In-vitro release and transdermal fluxes of a highly lipophilic drug and of enhancers from matrix TDS

Effects of various penetration enhancers on penetration of aminophylline through shed snake skin

BACKGROUND

Cellulite is the accumulation of subcutaneous fat and connective tissue in tights and buttocks. Xanthines, such as aminophylline, are used as phosphodiesterase inhibitors, and are also adenosine receptor antagonists.

OBJECTIVES

The aim of the present study was to characterize in vitro aminophylline transdermal absorption through shed snake skin, and to investigate the absorption enhancing effect of various enhancers.

MATERIALS AND METHODS

Aminophylline gels were prepared using theophylline and ethylenediamine as raw materials of aminophylline, hydroxypropyl methyl cellulose (HPMC) F4M as gelling agent, and propylene glycol as a co-solvent. Sodium tauroglycocholate (STGC) (100, 200, and 500 μg/mL), lauric acid (1.7 and 15%), and ethanol (60%) were added as enhancers. In vitro percutaneous absorption experiments were performed on snake skin using Franz diffusion cells. Flux (J), permeability coefficient (P), and enhancement factor (EF) for each formulation were calculated.

RESULTS

The results indicated that all of enhancers significantly enhanced drug permeability. This effect was decreased by increasing the concentration of STGC; in contrast, by increasing the concentration of lauric acid from 1.7 to 15%, EF was enhanced Although ethanol (60%) and STGC (100 μg/mL) showed the highest EFs, the effect of ethanol on drug permeability appeared with a lag time.

CONCLUSIONS

According to the findings, type and concentration of penetration enhancers can effect on transdermal permeation of drug.

Aminolevulinic acid-loaded Witepsol microparticles manufactured using a spray congealing procedure: implications for topical photodynamic therapy

Objectives

The aim was to enhance aminolevulinic acid (ALA) stability by incorporation into low-melting microparticles prepared using a spray congealing procedure and to evaluate temperature-triggered release, allowing topical bioavailability following melting at skin temperature.

Methods

ALA-loaded Witepsol microparticles were prepared using a novel spray congealing technique. Entrapment efficiency was compared with conventional emulsion-based methods and modelled drug release profiles determined using a membrane separation technique. Raised receiver medium temperature was used to determine triggered release. Bioavailability and lipid-mediated enhancement of ALA penetration were determined in excised murine skin.

Key findings

ALA-loaded Witepsol microparticles were spherical, with a mean diameter of 20 μm. Loading and stability studies demonstrated effective encapsulation, ranging from 91% to 100%, with no evidence of degradation to pyrazine derivatives. ALA release correlated with dissolution medium temperature, triggered at temperatures close to that of skin. Results suggested that molten Witepsol enhanced cutaneous permeation, whereas incorporation of microparticles in a semi-solid vehicle attenuated ALA penetration. Optimal use was direct application under occlusion.

Conclusions

Spray congealing is superior to the emulsion-based procedures with respect to encapsulation efficiency of ALA in Witepsol matrices, providing temperature-triggered release, enhanced stability and improved penetration of ALA through keratinised skin. These features could improve ALA delivery to superficial lesions as part of photodynamic therapy.

Simultaneous Estradiol and Levonorgestrel Transdermal Delivery from a 7-day Patch: In Vitro and In Vivo Drug Deliveries of Three Formulations

A new drug-in-adhesive transdermal patch was developed to deliver both estradiol and levonorgestrel through the skin over a 7-day period, but at different rates. This report elucidates the in vitro and in vivo biopharmaceutical studies that were necessary during the development of this product. Three test patches had to be manufactured, all delivering estradiol at the same rate, but delivering levonorgestrel at three different rates so that a levonorgestrel dose response could be studied in the clinic. An in vitro hairless mouse skin model (HMS) using modified Franz diffusion cells was used to select the test products delivering levonorgestrel in the order of 1:2:3. HMS experiments also demonstrated that the presence of estradiol did not affect the flux of levonorgestrel. Two in vivo studies in postmenopausal women showed that at steady state (four weeks of once-weekly dosing) the three test products all delivered estradiol at comparable rates. Similarly, the levonorgestrel deliveries for the three test products were in the order expected. The target fluxes of both drugs were achieved in these three test products by varying the drug loads and patch size. That this approach was successful is evidence of the value of using the HMS penetration experiments in transdermal product development and should provide useful insights for other formulations having to develop complex systems. One of the test products is now marketed as Climara Pro.

