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Alkylator

Busulfan

Myleran · Bu

Alkylator · approved 1954 · 8 references

A conditioning alkylator that can injure the transplant endothelium and trigger microangiopathy.

Signature injury
Thrombotic Microangiopathy
Severity
Moderate
Reversibility
Variable
Onset
Weeks after conditioning/transplant.

Signature kidney injury & incidence

Thrombotic Microangiopathy.

Transplant-associated thrombotic microangiopathy (TA-TMA) with renal involvement complicates a subset of conditioning regimens; high-dose busulfan (e.g., 16 mg/kg) has been identified as an independent risk factor for post-transplant TMA, and high busulfan exposure also drives sinusoidal obstruction syndrome/VOD.

Source: Nakamae et al., Am J Hematol 2006

Reported injury signatures: Thrombotic Microangiopathy.

Onset timing & rechallenge

Subacute (~1–6 weeks) — Weeks after conditioning/transplant.

Mechanism of kidney injury

Conditioning-related endothelial injury - amplified by high busulfan AUC, calcineurin inhibitors, GVHD, infection and complement dysregulation - drives a thrombotic microangiopathy with platelet/fibrin microthrombi in the renal microvasculature, microangiopathic hemolysis and renal ischemia. The same endothelial toxicity at high exposure produces hepatic sinusoidal obstruction syndrome (VOD), which can cause hepatorenal-type renal hypoperfusion. TA-TMA is multifactorial; busulfan intensity is one contributing factor.

Clinical presentation

Microangiopathic hemolytic anemia (schistocytes, elevated LDH, low haptoglobin), thrombocytopenia, hypertension, proteinuria and rising creatinine after transplant; if VOD coexists, weight gain, hepatomegaly and hyperbilirubinemia with secondary renal hypoperfusion.

Management

Identify and treat triggers (reduce/adjust calcineurin inhibitor, treat GVHD/infection), supportive care, and consider complement-directed therapy (eculizumab) in severe TA-TMA. Renal outcomes range from recovery to chronic kidney disease.

Risk factors

  • High-dose / high-AUC busulfan conditioning
  • Calcineurin inhibitors (tacrolimus/cyclosporine)
  • Acute graft-versus-host disease
  • Concurrent infection / total body irradiation / sinusoidal obstruction syndrome

Prevention

  • Therapeutic busulfan dosing with PK/AUC level monitoring to limit excess exposure
  • Minimize additive endothelial insults where possible

Renal dose adjustment

Busulfan clearance is largely hepatic (GST-mediated); no formal renal CrCl dose banding, but AUC-targeted (therapeutic-drug-monitoring) dosing is standard to avoid the high exposures linked to TMA and VOD. Reduced clearance at high doses warrants level monitoring.

Dialyzability & ESKD dosing

Busulfan is moderately dialyzable in principle, but TDM-guided dosing (not dialysis) is the control strategy; dialysis is reserved for managing TA-TMA-related renal failure rather than for drug removal.

Differential diagnosis

TA-TMA (schistocytes, elevated LDH, low haptoglobin, thrombocytopenia, hypertension, proteinuria) vs calcineurin-inhibitor nephrotoxicity (often without hemolysis), vs VOD-related hepatorenal hypoperfusion (weight gain, hyperbilirubinemia), vs sepsis/ATN. ADAMTS13 is typically not severely deficient, distinguishing TA-TMA from TTP.

Monitoring

  • Busulfan plasma levels/AUC (therapeutic drug monitoring) during conditioning
  • Schistocytes, LDH, haptoglobin, platelets and creatinine post-transplant (TA-TMA panel)
  • Bilirubin/weight/liver exam for sinusoidal obstruction syndrome

Key trials & series

  • Ho BMT-CTN consensus Biol Blood Marrow Transplant 2005 - defines post-transplant TMA including the renal component
  • Nakamae Am J Hematol 2006 - high-dose busulfan as an independent TA-TMA risk factor
  • Tolbert Biol Blood Marrow Transplant 2019 - conditioning regimen as key determinant of TA-TMA with renal injury

Clinical pearls

  • PK-guided (AUC-targeted) busulfan dosing is the single best lever to reduce both TA-TMA and VOD risk.
  • TA-TMA is a complement-mediated, multifactorial endothelial injury - busulfan is a contributor, not the sole cause.
  • Look for the haptoglobin/LDH/schistocyte triad with rising creatinine weeks post-transplant before anchoring on calcineurin-inhibitor toxicity.

