Giving drugs a spray
Fifteen years ago, Monash University researchers discovered that sunscreens help move compounds through human skin. PENNY FANNIN reports on how that discovery has led to trials of a spray-on hormone replacement therapy and the possibility of cosmetics that target the exact site of skin damage.
Human skin is tough to penetrate - and even more so when you're in the business of drug delivery.
Tablets, mixtures and injections are all used for delivering drugs, but drugs administered through the skin are rare. This is because human skin is a natural barrier, with a multitude of defences to stop foreign compounds from entering the bloodstream.
Yet several years ago, Dr Barrie Finnin and Professor Barry Reed from the Department of Pharmaceutics at the Victorian College of Pharmacy discovered that sunscreens increase the penetration of compounds through the skin.
This knowledge has led to the development of a device that - with a simple squirt - allows drugs to be delivered through the skin. In 1998, a company, Acrux Pty Ltd, was set up so that this 'transdermal spray' technology could be licensed from Monash University.
The research collaboration between Monash and Acrux has now led to world-first trials of a spray-on hormone replacement therapy for treating low testosterone levels in women.
The spray's formulation, says Dr Finnin, is basically ethanol, a sunscreen 'enhancer' that takes the drug into the skin, and the drug itself. Work is ongoing into why the spray-on technology is effective at penetrating the skin.
"For all technologies that deliver drugs through the skin, it's hard to get high amounts through because the skin is a good barrier," says Dr Finnin. "But by understanding the mechanism, we can stretch the limits. We understand how the sunscreens are interacting with the skin, and we have some understanding of the interaction between the skin, the enhancer and the drug."
|Dr Barrie Finnin is breaking the barriers with spray-on technology.
This information is important in deciding how much drug to put in the formulation and also the concentration of the enhancer to be included.
The research could also lead to improved cosmetic preparations. "We are looking at incorporating the enhancer technology into cosmetic formulations because for preparations such as anti-ageing creams to have some effect, their ingredients need to penetrate to a certain skin layer," says Dr Finnin. "It should be possible to deliver treatments directly to the skin layer in need of repair."
But in order to deliver drugs through the skin, researchers need to find ways of penetrating its natural barrier.
"The outer cells of the skin layer have no nucleus and lots of keratin (a protein)," says Dr Finnin. "Drugs seem to move around these cells rather than go through the bricks of keratin. Between the cells on the outer surface of the skin is a meshwork of lipids (mainly cholesterol and ceramides) and water."
The ease with which a drug can get through these water/lipid layers and into the bloodstream depends on how densely packed the lipids are. The sunscreen enhancer disrupts the packing, allowing the drug to get through.
Dr Finnin says that although the spray-on technology could be used to deliver treatments for pain relief, anxiety or incontinence, the focus is on developing spray-on versions of drugs that are currently delivered by patches.
Although effective, patches are expensive to produce, can cause skin irritation and are clearly visible - making it evident that a person is on medication.
Action: For further information, contact Dr Barrie Finnin at email@example.com or visit the project website.