Tablets, insertable rings and dissolving films can effectively deliver drugs to help protect women and perhaps men from infection with the AIDS virus, researchers reported on Monday.

They also found evidence that using such an approach — called a microbicide — may help overcome some of the risks of drug resistance that can come with taking pills to prevent infection.

Here are some of the findings from the International Microbicides Conference being held in Pittsburgh:

— A flexible ring designed for use in the vagina can continually deliver two AIDS drugs for up to a month. Andrew Loxley of Bethlehem, Pennsylvania-based Particle Sciences, Inc., and colleagues lab tested a vaginal ring that time-released dapivirine, a drug made by Johnson & Johnson's Tibotec Inc and licensed to the International Partnership for Microbicides, and the entry inhibitor maraviroc sold by Pfizer under the brand name Selzentry. It has not been tested in people yet.

— A vaginal tablet worked in similar fashion, time-releasing maraviroc and another experimental HIV drug called DS003, licensed to the International Partnership for Microbicides by Bristol-Myers Squibb, Sanjay Garg of the University of Auckland in New Zealand told the conference. The tablet uses a polymer designed to attach to the moist lining inside the vagina.

— A third approach uses a film, Anthony Ham of ImQuest BioSciences of Frederick, Maryland reported. ImQuest is testing the HIV drug IQP-0528 in a film smaller and thinner than a stick of gum, similar to a mouthwash strip.

— Susan Schader of McGill University in Montreal, Canada, and colleagues said tests of these and other HIV drugs used as microbicides showed that drug resistance emerged only if HIV was in the lab dish first — which suggests people would only develop drug-resistant infections by using microbicides when they were already infected.

— The AIDS virus infects more than 33 million people globally and it has killed 25 million, according to the United Nations AIDS agency UNAIDS. Globally, more than half of those with HIV are women, most infected by husbands or steady partners and many of whom who are unable to insist on use of a condom.

— AIDS experts have long been searching for a microbicide — a cream, gel or vaginal ring that women or men could use as a chemical shield to protect themselves from sexual transmission of the deadly and incurable virus.

— Microbicides using HIV drugs would represent a large new market for the companies that make the drugs, which are now used only to treat infection.