Anticancer mechanism

Bifunctional alkylsulfonate that cross-links DNA, intensely myelosuppressive with a narrow therapeutic window. Used historically for chronic myeloid leukemia and, principally, as a high-dose conditioning agent (with cyclophosphamide or fludarabine) before hematopoietic stem cell transplant.

Guidelines & consensus

Each recommendation below is this atlas's faithful summary of the source, not a quotation from it — follow the PubMed link for the wording the society published. Summaries may be superseded; consult the current full text and individualize to the patient.

  • ADQI (2026) — Conventional cytotoxic chemotherapy-associated nephrotoxicity: consensus report of the 34th Acute Disease Quality Initiative (ADQI) WorkgroupCisplatin is identified as a leading cytotoxic nephrotoxin; the workgroup details preventive measures (adequate isotonic hydration, correction of volume depletion, avoidance of concurrent nephrotoxins, attention to electrolyte/magnesium wasting) and management of cisplatin-associated AKI, with a research agenda for knowledge gaps.Kidney Int · PMID 41881107
  • ADQI (2026) — The nephrotoxic effects of anti-cancer therapies: consensus report of the 34th Acute Disease Quality Initiative workgroupProvides expert-based statements (modified Delphi) on preventing and managing cisplatin/platinum-associated AKI, including isotonic IV hydration, attention to volume status and concomitant nephrotoxins, and incorporates evidence that IV magnesium supplementation may reduce cisplatin-associated AKI; emphasizes risk stratification and standardized AKI definitions.Nat Rev Nephrol · PMID 41361704
  • SIRM (2022) — SIRM-SIN-AIOM: appropriateness criteria for evaluation and prevention of renal damage in the patient undergoing contrast medium examinations-consensus statements from Italian College of Radiology (SIRM), Italian College of Nephrology (SIN) and Italian Association of Medical Oncology (AIOM)Recommends eGFR-based renal risk assessment and pre/post-contrast isotonic saline or sodium bicarbonate hydration; advises maintaining a 5-7 day interval between iodinated contrast administration and cisplatin in cancer patients to reduce additive nephrotoxicity.Radiol Med · PMID 35303246
  • KDIGO (2020) — KDIGO Controversies Conference on onco-nephrology: understanding kidney impairment and solid-organ malignancies, and managing kidney cancerIdentifies platinum compounds (especially cisplatin) as leading cytotoxic causes of acute tubular injury, AKI, and electrolyte/magnesium wasting; calls for interdisciplinary onco-nephrology care, accurate GFR estimation, and individualized drug dosing in patients with reduced kidney function.Kidney Int · PMID 33126977
  • KDIGO (2020) — KDIGO Controversies Conference on onco-nephrology: kidney disease in hematological malignancies and the burden of cancer after kidney transplantationAddresses chemotherapy-associated AKI/CKD in hematologic cancer, GFR estimation and chemotherapy dosing in patients with reduced kidney function, and management priorities and research gaps for onco-nephrology care.Kidney Int · PMID 33276867
  • ADDIKD (2025) — Integrating International Consensus Guidelines for Anticancer Drug Dosing in Kidney Dysfunction (ADDIKD) into everyday practiceProvides GRADE-based, drug-specific dose-adjustment recommendations for anticancer agents in kidney dysfunction (illustrated for methotrexate, cisplatin, carboplatin and nivolumab); the recommendations build on Part 1's standardised CKD-EPI eGFR assessment rather than Cockcroft-Gault creatinine clearance.EClinicalMedicine · PMID 40290844
  • ADDIKD (2025) — Aligning kidney function assessment in patients with cancer to global practices in internal medicineThree consensus recommendations: assess kidney function by GFR (measured GFR or CKD-EPI eGFR), classify it using KDIGO categories, and use this uniform approach to dose anticancer drugs — moving cancer medicine away from Cockcroft-Gault estimated creatinine clearance.EClinicalMedicine · PMID 40290845
  • ADDIKD (2025) — A methodology for determining dosing recommendations for anticancer drugs in patients with reduced kidney functionEstablishes that, where RCT evidence is lacking, anticancer drug dosing recommendations in kidney dysfunction should be derived by critically appraising observational literature via GRADE combined with structured international multidisciplinary consensus voting.EClinicalMedicine · PMID 40290846
  • KDIGO (2013) — Diagnosis, evaluation, and management of acute kidney injury: a KDIGO summary (Part 1)Defines/stages AKI by serum creatinine and urine output; emphasizes avoiding nephrotoxins, maintaining euvolemia/perfusion, dose-adjusting drugs to kidney function, and monitoring high-risk patients — the framework applied to nephrotoxic anti-cancer agents.Crit Care · PMID 23394211
  • KDIGO (2024) — Executive summary of the KDIGO 2024 Clinical Practice Guideline for the Evaluation and Management of Chronic Kidney Disease: known knowns and known unknownsEvaluate and risk-stratify CKD, manage to delay progression and its complications, and practise explicit medication management and drug stewardship — the framework the atlas's G1–G5 eGFR banding and every renal dose-adjustment recommendation sit inside. Because the guideline excludes dialysis and transplant recipients by its own statement of scope, its recommendations do not carry to those settings, where this atlas's dialyzability and post-transplant guidance rests on other sources.Kidney Int · PMID 38519239
  • KDIGO (2021) — Executive summary of the KDIGO 2021 Guideline for the Management of Glomerular DiseasesProvides the staging/treatment framework for drug-associated glomerular lesions (e.g., bisphosphonate- and interferon-related collapsing FSGS, VEGF-inhibitor podocytopathy/proteinuria), including immunosuppression and supportive RAAS-blockade strategies.Kidney Int · PMID 34556300
  • KDIGO (2024) — Executive summary of the KDIGO 2024 Clinical Practice Guideline for the Management of ANCA-Associated VasculitisUpdates immunosuppressive induction (rituximab/cyclophosphamide), incorporates avacopan and lower-dose or glucocorticoid-sparing regimens — the management framework for drug- and checkpoint-inhibitor-associated ANCA/pauci-immune glomerulonephritis.Kidney Int · PMID 38388147
  • KDIGO (2024) — Executive summary of the KDIGO 2024 Clinical Practice Guideline for the Management of Lupus NephritisUpdates first-line lupus nephritis therapy to combination immunosuppression with the addition of belimumab or a calcineurin inhibitor (voclosporin) — informs management of immune-complex/lupus-like glomerulonephritis encountered with immunotherapy.Kidney Int · PMID 38182299
  • KDIGO (2025) — Executive summary of the KDIGO 2025 Clinical Practice Guideline for the Management of Immunoglobulin A Nephropathy (IgAN) and Immunoglobulin A Vasculitis (IgAV)Encourages liberal kidney biopsy and stricter proteinuria control (<0.5 g/d, ideally <0.3 g/d) with RAAS blockers, SGLT2 inhibitors, and targeted-release budesonide — the framework for IgA-dominant glomerular lesions, including those triggered by immune-modulating cancer therapy.Kidney Int · PMID 40975525

