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What is foscarnet?

Foscarnet (also called Foscavir®) is a medicine used to treat viral infections caused by cytomegalovirus (also called CMV) and other viruses. It is available as a clear liquid given into a vein (IV) over a period of one (1) to 2 hours.

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Possible side effects

  • Nausea, vomiting
  • Fever
  • Headache

Symptoms of an allergic reaction include: rash, hives, itching, chills, fever, headache, muscle ache, shortness of breath, coughing, tightness in the throat, swelling of the face or neck.

Not all patients who take foscarnet will experience these side effects. Common side effects are bolded, but there may be others. Please report all suspected side effects to your doctor or pharmacist.

Find more information on side effects.

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Possible late effects

  • Decreased kidney function
  • Changes in electrolyte levels
  • Changes in liver function
  • Decreased calcium levels
  • Diarrhea

If you have any of these side effects, tell the doctor right away:

  • Seizures
  • Decrease in how much or how often you urinate
  • Numbness or tingling of the feet or hands
  • An allergic reaction including itching, trouble breathing, pain in the chest, blue skin color, or swelling of face, lips, tongue or throat
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Tips for patients and families

Be sure to discuss all questions and instructions with your doctor or pharmacist. 

  • Drinking plenty of liquids will reduce the chance of kidney damage while you are receiving foscarnet. The doctor or nurse will tell you how much liquid you should drink.
  • To help hydrate you, the staff will also give saline solution by vein (IV) before a foscarnet infusion.
  • Electrolyte supplements may be needed during therapy with foscarnet. Electrolytes can be given by mouth or given by vein in IV fluids.
  • While you are receiving foscarnet, blood tests will be done to check for changes in kidney or liver function and to monitor blood counts and electrolytes.
  • Foscarnet can cause birth defects. If you are sexually active, you should use 2 forms of birth control while you are receiving foscarnet and for 90 days after the foscarnet therapy ends.