A 28-year-old woman presents with nephrotic syndrome (proteinuria 8 g/day, serum albumin 2.1 g/dL, edema). Renal biopsy shows membranous nephropathy. She is seronegative for anti-PLA2R antibodies. What is the drug of choice for induction of remission in this patient?

Explanation

## First-Line Immunosuppression in Membranous Nephropathy **Key Point:** Cyclophosphamide combined with corticosteroids is the gold-standard induction regimen for membranous nephropathy with nephrotic syndrome, particularly in seronegative disease or when rapid remission is needed. ### Rationale for Cyclophosphamide **High-Yield:** Cyclophosphamide achieves complete remission in 60–70% of patients with membranous nephropathy when combined with corticosteroids. The Ponticelli regimen (alternating months of methylprednisolone + cyclophosphamide with oral prednisone) is the most widely validated induction protocol. **Clinical Pearl:** Seronegative anti-PLA2R membranous nephropathy has a more aggressive course and higher relapse risk than seropositive disease; cyclophosphamide is preferred over calcineurin inhibitors in this subset. ### Mechanism - Alkylating agent causing cross-linking of DNA - Profound B-cell and T-cell depletion - Durable remission with lower relapse rates compared to other agents ### Dosing & Monitoring - Intravenous cyclophosphamide: 0.5–1 g/m² monthly for 6 months (Ponticelli regimen) - Requires mesna for bladder protection - Monitor CBC, urinalysis for hemorrhagic cystitis - Cumulative dose limit: typically ≤20–25 g to minimize infertility and malignancy risk ### Alternative Agents & When to Use Them | Agent | Indication | Advantage | Limitation | |-------|-----------|-----------|------------| | **Mycophenolate mofetil** | Mild–moderate disease; steroid-sparing | Fewer infections; oral | Slower onset; lower remission rates | | **Tacrolimus** | Steroid-dependent; contraindication to cyclophosphamide | Reversible; faster onset | Relapse-prone; nephrotoxicity risk | | **Azathioprine** | Maintenance only; not induction | Steroid-sparing | Weak immunosuppression; not first-line | **Warning:** Calcineurin inhibitors (tacrolimus, cyclosporine) induce remission but have high relapse rates (50–60%) and are reserved for steroid-dependent disease or cyclophosphamide contraindications (age >60, severe infection, prior malignancy). ### Treatment Algorithm ```mermaid flowchart TD A[Membranous Nephropathy + Nephrotic Syndrome]:::outcome --> B{Serology & Disease Severity?}:::decision B -->|Seronegative or aggressive| C[Cyclophosphamide + Corticosteroids]:::action B -->|Seropositive, mild| D[Observation vs. MMF]:::action C --> E[Ponticelli regimen: 6 months]:::action E --> F{Response at 6 months?}:::decision F -->|Complete/partial remission| G[Maintenance: low-dose prednisolone]:::action F -->|No remission| H[Switch to MMF or Tacrolimus]:::action D --> I[Reassess at 3–6 months]:::decision ``` **Key Point:** The Ponticelli regimen is the most evidence-based induction protocol and should be offered to all patients with membranous nephropathy and nephrotic-range proteinuria unless contraindicated.