What is the appropriate cyclophosphamide dosing regimen for an adult with focal segmental glomerulosclerosis (FSGS)?

Cyclophosphamide Dosing for FSGS in Adults

For adults with steroid-resistant idiopathic FSGS and nephrotic syndrome, cyclophosphamide is NOT a first-line agent—cyclosporine at 3-5 mg/kg/day in divided doses for at least 4-6 months is the preferred immunosuppressive therapy after steroid failure. 1

Treatment Algorithm for FSGS

Initial Therapy (First-Line)

• Prednisone 1 mg/kg/day (maximum 80 mg) or 2 mg/kg on alternate days (maximum 120 mg) 1
• Continue high-dose for minimum 4 weeks, up to maximum 16 weeks or until complete remission 1
• Taper slowly over 6 months after achieving complete remission 1

For Steroid-Resistant FSGS (Second-Line)

Cyclosporine is the recommended agent, not cyclophosphamide:

• Cyclosporine 3-5 mg/kg/day in divided doses for at least 4-6 months 1
• If partial or complete remission occurs, continue for at least 12 months, then slow taper 1

When Cyclophosphamide May Be Considered (Third-Line)

Only if cyclosporine is not tolerated or contraindicated:

• Combination of MMF and high-dose dexamethasone is suggested before cyclophosphamide 1

Cyclophosphamide Dosing (If Used)

Oral Regimen

• 2 mg/kg/day for 8-12 weeks (maximum cumulative dose 168 mg/kg) 2
• Monitor complete blood count within 2 weeks of starting, then every 4 weeks 2
• Do NOT repeat courses of cyclophosphamide 2

Intravenous Regimen (Alternative)

• 500 mg/m² monthly for maximum 4 months 2
• Monitor CBC within 1-2 weeks and before each infusion 2

Concurrent Steroid Therapy

When cyclophosphamide is used, combine with:

• Prednisone 60 mg/m²/day for 6 weeks, then 40 mg/m² on alternate days for 4 weeks 2
• Taper to 10 mg/m² alternate days during therapy period 2

Critical Evidence Limitations

The evidence for cyclophosphamide in FSGS is weak and contradictory:

• A major pediatric RCT (60 children) showed cyclophosphamide provided NO benefit over prednisone alone in steroid-resistant FSGS, with higher treatment failure rates (57% vs 36%) 3
• Small observational studies show variable response rates (20-65% remission) 4, 5, 6, 7
• Most positive data comes from secondary steroid-resistant cases, not primary steroid resistance 6
• A 2022 Cochrane review found cyclosporine superior to other agents for achieving remission in steroid-resistant FSGS 8

Important Caveats

Contraindications to Cyclophosphamide

• Urinary outflow obstruction (must be excluded/corrected first) 9
• Severe renal impairment (eGFR <25-30 mL/min/1.73m²) 1
• Active severe infections 1

Monitoring Requirements

• Force diuresis during/after administration to reduce hemorrhagic cystitis risk 9
• Administer in the morning 9
• Monitor for myelosuppression, infections, hemorrhagic cystitis 9
• Risk of infertility, especially in young patients 10

When NOT to Use Immunosuppression

Do not treat FSGS with immunosuppression if:

• Non-nephrotic range proteinuria 1
• Secondary FSGS (genetic, medication-induced, adaptive) 11, 12
• Serum creatinine persistently >3.5 mg/dL or eGFR <30 mL/min/1.73m² 1

Bottom Line

Cyclophosphamide should be reserved as a third-line or later option in adult FSGS after failure of corticosteroids and cyclosporine. The KDIGO guidelines do not recommend cyclophosphamide as initial therapy for steroid-resistant FSGS, and the evidence supporting its use is limited and conflicting. Cyclosporine remains the evidence-based second-line agent with superior efficacy data 1, 8.