Doxorubicin
Adriamycin · Anthracycline
Experimental podocyte model; clinical proteinuria rare.
GLOM
MildOpen →
mTOR inhibitor
Sirolimus
Rapamune · SIR
An mTOR inhibitor long called 'non-nephrotoxic' that can nonetheless unmask podocyte injury, proteinuria, and stall tubular repair.
ModeratemTOR inhibitor · approved 1999
Renal allograft rejection prophylaxis (immunosuppression)Perivascular epithelioid cell tumor (PEComa)LymphangioleiomyomatosisKaposi sarcoma (post-transplant)
Signature kidney injury
Glomerular Injury / Proteinuria
New or worsening proteinuria occurs in a substantial minority of treated patients in transplant cohorts (more pronounced after conversion from a calcineurin inhibitor than with de novo use), but oncology-specific renal incidence is not well quantified and is described largely at the case and small-series level. Acute renal dysfunction (e.g., delayed graft recovery) is recognized but variable.
Source: Diekmann, Transplant Rev 2012
Mechanism of kidney injury
mTOR inhibition disrupts pathways essential for podocyte integrity: sirolimus lowers podocyte VEGF and interferes with Akt/WT1 signaling, promoting podocyte dedifferentiation and effacement that increases glomerular capillary permeability and causes proteinuria; at high troughs this can manifest as de novo or worsening focal segmental glomerulosclerosis. In parallel, mTORC1 inhibition blunts the compensatory proliferative hypertrophy that surviving podocytes use to cover denuded glomerular basement membrane, accelerating glomerulosclerosis, and suppresses regenerative proliferation of injured proximal tubular epithelium (while favoring apoptosis), impairing recovery from acute tubular injury and contributing to delayed graft function.
Clinical presentation
New or rising proteinuria (subnephrotic to occasionally nephrotic-range with edema and hypoalbuminemia), a creeping serum creatinine, and—when superimposed on existing chronic damage—an acute decline in GFR. Frequently accompanied by the broader sirolimus toxicity profile: hyperlipidemia, cytopenias, mouth ulcers, and impaired wound healing.
Onset
Variable—weeks to months after initiation or dose escalation; proteinuria characteristically emerges or worsens within months after calcineurin-inhibitor withdrawal/conversion.
Reversibility
Partially reversible
Anticancer mechanism
Binds the immunophilin FKBP12; the sirolimus-FKBP12 complex inhibits mTOR complex 1 (mTORC1), blocking p70S6K/4E-BP1-driven protein synthesis, cell-cycle progression at the G1/S checkpoint, and pro-survival/angiogenic (VEGF) signaling. Used as an antiproliferative immunosuppressant and, within the broader mTOR-inhibitor class (with everolimus and temsirolimus), in oncology settings including renal cell carcinoma, perivascular epithelioid cell tumors, and lymphangioleiomyomatosis.
Management
Quantify proteinuria and assess GFR; start or optimize ACE inhibitor/ARB therapy and treat dyslipidemia. Reduce dose to lower troughs, and discontinue sirolimus with switch to an alternative agent if proteinuria is progressive (especially nephrotic-range) or renal function declines—proteinuria often improves, though established glomerulosclerosis may persist.
Risk factors
- Pre-existing chronic kidney disease or reduced GFR
- Underlying glomerular disease (e.g., FSGS)
- Conversion from a calcineurin inhibitor to sirolimus
- Higher drug trough levels
Prevention
- Baseline and serial monitoring of proteinuria (urine protein/creatinine ratio) and serum creatinine
- Therapeutic drug-level monitoring to avoid excessive troughs
- RAAS blockade (ACE inhibitor or ARB) if proteinuria develops
- Avoid use in patients with significant pre-existing glomerular injury when alternatives exist
Note · Historically labeled 'non-nephrotoxic' because it lacks the afferent-arteriolar vasoconstriction of calcineurin inhibitors, but podocyte injury, proteinuria, and impaired tubular repair are well documented in susceptible patients. Renal data derive mainly from transplant and glomerular-disease populations and extend by class reasoning to oncologic mTOR-inhibitor use.
Clinical depth
Renal dose adjustment
No mandatory dose reduction for renal impairment per se (sirolimus is hepatically metabolized via CYP3A4), but troughs should be kept toward the lower end and proteinuria monitored when GFR is reduced. Avoid initiating or escalating in the setting of significant proteinuria or progressive glomerular disease.
Dialyzability & ESKD dosing
Not meaningfully dialyzable—sirolimus is large, highly lipophilic, extensively (~92%) protein/erythrocyte bound with a very large volume of distribution; hemodialysis does not remove clinically relevant amounts and no supplemental dosing is needed after HD.
