Nystatin: veterinary dose and monograph

At a glance

Drug class

Antifungal

Also known as

Mycostatin, Nystan, Candid (nystatin)

Species with doses

Dogs, Cats, Horses, Birds and Reptiles

Routes

PO, Intrauterine

Last reviewed

1 October 2026

Indications

• Gastrointestinal candidiasis (Candida enteritis) — oral, gut-local
• Oral/mucocutaneous candidiasis (thrush)
• Avian crop mycosis / candidiasis ("sour crop")
• Topical cutaneous candidiasis (often with other agents)

Nystatin dose by species

Doses are per administration unless stated. mg/kg doses scale with body weight; per-animal, per-quarter and infusion-rate doses are shown as the reference writes them.

Dogs

• Oral / GI candidiasis: Plumb’s p.902: 100,000 U PO q6h (Kirk); 50,000–150,000 U q8h (Jenkins & Boothe); 22,000 U/kg/day (Huber). Not absorbed — acts locally.

Cats

• Oral / GI candidiasis: Plumb’s p.902 (Kirk 1989): 100,000 U PO q6h. Local action only.

Horses

• Fungal endometritis (intrauterine): Plumb’s p.902 (Perkins 1999): 250,000–1,000,000 IU; mix with sterile water (precipitates in saline). Little science supports specific protocols. (The previous oral foal row had no reference dose.)

Birds

• Crop mycosis / candidiasis: UNITS/kg. Plumb’s p.902 (Flammer 2003): enteric yeast 200,000–300,000 U/kg PO q8–12h (large volume, 2–3 mL); 1 mL of 100,000 U/mL per 300 g body weight 1–3 times daily for 7–14 days (Clubb). Do not gavage if treating mouth lesions. Poultry: medicated feed per label.

Reptiles

• Enteric yeast infection: UNITS/kg. Plumb’s p.902: 100,000 U/kg PO once daily (Jacobson 1999); turtles for 10 days (Gauvin 1993).

Contraindications

Systemic fungal infection (no systemic absorption — ineffective). Known hypersensitivity. Otherwise minimal — its lack of absorption makes it very safe.

Species-specific warnings

Birds: Crop candidiasis is often secondary — treat with nystatin AND correct the underlying husbandry/immunosuppression/concurrent disease.

Adverse effects

• GI upset (vomiting, diarrhoea) at high oral doses
• Local irritation (topical)
• Bitter taste (reduced acceptance)
• Essentially no systemic toxicity (not absorbed)

Drug interactions

• No significant systemic drug interactions (not absorbed)
• Local antifungal combinations: complementary

Pregnancy and lactation

Considered safe (negligible systemic absorption).

Monitoring

• Clinical/cytologic resolution of candidiasis
• GI tolerance at higher oral doses
• Address predisposing factors (immunosuppression, prolonged antibiotics, husbandry in birds)

Toxicity and overdose

Extremely safe systemically because it is not absorbed; high oral doses cause only GI upset, and topical use causes only local irritation. Its "limitation" is the flip side of its safety — no systemic activity.

Management: Supportive only; no specific antidote needed. Manage GI upset symptomatically.

Clinical pearls

• A safe, local "contact" anticandidal — perfect for gut/oral/crop Candida, useless for systemic mycoses (it isn't absorbed)
• Classic for avian crop mycosis/sour crop — pair with correcting the underlying husbandry/disease
• Dosed in IU; the suspension must physically contact the yeast, so coat the mouth/swish where relevant
• Look for and address the predisposing cause (e.g. prolonged broad-spectrum antibiotics, immunosuppression)

Mechanism of action

A polyene that binds ergosterol in the fungal cell membrane and forms pores, causing leakage of intracellular potassium and other contents and killing the yeast (fungicidal against Candida). It is too large/toxic to be absorbed or given systemically, so its action is confined to the surface (gut lumen, mucosa, skin) where it is applied — which is exactly why it is both safe and limited to local infections.

Formulations and products

• Oral suspension 100,000 IU/mL
• Topical cream/ointment 100,000 IU/g
• Mycostatin / Nystatin — 100,000 IU/mL suspension; topical, Oral suspension / topical (human-label)

Storage

Suspension/topical: 15–30 °C, protect from light; do not freeze suspension. Shake suspension well.

Before you use this dose

Reference doses for veterinary professionals. Confirm the dose against the product label, the patient’s condition, current guidance and local regulations before use; the attending veterinarian remains responsible for every clinical decision.

Other antifungals

• Itraconazole
• Ketoconazole
• Lime Sulfur (Lime Sulphur Dip)
• Miconazole
• Posaconazole
• Terbinafine
• Voriconazole

Frequently asked questions