News emerged today that a phase III efficacy trial of a microbicide candidate called Ushercell (cellulose sulphate) has been halted. The decision to stop the trial was made after a preliminary analysis revealed a slightly higher rate of HIV infection in women using the microbicide compared to a placebo (inactive substance). A second study of Ushercell was also halted as a precaution, although in that trial there was no evidence suggesting an increased risk of HIV infection in Ushercell recipients. Keith Alcorn provides excellent coverage of the story in his article for AIDSmap. Ushercell belongs to a class of microbicide candidates called adsorption inhibitors; in vitro these compounds block the binding of HIV to target cells. Efficacy trials of two other adsorption inhibitors - Carraguard and PRO2000 - are ongoing, and interim analyses have not revealed any safety concerns necessitating the early termination of these studies.