Differential diagnosis
Distinguish sirolimus podocytopathy/FSGS from recurrent or primary glomerular disease, transplant-glomerulopathy, and calcineurin-inhibitor arteriolopathy—the temporal link to drug initiation/conversion or high troughs and improvement on dose reduction supports drug attribution; biopsy clarifies FSGS pattern and excludes rejection. Delayed graft function from impaired tubular repair must be separated from acute rejection and ischemic ATN.
Monitoring
- Whole-blood sirolimus trough levels (therapeutic drug monitoring)
- Urine protein/creatinine ratio at baseline and periodically
- Serum creatinine/eGFR each clinic visit
- Fasting lipid panel (frequent hyperlipidemia)
Key trials & series
- Letavernier CJASN 2007 sirolimus de novo FSGS series
- Cho AJKD 2007 sirolimus-in-FSGS trial halted for nephrotoxicity
- Diekmann Transplant Rev 2012 mTOR-inhibitor proteinuria analysis
Clinical pearls
- The 'non-nephrotoxic' label is misleading: sirolimus causes a podocyte-VEGF-mediated proteinuria, not a vasomotor lesion.
- Proteinuria classically appears or worsens after switching from a calcineurin inhibitor to sirolimus—check a baseline UPCR before conversion.
- Because mTOR inhibition blocks tubular regeneration, avoid starting sirolimus in the early post-transplant or post-ATN window when repair is most needed.
- High troughs are the modifiable driver of de novo FSGS—keep levels low and recheck proteinuria after any escalation.
Where it strikes
Nephron segments
Glomerulus
Filtration barrier (podocytes + endothelium)
Proximal Tubule
Bulk reabsorption + drug uptake (OCT2, OATs)
Injury signatures
Glomerular Injury / ProteinuriaAcute Tubular Necrosis
Beyond the kidney
Class-level context for the major non-renal toxicities of mtor inhibitors.
Pulmonary
Pneumonitis, ILD, effusions, hypertension
- Non-infectious pneumonitis
Endocrine
Thyroiditis, hypophysitis, diabetes
- Hyperglycemia, hyperlipidemia
Gastrointestinal
Diarrhea, colitis, mucositis, perforation
- Stomatitis
Immune / Infusion
CRS, infusion reactions, irAEs, anaphylaxis
- Immunosuppression / infection
Evidence
9 peer-reviewed references. Citation metadata via PubMed / NLM.
LandmarkSirolimus-associated proteinuria and renal dysfunction.Rangan GK · Drug Saf 2006 · PMID 17147461Review of mechanisms of sirolimus-associated proteinuria and acute renal dysfunction, including impaired tubular repair.PMIDSirolimus therapy of focal segmental glomerulosclerosis is associated with nephrotoxicity.Cho ME et al. · Am J Kidney Dis 2007 · PMID 17261434Phase 2 trial halted early for precipitous GFR decline and worsening proteinuria on sirolimus in FSGS.PMIDHigh sirolimus levels may induce focal segmental glomerulosclerosis de novo.Letavernier E et al. · Clin J Am Soc Nephrol 2007 · PMID 17699432Clinical series linking high sirolimus troughs to de novo FSGS/nephrotic syndrome with podocyte dedifferentiation.PMIDSirolimus interacts with pathways essential for podocyte integrity.Letavernier E et al. · Nephrol Dial Transplant 2008 · PMID 18927120Mechanistic study showing sirolimus reduces podocyte VEGF/Akt/WT1 signaling, explaining proteinuria.PMIDmToR inhibitors-induced proteinuria: mechanisms, significance, and management.Letavernier E et al. · Transplant Rev (Orlando) 2008 · PMID 18631865Focused review of the mechanisms, significance, and management of mTOR-inhibitor proteinuria.PMIDmTOR inhibitor-associated proteinuria in kidney transplant recipients.Diekmann F et al. · Transplant Rev (Orlando) 2012 · PMID 22137729Synthesis of proteinuria incidence across de novo versus conversion mTOR-inhibitor use.PMIDmTOR-mediated podocyte hypertrophy regulates glomerular integrity in mice and humans.Puelles VG et al. · JCI Insight 2019 · PMID 31534053Shows mTOR-driven podocyte hypertrophy protects glomerular integrity; its pharmacologic inhibition provokes albuminuria and glomerulosclerosis.PMIDRole of apoptosis in the pathogenesis of acute renal failure.Bonegio R et al. · Curr Opin Nephrol Hypertens 2002 · PMID 11981260Mechanistic basis for rapamycin delaying ATN recovery by inhibiting tubular regeneration and increasing tubular apoptosis.PMIDStrategies for the management of adverse events associated with mTOR inhibitors.Kaplan B et al. · Transplant Rev (Orlando) 2014 · PMID 24685370Class review covering proteinuria, nephrotoxicity, delayed graft function, and their management with mTOR inhibitors.
Related agents
Other agents sharing the same signature kidney injury.