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Flucytosine

Prescription

Antifungal (Fluorinated Pyrimidine Analog)

Last reviewed 21 Apr 2026 · PetCare.AI Editorial Team

Species

Dog, Cat

Brands

1 available

Interactions

1 documented

Formulations

Mechanism of action

Converted intracellularly by fungal cytosine deaminase to 5-fluorouracil, which is incorporated into fungal RNA and inhibits thymidylate synthase. Mammalian cells lack cytosine deaminase — selective toxicity.

At a glance

Class

Antifungal (Fluorinated Pyrimidine Analog)

Schedule

Prescription

Storage

Store at room temperature 15–30°C

Dosing

🐕

Dog

Used ONLY in combination for cryptococcosis and systemic candidiasis — rapid res

Dose

25–50 mg/kg

Route

Frequency

q6–8h

🐈

Cat

Used for feline cryptococcosis (combined with fluconazole or amphotericin B)

Dose

25–50 mg/kg

Route

Frequency

q6–8h

Educational reference only

This information is provided for educational purposes and is not a substitute for professional veterinary advice, diagnosis, or treatment. Always consult a qualified veterinarian before administering any medication to your pet. Find a vet near you →

Formulations

💊

Other — 1

Strength

—

Storage

Store at room temperature 15–30°C

Safety

Monitoring parameters

CBC every 1–2 weeksHepatic enzymesRenal functionSerum flucytosine levelsFungal culture/antigen

Educational reference only

Interactions

Moderate — 1

Amphotericin B

moderate

Amphotericin B damages renal tubular cells, reducing flucytosine clearance (renally eliminated) and increasing myelosuppression risk. However, amphotericin B also enhances flucytosine uptake by fungi (synergistic antifungal effect).

Management: Intentional therapeutic combination for cryptococcosis and systemic candidiasis. Monitor flucytosine levels (target 25-100 mcg/mL), renal function, and CBC closely.

Educational reference only

Brands

Other markets

Ancobon

FAQs

Frequently asked questions

›What is Flucytosine?

Flucytosine is a antifungal (fluorinated pyrimidine analog) used in pets. Converted intracellularly by fungal cytosine deaminase to 5-fluorouracil, which is incorporated into fungal RNA and inhibits thymidylate synthase. Mammalian cells lack cytosine deaminase — selective toxicity.

›What is Flucytosine used for in pets?

Flucytosine is used in veterinary medicine for: Used ONLY in combination for cryptococcosis and systemic candidiasis — rapid res; Used for feline cryptococcosis (combined with fluconazole or amphotericin B).

›What is the Flucytosine dose for dogs?

For dogs, Flucytosine is typically dosed as follows — Used ONLY in combination for cryptococcosis and systemic candidiasis — rapid res: 25–50 mg/kg PO q6–8h. Always consult your veterinarian for a dose tailored to your pet's weight, age, and condition.

›What is the Flucytosine dose for cats?

For cats, Flucytosine is typically dosed as follows — Used for feline cryptococcosis (combined with fluconazole or amphotericin B): 25–50 mg/kg PO q6–8h. Always consult your veterinarian for a dose tailored to your pet's weight, age, and condition.

›Does Flucytosine need a prescription?

Yes. Flucytosine is a prescription medication and should only be administered under veterinary supervision.

Educational reference only