BUSULFEX
Clinical safety rating: caution
Comprehensive clinical and safety monograph for BUSULFEX (BUSULFEX).
Busulfan is a bifunctional alkylating agent that cross-links DNA, leading to inhibition of DNA replication and cell death.
| Metabolism | Primarily hepatic metabolism via glutathione S-transferase (GST) conjugation; minor involvement of cytochrome P450 enzymes (CYP3A4). |
| Excretion | Primarily hepatic metabolism via conjugation with glutathione, followed by renal excretion of metabolites. Less than 2% of the parent drug is excreted unchanged in urine. Fecal excretion is negligible. |
| Half-life | Terminal elimination half-life is approximately 2.5 hours (range: 1.5-4.0 hours) in adults. In children, half-life is shorter (~1.4 hours). Clinically, this supports high-dose, fractionated dosing regimens (e.g., every 6 hours) to maintain therapeutic levels. |
| Protein binding | Approximately 32% reversibly bound to plasma proteins, primarily albumin. |
| Volume of Distribution | Volume of distribution at steady-state is approximately 0.6 L/kg (range 0.4-0.8 L/kg), indicating distribution into total body water. Higher Vd may be seen in obesity. |
| Bioavailability | Intravenous: 100% bioavailable. Oral: Not commercially available; oral busulfan bioavailability is variable (70-90%) due to first-pass hepatic metabolism, but not relevant for Busulfex (IV formulation). |
| Onset of Action | Intravenous: Myeloablation begins within 1-2 days, with maximal effect on hematopoietic stem cells observed by day 4-5. Onset of antileukemic effect is variable and depends on disease status. |
| Duration of Action | Hematologic recovery (neutrophil engraftment) typically occurs 13-20 days post-transplant. Myelosuppression duration is prolonged and depends on stem cell source and conditioning regimen. Non-hematologic toxicities (e.g., veno-occlusive disease) may persist weeks. |
Busulfan 0.8 mg/kg IV every 6 hours for 4 days (total 16 doses) or 3.2 mg/kg IV once daily for 4 days, based on ideal body weight or actual body weight (whichever is lower).
| Dosage form | INJECTABLE |
| Renal impairment | No specific renal dose adjustment recommended; monitor for myelosuppression and seizures. GFR <30 mL/min: use with caution due to potential accumulation. |
| Liver impairment | Child-Pugh A: no adjustment. Child-Pugh B: consider 50% dose reduction. Child-Pugh C: avoid use or use with extreme caution; no established guidelines. |
| Pediatric use | IV: 1.0 mg/kg (ideal body weight) every 6 hours for 16 doses (total dose 16 mg/kg) for patients weighing ≤12 kg; for >12 kg, use 0.8 mg/kg (ideal body weight) every 6 hours for 16 doses. Oral: 1.0 mg/kg every 6 hours for 16 doses (total 16 mg/kg), based on actual body weight. |
| Geriatric use | No specific dose adjustment; pharmacokinetics not significantly altered; monitor for increased toxicity (myelosuppression, mucositis). Start at standard dosing with close monitoring. |
| 1st trimester | Consult provider |
| 2nd trimester | Consult provider |
| 3rd trimester | Consult provider |
Clinical note
Comprehensive clinical and safety monograph for BUSULFEX (BUSULFEX).
| Breastfeeding | Not recommended. Excreted in breast milk; M/P ratio unknown. Potential for severe adverse effects (myelosuppression, carcinogenesis) in nursing infant. Discontinue breastfeeding or drug. |
| Teratogenic Risk | Pregnancy Category D. First trimester: High risk of fetal malformations including craniofacial, CNS, and skeletal anomalies due to alkylating activity. Second and third trimesters: Risk of fetal growth restriction, myelosuppression, and spontaneous abortion. Avoid use unless maternal benefit outweighs fetal risk. |
■ FDA Black Box Warning
Busulfan causes severe myelosuppression at therapeutic doses, resulting in profound neutropenia, thrombocytopenia, and anemia. Hepatic veno-occlusive disease (VOD) is a serious and potentially fatal complication, especially with high doses. Seizures have been reported, and prophylactic anticonvulsant therapy is recommended.
| Serious Effects |
History of hypersensitivity to busulfan or any component of the formulation; use in non-malignant conditions in pediatrics (relative); pregnancy (FDA category D).
| Precautions | Myelosuppression (fatal pancytopenia); hepatic veno-occlusive disease (hyperbilirubinemia, hepatomegaly, ascites); seizures (use anticonvulsant prophylaxis); pulmonary toxicity (pneumonitis, fibrosis); cardiac tamponade; sinusoidal obstruction syndrome; secondary malignancies; mutagenicity; carcinogenicity; embryo-fetal toxicity. |
| Food/Dietary | Avoid grapefruit and grapefruit juice as they may inhibit CYP3A4 metabolism and increase busulfan toxicity. No other significant food interactions reported. |
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| Fetal Monitoring |
| Complete blood count (CBC) weekly during therapy; liver function tests (LFTs) and serum creatinine at baseline and periodically; fetal ultrasound and growth monitoring if pregnancy occurs; monitor for signs of myelosuppression (fever, infection, bleeding) in mother and potential fetal effects. |
| Fertility Effects | Causes ovarian failure, amenorrhea, and azoospermia in both sexes. May lead to permanent infertility, especially with prolonged or high-dose therapy. Sperm and oocyte cryopreservation recommended prior to treatment. |
| Clinical Pearls | Busulfan is highly emetogenic; administer prophylactic antiemetics. Monitor for hepatic veno-occlusive disease (VOD), especially in high-dose conditioning regimens. Use therapeutic drug monitoring (TDM) to target AUC (e.g., 900-1500 µmol·min/L per dose) and adjust dosing to reduce seizure risk. Co-administer phenytoin or benzodiazepines for seizure prophylaxis when high doses are used. Busulfan clearance is affected by age, liver function, and concomitant medications (e.g., itraconazole decreases clearance). |
| Patient Advice | Take busulfan exactly as prescribed, usually on an empty stomach. Do not chew or crush tablets. · Report any signs of infection (fever, chills), bleeding (unusual bruising), or yellowing of skin/eyes immediately. · Use effective contraception during treatment and for at least 6 months after stopping. · Do not receive live vaccines during or shortly after treatment. · Avoid grapefruit and grapefruit juice during therapy as they may interact with busulfan. |