This article was published in Scientific American’s former blog network and reflects the views of the author, not necessarily those of Scientific American
The Viagra (sildenafil citrate) ads that seem to accompany every televised sporting event end typically with several caveats—including warnings of a dozen or so side effects, including a possible sudden loss of hearing or vision, chest pain and an erection that is painful or lasts longer than four hours. A team of Egyptian scientists is studying ways nanotechnology might to someday replace those little blue pills with a transdermal patch that could deliver this and other drugs more quickly and effectively via the skin while reducing side effects.
About 70 percent of an oral dose of sildenafil citrate is wasted as it is metabolized by the liver without having any effect, according to a study, published by Alexandria University and Pharos University researchers in the latest issue of the International Journal of Nanotechnology. Sildenafil citrate is difficult to deliver via the skin, however, for several reasons, including its low oil and water solubility and poor membrane permeability.
The researchers experimented with two types of nanocarriers made using fat-like lipid molecules. The first involved forming an emulsion with sildenafil citrate using a surfactant compound (which can lower the surface tension of a liquid) to allow the lipid molecules and drug to mix, much like soap will emulsify oil and water. The second approach was to encapsulate the drug in "self-nanoemulsifying drug delivery systems" (SNEDDS) that can more readily cross membranes, including the skin. Whereas neither was obviously tested on actual skin, both showed potential in the lab as a means for developing a Viagra patch, according to the researchers.
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There are several transdermal medications already on the market that use medicated adhesive patches placed on the skin to deliver specific doses of medication through the skin and into the bloodstream. Some of the best-known examples include nicotine patches to control addiction to tobacco, estrogen patches sometimes prescribed to treat menopausal symptoms and methylphenidate patches for Attention Deficit Hyperactivity Disorder (ADHD).
"Production of transdermal patches for different drugs is one of the current interests of our work group," says Yosra S.R. Elnaggar, a lecturer of pharmaceutics at Alexandria University.
The work with Viagra follows the researchers' similar experiments to find a transdermal delivery method for tamoxifen citrate, an antiestrogen taken orally for breast cancer treatment. Both sildenafil citrate and tamoxifen citrate, which is a selective estrogen receptor modulator (SERM), were chosen for these experiments because they are high-profile drugs in their respective areas that have reduced effectiveness in pill form, Elnaggar says. Tamoxifen citrate encounters problems of poor water solubility and is prone to be broken down by both intestine and liver enzymes before reaching target areas.
The researchers are now considering other SERM drugs, including raloxifene hydrochloride, for distribution via SNEDDS, Elnaggar says. Raloxifene is used to prevent and treat osteoporosis—in which the bones become thin and weak and break easily—among post-menopausal women. It is also prescribed under the brand name Evista to decrease the risk of developing invasive breast cancer in women at high risk of developing this type of cancer or who have osteoporosis.
Image of Nicoderm CQ patch courtesy of RegBarc, via Wikimedia Commons