Results from an Italian study suggest that cidofovir (Vistide) may be useful for people with progressive multifocal leukoencephalopathy (PML). PML is a relatively rare disease in people living with HIV, affecting the brain. It is caused by a virus, called the JC virus. Most adults (about 80%) are exposed to this virus but it usually only causes disease in people with very low CD4+ cell counts. In rare circumstances, PML can occur in people with higher CD4+ cell counts (e.g. above 200).

PML is typically an aggressive and extremely unpleasant disease, often leading to a rapid and complete loss of mental faculties. Historically, the average time from PML diagnosis to death was about 90 days. Since the availability and use of potent anti-HIV therapies, however, the incidence of PML has fallen sharply and survival time after a diagnosis with PML has extended significantly, with a number of people having post-PML diagnosis survival of two to five years (and counting!).

Because PML affects the brain, diagnosing the disease is difficult and frequently it is diagnosed presumptively (i.e. based on symptoms and not definitive laboratory tests, which would include a brain biopsy). Treatments for PML are, at best, rather ineffective. The most common approach to treatment was an antiviral drug called ARA-C, although that drug was never proven to have a major effect against PML. Because ARA-C has many side effects and must be delivered directly into the brain, many people choose not to treat PML. Fortunately, some people have had an effective response against PML simply from using potent anti-HIV therapies.

The most recent study involved 40 people with PML all of whom were taking potent anti-HIV therapy. Fourteen were also given cidofovir, a drug approved for the treatment of cytomegalovirus (CMV). The dose of cidofovir used in this study was 5mg/kg every week for the first two weeks then 5mg/kg every other week. People receiving cidofovir had a more pronounced increase in CD4+ cell counts and prolonged survival compared to people receiving only potent anti-HIV therapy.

Further analysis of the results show that several factors contributed to prolonged survival: use of cidofovir, lower JC virus levels at the start of the study and starting potent anti-HIV therapy prior to developing PML.

Cidofovir is a very difficult drug to take. It has to be given by injection directly into the vein (intravenously) and has to be given with probenecid to reduce the risk of developing kidney toxicities. Even with the use of probenecid, a fair number of people have problems tolerating the drug. Still, the side effects of cidofovir seem less significant than those of ARA-C and pale when compared to the effects of a bad case of PML.

Commentary

While there are no standard of care guidelines for PML, this study suggests that the addition of cidofovir to potent anti-HIV therapy should be considered. However, the side effect profile for cidofovir is still of great concern.

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