Transdermal delivery of tea catechins and theophylline enhanced by terpenes: a mechanistic study

Using in vitro and in vivo techniques, terpenes were evaluated as enhancers to improve the skin permeation of therapeutically active agents derived from tea, including tea catechins and theophylline. The in vitro permeation was determined by Franz cells. The skin deposition and subcutaneous amounts of drugs sampled by microdialysis were evaluated in vivo. Terpenes varied in their activities of enhancing drug permeation. The oxygen-containing terpenes were effective enhancers of drug permeation, whereas the hydrocarbon terpenes were much less efficient. Oxygen-containing terpenes with a bicyclic structure had reduced enhancing activity. Terpenes enhanced tea catechin permeation to a much greater degree than they did theophylline. The isomers of (+)-catechin and (-)-epicatechin showed different permeation behaviors when incorporated with terpenes. In the in vivo status, terpenes promoted the skin uptake but not the subsequent subcutaneous concentration of (-)-epigallocatechin gallate (EGCG). Both increased skin/vehicle partitioning and lipid bilayer disruption of the stratum corneum (SC) contributed the enhancing mechanisms of terpenes for topically applied tea catechins and theophylline based on the experimental results from the partition coefficient and transepidermal water loss (TEWL). alpha-Terpineol was found to be the best enhancer for catechins and theophylline. The high enhancement by alpha-terpineol was due to macroscopic perturbation of the SC and the biological reaction in viable skin as evaluated by TEWL and colorimetry.

Transdermal absorption of propofol in rats

Propofol (PF), a highly lipophilic anesthetic, has several desirable properties, such as the rapid onset and cessation of its effects upon intravenous infusion. In this study, the transdermal absorption of PF was investigated with the aim of the development of an alternative route of administration. PF solutions containing isopropyl myristate (IPM), ethanol or propylene glycol (PG) at various concentrations were prepared and applied to the abdominal skin of rats. Petrolatum and fatty alcohol propylene glycol (FAPG) ointments containing PF were also prepared and applied to the dorsal skin. Eyelid opening was measured and the ratio of the measured value to the initial value was calculated to evaluate the level of the pharmacological effect of the preparation. The PG solution containing 80% PF achieved higher plasma PF concentrations than the 100% PF solution. The PF-FAPG ointment produced a higher plasma PF concentration than the PF-petrolatum ointment. Furthermore, a drowsy state was confirmed after transdermal administration of 42% PF-FAPG ointment. These results indicate that the combination of PF and PG was appropriate for the transdermal absorption of PF, and PF was absorbed through the rat skin to an extent sufficient to cause a continuous sedative effect.

In vitro/in vivo correlation studies for transdermal delta 8-THC development

The present study was carried out in order to develop a transdermal therapeutic system (TTS) for Delta(8)-THC. The in vitro permeability studies of Delta(8)-THC in human skin and hairless guinea pig skin with and without a rate-controlling membrane were conducted in flow-through diffusion cells. Delta(8)-THC pharmacokinetic parameters were determined after topical application of transdermal patches and intravenous administration in guinea pigs. The in vitro results indicated that there was no significant difference in the mean flux or in the permeability coefficient of Delta(8)-THC in human skin versus hairless guinea pig skin. The flux of Delta(8)-THC through the human skin/membrane composite was not significantly lower than that through the hairless guinea pig skin/membrane composite; and the skin controlled the Delta(8)-THC delivery rate. Intravenous doses of Delta(8)-THC followed a two-compartment model with a significant distribution phase. On application of the TTS patch, the plasma concentration of Delta(8)-THC reached a mean steady-state level of 4.4 ng/mL within 1.4 h and was maintained for at least 48 h. Significant amounts of metabolites were observed in the plasma after topical application. The in vitro-study predicted plasma concentration following application of the transdermal patch was in agreement with the observed guinea pig plasma concentrations of Delta(8)-THC.

