A 35-year-old woman with SLE presents with Class IV lupus nephritis (proteinuria 3.5 g/day, serum creatinine 1.8 mg/dL, active urinary sediment). She has failed to respond adequately to 3 months of corticosteroids and mycophenolate mofetil. What is the drug of choice for induction therapy?
A. Cyclophosphamide
B. Azathioprine
C. Belimumab
D. Rituximab
Explanation
Induction Therapy for Severe Lupus Nephritis (Class IV)
Key Point
Cyclophosphamide is the gold-standard induction agent for severe, refractory lupus nephritis (Class III–IV) and is the preferred choice when conventional therapy (corticosteroids + MMF) has failed or disease is rapidly progressive.
Pathophysiology of Class IV Lupus Nephritis
Diffuse proliferative glomerulonephritis with immune complex deposition
Requires aggressive immunosuppression to prevent progression to ESRD
Standard induction: high-dose corticosteroids + cyclophosphamide or MMF
Cyclophosphamide achieves complete or partial renal remission in 60–70% of Class IV nephritis cases. The Euro-Lupus protocol is increasingly preferred due to lower cumulative toxicity while maintaining efficacy.
Mechanism of Cyclophosphamide
1.
Alkylating agent; cross-links DNA
2.
Depletes T and B lymphocytes
3.
Reduces autoantibody production and immune complex formation
4.
Particularly effective for rapidly progressive, proliferative disease
Toxicity Management
Mesna: Co-administered to prevent hemorrhagic cystitis
Hydration: Aggressive IV hydration to dilute urine
Monitoring: Baseline CBC, renal function, urinalysis; repeat before each dose
Contraception: Absolute requirement (teratogenic); counsel all women of childbearing age
Infection prophylaxis: PCP prophylaxis if CD4 <200 cells/μL
Clinical Pearl
Cyclophosphamide is the only agent with proven superiority over MMF in head-to-head trials for Class IV nephritis, particularly in rapidly progressive disease or when renal function is declining.
Why Other Agents Are Not First-Choice for Refractory Class IV Nephritis
Table
Agent
Role
Limitation
Rituximab
B-cell depletion; emerging role
Not FDA-approved for lupus nephritis; limited evidence for monotherapy in Class IV
Belimumab
BLyS inhibitor; approved for SLE
Modest efficacy; not recommended for active nephritis; slower onset
Azathioprine
Maintenance after induction
Insufficient as monotherapy for severe nephritis; used after cyclophosphamide
Mnemonic
CYCLO = Cyclophosphamide for Class IV lupus nephritis (severe, refractory).
Harrison 21e Ch 319; Robbins 10e Ch 6
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