Vaginal drug absorption in rhesus monkeys I: development of methodology

Advances and future perspectives in epithelial drug delivery

Epithelial surfaces protect exposed tissues in the body against intrusion of foreign materials, including xenobiotics, pollen and microbiota. The relative permeability of the various epithelia reflects their extent of exposure to the external environment and is in the ranking: intestinal≈ nasal ≥ bronchial ≥ tracheal > vaginal ≥ rectal > blood-perilymph barrier (otic), corneal > buccal > skin. Each epithelium also varies in their morphology, biochemistry, physiology, immunology and external fluid in line with their function. Each epithelium is also used as drug delivery sites to treat local conditions and, in some cases, for systemic delivery. The associated delivery systems have had to evolve to enable the delivery of larger drugs and biologicals, such as peptides, proteins, antibodies and biologicals and now include a range of physical, chemical, electrical, light, sound and other enhancement technologies. In addition, the quality-by-design approach to product regulation and the growth of generic products have also fostered advancement in epithelial drug delivery systems.

Porcine Vagina Ex Vivo as a Model for Studying Permeability and Pathogenesis in Mucosa

The vaginal mucosa is commonly exposed to a variety of topical agents, including chemical contraceptives, drugs for the treatment of specific pathological conditions, and pathogenic microorganisms. In vitro models can provide important information regarding the penetration and efficacy of topical compounds as well as the pathogenesis of various diseases such a menstrual toxic shock syndrome. Realistic and reproducible test systems are important if new agents are to fulfill their therapeutic potential in human populations. The selection of appropriate animal species and tissue and the use of valid in vitro systems can avoid many of the shortcomings of current animal and cell culture test systems. This review provides information about the factors that should be considered when selecting the best model to study the permeability of the human vagina. The characteristics of an ex vivo porcine model are explored and the validity of this model is demonstrated in terms of its histology, ultrastructure and composition and organization of the permeability barrier; data indicate excellent correlation of permeability and tissue response between human and porcine vaginal tissue.

Intravaginal gels as drug delivery systems

Recently, there has been a great deal of interest in the design and application of different dosage forms via the vaginal route. Several studies have proven that the vagina is an effective route for drug administration intended mainly for local action, but systemic effects of some drugs also can be attained. The major advantages of this route include accessibility, good blood supply, the ability to bypass first-pass liver metabolism, and permeability to large molecular weight drugs, such as peptides and proteins. Among the delivery systems proposed for this route is the use of intravaginal gels, which have been found to be potential vaginal drug delivery systems. The bioadhesives used in the formulation of gels play a key role in the release of the drug through the attachment to the vaginal mucosa, where the drug diffuses from the gel to the mucus.

Hydration and percutaneous absorption: I. Influence of hydration on alkanol permeation through hairless mouse skin

A method to study the influence of hydration on skin permeability where the skin is immersed in saline for up to 30 hr and under circumstances where a steady state rate of permeation can be established in several minutes is indicated. These circumstances allow multiple, sequential runs over a period where the permeability coefficients of some chemicals are gradually changing. It has been found that the permeabilities of water, methanol and ethanol are little affected by such hydration. However, there is a doubling of the permeability coefficients of butanol and hexanol during the first 10 hr of immersion. More hydrophobic alkanols seem to be less sensitive to the protracted aqueous conditioning. In general the results indicate that there are complex molecular structure-permeability relationships operating in skin. More specifically, the hydration effects are insightful with respect to developing barrier models for skin as they are further indications that different parallel diffusional paths are followed by polar and semi- and nonpolar species.