Drug delivery systems for oestrogenic hormones and antagonists: the need for selective targeting in estradiol-dependent cancers

The pleiotropic activity of oestrogens and their mechanism of action via their binding to the two oestrogen receptors alpha (ER alpha) and beta (ER beta) subtypes in the different tissues where oestrogens exert their action have been briefly described. The fate of these compounds trapped into different galenic forms is discussed with regard to their therapeutic applications. Firstly, the advantages and disadvantages of the different forms (pills, i.v. forms and transdermal patches) used in contraception are compared. Secondly, the therapeutic use of formulated oestrogens for the post-menopausal hormone replacement therapy (HRT) is analysed through the various results obtained in different trials. The link between HRT and the risks of breast cancer and cardiovascular disease is underlined. Finally, comparing the activity of selective oestrogen receptor modulators such as tamoxifen and pure anti-oestrogens such as RU58668 and ICI182780, we analysed the reasons leading to the need for a tumor targeting of the latters, but not of the former for the treatment of oestrogen-dependent breast cancer. Different injectable and biodegradable formulations, that lead to a remarkable anti-tumor efficiency in xenografts, have been recently developed and we believe that they may represent promising new administration ways of added therapeutic values for anti-oestrogens. Such devices could be extended to the delivery of other anti-cancer drugs with more aggressive activities than anti-oestrogens.

Effect of lipid bilayer alteration on transdermal delivery of a high-molecular-weight and lipophilic drug: Studies with paclitaxel

Skin forms an excellent barrier against drug permeation, due to the rigid lamellar structure of the stratum corneum (SC) lipids. Poor permeability of drugs can be enhanced through alteration in partition and diffusion coefficients, or concentration gradient of drug with an appropriate choice of solvent system, along with penetration enhancers. The aim of the current investigation was to assess applicability of lipid bilayer alteration by fatty acids and terpenes toward the permeation enhancement of a high-molecular-weight, lipophilic drug, paclitaxel (PCL) through rat skin. From among the fatty acids studied using ethanol/isopropyl myristate (1:1) vehicle, no significant enhancement in flux of PCL was observed (p > 0.05). In the case of cis mono and polyunsaturated fatty acids lag time was found to be similar to control (p > 0.05). This suggests that the permeation of a high-molecular-weight, lipophilic drug may not be enhanced by the alteration of the lipid bilayer, or the main barrier to permeation could lie in lower hydrophilic layers of skin. A significant increase in lag time was observed with trans unsaturated fatty acids unlike the cis isomers, and this was explained on the basis of conformation and preferential partitioning of fatty acids into skin. From among the terpenes, flux of PCL with cineole was significantly different from other studied terpenes and controls, and after treatment with menthol and menthone permeability was found to be reduced. Menthol and menthone cause loosening of the SC lipid bilayer due to breaking of hydrogen bonding between ceramides, resulting in penetration of water into the lipids of the SC lipid bilayer that leads to creation of new aqueous channels and is responsible for increased hydrophilicity of SC. This increased hydrophilicity of the SC bilayer might have resulted in unfavorable conditions for ethanol/isopropyl myristate (1:1) along with PCL to penetrate into skin, therefore permeability was reduced. The findings of this study suggest that the permeation of a high-molecular-weight and lipophilic drug cannot be enhanced through bilayer alteration by penetration enhancers, and alteration in partitioning of drug into skin could be a feasible mode to enhance the permeation of drug.

Development of matrix patches for transdermal delivery of a highly lipophilic antiestrogen

The aim of this study was to develop matrix-type transdermal systems (TDSs) containing the highly lipophilic (log P = 5.82) antiestrogen (AE) and the permeation enhancers propylene glycol and lauric acid. For that purpose, permeation of AE from various adhesive matrices through excised skin of hairless mice was evaluated. It was found that pretreatment of the skin with permeation enhancers raised the transdermal flux of subsequently applied antiestrogen. Highest steady-state transdermal fluxes (1.1 microg cm(-2) h(-1)) were obtained from Gelva, polyacrylate adhesive, followed by 0.55 microg cm(-2) h(-1) from Oppanol polyisobutylene, 0.31 microg cm(-2) h(-1) from BIO-PSA silicone, and 0.12 microg cm(-2) h(-1) from Sekisui polyacrylate matrices. In order to develop TDS with high content of fluid permeation enhancer propylene glycol, two different strategies were investigated. One strategy was the addition of hydroxypropyl cellulose (HPC) as thickening agent to Gelva matrices. This allowed for propylene glycol loading levels of up to 30%, resulting in transdermal AE fluxes of 0.09 microg cm(-2) h(-1). On the other hand, a fleece-laminated backing foil was loaded with the described permeation enhancer formulation and laminated with polyacrylate adhesive layer, resulting in transdermal AE fluxes of 0.06 microg cm(-2) h(-1). However, application of these TDSs on skin pretreated with permeation enhancers raised the fluxes to 2.6 microg cm(-2) h(-1) from Gelva/HPC and 0.46 microg cm(-2) h(-1) from fleece/Sekisui.