An antifolate, an acidic tubule, and enzymatic rescue

High-dose methotrexate crystal nephropathy

High-dose methotrexate is cleared by the kidney, so when it and its poorly-soluble metabolite crystallize in the acidic tubular lumen the kidney injures itself — and because that same kidney is what clears the drug, injury feeds a spiral of rising levels that leucovorin cannot break but an enzyme can.

2%–12%: develop AKIAcute kidney injury in patients receiving high-dose methotrexate (defined as >500 mg/m²), from crystallization of methotrexate in the renal tubular lumenPMID 27496039
1.8%: grade ≥2 nephrotoxicityShare of osteosarcoma patients (68 of 3,887) who developed grade ≥2 HD-MTX nephrotoxicity on clinical protocols with optimal supportive carePMID 15139068
4.4%: mortality when it strikesDeaths among the 68 osteosarcoma patients (3 of 68) with HD-MTX-induced renal dysfunction — the injury is uncommon but can be life-threateningPMID 15139068
99%: cut in MTX by glucarpidaseMedian reduction in plasma methotrexate at the first post-dose measurement (median 15 minutes) after glucarpidase, which cleaves circulating MTX to inactive metabolitesPMID 24132809
64%: renal recovery after rescueShare of patients with grade ≥2 renal impairment who recovered to grade 0/1 at a median of 12.5 days after glucarpidase, in a pooled compassionate-use analysisPMID 24132809

Crystal / Obstructive Nephropathy Acute Tubular Necrosis Methotrexate (high-dose) profile

Teaching case · illustrative composite, not a real patient

A 17-year-old with osteosarcoma is 42 hours into recovery from a 12 g/m² high-dose methotrexate infusion when the plasma methotrexate, expected to be falling below 1 µmol/L, is instead 18 µmol/L, and the creatinine has risen from 0.7 to 1.9 mg/dL. Urine pH is 5.5 despite the alkalinization protocol, and urine output has dropped. Mucositis is beginning.

The picture — a rising creatinine with a plateauing, still-toxic methotrexate level in the days after an HD-MTX infusion — is recognized as methotrexate crystal nephropathy with delayed clearance. Intravenous hydration and sodium bicarbonate are intensified to drive urine pH ≥7 and restore flow; leucovorin is escalated against the measured level; interacting drugs are held. Because the level is high and the kidney is failing, glucarpidase is given, cleaving the circulating methotrexate by ~99% within minutes. Leucovorin is continued (dosed apart from the glucarpidase, which also degrades it), and immunoassay methotrexate results are treated as unreliable for the next ~48 hours because the DAMPA cleavage product cross-reacts. Renal function recovers over the following one to two weeks.

Teaching point — HD-MTX nephrotoxicity is a crystal nephropathy of the acidic tubule, and it is self-amplifying: the kidney clears methotrexate, so once it is injured the level climbs and drives further renal, marrow, mucosal, and hepatic toxicity. Prevention is high urine flow plus alkalinization to pH ≥7 (methotrexate solubility rises several-fold from pH 6 to 7). When AKI with toxic levels occurs anyway, glucarpidase — not dialysis — is the definitive move: it removes the drug in minutes, whereas leucovorin protects tissues without lowering the level at all. Watch the assay artifact and keep leucovorin going.

How it happens

The pathophysiology as a cascade — select a step to follow the mechanism.

Methotrexate and its metabolite 7-hydroxy-methotrexate are predominantly renally excreted, so after a high-dose infusion they are concentrated in the tubular lumen — the setting for precipitation.
PMID 16794248 (opens PubMed in a new tab)
Methotrexate and 7-OH-MTX are poorly soluble at low pH; in acidic urine they precipitate as crystals in the tubular lumen, causing direct tubular toxicity and obstruction. Solubility rises several-fold between pH 6 and 7 — the rationale for alkalinization.
PMID 27496039 (opens PubMed in a new tab)
Because the kidney is what clears methotrexate, renal injury reduces clearance, which raises and prolongs the toxic methotrexate level, which worsens renal injury (and marrow, mucosal, and hepatic toxicity) in turn — the reason a rising level and a rising creatinine must both be caught early.
PMID 27496039 (opens PubMed in a new tab)
Leucovorin bypasses the folate blockade to protect normal cells but does NOT lower the methotrexate concentration. Glucarpidase (carboxypeptidase-G2) hydrolyzes circulating methotrexate to inactive metabolites within minutes, which is why it — not dialysis — is the definitive way to cut the drug burden.
PMID 24132809 (opens PubMed in a new tab)

