Cyclophosphamide
Cytoxan · Oxazaphosphorine alkylator
Vasopressin-independent hyponatremia; hemorrhagic cystitis.
SIADHCYST
MildOpen →
Alkylator
Melphalan
Alkeran · Mel
The myeloma workhorse whose high-dose conditioning can quietly drop the serum sodium.
MildAlkylator · approved 1964
Multiple myelomaAutologous stem cell transplant conditioningLight-chain (AL) amyloidosisOvarian cancer; regional perfusion for melanoma
Signature kidney injury
SIADH / Hyponatremia
High-dose intravenous melphalan can cause hyponatremia/SIADH; in a small high-dose series most patients showed declining sodium, but this is reported at case/series level rather than as a large quantified rate. Notably, melphalan PK is not adversely affected by renal failure, so transplant in renal impairment is feasible with dose reduction.
Source: Greenbaum-Lefkoe et al., Cancer 1985
Mechanism of kidney injury
High-dose bolus melphalan can precipitate inappropriate antidiuretic hormone secretion with free-water retention and dilutional hyponatremia; conditioning-related mucositis and diarrhea cause additional volume and sodium disturbances (some hyponatremia is GI-loss rather than true SIADH). Melphalan is partly renally cleared, so impaired kidney function raises systemic and mucosal toxicity and motivates dose reduction (e.g., 200 to 140 mg/m2) in renal failure/amyloidosis.
Clinical presentation
Hyponatremia with inappropriately concentrated urine and ongoing natriuresis (SIADH pattern); in the conditioning setting, accompanying mucositis, diarrhea and volume shifts. Direct tubular nephrotoxicity is not characteristic.
Onset
Days after high-dose administration.
Reversibility
Reversible
Anticancer mechanism
Phenylalanine-mustard bifunctional alkylating agent that cross-links DNA. Backbone of multiple myeloma therapy and the standard high-dose conditioning agent before autologous stem cell transplant; also used in light-chain (AL) amyloidosis and (regional perfusion) melanoma.
Management
Manage SIADH with fluid restriction and careful, rate-limited sodium correction; treat volume and electrolyte derangements supportively. Hyponatremia typically resolves as the acute effect and mucositis abate.
Risk factors
- High-dose / bolus IV administration (conditioning)
- Renal impairment (reduced clearance, greater mucosal toxicity)
- Concurrent hypotonic fluids
- Mucositis/diarrhea-related volume loss
Prevention
- Monitor serum sodium and fluid balance during high-dose therapy
- Avoid excess hypotonic fluids
- Dose-reduce (e.g., 140 mg/m2) and monitor in renal impairment / amyloidosis
Note · Marked direct intrinsic nephrotoxicity is not characteristic; the renal-relevant signals are SIADH/hyponatremia in high-dose use and the need to account for renal clearance when dosing.
Clinical depth
Renal dose adjustment
For high-dose conditioning, reduce from 200 to 140 mg/m2 in significant renal impairment / dialysis dependence and in AL amyloidosis. PK studies show high-dose melphalan can be given in renal failure with acceptable toxicity at the reduced dose.
Dialyzability & ESKD dosing
Melphalan is short-lived (rapid chemical hydrolysis) so it is not reliably removed by dialysis as a rescue; however, high-dose autotransplant has been performed safely in dialysis-dependent patients using the reduced 140 mg/m2 dose with attention to mucositis.
Differential diagnosis
Euvolemic hyponatremia with concentrated urine and natriuresis points to SIADH; hypovolemic hyponatremia with low urine sodium and clinical volume loss points to mucositis/diarrhea-driven depletion. The distinction changes management (fluid restriction vs cautious repletion).
Monitoring
- Serum sodium and fluid balance during/after high-dose therapy
- Mucositis severity and volume status (diarrhea-related hyponatremia)
- CBC and renal function across conditioning
Key trials & series
- Greenbaum-Lefkoe Cancer 1985 - original SIADH/hyponatremia description after high-dose IV melphalan
- Tricot Clin Cancer Res 1996 - PK/toxicity of high-dose melphalan autotransplant in renal failure
- Sanchorawala Bone Marrow Transplant 2001 - HDM/SCT in AL amyloidosis with renal involvement
Clinical pearls
- Check sodium after high-dose melphalan - SIADH is the signature renal-electrolyte event, not tubular injury.
- Renal failure is NOT a contraindication to high-dose melphalan transplant; reduce to 140 mg/m2 and watch mucositis.
- Not all post-conditioning hyponatremia is SIADH - GI losses from mucositis/diarrhea are a common, differently managed cause.
Where it strikes
Nephron segments
Distal Tubule / Collecting Duct
Fine-tuning of Na, K, Mg, acid & water
Injury signatures
SIADH / HyponatremiaElectrolyte Wasting
Beyond the kidney
Class-level context for the major non-renal toxicities of alkylators.
Hematologic
Cytopenias, thrombosis, TMA
- Myelosuppression; secondary malignancy risk
Neurologic
Neuropathy, encephalopathy, ICANS, PRES
- Ifosfamide encephalopathy (chloroacetaldehyde)
Cardiac
Cardiomyopathy, QT, ischemia, myocarditis
- High-dose cyclophosphamide cardiotoxicity
Evidence
7 peer-reviewed references. Citation metadata via PubMed / NLM.
LandmarkSyndrome of inappropriate antidiuretic hormone secretion. A complication of high-dose intravenous melphalan.Greenbaum-Lefkoe B et al. · Cancer 1985 · PMID 3965085Original description of SIADH/hyponatremia after high-dose IV melphalan.PMIDL-phenylalanine mustard-dianhydrogalactitol and hyponatremia.Helson L et al. · Pediatr Hematol Oncol 1986 · PMID 3153241Hyponatremia after high-dose melphalan-containing therapy, here linked to diarrhea.PMIDSafety of autotransplants with high-dose melphalan in renal failure: a pharmacokinetic and toxicity study.Tricot G et al. · Clin Cancer Res 1996 · PMID 9816255High-dose melphalan PK not adversely affected by renal failure; supports reduced-dose transplant.PMIDHigh-dose therapy in patients with plasma cell dyscrasias and renal dysfunction.Pineda-Roman M et al. · Contrib Nephrol 2007 · PMID 17075230Onconephrology review of melphalan dosing on dialysis and dialysis-independence outcomes.PMIDAn overview of the use of high-dose melphalan with autologous stem cell transplantation for the treatment of AL amyloidosis.Sanchorawala V et al. · Bone Marrow Transplant 2001 · PMID 11704785HDM/SCT in AL amyloidosis with renal/nephrotic involvement and dose adjustment.PMIDAdvances in biology and therapy of multiple myeloma.Barille-Nion S et al. · Hematology Am Soc Hematol Educ Program 2003 · PMID 14633785Reviews melphalan dose reduction (200 to 140 mg/m2) in renal failure/amyloidosis.PMIDAnticancer drug-induced kidney disorders.Kintzel PE · Drug Saf 2001 · PMID 11219485General onconephrology context for alkylator electrolyte and renal effects.