.