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Foscavir (Foscarnet)

What is in Foscavir?

Each ml of solution contains 24 mg of the active ingredient, foscarnet trisodium hexahydrate in water. The product also contains sufficient hydrochloric acid to adjust the acidity of the solution to be similar to the blood.

Foscavir is a sterile solution for injection into a vein. It comes in bottles containing 250 ml.

What is Foscavir used for?

The active ingredient in Foscavir – foscarnet – is an antiviral agent and works by preventing some viruses from multiplying. Foscavir is used in the treatment of a viral eye infection (retinitis) caused by cytomegalovirus (CMV) in patients with AIDS. Foscavir prevents the condition from getting worse but cannot repair the damage already done. Foscavir is also used in patients with impaired immune function (i.e. immune system cannot defend against infection properly) who have Herpes Simplex Virus (HSV) and have not responded to acyclovir.

Before taking your medicine

Let your doctor know if you have had Foscavir before and if you had any problems while taking it. Foscavir should not be used in pregnancy or while breast-feeding – if this applies to you, or you are thinking about becoming pregnant, tell your doctor.

In some people Foscavir can affect the kidneys and so particular care is needed. It is important that you tell your doctor of any current or past kidney problems you have had. Your doctor may monitor your kidney function and blood before and during treatment.

Lastly, make sure you have told your doctor about all the other medicines that you are taking including any that you have obtained without a prescription. It is very important not to mix certain medications with Foscavir, in particular, some antibiotics: amphotericin B, cyclosporin A and pentamidine (injections), and some protease inhibitors such as ritonavir and saquinavir should not be taken when undergoing Foscavir treatment.

Taking Foscavir

The amount of Foscavir solution that is correct for you is calculated by your doctor, based on your body weight and blood test results. Foscavir is given as a slow injection (infusion) into a vein. When a small vein is to be used, the solution will need to be diluted first with either saline or dextrose 5%. This will be done by the hospital pharmacy. More fluid may be given, also by infusion, to prevent kidney problems.

If you are receiving treatment for CMV retinitis there are two stages to Foscavir therapy: induction then maintenance. Induction therapy is the initial stage where infusions lasting over one hour are given at eight hour intervals every day for two or three weeks. Depending on how the virus responds, this will be changed to the maintenance phase of treatment. During maintenance, infusions are given once a day. If the virus infection becomes worse at any time, treatment can go back to induction levels. Your doctor will advise at all times of necessary changes to infusion times and will alter the dose whenever required, to either increase the antiviral therapy or to reduce risk of kidney damage.

If you are receiving treatment for HSV there is only one stage. The infusion will be given at 8 hourly intervals for 2-3 weeks or until healing.

If you are having treatment at home, it is important to follow the doctor’s instructions. Check with your doctor or nurse if you have any questions. In particular, do not change the speed of your infusion without discussing it first with your doctor or nurse.

Taken too much?

If you think you may have received/taken too much, talk to your doctor immediately.

Missed a dose?

If you think you may have missed a dose, talk to your doctor immediately.


For CMV retinitis the usual starting dose is 60-90 mg/kg of body weight over a period of not less than 1 hour. The maintenance dose is 90-120 mg/kg. For HSV the usual dose is 40 mg/kg.

After taking Foscavir?

Side effects that may occur:

  • Kidney problems (reduced kidney function) which in most cases is reversible if Foscavir is stopped or the amount given is reduced.
  • Tingling or numbness of the skin and twitching of muscles which are, in most cases, due to a temporary imbalance of salts in the blood.
  • Headaches and dizziness.
  • Anaemia.
  • Genital sores, most probably due to foscarnet in the urine. It is important to carefully wash your genitals after urination to avoid sores developing.
  • Fits or convulsions have occurred in some people.
  • Feeling very thirsty and frequently passing water.
  • Pain on passing water.
  • Feeling or being sick, tiredness, weakness, unsteadiness on your feet.
  • Fever or chills.
  • Blood problems.
  • Diarrhoea or constipation, abdominal pains or indigestion.
  • Inflammation of the pancreas.
  • Nervous disorders.
  • Rash or itching.
  • Liver or heart problems.
  • Changes in blood pressure.
  • Inflammation of the veins.
  • Muscle problems.

It is not known if all of these side effects are a direct result of taking Foscavir.

If you notice any of these or any other unusual symptoms tell your doctor.

Important: Foscavir may affect your ability to drive or use machines. You must discuss this with your doctor before you do either of these.

Warning: If the skin or eye comes into contact with Foscavir solution accidentally, the area should be rinsed with water immediately.

Storing Foscavir

Keep Foscavir in a safe place where children cannot see or reach it.

Foscavir should be stored at room temperature (not above 30°C) not in the fridge.

However, any diluted Foscavir should be refrigerated but discarded after 24 hours.

Do not use after the expiry date printed on the label.

If you are being treated at home, the solution will have been prepared for you in the hospital pharmacy and you must follow the pharmacist’s instructions with regard to the expiry or ‘use by’ date of each preparation.

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