In the U.S.—

• Antiviral, systemic

Cidofovir ( si-DOF-o-veer) is an antiviral. It is used to treat infections caused by viruses.

Cidofovir is used to treat the symptoms of cytomegalovirus (CMV) infection of the eyes (CMV retinitis) in patients with acquired immune deficiency syndrome (AIDS). Cidofovir will not cure this eye infection, but it may help to keep the symptoms from becoming worse.

This medicine is available only with your doctor's prescription, in the following dosage form:

Parenteral
• Injection (U.S.)

In deciding to use a medicine, the risks of using the medicine must be weighed against the good it will do. This is a decision you and your doctor will make. For cidofovir, the following should be considered:

Allergies—Tell your doctor if you have ever had any unusual or allergic reaction to cidofovir or probenecid. Also tell your health care professional if you are allergic to any other substances, such as foods, preservatives, or dyes.

Pregnancy—Cidofovir has not been studied in pregnant women. However, in animal studies, cidofovir has been shown to cause harmful effects on both the mother and infant. Discuss with your doctor whether or not you should continue to receive this medicine if you become pregnant.

Breast-feeding—It is not known whether cidofovir passes into breast milk. However, breast-feeding is usually not recommended in AIDS patients because of the risk of passing the AIDS virus on to the infant.

Children—Cidofovir can cause serious side effects, including possible cancer and trouble in having children later. Therefore, it is especially important that you discuss with the child's doctor the good that this medicine may do as well as the risks of using it.

Older adults—Many medicines have not been studied specifically in older people. Therefore, it may not be known whether they work exactly the same way they do in younger adults or if they cause different side effects or problems in older people. There is no specific information comparing use of cidofovir in the elderly with use in other age groups.

Other medicines—Although certain medicines should not be used together at all, in other cases two different medicines may be used together even if an interaction might occur. In these cases, your doctor may want to change the dose, or other precautions may be necessary. When you are receiving cidofovir, it is especially important that your health care professional know if you are taking any of the following:

• Carmustine (e.g., BiCNU) or
• Cisplatin (e.g., Platinol) or
• Combination pain medicine containing acetaminophen and aspirin (e.g., Excedrin) or other salicylates (with large amounts taken regularly) or
• Cyclosporine (e.g., Sandimmune) or
• Deferoxamine (e.g., Desferal) (with long-term use) or
• Gold salts (medicine for arthritis) or
• Inflammation or pain medicine, except narcotics, or
• Lithium (e.g., Lithane) or
• Other anti-infectives (e.g., amphotericin B) or
• Penicillamine (e.g., Cupramine) or
• Streptozocin (e.g., Zanosar) or
• Tiopronin (e.g., Thiola)—Use of these medicines may increase the chance of side effects affecting the kidneys

• Probenecid (e.g., Benemid)—Probenecid is usually given along with cidofovir; however, probenecid may cause other medications you may be taking to be removed from your body more slowly, and there is a possibility that effects of some of these medicines may be increased

• Kidney disease—Cidofovir can cause harmful effects on the kidney

To get the best results, cidofovir must be given for the full time of treatment. Also, this medicine works best when there is a constant amount in the blood. To help keep the amount constant, cidofovir must be given on a regular schedule.

Dosing—

The dose of cidofovir will be different for different patients. If you are receiving this medicine at home, follow your doctor's orders or the directions on the label. The following information includes only the average doses of cidofovir. If your dose is different, do not change it unless your doctor tells you to do so.

• For injection dosage form:
  • For treatment of cytomegalovirus (CMV) retinitis:
    • Adults—Dose is based on body weight and must be determined by your doctor. At first, 5 milligrams (mg) per kilogram (kg) (2.3 mg per pound) of body weight is injected slowly into a vein once a week for two weeks in a row. Then the dose is reduced to 5 mg per kg (2.3 mg per pound) of body weight injected slowly into a vein once every two weeks. Probenecid is taken along with each dose of cidofovir; follow your doctor's instructions for how much and when to take probenecid.
    • Children—Use and dose must be determined by your doctor.

It is very important that your doctor check you at regular visits for any blood problems that may be caused by this medicine.

It is very important that your ophthalmologist (eye doctor) check your eyes at regular visits since it is still possible that you may have some loss of eyesight during cidofovir treatment.

Along with its needed effects, a medicine may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention.

Medicines like cidofovir can sometimes cause serious side effects such as blood problems and kidney problems; these are described below. Cidofovir has also been found to cause cancer in animals, and there is a chance it could cause cancer in humans as well. Discuss these possible side effects with your doctor.

Check with your doctor immediately if any of the following side effects occur:

• More common
  • Fever, chills, or sore throat 
  
  

Also, check with your doctor as soon as possible if any of the following side effects occur:

• More common
  • Decreased urination;  increased thirst and urination 
  
  

• Rare
  • Decreased vision or any change in vision 
  
  

Other side effects may occur that usually do not need medical attention. These side effects may go away during treatment as your body adjusts to the medicine. However, check with your doctor if any of the following side effects continue or are bothersome:

• More common
  • Diarrhea;  headache;  loss of appetite;  nausea;  vomiting 
  
  

• Less common
  • Generalized weakness;  loss of strength  
  
  

Other side effects not listed above may also occur in some patients. If you notice any other effects, check with your doctor.