What is the recommended treatment for C3 glomerulonephritis in a patient with 2.5 g/day proteinuria and a serum creatinine of 3 mg/dL?

Treatment of C3 Glomerulonephritis with 2.5g Proteinuria and Creatinine 3 mg/dL

Start with mycophenolate mofetil (MMF) 2-3 g/day combined with corticosteroids (methylprednisolone pulses followed by oral prednisone), while aggressively controlling blood pressure with ACE inhibitors or ARBs titrated to maximum tolerated dose, targeting systolic BP <120 mmHg and proteinuria reduction to <0.5-0.7 g/day by 12 months.

Rationale and Treatment Algorithm

Primary Immunosuppression Strategy

The most recent high-quality evidence from the 2025 VALIANT trial 1 demonstrates that complement inhibition with pegcetacoplan achieved a 67.2% reduction in proteinuria compared to placebo in C3G patients, with 49% meeting composite renal endpoints (eGFR stabilization + ≥50% proteinuria reduction). However, pegcetacoplan is not yet widely available outside clinical trials, making MMF-based regimens the practical first-line approach.

MMF-based therapy is recommended because:

• Registry data from 371 C3G patients 2 shows that achieving UPCR <100 mg/mmol at 12 months is associated with substantially lower kidney failure risk (HR 0.10,95% CI 0.03-0.30)
• Your patient's 2.5g proteinuria and Cr 3.0 represents high-risk disease requiring aggressive intervention
• MMF-based and non-MMF based treatments showed similar efficacy in retrospective studies 3, but MMF has better tolerability than cyclophosphamide

Specific Treatment Protocol

Induction Phase (0-6 months):

• MMF 2-3 g/day (start 1g BID, increase to 1.5g BID as tolerated) 4
• Methylprednisolone IV pulses: 500-750 mg for 3 consecutive days 5
• Oral prednisone: 0.3-0.5 mg/kg/day for 4 weeks, then taper to ≤7.5 mg/day by 3-6 months 4

Maintenance Phase (6+ months):

• Continue MMF 1-2 g/day for at least 3 years 4
• Maintain prednisone 5-7.5 mg/day 5

Critical Adjunctive Measures

Blood Pressure and Proteinuria Control:

• ACE inhibitor or ARB titrated to maximum tolerated dose 6
• Target systolic BP <120 mmHg using standardized office measurement 6
• Do NOT stop ACEi/ARB if creatinine rises up to 30% - this is expected and acceptable 6
• Only discontinue if creatinine continues worsening or refractory hyperkalemia develops

Monitoring Strategy:

• Assess proteinuria at 3,6, and 12 months
• Target: ≥25% reduction by 3 months, ≥50% by 6 months, <0.5-0.7 g/day by 12 months 4
• Your patient's baseline 2.5g proteinuria may require additional 6-12 months to reach complete response 4

Alternative and Rescue Therapies

If inadequate response at 6 months:

1. Consider complement inhibition if available:

   • Pegcetacoplan (most evidence) 1 - 68% relative proteinuria reduction
   • Iptacopan 7 - 45% proteinuria reduction at 12 weeks
   • Eculizumab 8, 9 - heterogeneous response, requires continuous treatment

2. Switch to cyclophosphamide if MMF fails 5

3. Add calcineurin inhibitor (tacrolimus preferred) to MMF for synergistic effect 4

Prognostic Considerations

Your patient has concerning features:

• Creatinine >2.3 mg/dL at presentation is associated with decreased renal survival 3
• 21% of C3G patients progress to ESRD 3
• Up to 50% reach kidney failure in long-term follow-up 10

However, aggressive proteinuria reduction changes outcomes:

• Achieving 50% proteinuria reduction is strongly associated with kidney survival 2
• UPCR <100 mg/mmol at 12 months dramatically reduces kidney failure risk 2

Common Pitfalls to Avoid

1. Do not delay ACEi/ARB - start immediately alongside immunosuppression
2. Do not stop ACEi/ARB prematurely for modest creatinine rises (up to 30% acceptable) 6
3. Do not undertitrate MMF - target 2-3 g/day, not lower doses
4. Do not switch therapy too early - allow 6 months for response, especially with nephrotic-range proteinuria 4
5. Do not use corticosteroids alone - always combine with steroid-sparing agent (MMF) 5, 4

Monitoring for Treatment Toxicity

• Weekly labs initially: CBC, CMP, check for leukopenia (MMF), hyperkalemia (ACEi/ARB)
• Monthly after stabilization: Continue monitoring renal function and electrolytes
• Counsel patient to hold ACEi/ARB and diuretics during volume depletion (sick days) 6
• Infection prophylaxis: Consider PCP prophylaxis with high-dose steroids