For many people who have to take prescription drugs to treat chronic conditions, being able to use a patch similar to those used to help fight addiction or deliver hormones could greatly enhance their quality of life. Patches are rarely used to deliver drugs, but a new high-throughput screening technique could go some way to changing this.

Delivering drugs using patches is not easy because the skin is designed to have a very low permeability - something which usually works in our favour to prevent toxins from entering the body. High-molecular-weight drugs, in particular, are notoriously difficult to carry through the skin. So-called chemical penetration enhancers (CPEs) can help; these generally work by disrupting the skin's lipid bilayers. However, finding CPEs to deliver high-molecular-weight molecules is not an easy task and the compounds frequently irritate the skin, leading to inflammation.

Rather than look for new chemicals which might act as CPEs, a team of researchers from the University of California, Santa Barbara, US, has come up with a new way to screen existing compounds, allowing them to combine substances to form safe and potent CPE mixtures. They developed a technique to screen CPEs called In vitro skin impedance guided high-throughput screening (Insight). The Insight technology consists of a piece of pig skin, sandwiched between two plates, each of which contains 100 wells. The researchers place test compounds in the wells in one of the plates, apply an electric current and measure the skin's conductivity and permeability to see how well the CPEs work. Some of the new compound combinations made the skin 100 times more permeable to a number of therapeutic drugs. Insight's first trial gave two CPE combinations: N-lauroylsarcosine and sorbitan monolaurate; and sodium laureth sulphate and phenyl piperazine. The researchers tested these combinations and found them to increase greatly the movement of macromolecules such as heparin. In tests on rats, the new combinations caused no skin irritation.

Samir Mitragotri, who headed the research team, told Chemistry World that the Insight technology has been licensed to a Californian company and 'can be used for various applications including therapeutic drug delivery, dermatologics and cosmetics'. The team is considering performing human trials on the new CPE combinations, but is currently continuing to screen for even more potent mixtures. 

ED