Busulfan
1,4-butanediol dimethanesulfonate
Also known as: Myleran · Busulfex · Busulivex · Mielucin · Misulban · bussulfam · busulfanum · busulphan · CB-2041 · GT-41 · myelosan · NSC-750 · WR-19508
Reviewed by the VetSheet Veterinary TeamUpdated Apr 5, 2026Evidence-based veterinary reference
This dose is based on body surface area (mg/m²). Convert body weight to body surface area before dosing.
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Dosing by species
🌎 NA — North America🌍 EU — Europe
Dogs
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Adjunctive therapy of chronic granulocytic leukemias or polycythemia vera | 2-4 mg/m2 | PO | once daily | — | 🌎 NA |
- Adjunctive therapy of chronic granulocytic leukemias or polycythemia vera: NOT mg/kg. Rarely used in veterinary medicine.
Cats
| Indication | Dose | Route | Frequency | Duration | Region |
|---|---|---|---|---|---|
| Adjunctive therapy of chronic granulocytic leukemias or polycythemia vera | 2-4 mg/m2 | PO | once daily | — | 🌎 NA |
- Adjunctive therapy of chronic granulocytic leukemias or polycythemia vera: NOT mg/kg. Rarely used in veterinary medicine.
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Overview
Busulfan is a potent bifunctional alkylating antineoplastic agent primarily utilized in veterinary medicine for the adjunctive treatment of chronic granulocytic leukemias (CML) and polycythemia vera in small animals.
- Clinical Pearl: While not commonly used in routine veterinary practice due to the advent of newer targeted therapies (such as hydroxyurea for polycythemia vera), it remains a viable option for specific myeloproliferative disorders.
- It carries a significant risk of severe myelosuppression, necessitating rigorous hematological monitoring.
- Therapy may elevate serum uric acid levels due to rapid tumor lysis and cellular breakdown, sometimes requiring concurrent allopurinol therapy to prevent uric acid nephropathy.
Mechanism of action
Busulfan is a cell cycle-phase nonspecific alkylating agent.
- Mechanism: It undergoes intracellular hydrolysis to release methanesulfonate groups → forms reactive carbonium ions → alkylates DNA by cross-linking guanine bases on DNA strands.
- Pathway: DNA cross-linking → inhibition of DNA replication and RNA transcription → apoptosis (programmed cell death).
- Target: It exhibits highly selective toxicity toward cells of the granulocytic series and myeloid precursors in the bone marrow, making it particularly effective against myeloproliferative diseases.
Safety & warnings
Contraindications
- Patients with known hypersensitivity to busulfan
- Patients who have shown resistance to the drug in the past
- Pregnancy (FDA Category D), unless potential benefits outweigh the risks
- Nursing dams
Adverse effects
- Myelosuppression (anemia, leukopenia, thrombocytopenia)
- Pancytopenia (can take months to years for recovery)
- Bronchopulmonary dysplasia with pulmonary fibrosis (uncommon, chronic use)
- Uric acid nephropathy
- Stomatitis
Precautions
Warning: Only veterinarians with the experience and resources to monitor the toxicity of this agent should administer this drug.
- Bone Marrow Depression: The risk versus benefits of therapy must be carefully considered in patients with preexisting bone marrow depression or concurrent infections.
- Radiation Therapy: Additive bone marrow depression may occur in patients undergoing concomitant radiation therapy.
- Teratogenicity: Mutagenic in mice and may potentially cause a variety of fetal abnormalities. Avoid during pregnancy unless absolutely necessary.
Drug interactions
Use within 72 hours prior to busulfan can reduce busulfan clearance by reducing glutathione concentrations in tissues and blood.
Can potentially reduce clearance of busulfan, probably by competing for available glutathione.
Potential decreased busulfan clearance.
Concurrent use with other bone marrow depressant medications may result in additive myelosuppression.
Possible increased clearance of busulfan.
Used concomitantly with busulfan may result in hepatotoxicity.
Monitoring
- CBC (Complete Blood Count)
- Serum uric acid
- Clinical efficacy
Pharmacokinetics
Absorption
Well absorbed after oral administration.
Distribution
Distribution characteristics are not well described in animals, but in humans, drug concentrations in the CSF are nearly equal to those found in plasma. Unknown if it enters maternal milk.
Metabolism
Rapidly, hepatically metabolized to at least 12 different metabolites.
Elimination
Slowly excreted into the urine.
Overdose
There is limited experience with busulfan overdoses. The LD50 in mice is 120 mg/kg.
- Chronic vs Acute: Chronic overdosage is more likely to cause serious bone marrow suppression than is an acute overdose.
- Treatment: Any overdose should be treated seriously with standard gut emptying protocols used when appropriate and supportive therapy initiated when required.
- Antidote: There is no known specific antidote for busulfan intoxication.
Available products
Formulations
- Oral tablets
- Injection solution
Human-labeled
- Busulfan Oral Tablets: 2 mg; Myleran (GlaxoSmithKline); (Rx)
- Busulfan Injection Solution: 6 mg/mL in 10 mL single-use amps with syringe filters; Busulfex (Otsuka America); (Rx)
Regulatory status
No regulatory data for: 🇺🇸 US · 🇪🇺 EU · 🇬🇧 UK · 🇭🇰 HK · 🇹🇼 TW · 🇯🇵 JP · 🇰🇷 KR · 🇦🇺 AU
Storage & stability
Busulfan tablets should be stored in well-closed containers at room temperature.
Client information
Important Safety Warning: Busulfan is a potent chemotherapy drug. Handle with extreme care to protect yourself, your family, and the environment.
- Handling: Always wear disposable gloves when handling the medication. Wash hands thoroughly afterward. Do not crush, break, or split tablets.
- Waste Management: Treat your pet's waste (urine, feces, vomit) as hazardous for at least 48-72 hours post-dose. Clean up with gloves and dispose of waste in sealed plastic bags.
- Adverse Signs: Contact your veterinarian immediately if you notice signs of toxicity such as:
- Abnormal bleeding or unexplained bruising (signs of low platelets)
- Lethargy, severe depression, or weakness (signs of anemia)
- Fever or signs of infection (signs of low white blood cells)
- Shortness of breath or difficulty breathing
- Changes in urination
VetSheet drug reference is intended for licensed veterinary professionals as a clinical decision-support aid, not a substitute for professional judgement or the manufacturer’s current label.