How we learned it

2004
Widemann and colleagues quantify HD-MTX nephrotoxicity in osteosarcoma — 1.8% (68/3,887) with grade ≥2 renal dysfunction, 4.4% mortality among them — and show dialysis removes methotrexate poorly compared with the >98% reductions from carboxypeptidase-G2 (glucarpidase).
Established both the modern incidence under optimal supportive care and that enzymatic cleavage, not dialysis, is the effective way to lower a toxic methotrexate level.
PMID 15139068 (opens PubMed in a new tab)
2006
Widemann and Adamson review the mechanism and management of methotrexate nephrotoxicity, reporting that carboxypeptidase-G2 produces consistent, rapid reductions in plasma methotrexate by a median of 98.7% (range 84–99.5%).
The mechanistic reference — renal handling, tubular crystallization, and the case for early enzymatic rescue alongside leucovorin.
PMID 16794248 (opens PubMed in a new tab)
2014
A pooled analysis of four compassionate-use trials (476 patients) shows glucarpidase achieves a sustained ~99% reduction in methotrexate and that 64% of patients with grade ≥2 renal impairment recover to grade 0/1 at a median of 12.5 days.
The efficacy evidence base underpinning glucarpidase (Voraxaze) as noninvasive rescue for HD-MTX-induced AKI.
PMID 24132809 (opens PubMed in a new tab)
2016
Howard et al. publish a comprehensive framework for preventing and managing HD-MTX toxicity, defining HD-MTX as >500 mg/m², AKI at 2–12%, and the crystallization mechanism, with hydration/alkalinization, leucovorin, and glucarpidase as the management spine.
The practical clinical reference clinicians reach for — risk factors, monitoring, and when glucarpidase replaces dialysis.
PMID 27496039 (opens PubMed in a new tab)
2018
An international expert panel (Ramsey et al.) issues a consensus guideline defining exactly when to give glucarpidase — by methotrexate level at 36/42/48 h with a rising creatinine — and that it should be given within 48–60 h, being far less effective beyond 60 h.
Codified the threshold and timing for glucarpidase rescue, turning the efficacy data into an actionable decision rule.
PMID 29079637 (opens PubMed in a new tab)

The landmark studies

Literature + clinical-trial database review with a compassionate-use CPDG2 series

High-dose methotrexate-induced nephrotoxicity in patients with osteosarcoma

Widemann BC, et al. · Cancer 2004 · PMID 15139068

Under optimal supportive care HD-MTX nephrotoxicity still occurs in ~1.8% of osteosarcoma patients; carboxypeptidase-G2 lowers plasma methotrexate far faster and more completely than dialysis-based removal.

Grade ≥2 nephrotoxicity 68/3,887 (1.8%); mortality 3/68 (4.4%); CPDG2 plasma-MTX reduction >98% vs limited dialysis effect

Pooled analysis of four multicenter single-arm compassionate-use trials, 476 patients

Efficacy of glucarpidase (carboxypeptidase G2) in patients with AKI after high-dose methotrexate therapy

Widemann BC, et al. · Pharmacotherapy 2014 · PMID 24132809

Glucarpidase produced a rapid, sustained ~99% reduction in plasma methotrexate and allowed most renally-impaired patients to recover kidney function without dialysis.

Median 99% reduction (first measure median 15 min); median pre-glucarpidase MTX 11.7 µmol/L; RSCIR 83/140 (59%); renal recovery to grade 0/1 in 64% at median 12.5 days

Clinical review / management framework

Preventing and Managing Toxicities of High-Dose Methotrexate

Howard SC, et al. · The Oncologist 2016 · PMID 27496039

AKI complicates 2–12% of patients receiving HD-MTX through tubular crystallization; hydration, urinary alkalinization, leucovorin, and — when AKI occurs — glucarpidase usually allow renal recovery without dialysis.

HD-MTX defined >500 mg/m²; AKI 2–12%; risk factors: prior renal dysfunction, volume depletion, acidic urine, drug interactions

International expert-consensus guideline

Consensus Guideline for Use of Glucarpidase in HD-MTX-Induced AKI and Delayed MTX Clearance

Ramsey LB, et al. · The Oncologist 2018 · PMID 29079637

Defines the methotrexate-level thresholds (with a rising creatinine) and the 48–60 h window for giving glucarpidase, beyond which it is far less effective.

