http://drugdelivery.chbe.gatech.edu/Papers/2004/Prausnitz%20ADDR%202004.pdf

Microneedles for transdermal drug delivery.

The past twenty five years have seen an explosion in the creation and discovery of new medicinal agents. Related innovations in drug delivery systems have not only enabled the successful implementation of many of these novel pharmaceuticals, but have also permitted the development of new medical treatments with existing drugs. The creation of transdermal delivery systems has been one of the most important of these innovations, offering a number of advantages over the oral route. In this article, we discuss the already significant impact this field has made on the administration of various pharmaceuticals; explore limitations of the current technology; and discuss methods under exploration for overcoming these limitations and the challenges ahead.

Current status and future potential of transdermal drug delivery

Microneedles for drug and vaccine delivery.

Biodegradable polymer microneedles: fabrication, mechanics and transdermal drug delivery

Arrays of micrometer-scale needles could be used to deliver drugs, proteins, and particles across skin in a minimally invasive manner. We therefore developed microfabrication techniques for silicon, metal, and biodegradable polymer microneedle arrays having solid and hollow bores with tapered and beveled tips and feature sizes from 1 to 1,000 μm. When solid microneedles were used, skin permeability was increased in vitro by orders of magnitude for macromolecules and particles up to 50 nm in radius. Intracellular delivery of molecules into viable cells was also achieved with high efficiency. Hollow microneedles permitted flow of microliter quantities into skin in vivo, including microinjection of insulin to reduce blood glucose levels in diabetic rats.

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Microfabricated needles for transdermal delivery of macromolecules and nanoparticles: Fabrication methods and transport studies

Skin is an attractive target for delivery of genetic therapies and vaccines. However, new approaches are needed to access this tissue more effectively. Here, we describe a new delivery technology based on arrays of structurally precise, micron-scale silicon projections, which we term microenhancer arrays (MEAs). In a human clinical study, these devices effectively breached the skin barrier, allowing direct access to the epidermis with minimal associated discomfort and skin irritation. In a mouse model, MEA-based delivery enabled topical gene transfer resulting in reporter gene activity up to 2,800-fold above topical controls. MEA-based delivery enabled topical immunization with naked plasmid DNA, inducing stronger and less variable immune responses than via needle-based injections, and reduced the number of immunizations required for full seroconversion. Together, the results provide the first in vivo use of microfabricated devices to breach the skin barrier and deliver vaccines topically, suggesting significant clinical and practical advantages over existing technologies.

Improved genetic immunization via micromechanical disruption of skin-barrier function and targeted epidermal delivery.

A new anthrax vaccine under clinical investigation is based on recombinant Bacillus anthracis protective antigen (rPA). Here, we investigated microneedle-based cutaneous and nasal mucosal delivery of rPA in mice and rabbits. In mice, intradermal (id) delivery achieved up to 90% seroconversion after a single dose, compared with 20% after intramuscular (im) injection. Intranasal (inl) delivery of a liquid formulation required 3 doses to achieve responses that were comparable with those achieved via the id or im routes. In rabbits, id delivery provided complete protection against aerosol challenge with anthrax spores; in addition, novel powder formulations administered inl provided complete protection, whereas a liquid formulation provided only partial protection. These results demonstrate, for the first time, that cutaneous or nasal mucosal administration of rPA provides complete protection against inhalational anthrax in rabbits. The novel vaccine/device combinations described here have the potential to improve the efficacy of rPA and other biodefense vaccines.

Protective Immunization against Inhalational Anthrax: A Comparison of Minimally Invasive Delivery Platforms

The recombinant protective antigen (rPA) of Bacillus anthracis is a promising anthrax vaccine. We compared serum immunoglobulin G levels and toxin-neutralizing antibody titers in rabbits following delivery of various doses of vaccine by microneedle-based intradermal (i.d.) delivery or intramuscular (i.m.) injection using conventional needles. Intradermal delivery required less antigen to induce levels of antibody similar to those produced via i.m. injection during the first 2 weeks following primary and booster inoculation. This dose-sparing effect was less evident at the later stages of the immune response. Rabbits immunized i.d. with 10 μg of rPA displayed 100% protection from aerosol spore challenge, while i.m. injection of the same dose provided slightly lower protection (71%). Groups immunized with lower antigen doses were partially protected (13 to 29%) regardless of the mode of administration. Overall, our results suggest rPA formulated with aluminum adjuvant and administered to the skin by a microneedle-based device is as efficacious as i.m. vaccination.

Microneedle-based intradermal delivery of the anthrax recombinant protective antigen vaccine.

The present invention provides improved methods for delivery of substances into the skin. It has been discovered that delivery of substances such as nucleic acids, amino acids, amino acid derivatives, peptides and polypeptides simultaneously with abrasion of the skin enhances delivery and the biological response as compared to application of the substance to previously abraded skin.

Topical delivery of vaccines

The present invention relates to methods and devices for delivering one or more biologically active agents, particularly a diagnostic agent to the intradermal compartment of a subject's skin. The present invention provides an improved method of delivery of biologically active agents in that it provides among other benefits, rapid uptake into the local lymphatics, improved targeting to a particular tissue, improved bioavailability, improved tissue bioavailability, improved tissue specific kinetics, improved deposition of a pre-selected volume of the agent to be administered, and rapid biological and pharmacodynamics and biological and pharmacokinetics. This invention provides methods for rapid transport of agents through lymphatic vasculature accessed by intradermal delivery of the agent. Methods of the invention are particularly useful for delivery of diagnostic agents.

John M. Brittingham

Papers

Improved genetic immunization via micromechanical disruption of skin-barrier function and targeted epidermal delivery.

Protective Immunization against Inhalational Anthrax: A Comparison of Minimally Invasive Delivery Platforms

Microneedle-based intradermal delivery of the anthrax recombinant protective antigen vaccine.

Topical delivery of vaccines

Intra-dermal delivery of biologically active agents