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Spray-on female contraceptive to start trial

15:47 27 November 03 news service

The world's first trial of a female contraceptive spray will begin in Australia early in 2004. The approach involves a new technique for transferring hormones across the skin and a novel low-dose contraceptive hormone.

Separate studies involving each component suggest they will work well in combination, says the Population Council, a US-based non-profit organisation involved in the new trial.

The spray will be used daily to deliver Nestorone, a synthetic progestin for which the Population Council holds the rights. Nestorone cannot be used in pill form because it is completely broken down in the gut, preventing it from entering the bloodstream.

Trials in women using Nestorone in a skin gel or under-the-skin implant show it works well and is safe, says Ian Fraser, a reproductive medicine expert at the University of Sydney, where the new trial will be conducted.

But for some women there could be advantages to using it in a spray. For example, the hormone would be transferred almost instantaneously across the skin, so it could not be washed off, unlike a gel.

"This sounds excellent, like it would be very easy for women to use," says Louis Salamonsen, who is involved in contraceptive research at the Prince Henry Institute of Medical Research in Melbourne. "The only disadvantage compared with something like an implant is that a woman would still have to remember to do it every day."

Steady delivery

The spray system exploits the properties of chemicals also used in water-resistant sunscreens. These compounds modify the structure of the outer layer of skin, allowing sunscreen - or in this case hormones - to penetrate.

Trials of the technique for use in hormone replacement therapy in post-menopausal women show that once under the skin, the hormone collects in a reservoir. This reservoir then very slowly diffuses into the bloodstream.

"This means we get a nice steady delivery of the drug - very different to what happens with the contraceptive pill, where there is a quick peak with a rapid drop-off," says Andrew Humberstone, director of research at Acrux, the Melbourne-based company that is commercialising the spray technology.

This could mean that lower doses would be needed in a spray, compared with existing pills, potentially reducing the risk of side effects. It also means a Nestorone spray would not have to be used at exactly the same time every day, unlike current contraceptive pills.

Nestorone itself could have other advantages over current contraceptives. Breast-feeding women could use it knowing that any hormone that was secreted into milk would be broken down in their baby's gut.

"Most contraceptive research today is about giving women a choice," says Fraser. "There are cons with everything. But for some women, I think this will turn out to be an excellent method of contraception."

Emma Young, Sydney

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