A 42-year-old woman with newly diagnosed granulomatosis with polyangiitis (GPA) presents with pulmonary infiltrates, glomerulonephritis, and positive c-ANCA/PR3 antibodies. What is the preferred induction regimen?

Explanation

## Induction Therapy for Granulomatosis with Polyangiitis (GPA) ### First-Line Induction Regimen **Key Point:** Cyclophosphamide combined with high-dose corticosteroids is the gold standard induction therapy for generalized GPA with organ-threatening disease (pulmonary and renal involvement). ### Cyclophosphamide-Based Induction #### Dosing Options 1. **Intravenous pulse cyclophosphamide** (preferred in most centers) - Dose: 0.5–1 g/m² IV monthly × 3–6 pulses - Advantages: Lower cumulative dose, reduced bladder toxicity, better tolerability 2. **Oral cyclophosphamide** (alternative) - Dose: 1.5–2 mg/kg/day orally - Higher cumulative toxicity; reserved when IV access unavailable #### Corticosteroid Component - **Induction:** Prednisolone 1 mg/kg/day (max 80 mg) or IV methylprednisolone 500–1000 mg daily × 3 days - **Taper:** Gradual reduction over 3–6 months as remission achieved ### Maintenance Phase (After Remission) | Agent | Duration | Indication | |-------|----------|------------| | Azathioprine 1.5–2 mg/kg/day | 12–24 months | Standard maintenance after cyclophosphamide induction | | Methotrexate 20–25 mg/week | 12–24 months | Alternative if azathioprine contraindicated | | Rituximab (375 mg/m² IV × 4 weekly) | 6 months | Emerging option for maintenance; reduces relapse | ### Why Cyclophosphamide for Induction **High-Yield:** Cyclophosphamide is superior to methotrexate and azathioprine in inducing remission in generalized GPA with organ-threatening disease (pulmonary and renal involvement). - **Remission rates:** 75–90% achieve complete remission with cyclophosphamide vs. 60–70% with methotrexate - **Speed of response:** Rapid control of systemic inflammation and prevention of end-stage renal disease - **Evidence base:** EULAR guidelines and American College of Rheumatology recommend cyclophosphamide for severe GPA - **Organ protection:** Prevents irreversible renal damage and pulmonary hemorrhage ### Rituximab as Alternative **Clinical Pearl:** Rituximab (anti-CD20 monoclonal antibody) is now an FDA-approved alternative to cyclophosphamide for induction in GPA, particularly in ANCA-associated vasculitis. However, cyclophosphamide remains the standard for severe, life-threatening disease due to longer track record and proven efficacy. ### Supportive Measures - **Mesna:** Co-administered with IV cyclophosphamide to prevent hemorrhagic cystitis - **Prophylaxis:** Trimethoprim-sulfamethoxazole (TMP-SMX) for Pneumocystis jirovecii prophylaxis during immunosuppression - **Monitoring:** Monthly CBC, renal function, urinalysis; baseline and serial pulmonary imaging **Warning:** Cyclophosphamide carries significant toxicity (infertility, secondary malignancy, hemorrhagic cystitis, infection). Fertility counseling and cryopreservation should be offered to reproductive-age patients before initiation. [cite:Harrison 21e Ch 297]