PML is a demyelinating disease of the brain's white matter, occurring when the JC virus infects the brain of patients infected with HIV-1. Cidofovir is known to be an effective treatment for cytomegalovirus of the eye and, in laboratory and animal testing, has also been shown to be effective against several other viruses. However, cidofovir is considered investigational as a treatment for PML.

In this multicenter, open-label study 24 patients receive cidofovir iv over 1 hr on days 0, 7, then every 2 wk for a total of 13 doses.

Oral probenecid is given 3h prior to and 2h and 8h following cidofovir administration. Nucleoside and non-nucleoside reverse transcriptors are withheld on days of probenecid administration. Protease inhibitors are continued during probenecid administration.