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Last Updated: Friday, 19 September, 2003, 23:18 GMT 00:18 UK
STD treatment could prevent HIV
Infected HIV cell
Researchers say the ring may prevent HIV infection
A vaginal ring that releases antibiotics could be used to prevent HIV infections, researchers claim.

The ring's primary use would be to treat sexually transmitted diseases.

But researchers from Queen's University Belfast said such diseases could increase the risk of people contracting HIV.

They told the British Pharmaceutical Conference in Harrogate that treating the infections would make the vagina far more hostile to the virus.

The intravaginal rings are made of silicone rubber and positioned high in the vagina.

They can deliver drugs over weeks, or even months, as required.

The new ring has been designed to release the antibiotic metronidazole which is used to treat bacterial vaginosis, a common vaginal infection.

The drug is diffused through the silicone and dissolves in the vaginal fluid.

Side effects

Laboratory research showed that when metronidazole was released from the ring over 14 days it was effective in killing Gardnerella vaginalis, one of organisms which causes bacterial vaginosis.

The disease is usually treated by giving the drug orally or in the form of a vaginal gel.

But the researchers say oral administration can cause side effects including nausea and vomiting.

The gel is difficult to apply and an ineffective method of delivering the drug, they added.

Karl Malcolm, who carried the research, said: "Metronidazole is released in steadily decreasing amounts over the treatment period.

"The release profile mimics the reduction in bacterial population and avoids unnecessary exposure to drug."

'Massive impact'

He said the device could also work in relation to HIV prevention, either alone or in conjunction with an antiretroviral agent.

"Bacterial vaginosis, and other sexually transmitted diseases, have been widely implicated in an increased risk of sexually transmitted HIV infection.

"Whereas HIV does not survive long in the normal acidic environment of the vagina, it thrives at the elevated pH associated with bacterial vaginosis infection.

"Simply treating existing, and in many cases asymptomatic, vaginal infections could have a massive impact on sexually transmitted HIV statistics."

Mr Malcolm added: "The chance of an effective HIV vaccine being developed and marketed within the next 10 years is slim to say the least.

"Of course, it is imperative that the vaccine research continues, but it is equally imperative that alternative preventative strategies are pursued. Vaginal microbicides are the obvious alternative."

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