Microneedles Enhance Drug Delivery

by Ann Blackford, UK Public Relations
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In a first-of-its-kind study involving human subjects, researchers at the University of Kentucky College of Pharmacy and the Georgia Institute of Technology have demonstrated that patches coated on one side with microscopic needles can facilitate transdermal delivery of a drug that normally cannot pass through the skin.

By painlessly punching a series of microscopic holes in the outer layer of skin, microneedles promise to expand the range of drugs and vaccines that can be delivered transdermally. And microneedles offer other advantages over oral or injected drugs, including an ability to produce therapeutic drug levels with lower doses.

Transdermal drug delivery has proven successful in a number of applications, including pain management and hormone replacement, but has been limited to a narrow range of compounds that easily pass through the skin.

Daniel Wermeling, associate professor in the UK pharmacy practice and science department who led this work, says, “This proof-of-concept study shows that microneedles work in humans for transdermal drug delivery.” He emphasizes that microneedles present a new opportunity to deliver current and future biotech drugs, which are almost exclusively proteins, peptides, vaccines, and antibodies. Because these types of drugs are large molecules and/or water soluble, they can’t pass through the skin and must be delivered with a hypodermic needle.

The research team included microneedle inventor Mark Prausnitz (Georgia Institute of Technology), Wermeling and UK colleagues David Hudson (psychiatry department fellow), Audra Stinchcomb (pharmaceutical sciences associate professor), and Stan Banks (a pharmacy graduate student).

Working with a small group of healthy volunteers, the UK researchers first prepared a section of skin on each subject’s arm by pressing and removing thumb-sized patches that contained 50 stainless steel microneedles each about 1/40th of an inch in length. Next, gel containing naltrexone, a skin-impermeable compound used to treat opiate and alcohol addiction, was applied to the prepared area and covered by an adhesive patch and protective dressing.

The concentration of the drug in each subject’s bloodstream was monitored for 72 hours. The researchers quickly saw levels of the drug reach pharmacologically active concentrations, and those levels remained steady for at least 48 hours in the six test subjects.

Control subjects were treated in the same way, but without the microneedle preparation prior to application of the naltrexone gel. None of the control subjects had detectable levels of the drug in their bloodstream.
Microneedle administration also reduced the amount of drug required to reach therapeutic levels, replacing a 50 milligram tablet with 10 to 12 milligrams of drug in the gel. Use of the microneedles also produced steady bloodstream levels of the drug, without the initial peak that occurs with oral delivery.

“There are a number of ways microneedles can be used,” says, Prausnitz, who has been developing the devices for more than 10 years. “This study addressed the simplest use of microneedles—the needles are inserted and removed from the skin, and a drug patch applied. To understand how broadly microneedles can be used in medicine, we will also need to study delivery of other therapeutics, such as lidocaine, insulin and flu vaccine.”

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Microneedles enhance delivery of drugs through the skin.

Mark Prausnitz

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