Structure of Vistide

Drug: Cidofovir (“Vistide”)

Cidofovir is a nucleotide analog marketed under the name Vistide, and is used to delay the progression of CMV retinitis by suppressing CMV replication. The drug inhibits CMV DNA polymerase by incorporating itself into the growing viral DNA chain, thus inhibiting viral DNA synthesis.

Cidofovir is taken in two stages: Induction therapy stabilizes present damage, and maintenance therapy, which keeps the infection under control. The drug is given intravenously, and induction therapy is given once a week for two weeks, and maintenance therapy is every other week.

Though the drug is able to inhibit viral polymerase at concentrations 8-600 times lower than necessary for inhibition of human polymerase, by far the most serious side effect of the drug is irreversible kidney damage. To prevent this, saline is administered before the drug, and probenecid pills are taken the day of the treatment. However, lab tests which monitor kidney function must be performed on a regular basis. Other less serious side effects include nausea and vomiting, fever, weakness, rash, headache, diarrhea, hair loss, and shortness of breath.

Though resistance to cidofovir has yet to be documented, it is hypothesized that, as the virus changes its structure, cidofovir could potentially lose its effectiveness. Very few studies have been done so far, but studies have shown potential cross-resistance between other drugs used to combat CMV: Viruses resistant to the drugs ganciclovir and foscarnet have also shown resistance to cidofovir.