FLUCYTOSINE

FLUCYTOSINE
(floo-sye'toe-seen)
Ancobon, Ancotil

Classifications: antibiotic; antifungal;
Therapeutic: antibiotic; antifungal
Prototype: Fluconazole
Pregnancy Category: C

Availability

250 mg, 500 mg capsules

Action

Ineffective for cancerous tumors possibly because it does not enter mammalian cells. Selectively penetrates fungal cell and is converted to fluorouracil, an antimetabolite believed to be responsible for antifungal activity.

Therapeutic Effect

Has antifungal activity against Cryptococcus and Candida as well as Chromomycosis.

Uses

Alone or in combination with amphotericin B for serious systemic infections caused by susceptible strains of Cryptococcus and Candida species.

Unlabeled Uses

Chromomycosis.

Contraindications

Pregnancy (category C), lactation.

Cautious Use

Extreme caution in impaired kidney function; hepatic disease; electrolyte imbalance; bone marrow depression, hematologic disorders, patients being treated with or having received radiation or bone marrow depressant drugs.

Route & Dosage

Fungal Infection
Adult: PO 50–150 mg/kg/d divided q6h
Child: PO <50 kg, 1.5–4.5 g/m²/d divided q6h; >50 kg, 50–150 mg/kg/d divided q6h
Neonate: PO 50–100 mg/kg/d in 1–2 divided doses

Administration

Oral

Give lower dosages with longer dosage intervals in patients with serum creatinine of 1.7 mg/dL or higher. Check with physician.
Give capsules a few at a time over 15 min to decrease incidence and severity of nausea and vomiting.
Store in light-resistant containers at 15°–30° C (59°–86° F).

Adverse Effects (≥1%)

CNS: Confusion, hallucinations, headache, sedation, vertigo. GI: Nausea, vomiting, diarrhea, abdominal bloating, enterocolitis. Hematologic: Hypoplasia of bone marrow: anemia, leukopenia, thrombocytopenia, agranulocytosis, eosinophilia. Skin: Rash. Metabolic: Elevated levels of serum alkaline phosphatase, AST, ALT, BUN, serum creatinine. GI: Hepatomegaly, hepatitis.

Diagnostic Test Interference

False elevations of serum creatinine can occur with Ektachem analyzer.

Interactions

Drug: Amphotericin B produces additive or synergistic effects and can increase flucytosine toxicity by inhibiting its renal clearance.

Pharmacokinetics

Absorption: Readily from GI tract. Peak: 2 h. Distribution: Widely distributed in body tissues including aqueous humor and CSF; crosses placenta. Metabolism: Minimal. Elimination: 75–90% in urine unchanged. Half-Life: 3–6 h.

Nursing Implications

Assessment & Drug Effects

C&S tests should be performed before initiation of therapy and at weekly intervals during therapy. Organism resistance has been reported.
Lab tests: Obtain baseline hematology, kidney and liver function on all patients before and at frequent intervals during therapy. Twice weekly leukocyte and differential counts with WBC with differential and platelet counts are recommended.
Do frequent assays of blood drug level, especially in patients with impaired kidney function to determine adequacy of drug excretion (therapeutic range: 25–120 mg/mL).
Monitor I&O. Report change in I&O ratio or pattern. Because most of drug is eliminated unchanged by kidneys, compromised function can lead to drug accumulation.

Patient & Family Education

Report fever, sore mouth or throat, and unusual bleeding or bruising tendency to physician.
Be aware that the general duration of therapy is 4–6 wk, but it may continue for several months.

Common adverse effects in italic, life-threatening effects underlined; generic names in bold; classifications in SMALL CAPS; Canadian drug name; Prototype drug

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