Melbourne biotech Starpharma has begun a US trial of its microbicidal gel VivaGel in sexually active young women.

The Microbicide Trials Network (MTN) is leading the study, funded by the US National Institutes of Health (NIH), in which VivaGel will be tested to determine its safety, acceptability and ease of use.

VivaGel is being developed as a vaginal microbicide for the prevention of HIV and genital herpes.

The expanded safety study is being conducted at the University of South Florida in Tampa and the University of Puerto Rico in San Juan.

"We have already conducted clinical trials on the safety of VivaGel in sexually inactive women and men, but this is the first time the product will be used in sexually active young women, one of our target populations," Starpharma's CEO, Dr Jackie Fairley, said in a statement.

"This study, in addition to the usual safety data, will collect valuable information regarding the product's use and acceptability in the consumer setting."

Nearly 50 per cent of people infected with HIV/AIDS today are women and most of them become infected through sexual intercourse with male partners. Women under the age of 25 are particularly at risk of infection.

The study will enroll 40 sexually active, HIV-negative women aged 18 to 24 years. Participants will be randomly assigned to one of two study groups. One group will apply VivaGel twice a day for two weeks and the other will apply a placebo gel.

VivaGel is the subject of two active investigational new drug (IND) applications with the US FDA. The product shows significant protection from HIV and herpes simplex virus infection in animals, and has shown to be well tolerated in healthy, sexually abstinent men and women. VivaGel also has a potent contraceptive effect in animals.