An algae-based gel, highly effective at controlling replication in HIV, has passed initial trials in Brazil.
Designed to block sexual transmission of the virus, the gel could provide vital protection for women in poorer countries where condom use is erratic.
In the first phase of trials, the substance — dolabelane diterpene, derived from the algae Dictyota pfaffii found off the coast of Brazil — stopped 95 per cent of HIV replication in immune system cells.
"We will certainly obtain a final product with efficiency higher than 50 per cent," said lead researcher Luiz Castello Branco, of the Oswaldo Cruz Institute, Brazil.
The researchers hope the gel will be available in seven years, after two more rounds of testing. The second phase is due to begin in February.
Effective microbicides mean women can act independently to protect themselves against HIV/AIDS. This is particularly important in poorer countries, where infection is on the rise but cultural norms prevent them from asking their partner to wear a condom.
"Women can use the gel without the knowledge of their partner," said Branco, who believes the method could help reduce the incidence of HIV/AIDS in areas such as Central and Southern Africa where the disease is rampant.
The new gel has a double action, inhibiting two enzymes involved in virus replication and infection of other cells. Branco believes the gel will have few side effects, since it is a natural product and will be used topically.
The researchers hope to make the gel as affordable as possible for developing countries.Other microbicides, currently being trialed in Europe and North America, are expected to be available within five years.