Hydroxyurea

What is this medication for?

• Polycythemia vera (also Hct-reduction adjunct in right-to-left PDA/Tetralogy); CML unresponsive to busulfan; leukemias; meningioma adjunct (investigational)
• Polycythemia vera, mastocytomas, leukemias; feline hypereosinophilic syndrome (potential)

How is it given?

Give exactly as your veterinarian prescribed — never change the dose or stop on your own unless your veterinarian has told you to.

What if I miss a dose?

• Give it as soon as you remember — unless it is almost time for the next dose (then skip the missed one; never double up).
• Call your clinic if you miss more than one dose in a row.

Side effects — what should I watch for?

Effects listed as common in this handout

• stomach/intestinal effects, mouth sores, nail sloughing, alopecia, dysuria (Characteristic set)
• Urate stone promotion (Caution with urate history)

Worth a phone call to your veterinarian

• Bone marrow depression (Most serious)
• Pulmonary fibrosis (Serious, less common)

⚠️ Contact your veterinarian or an emergency clinic IMMEDIATELY if you notice

• Trouble breathing, collapse, seizures, severe vomiting or diarrhea, facial swelling, or pale gums

Before starting (or refilling), tell your veterinarian if your pet:

• has or has had: Anemia/marrow depression, infection, renal impairment, prior chemo/radiation, urate urolith history; Hct-driven titration

• is pregnant, nursing, or used for breeding
• is taking any other medications, supplements, or flea/tick products, including:
  • Other myelosuppressives
  • Uricosurics/xanthine-oxidase inhibitors (allopurinol)

Storage and handling

Cytotoxic capsule — gloves handling; owners must not crush/split without protection.

Good to know

• The polycythemia vera drug: PV's sticky-blood symptoms (rubbery red mucosa, neuro signs) resolve as Hct falls — titrate 20–25 mg/kg bid → every 2 days maintenance at Hct <60%, checking PCV like a diabetic's glucose.
• Right-to-left shunting PDA/Fallot: lowering Hct reduces viscosity/sludging — medical bridge alongside (not instead of) surgical decisions.
• Nail sloughing + dysuria is the odd adverse pair to recognize on exam vs. the generic "marrow + stomach/intestinal" of most chemo.
• Teratogenic with document-handling warnings — same dispensing conversation as MTX/cyclophosphamide.