References

8 peer-reviewed references. Citation metadata via PubMed / NLM.

  1. 1.Blood and marrow transplant clinical trials network toxicity committee consensus summary: thrombotic microangiopathy after hematopoietic stem cell transplantation.Ho VT et al. · Biol Blood Marrow Transplant · 2005 · PMID 16041306
  2. 2.Risk factor analysis for thrombotic microangiopathy after reduced-intensity or myeloablative allogeneic hematopoietic stem cell transplantation.Nakamae H et al. · Am J Hematol · 2006 · PMID 16755559
  3. 3.Risk Factors for Transplant-Associated Thrombotic Microangiopathy after Autologous Hematopoietic Cell Transplant in High-Risk Neuroblastoma.Tolbert VP et al. · Biol Blood Marrow Transplant · 2019 · PMID 31199983
  4. 4.Phase I study of dose-escalated busulfan with fludarabine and alemtuzumab as conditioning for allogeneic hematopoietic stem cell transplant: reduced clearance at high doses and occurrence of late sinusoidal obstruction syndrome/veno-occlusive disease.O'Donnell PH et al. · Leuk Lymphoma · 2010 · PMID 20919852
  5. 5.GSTA1 diplotypes affect busulfan clearance and toxicity in children undergoing allogeneic hematopoietic stem cell transplantation: a multicenter study.Ansari M et al. · Oncotarget · 2017 · PMID 29207608
  6. 6.Diagnosis and treatment of transplantation-associated thrombotic microangiopathy: real progress or are we still waiting?Batts ED et al. · Bone Marrow Transplant · 2007 · PMID 17603513
  7. 7.Thrombosis in stem cell transplantation.Kansu E · Hematology · 2012 · PMID 22507809
  8. 8.Anticancer drug-induced kidney disorders.Kintzel PE · Drug Saf · 2001 · PMID 11219485
Educational monograph from NephTox (nephtox.com). Not medical advice — verify against current guidelines before any clinical decision.