Flucytosine (5-FC) is a pyrimidine antimetabolite which belongs to the group of medicines called antifungals. After uptake into fungal cells, it is converted into 5-fluorouracil and then to 5-fluorodeoxyuridylic acid which is an inhibitor of thymidylate synthesis. Thymidylic acid is a component of DNA.
The fungal selectivity of flucytosine (5-FC) depends on the fact that mammalian cells (except some marrow cells) have low capacity to convert 5-FC into 5-fluorouracil, which is a potent anticancer drug. Although flucytosine (5-FC) is a narrow spectrum fungistatic drug, it is active against Cryptococcus neoformans, Torula, Chromoblastomyces; and a few strains of Candida.
Flucytosine is not employed as the sole therapy except occasionally in chromoblastomycosis. Rapid development of resistance limits its utility in deep mycosis. In cryptococcosis (both meningeal and nonmeningeal) its synergistic action with amphotericin B (AMB) is utilized to reduce the total dose of the more toxic latter drug. Thus, this drug therapy is generally limited to first 14 days of AMB regimen to avoid its bone marrow toxicity.
This medicine is available in capsule as well as tablet form, and you can get this product only with your doctor's prescription.
2 What to Know Before Using
If you are about to start a drug therapy, the risk-benefit ratio of taking the drug should be considered carefully. The suitable drug therapy is to be chosen with active participation of both the doctor and the patient. There are some important factors such as drug interactions, metabolic impairment, hypersensitivity reaction, pregnancy, lactation etc. which may alter the desired therapeutic effects of such medications.
Sometimes the presence of other health disorders affects the beneficial effects of this medicine and even may cause serious toxic effects. If you have had any allergic reactions to any medicine then you must inform your doctor about that.
Further, you should not use this drug if you have any of the following health disorders:
Known hypersensitivity to flucytosine.
Moderate to severe hepatic impairments (e.g. liver cirrhosis)
Severe kidney diseases (e.g. acute renal failure)
However, certain drugs should not be used concurrently with such medications. It is always recommended to consult with your doctor if you are in need of some other medications or even any over-the-counter medicine for another health problem in order to avoid unwanted toxic effects.
In addition, using this medicine with any of the following medicines is not recommended:
Zidovudine, ganciclovir, and interferon –associated with increased bone marrow suppression.
Cytarabine or cytosine arabinoside –inactivate the antifungal activity of flucytosine by competitive inhibition. Thus, you should avoid co-administration.
Levomethadyl acetate –a synthetic opioid similar in structure to methadone.
Tegafur –a chemotherapeutic fluorouracil prodrug used in the treatment of cancers.
Moreover, animal studies performed with flucytosine have shown an adverse effect to the fetus but there are no adequate studies in pregnant and lactating women. Thus, this medicine can be used during pregnancy and lactation if clearly needed.
The dosage schedule and the duration of drug therapy depend on the particular medical problem for which you are using this medicine. The therapeutic dose may also vary with patient’s condition or requirement and the strength of the medicine as well. Thus, you should use this medicine following the directions given by your doctor.
Flucytosine is generally indicated in the treatment of certain serious infections (e.g. septicemia, meningitis, endocarditis, pulmonary infections and urinary system infections) caused by susceptible strains of Candida and/or Cryptococcus. For the treatment of these fungal infections, the usual dose of flucytosine is 12.5 to 37.5 mg/kg (5.7 to 17 mg/lb) of body weight every 6 hours.
If you miss any dose of this medicine, you should take it as soon as possible. But if it is time for your next dose, then you should skip the missed dose and go back to your regular treatment schedule.
Further, it is advised to store the medicine in a closed container at room temperature away from heat, moisture, and direct light. All kinds of medicines should be kept out of the reach of children. However, outdated medicines should be disposed by an appropriate way.
4 Precautions to Take
Firstly, regular visits to your doctor are recommended to check that this medicine is working properly or not.
Additionally, the following guidelines should be followed while you are using such medications:
Since flucytosine is excreted through urine, renal impairment may lead to accumulation of the drug. Thus, this drug must be given with extreme caution to patients with impaired renal function. Further, plasma concentration of flucytosine should be monitored to determine the adequacy of renal excretion in such patients.
This medicine must not be used in patients with bone marrow depression because of increased risk of depression of bone marrow function.
Frequent monitoring of liver function and of the hematopoietic system is recommended during this drug therapy.
Before therapy with flucytosine is started, electrolytes (because of hypokalemia) and the hematologic status of the patient should be determined.
Certain blood problems have been reported following flucytosine therapy. These problems may result in bleeding of the gums. Therefore, you should be more careful at the time of using regular toothbrushes, dental floss, and toothpicks.
Moreover, flucytosine makes your skin more sensitive to sunlight which may cause severe sunburn associated with skin rash, itching, or discoloration of the skin. Thus, you should stay out of direct sunlight. You can use sun block products to avoid severe reactions from the sun.
5 Potential Side Effects
There are some unwanted side-effects associated with each drug that usually do not need medical attention. These side-effects usually go away during the treatment episode as your body adjusts to the medicine. In addition, your doctor may advise you about the ways how to prevent or reduce those unwanted side-effects.
Further, you may need to consult with the doctor when the following problems become significant:
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