In the U.S.—

In Canada—

Other commonly used names are 5-fluorocytosine; 5-FC.

• Antifungal, systemic

Flucytosine (floo-SYE-toe-seen) belongs to the group of medicines called antifungals. It is used to treat certain fungus infections.

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

Oral
• Capsules (U.S. and Canada)

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

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

Pregnancy—Flucytosine has not been reported to cause birth defects or other problems in humans. However, studies in rats have shown that flucytosine causes birth defects.

Breast-feeding—It is not known if flucytosine passes into breast milk. Discuss with your doctor whether or not you should discontinue breast-feeding while using this medicine.

Children—Although there is no specific information comparing use of flucytosine in children with use in other age groups, this medicine is not expected to cause different side effects or problems in children than it does in adults.

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. Although there is no specific information comparing use of flucytosine in the elderly with use in other age groups, this medicine is not expected to cause different side effects or problems in older people than it does in younger adults.

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 taking flucytosine, it is especially important that your health care professional knows if you are taking any of the following:

• Amphotericin B by injection (e.g., Fungizone) or
• Antineoplastics (cancer medicine) or
• Antithyroid agents (medicine for overactive thyroid) or
• Azathioprine (e.g., Imuran) or
• Chloramphenicol (e.g., Chloromycetin) or
• Colchicine or
• Cyclophosphamide (e.g., Cytoxan) or
• Ganciclovir (e.g., Cytovene) or
• Interferon (e.g., Intron A, Roferon-A) or
• Mercaptopurine (e.g., Purinethol) or
• Methotrexate (e.g., Mexate) or
• Plicamycin (e.g., Mithracin) or
• Zidovudine (e.g., AZT, Retrovir) or
• X-ray treatment—Use of flucytosine with any of these medicines may increase the chance for side effects of the blood

• Blood disease—Flucytosine may cause blood problems

• Kidney disease—Patients with kidney disease may have an increased chance of side effects

• Liver disease—Flucytosine may cause liver side effects

In some patients this medicine may cause nausea or vomiting. If you are taking more than 1 capsule for each dose, you may space them out over a period of 15 minutes to help lessen the nausea or vomiting. If this does not help or if you have any questions, check with your doctor.

To help clear up your infection completely, keep taking this medicine for the full time of treatment, even if you begin to feel better after a few days. Do not miss any doses.

Dosing—

The dose of flucytosine will be different for different patients. Follow your doctor's orders or the directions on the label. The following information includes only the average doses of flucytosine. If your dose is different, do not change it unless your doctor tells you to do so.

• For oral dosage form (capsules):
  • For fungus infections:
    • Adults and children—Dose is based on body weight. The usual dose is 12.5 to 37.5 milligrams (mg) per kilogram (kg) (5.7 to 17 mg per pound) of body weight every six hours.

Missed dose—

If you miss a dose of this medicine, take it as soon as possible. However, if it is almost time for your next dose, skip the missed dose and go back to your regular dosing schedule. Do not double doses.

Storage—

To store this medicine:

• Keep out of the reach of children.
• Store away from heat and direct light.
• Do not store in the bathroom, near the kitchen sink, or in other damp places. Heat or moisture may cause the medicine to break down.
• Do not keep outdated medicine or medicine no longer needed. Be sure that any discarded medicine is out of the reach of children.

Your doctor should check your progress at regular visits to make sure that this medicine does not cause unwanted effects.

Flucytosine may cause blood problems. These problems may result in a greater chance of infection, slow healing, and bleeding of the gums. Therefore, you should be careful when using regular toothbrushes, dental floss, and toothpicks. Dental work, whenever possible, should be done before you begin taking this medicine or delayed until your blood counts have returned to normal. Check with your medical doctor or dentist if you have any questions about proper oral hygiene (mouth care) during treatment.

Flucytosine may cause your skin to be more sensitive to sunlight than it is normally. Exposure to sunlight, even for brief periods of time, may cause skin rash, itching, redness, or other discoloration of the skin, or a severe sunburn. When you begin taking this medicine:

• Stay out of direct sunlight, especially between the hours of 10:00 a.m. and 3:00 p.m., if possible.
• Wear protective clothing, including a hat. Also, wear sunglasses.
• Apply a sun block product that has a skin protection factor (SPF) of at least 15. Some patients may require a product with a higher SPF number, especially if they have a fair complexion. If you have any questions about this, check with your health care professional.
• Apply a sun block lipstick that has an SPF of at least 15 to protect your lips.
• Do not use a sunlamp or tanning bed or booth.

If you have a severe reaction from the sun, check with your doctor.

This medicine may also cause some people to become dizzy, lightheaded, drowsy, or less alert than they are normally. Make sure you know how you react to this medicine before you drive, use machines, or do anything else that could be dangerous if you are dizzy or are not alert . If these reactions are especially bothersome, check with your doctor.

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.

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

• More common
  • Skin rash, redness, or itching;  sore throat and fever;  unusual bleeding or bruising;  unusual tiredness or weakness;  yellow eyes or skin 
  
  

• Less common
  • Confusion;  hallucinations (seeing, hearing, or feeling things that are not there);  increased sensitivity of skin to sunlight 
  
  

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
  • Abdominal pain;  diarrhea;  loss of appetite;  nausea or vomiting  
  
  

• Less common
  • Dizziness or lightheadedness;  drowsiness ;  headache 
  
  

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