In a study of people whose CMV retinitis was progressing on other treatments, time to further progression or stopping of cidofovir treatment was 35-49 days, depending on the dose used. Cidofovir can be harmful to the kidneys. To try and prevent kidney damage, cidofovir is given with a lot of fluids. Probenecid, a drug that helps protect the kidneys, must also be given with cidofovir. Unfortunately, probenecid contains sulfa, a substance that can cause allergic reactions.
Side effects caused by reactions to sulfa-containing drugs can include rash and fever.
If someone is taking cidofovir, doctors need to watch for early signs of kidney problems using blood and urine tests. Decreased urination, increased thirst, or light-headedness after standing up can also be early warning signs of kidney problems. If a person already has kidney problems, cidofovir may not be an appropriate treatment for them. Cidofovir is also being studied in an intravitreal formulation. Intravitreal means the drug is given directly into the eye.