Consider glucarpidase for MTX >30 µM at 36 h, >10 µM at 42 h, or >5 µM at 48 h + elevated creatinine; give within 48–60 h of infusion start

All landmark evidence in this field

What the data says now

How disproportionately each agent's FAERS reports name these phenotypes vs. all other drugs (reporting odds ratio; significant signals only, 95% CI lower bound > 1; as of 2026-09-01). A reporting signal, not incidence or proven causation. A dash means tested without reaching significance, not a phenotype that never occurs — ATN and AIN undercount badly, most true cases filing as generic “acute kidney injury”. Computed by this atlas on the current snapshot — a published disproportionality analysis will not match cell for cell (different window, different term set).

Per-agent FAERS reporting odds ratio for each injury phenotype in this syndrome.
Agent	XTAL	ATN
Methotrexate (high-dose)	Methotrexate (high-dose), Crystal / Obstructive Nephropathy: ROR 2.07, 2,624 reports	Methotrexate (high-dose), Acute Tubular Necrosis: ROR 1.14, 262 reports

2%–12%

AKI in HD-MTX patients

Patients receiving high-dose methotrexate (>500 mg/m²)

PMID 27496039

1.8%

Grade ≥2 nephrotoxicity (osteosarcoma)

Osteosarcoma patients on clinical protocols (68/3,887)

PMID 15139068

4.4%

Mortality among affected

Osteosarcoma patients with HD-MTX nephrotoxicity (3/68)

PMID 15139068

20.9%

Delayed methotrexate elimination

412 HD-MTX cycles (≥1 g/m²) in a hematology cohort

PMID 28983943

64%

Renal recovery after glucarpidase

Grade ≥2 renal impairment, pooled compassionate-use analysis

PMID 24132809

How it's managed

1
Prevent: hydration + urinary alkalinization to pH ≥7
Vigorous isotonic hydration with sodium bicarbonate to keep urine pH ≥7 and urine output high before, during, and after the infusion — methotrexate and 7-OH-MTX solubility rises several-fold from pH 6 to 7, so alkalinization is the core of crystal prevention.
Management framework — crystallization mechanism and preventive protocol · PMID 27496039 (opens PubMed in a new tab)
2
Monitor serial MTX levels and creatinine; escalate leucovorin
Pharmacokinetically-guided leucovorin titrated against serial plasma methotrexate levels (e.g. 24/48/72 h) with daily creatinine; a rising or plateauing level with a creatinine bump signals delayed clearance and impending toxicity, and triggers leucovorin escalation.
Management framework — monitoring and leucovorin titration · PMID 27496039 (opens PubMed in a new tab)
3
Glucarpidase for AKI with toxic levels — not dialysis
When methotrexate stays above the level thresholds at 36/42/48 h with a rising creatinine, give glucarpidase within 48–60 h of the infusion start (it is far less effective beyond 60 h); it cleaves circulating methotrexate by ~99% within minutes and largely supplants dialysis, which removes the drug poorly.
Consensus guideline thresholds + pooled efficacy (99% reduction, 64% renal recovery) · PMID 29079637 (opens PubMed in a new tab)
4
Continue leucovorin and beware the assay artifact
Keep leucovorin going after glucarpidase (dosed apart from it, since glucarpidase also degrades leucovorin), and do not trust immunoassay methotrexate levels for ~48 h — the inactive cleavage product DAMPA cross-reacts and falsely elevates the reported concentration; use a chromatographic assay.
Consensus guideline — post-glucarpidase leucovorin dosing and assay caveat · PMID 29079637 (opens PubMed in a new tab)

What the guidelines say

Society and consensus recommendations addressing this syndrome.

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.

Intl. Expert PanelConsensus Guideline for Use of Glucarpidase in Patients with High-Dose Methotrexate Induced Acute Kidney Injury and Delayed Methotrexate ClearanceOncologist 2018 · PMID 29079637For HDMTX infusions <=24 h, glucarpidase may be indicated when the methotrexate concentration is >30 uM at 36 h, >10 uM at 42 h, or >5 uM at 48 h together with a significantly elevated serum creatinine (indicating HDMTX-induced AKI); administer optimally within 48-60 h of infusion start, as it is far less effective beyond 60 h.ADQIConventional cytotoxic chemotherapy-associated nephrotoxicity: consensus report of the 34th Acute Disease Quality Initiative (ADQI) WorkgroupKidney Int 2026 · PMID 41881107Cisplatin 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.ADQIThe nephrotoxic effects of anti-cancer therapies: consensus report of the 34th Acute Disease Quality Initiative workgroupNat Rev Nephrol 2026 · PMID 41361704Provides 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.

Every citation on this page is a real, PubMed-verified reference. The teaching case is an illustrative composite, not a real patient. Medical-education content — not medical advice.