Systems approach to vaginal delivery of drugs III: Simulation studies interfacing steroid release from silicone matrix and vaginal absorption in rabbits

Studies and methodologies on vaginal drug permeation

The vagina stands as an important alternative to the oral route for those systemic drugs that are poorly absorbed orally or are rapidly metabolized by the liver. Drug permeation through the vaginal tissue can be estimated by using in vitro, ex vivo and in vivo models. The latter ones, although more realistic, assume ethical and biological limitations due to animal handling. Therefore, in vitro and ex vivo models have been developed to predict drug absorption through the vagina while allowing for simultaneous toxicity and pathogenesis studies. This review focuses on available methodologies to study vaginal drug permeation discussing their advantages and drawbacks. The technical complexity, costs and the ethical issues of an available model, along with its accuracy and reproducibility will determine if it is valid and applicable. Therefore every model shall be evaluated, validated and standardized in order to allow for extrapolations and results presumption, and so improving vaginal drug research and stressing its benefits.

Vaginal drug delivery systems for HIV prevention

Microbicides have become a principal focus for HIV prevention strategies. The successful design of drug delivery systems for vaginal microbicide drug candidates brings with it a multitude of challenges. It is imperative that the chemical and physical characteristics of the drug candidate and its mechanism of action be clearly understood and considered to successfully deliver and target drug candidates efficiently. In addition, an understanding of the dynamic nature of the vaginal environment, the tissue and innate barriers present, as well as patient preferences are critical considerations in the design of effective microbicide products. Although the majority of drug candidates clinically evaluated to date have been delivered using conventional semisolid aqueous-based gel dosage forms, drug delivery system design has recently been extended to include advanced delivery systems such as vaginal rings, quick-dissolve films, and tablets. Ultimately, it may be necessary to develop multiple dosage platforms for a single active agent to provide users with options that can be used within the constraints of their social environment, personal choice, and environmental conditions.

Permeability of tritiated water through human cervical and vaginal tissue

The increased incidence of human immunodeficiency virus infection in women has identified an urgent need to develop a female-controlled method to prevent acquisition of human immunodeficiency virus and other sexually transmitted diseases. Women would apply the product intravaginally before intercourse. Development of such a product requires a better understanding of the permeability characteristics of the tissues with which such products would come into contact. However, limited studies have been performed in this area. In the present study, water permeability of fresh human cervical and vaginal tissue was evaluated. The average apparent permeability coefficient was found to be 8 x 10(-5) cm/s for fresh human cervical tissue and 7 x 10(-5) cm/s for fresh human vaginal tissue. Considering the lack of regularity in obtaining cervical and vaginal tissue from surgical specimens, additional tests were performed to evaluate the effect of freezing on tritiated water permeability. No statistically significant differences were observed in the permeability values obtained when comparing fresh versus frozen tissues.

Ultrasonically mediated solute permeation through polymer barriers

The effects of ultrasound on the permeation of benzoic acid through polydimethylsiloxane, and hydrocortisone through cellulose was investigated. Ultrasonic irradiation resulted in a 23% increase in the permeability coefficient of hydrocortisone in a cellulose film. A 14% increase in permeability coefficient was observed for benzoic acid in a polydimethylsiloxane film. The effects of ultrasound on stagnant aqueous diffusion layers, membrane-solution interfacial temperature, membrane integrity, and diffusant stability were investigated. These factors were not responsible for the observed increases in permeability.

Controlled drug release from polymeric delivery devices V: Hydroxy group effects on drug release kinetics and thermodynamics

The effects of progesterone hydroxylation on silicone matrix drug release kinetics and thermodynamics were investigated. Hydroxylation at positions 11, 17, and/or 21 substantially reduced progesterone release. The magnitude of this reduction depended on the number and position of the hydroxy groups and could be attributed to decreased polymer matrix diffusivity (Dm) and polymer solubility (Cp). Thermodynamically, hydroxy group addition to positions 11 and/or 21 reduced the activation energy for matrix diffusion (Ed,m) but increased the solvation energy for dissolution in silicone polymer (delta HT,m)). Adding an hydroxy group to position 17 increased the Ed,m but decreased the delta HT,m. The overall (Ed,m) + delta H(T,m)) values were relatively constant and independent of hydroxylation.

Progestin permeation through polymer membranes II: diffusion studies on hydrogel membranes

The potential use of hydrogels in controlled-release drug delivery systems for contraceptive steroids was investigated. The permeabilities, diffusion coefficients, and partition coefficients for progesterone were determined for hydrogels made from hydroxyethyl methacrylate containing varying amounts of ethylene glycol dimethacrylate and tetraethylene glycol dimethacrylate. In addition, copolymers of hydroxyethyl methacrylate with methoxyethyl methacrylate and methoxyethoxyethyl methacrylate were investigated. The results were interpreted in terms of the mechanisms of permeation of progesterone through the hydrogels. This study showed that progesterone permeated these membranes primarily through loose pores in the hydrogel network except at high concentrations of the cross-linker, ethylene glycol dimethacrylate, where dissolution and diffusion of the progesterone in the polymer network was the dominant mechanism.