Gilead Sciences Inc. presented Phase II/III data at the 12th World AIDS Conference, in Geneva, showing that Preveon (adefovir dipivoxil), its reverse transcriptase inhibitor, achieved significant durable decreases in HIV levels in patients for 48 weeks.

Prior to the start of the conference, the Foster City, Calif., company reported 24-week data from the same study, which demonstrated Preveon's antiviral activity in patients who had developed resistance to AZT (zidovudine) and 3TC (lamivudine).

The Phase II/III trial is one of a series of late-stage clinical studies conducted by Gilead to support a Preveon new drug application, which is expected to be filed with the FDA by the end of this year.

In other news from the Geneva conference:

* Shaman Pharmaceuticals Inc., of South San Francisco, said data from a clinical trial of Provir (SP-303) demonstrated the drug, which is derived from the South American croton tree, significantly reduced diarrhea in AIDS patients. Over a four-day treatment period, 26 patients given Provir experienced less frequent and severe diarrhea than 25 patients who received a placebo.

* Chiron Corp., of Emeryville, Calif., said Phase II data from a trial conducted by the French National Agency on AIDS Research showed that Proleukin, which is interleukin- 2, produced comparable CD4 cell count elevations by subcutaneous and intravenous injections when administered intermittently. A Phase I/II study also demonstrated that infrequent administration of Proleukin is sufficient to sustain increases in CD4 cell counts after a six-month course of treatment.

* Procept Inc., of Cambridge, Mass., reported that its vaginal microbicide, PRO 2000 Gel, may provide protection against a number of sexually transmitted diseases, including AIDS. In vitro experiments showed the antiviral compound blocked infection by vaginal herpes simplex virus (HSV), types 1 and 2, and Chlamydia trachomatic. The company also reported its first in vivo evidence of the gel's efficacy in protecting against HSV-2 infection in mice. *