Clinical Testing of Microneedles for Transdermal Drug Delivery

Oral and subdermal delivery routes are successful methods of drug delivery, but have drawbacks that can affect efficacy and patient comfort. Larger drugs, like insulin, are not absorbed through the intestinal wall and are ineffective when taken orally. Hypodermic needle injections allow for solubilized drugs to be delivered directly into or near the bloodstream. Microneedles are designed to pierce and successfully deliver injections past the stratum corneum, but are too short to stimulate the pain nerves. Solid microneedles have been shown to increase skin permeability. Hollow microneedles were subsequently developed so that fluid could be injected through them. Microneedles can serve as a painless drug delivery alternative because they are too short to stimulate pain nerve endings, but long enough to bypass the stratum corneum. Maximum blood fluxes and the time to reach maximum flux were measured. The design of the microneedle can affect how quickly drugs can be introduced through the needles.